identifying and controlling immunotoxic substances

Identifying and Controlling ImmunotoxicSubstances

April 1991

OTA-BP-BA-75NTIS order #PB91-183145

Recommended Citation:

U.S. Congress, Office of Technology Assessment, Identifying & Controlling immunotoxicSubstances-Background Paper, OTA-BP-BA-75 (Washington, DC: U.S. GovernmentPrinting Office, April 1991).

For sale by the Superintendent of DocumentsU.S. Government Printing Office, Washington, DC 20402-9325

(order form can be found in the back of this report)

Foreword

Thousands of new chemical substances enter the market annually. Although the public continues toembrace the benefits of these substances, increasingly wary consumers now inquire about their downside,particularly health risks. While information about what chemicals are in the air or water and in whatquantities is usually forthcoming, answers about their human health effects are often vague and unsatisfying.

Much of the American public– scientists and laymen alike – finds this uncertainty troubling. A recentnovel described the impacts of an accidental chemical release on a small community. The following exchangecaptures the frustration of the townspeople trying to understand the consequences of the chemical exposure:

“Am I going to die?”

“Not as such,” he said.

“What do you mean?”“Not in so many words.”“How many words does it take?”

“Let me answer like so. If I was a rat, I wouldn’t want to be anywhere within a two hundred mileradius of the airborne event.”

“What if you were a human?”“I wouldn’t worry about what I can’t see or feel.”*

Nowadays, after years of research, answers about potential carcinogens come more readily than thoseconveyed in the novel. But noncancer health risks, such as potential, adverse effects of chemicals on thenervous, immune, or respiratory systems, have received less attention and remain more of a mystery. TheSenate Committee on Environment and Public Works and its Subcommittee on Toxic Substances, Environ-mental Oversight, Research and Development asked OTA to examine noncancer health risks in theenvironment, including the availability of testing technologies, future research needs, and the adequacy ofthe current regulatory scheme. This background paper, which describes Federal efforts to identify andcontrol substances that may harm the immune system, is one response to that request. It builds on previousOTA work on carcinogenic and neurotoxic substances.

OTA acknowledges the generous help of the workshop participants, reviewers, and contributors whogave their time to ensure the accuracy and completeness of this study. OTA, however, remains solelyresponsible for the contents of this background paper.

~ f ~

A-M ‘ >JOHN H. GIBBONS

~ Direc tor

*Don DeLillo, White Noise (New York, NY: Penguin Books, 1986), pp. 140-141.

. . .111

Workshop on Identifying and Controlling immunotoxic Substances, September 1990

Philip J. Landrigan, Workshop ChairChairman

Department of Community MedicineThe Mount Sinai Medical Center

New York, NY

Robert BurrellProfessorDepartment of Microbiology& ImmunologyHealth Sciences CenterWest Virginia UniversityMorgantown, WV

Joy A. CavagnaroSpecial Assistant to the DirectorOffice of Biologics ResearchCenter for Biologics Evaluation& ResearchU.S. Food and Drug AdministrationRockville, MD

Theodora E. ColburnSenior FellowWorld Wildlife Fund/The Conservation FoundationWashington, DC

Earon S. DavisEnvironmental Health ConsultantEvanston, IL

Jack H. DeanVice President of Drug SafetySterling Research GroupRensselaer, NY

Frank W. FitchAlbert D. Lasker Professor of Medical SciencesDepartment of PathologyUniversity of ChicagoChicago, IL

Michael I. LusterHead, immunotoxicology GroupSystemic Toxicology BranchDivision of Toxicology Research& TestingNational Institute of Environmental Health SciencesResearch Triangle Park, NC

Stephen MooserOutreach CoordinatorMount Sinai School of MedicineNew York, NY

William J. ReaDirectorEnvironmental Health CenterDallas, TX

MaryJane K. SelgradeChiefimmunotoxicolog SectionHealth Effects Research LaboratoryU.S. Environmental Protection AgencyResearch Triangle Park, NC

Abba I. TerrSan Francisco, CA

Robert F. VogtResearch ChemistDivision of Environmental HealthCenters for Disease ControlAtlanta, GA

NOTE: OTA appreciates and is grateful for the valuable assistance and thoughtful critiques provided by the workshop participants. Theparticipants do not, however, necessarily approve, disapprove, or endorse this background paper. OTA assumes full responsibilityfor the background paper and the accuracy of its contents.

iv

OTA Project Staff - Identifying and Controlling immunotoxic Substances

Roger C. Herdman, Assistant Director, OTAHealth and Life Sciences Division

Michael Gough, Biological Applications Program Manager

Holly L. Gwin, Project Director

Robyn Y. Nishimi, Senior Analyst

Peter R. Andrews, Research Assistant

Monica V. Bhattacharyya, Research Assistant

Timothy E. Sullivan, Intern

Desktop Publishing Specialists

Linda Rayford-Journiette

Carolyn Swarm

support staffCecile Parker, Office Administrator

Jene Lewis, Secretary

Contractor

Robert Burrell, West Virginia University, Morgantown, WV

Chapter 1.Chapter 2.Chapter 3.Chapter 4.

Contents

Introduction and Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .The Immune System and immunotoxicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .immunotoxicologicalTests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Federal Attention to immunotoxicants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

AppendixA. Income Replacement for Individuals Disabled by Immunotoxicants . . . . . . . . . . . . . . . . . .AppendixB. Reviewers and Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .AppendixC. Glossary of Terms and Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Boxes

l-A. General Principles of Toxicology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-A. Cell Surface Receptors of the Immune System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-B. “Allergy’’:SomeCommon Misperceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-A. Polybrominated Biphenyls: The Michigan Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-B. Polychlorinated Biphenyls: The Taiwan Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-C. Chemical-Induced Autoimmunity: Spanish Toxic Oil Syndrome . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figures

1-1. Spectrum of Adverse Immune System Effects.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-1. Structure of an Antibody Molecule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-2. White Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-3. Major Organs and Tissues of the Immune System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-4. Generation of Antibody Forming Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Tables

1-1.1-2.2-1.2-2.2-3.2-4.2-5.3-1.3-2.3-3.3-4.4-1.4-2.4-3.4-4.4-5.4-6.A-L

Common immunotoxicological Tests . . . . . . . . . . . . . . . . . . . . .Federal Agencies Engaged in Immunotoxicological ResearchMajor Cell Classes of Immunological Importance . . . . . . . . . .Major Functions of T Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Mechanisms of Cell-Mediated Immunity . . . . . . . . . . . . . . . . .Some Human Autoimmune Diseases . . . . . . . . . . . . . . . . . . . . .Some Immunodeficiency Disorders . . . . . . . . . . . . . . . . . . . . . .Known or Suspected Immunosuppressants . . . . . . . . . . . . . . . .Common Contact Sensitizers . . . . . . . . . . . . . . . . . . . . . . . . . . .Industrial Chemicals Associated With Occupational AsthmaSubstances Associated With Autoimmune Responses . . . . . .NTP’s Panel of Tests for Detecting immunotoxicity . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .or Regulation . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Substances Tested by NTP for Immunosuppression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Substances Tested by NTP for Hypersensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Major Federal Laws Controlling Toxic Substances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Sensitizers Regulated by OSHA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .EPA’s Revisited Subdivision M Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .State Workers’ Compensation Disability Benefit\ 1989 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Page3

132749

69788187

71622333440

414151819

68

14172021213538394050515254555971

vi

Chapt:er 1

Introduction and SUl1nm~Elry

Chapter 1

Introduction and Summary

INTRODUCTION

The potential for substances used in industry,transportation, and households to be simultaneouslybeneficial and toxic to human life creates a legislative andregulatory dilemma. The challenge of balancing a strongeconomy, one that delivers products that people needand desire, with the health and safety of the populacesometimes seems to be a tremendous burden.

Technological advances add to the weight of thatburden. Thousands of new, potentially toxic substancesenter the market annually. Advanced instruments helpscientists measure the presence of new and existing sub-stances in minute quantities. Substances formerly un-known or undetected suddenly become worrisome astechnology provides the means to predict human risksfrom these substances.

Governmental concern that a substance might createan adverse health effect historically concentrated oncarcinogenicity. Most Federal legislative and regulatoryefforts to prevent or minimize human exposure to toxicsubstances have focused on identifying and controllingcarcinogens. Physicians and researchers now recognizethe noncancer, toxic effects of many substances. Someof these effects, for instance teratogenicity, have becomethe subject of specific legislative concern. Federalregulatory attention to other types of toxic injury, e.g., tothe nervous system, the immune system, the respiratorysystem, depends on the more general mandate to protecthuman health. Some observers fear that historical em-phasis on carcinogenicity, combined with limited agencyresources, has led to neglect of problems such asneurotoxicity, immunotoxicity, or pulmonary toxicity–problems that may be as widespread and severe as car-cinogenicity.

The Senate Committee on Environment and PublicWorks, and its Subcommittee on Toxic Substances, En-vironmental Oversight, Research and Development,asked for assistance from the Office of Technology As-sessment (OTA) in evaluating technologies to identifyand control noncancer health risks in the environment.The committee’s interests include advances in toxicolo-

gy, research and testing programs in the Federal agen-cies, and the consequences of exposure to toxic sub-stances.

This background paper, which describes the state-of-the-art of identifying substances that can harm the im-mune system, represents one response to the committee’srequest. Chapter 2 provides basic information about theprincipal components of the immune system and thegeneral consequences that stem from perturbations to it.Chapter 3 describes methods for evaluating chemicalimmunotoxicity and reports on some known or suspectedimmunotoxicants. Chapter 4 summarizes Federal re-search and regulatory activities related to immuno-toxicity. Appendix A provides a very brief synopsis ofincome replacement programs available to persons dis-abled by toxic exposures.

TERMINOLOGY

This background paper examines a field of study rifewith jargon. Not all specialists in the field of im-munotoxicology--which combines the expertise of im-munologists and toxicologists — use terminology inprecisely the same manner. The following definitionsexplain how OTA applies the terms-of-art essential tothis study.

immunotoxicity, or an immunotoxic effect, is definedas an adverse or inappropriate change in the structure orfunction of the immune system after exposure to a foreignsubstance. Foreign substances capable of adversely af-fecting the immune system may be of synthetic or naturalorigin. This study focuses on chemicals, including in-dustrial, transportation, agricultural, and householdchemicals, drugs, and food additives.

immunotoxicity manifests at both ends of aspectrum— as an enhanced but inappropriate immuneresponse, and as a failure to mount an appropriate im-mune response. (See figure l-l.) This background paperexamines three types of adverse effects: immunosup-pression, hypersensitivity, and autoimmunity. Im-munosuppression is a generalized decrease in immuneresponsiveness that may result in increased incidence of

3

4 ● Identifying and Controlling Immunotoxic Substances

Figure 1-1- Spectrum of Adverse Immune System Effects

HypersensitivityAutoimmunity

Immunosuppression

SOURCE: Office of Technology Assessment, 1991.

infection or tumors. Immunologic hypersensitivity is aller-gy-an overreaction of the immune system to a sub-stance. Hypersensitivity is a normal immune response toa foreign substance, but one with deleterious conse-quences. Autoimmunity results from a breakdown in theability of the immune system to distinguish “self’ from“nonself.” An autoimmune reaction involves the bodymounting an immune response against some of its owncomponents.

Substances that provoke an immune response arecalled antigens. Antigens trigger beneficial responses,e.g., destruction of an infectious agent, and adverseresponses, e.g., hypersensitivity. Other substances candamage the immune system by destroying or inactivatingspecific elements within it, thereby suppressing immuneresponse. Substances that elicit adverse immune re-sponses or damage the immune system are called immu -notoxic substances, or immunotoxicants.

THE IMMUNE SYSTEM

The immune system is a complex, cooperative effortamong several types of cells, cell products, tissues, andorgans in the body. The simplified description that fol-lows should help the reader comprehend state-of-the-art

immunotoxicology, but by no means represents an ex-haustive examination of this complicated organ system.

The immune system involves several cell types. Mostof them belong to the large group of cells commonlylumped together as white cells. The white cells of prin-ciple interest to immunotoxicologists are macrophagesand lymphocytes. Macrophages ingest cellular debrisand infecting organisms, and they process and presentantigens to the lymphocytes. Lymphocytes include Bcells, T cells, and natural killer (NK) cells. B cells secreteantibodies (immunoglobulins), substances that inac-tivate antigens in the body. Each B cell makes antibodyspecific to a given antigen; the body can make antibodiesto thousands of antigens.

T cells regulate the immune system. T cells mustinteract with B cells for antibody production. Some Tcells can directly kill cells presenting antigens. T cells alsosecrete cytokines, protein molecules that transmit signalsto modulate (augment or suppress) immune responsebetween cells of the immune system. (Macrophages alsoproduce cytokines.) NK cells attack and destroy certainother cells. Most types of cells are resistant to NK cellactivity, but tumor cells and virus-infected cells appearto be susceptible.

The organs of the immune system– the lymphoid or-gans– include the bone marrow, the thymus, the lymphnodes, and the spleen, as well as the tonsils, the appendix,and clumps of tissue in the small intestine and therespiratory tract. The lymphoid organs are compartmen-talized collections of lymphocytes, macrophages, andother immune system cells. They produce, store, anddistribute the immune system cells. The lymphatic vesselnetwork also circulates lymphocytes.

Foreign substances provoke two basic types of im-mune response: nonspecific immunity and acquired im-munity. Nonspecific immunity, which involves functionsof the macrophages and NK cells, represents the body’sfirst line of defense. The nonspecific immune responseoccurs without prior exposure to antigens. Acquiredimmunity develops after the initial exposure to a foreign

Chapter 1—Introduction and Summary ● 5

substance and can be subdivided into humoral immunityand cell-mediated immunity. humoral immunity in-volves antibody production, which generally requiresmacrophages (to process and present the antigen), Tcells (to stimulate B cell production), and B cells (toproduce antibodies). The other basic type of acquiredimmunity, cell-mediated immunity, also begins with themicrophage but then relies on the T cell functions ofcytotoxicity and cytokine secretion. Although scientistsdistinguish between humoral and cell-mediated im-munity, most antigens can provoke both types of immuneresponse.

IDENTIFYING IMMUNOTOXICSUBSTANCES

The AIDS epidemic has heightened public interest inthe immune system and its potential for injury. A virus,not a chemical, causes AIDS, but the disease illustratesthe devastating effects of immunosuppression and sug-gests to people the importance of protecting the immunesystem. In response to increased public awareness, re-searchers have devoted greater effort in recent years todeveloping predictive tests to measure the potential im-munotoxicity of chemicals before they enter commerce.

As a result of these efforts, a number of tests now existto assess the effects of foreign substances on the com-ponents and processes of the immune system. Re-searchers testing a chemical’s immunosuppressivepotential often start with pathology, an examination oftissues and organs of the immune system for evidence ofdisease. The organs of experimental animals can beweighed or cells from organs or in peripheral blood canbe counted to get preliminary indications of how a sub-stance may affect the immune system. Other assays ofimmunosuppression assess whether exposure to a chemi-cal affects the ability to mount a particular type of im-mune response. Measures of humoral, cell-mediated,and nonspecific immunity exist and can be applied in thelaboratory. These tests usually involve experimentalanimals but occasionally direct assessment of humans.

The most comprehensive tests of immunosuppressionavailable to researchers today measure a subject’s abilityto fight infections or tumors after exposure to a suspectedimmunotoxicant. Scientists expose experimental animalsto a toxic substance and subsequently expose (challenge)the animals to an infectious agent or a tumor. If animals

exposed to the suspected toxicant show a significantincrease in the incidence of disease or death followingchallenge compared to unexposed animals, the sub-stance is suspected to be immunotoxic.

Researchers and manufacturers also use hypersen-sitivity assays. Whether a substance can induce hypersen-sitivity can be assessed using skin and respiratory tests.Antibodies can also be measured in the blood of animalsor humans who have had an allergic reaction to an an-tigen. (Table l-l lists common immunotoxicologicaltests.)

immunotoxicological testing presents an investigatorwith significant challenges in interpretation. Test resultscan differ depending on the subject’s age, species, sex, orrecent illnesses. Environmental factors, such as diet orother chemical exposures, can also affect immune systemperformance. Choosing the appropriate test dose andthe means and duration of exposure can prove difficultwhen the point of the exercise is to extrapolate from thetest to the predicted consequences of actual human ex-posure. (See box l-A.) These considerations presentthemselves in all types of toxicology, but the complexityof the immune system compounds these difficulties forimmunotoxicologists. immunotoxicology’s fledglingstatus as a field of scientific inquiry and the fact that fewtoxicologists have training in immunology further com-plicate study of immunotoxicity.

The immune system is thought to have a reservecapacity, although the size of that reserve is as yet un-determined. Thus tests that measure impairment of oneimmune system component may not, in fact, indicateoverall immunotoxicity, since other immune componentsor processes may compensate for the impairment. Fre-quently a decrease in a particular immune function isdiscerned but no clinical symptoms – certain infections orcancers, for instance– appear during the test period.There is still much to be learned about the long-termconsequences of weakening an individual component ofthe immune system.

Relatively few data exist on immunotoxicity in humans.Studies of radiation victims and patients receiving immu-nosuppressive drugs provide evidence of the conse-quences of long-term immunosuppression. A fewepidemiologic studies of toxic exposures that appearedto result in immunosuppression have been attempted,


Table l-l—Common immunotoxicological Tests

Category Test

Pathology . . . . . . . .

humoralimmunity . . . . . . .

Cell-mediatedimmunity . . . . . . .

Nonspecificimmunity . . . . . . .

Host-resistance . . .

Hypersensitivity . . .

HematologyOrgan weightsHistologyCellularity

Antibody plaque forming cell (PFC) responseB cell litogen responseImmunoglobulin levels in serumQuantitation of splenic and/or peripheral

blood B cells

T cell mitogen responseCytotoxic T lymphocyte (CTL) cytolysisDelayed hypersensitivity responseMixed leukocyte response (MLR)Quantitation of splenic and/or peripheral

blood T cells

Natural killer cell activityMicrophage countsNeutrophil countsSyngeneic tumor cells:. PYB6 sarcoma (tumor incidence). B16F1O melanoma (lung burden)Bacterial models:• Listeria monocytogenes (mortality)● Streptococcus species (mortality)Viral models:. Influenza (mortality)● Mouse cytomegalovirus (mortality)Parasite models:. Plasmodium yoelii (parasitemia)Draize testOpen epicutaneous testBuehler testFreund’s complete adjuvant testOptimization testSplit adjuvant testGuinea pig maximization testMouse ear swelling testRespiratory rate measurementSerum lgE measurementLocal lymphnode proliferation assav. .

NOTE: immunotoxicologists seldom perform each test or type of test for aparticular substance. They often divide the tests into tiers, usingtests that indicate immune system damage at a fairly gross level toscreen for potential immunotoxicants, and applying more sensitiveand specific tests only to those substances that indicate possibletoxicity in the primary screen. These tests are described inch. 3.


but with inconclusive results. On the other hand, workersand consumers have provided conclusive evidence thatseveral chemicals can induce hypersensitivity. At leastone epidemiologic study has examined humans for signsof autoimmunity resulting from chemical exposure.However, the overall lack of data makes it problematicto extrapolate from the results of tests of substances in

experimental animals to the likely effects of human ex-posure.

EXAMPLES OF immunotoxicSUBSTANCES

Scientists have identified several substances that sup-press the immune system, induce hypersensitivity, orcause autoimmunity in laboratory animals. This is truedespite the fact that testing for immunotoxicity has beendone on very few of the chemical substances, regulatedor unregulated, in commerce.

Substances That Suppress Immune Response

Substances that can suppress immune responses fallinto several general categories, including: therapeutics,solvents, pesticides, halogenated aromatic hydrocar-bons, polycyclic aromatic hydrocarbons, airborne pol-lutants, and metals. Testing has not been conducted onall individual substances in any particular category, andnot all substances tested within each of these categorieshave been shown to be immunotoxic. Not all categoriesof chemicals have been scrutinized.

Therapeutic drugs designed to prevent transplantrejection or treat cancer or autoimmune disorders arethe most thoroughly studied immunosuppressive chemi-cals. The most frequently used immunosuppressivedrugs fall into four basic categories-–alkylating agents(e.g., cyclophosphamide), glucocorticosteroids (e.g.,prednisolone), antimetabolites (e.g., azathioprine), andnatural products (e.g., cyclosporin A).

Benzene, a solvent commonly used in many industrialprocesses, has been linked to immune dysfunction.Workers chronically exposed to high levels of benzene(> 100 ppm in the air) experienced increased rates ofagranulocytosis and myelogenous leukemia, accom-panied by an increased risk of infection. The immu-notoxicity of benzene at levels closer to the currentregulatory level (1 to 5 ppm in the air) has not beendemonstrated.

Animal studies of, pesticides show evidence of im-munosuppressive potential, but little analysis of the ef-fects of human exposure has been done. Among thecommonly found halogenated aromatic hydrocarbons(HAHs), polybrominated biphenyls (PBB), polychlorinated

Chapter l—Introduction and Summary ● 7

biphenyls (PCBs), and dioxin have shown evidence of humans exist. Other airborne pollutants with immu-immune suppression in animal studies. However, the fewhuman studies on these substances have either beeninconclusive or have contradicted the animal evidence.

Carcinogenic polycyclic aromatic hydrocarbons(PAHs), the products of fossil fuel combustion, createclear signs of immunosuppression in animal studies.Humans are exposed to PAHs in the workplace and asairborne pollutants, but few data on their effects on

.nosuppressive potential include ozone, nitrogen dioxide,cigarette smoke, and trace metals. Metals shown to sup-press immune function in experimental animals includelead, cadmium, mercury, and organotins.

Substances That Induce Hypersensitivity

Contact sensitivity and other immune mediated skindisorders often arise from exposure to environmental


agents. A variety of substances, including drugs, cos-metics, and certain metals can give rise to allergic contactdermatitis, which manifests itself with a red rash, swell-ing itching, and sometimes blisters. Numerous inhalantscause immune-mediated respiratory disorders, includ-ing some types of asthma, hypersensitivity pneumonitis,allergic rhinitis, bronchopulmonary aspergillosis,silicosis, asbestosis, coalworkers’ pneumoconiosis, andpossibly byssinosis.

Among the known human allergens are certainprescription drugs, including penicillin and methyldopa.Over-the-counter drugs, cosmetics, and the metals foundin costume jewelry can also cause allergic reactions.Plastics and resins, particularly the isocyanates, causeboth asthma and contact dermatitis. Pesticides, too, haveprovoked hypersensitivity under certain conditions.

Substances That Induce Autoimmunity

Several drugs and heavy metals have been implicatedin autoimmune processes. Genetic susceptibility alsoplays an important role in autoimmunity. Because of thisstrong genetic component and a generally poorer under-standing of autoimmunity compared to other immuneresponses, deciphering the exact role of toxic chemicalsin the induction of autoimmunity is difficult.

FEDERAL ATTENTION TOimmunotoxic SUBSTANCES

The Federal Government is actively involved in ad-vancing the state-of-the-art of immunotoxicology. TheEnvironmental Protection Agency (EPA), Food andDrug Administration (FDA), Centers for Disease Con-trol, and National Institutes of Health have im-munotoxicological research programs. Each of theseagencies also contributes to the work of the NationalToxicology Program (NTP), whose immunotoxicologicalresearch program was the first coordinated Federal ef-fort to evaluate toxic substances for adverse effects onthe immune system.

Current Federal research in immunotoxicology isdirected toward developing and validating tests forevaluating substances for immunotoxic potential. NTPhas published a panel of tests for immunosuppressivepotential that has been validated in the mouse, and itcontinues to work on validating immunotoxicity tests inother species and on improving its current panel of tests.NTP is also applying the battery of tests for immunosup-pressive potential and standard hypersensitivity assays to

various substances. EPA is working independently andwith NTP on developing and validating immunotoxicitytests using the rat and the mouse, and has undertakenhuman inhalation studies on substances regulated underthe Clean Air Act. EPA has also published immu-notoxicity testing guidelines for certain pesticides. FDAconsiders the immune system an important target oftoxicological assessment and is involved in developingand applying tests to measure the potential im-munotoxicity of foods and drugs. (See table 1-2.)

Few substances have been regulated by the FederalGovernment on the basis of immunotoxicity. The Oc-cupational Safety and Health Administration (OSHA)has issued regulations for certain substances becausethey can provoke hypersensitivity. FDA has restrictedthe use of sulfites in foods because they can induceasthmatic attacks insensitive individuals. These agenciesand EPA regulate additional substances that have shownevidence of immunotoxicity, but other health effectsserve as the basis for those regulations.

Several Federal activities are designed to enhancepublic awareness of the hazards of toxic substances,including immunotoxicants. OSHA’S hazard com-munication standard requires that workers be providedwith information about known health hazards in theirjobs. However, since so little information is availableregarding immunotoxic effects, and since the standardcannot be used to compel testing, the standard does littleat present to protect workers from immunotoxic hazards.Community right-to-know legislation requires EPA tocollect information about substances that pose potentialtoxic hazards to local communities and make that infor-mation available to the public. As with the OSHA stan-

Table 1-2—Federal Agencies Engaged inimmunotoxicological Research or Regulation

Consumer Product Safety CommissionDepartment of AgricultureDepartment of DefenseDepartment of Health and Human Services

Agency for Toxic Substances and Disease RegistryAlcohol, Drug Abuse, and Mental Health AdministrationCenters for Disease ControlFood and Drug AdministrationNational Institutes of Health

Department of LaborMine Safety and Health AdministrationOccupational Safety and Health Administration

Environmental Protection AgencySOURCE: Office of Technology Assessment, 1991.

Chapter 1—Introduction and Summary . 9

dard, however, this program does not permit EPA torequire that health effects information be developedThe Federal Government also supports information dis-semination activities related to toxic substances under-taken by the National Library of Medicine and theAgency for Toxic Substances and Disease Registry.

RELATED ISSUES

As a science develops, experts continually disagree onwhether currently available evidence supports a par-ticular conclusion. In the ease of immunotoxicology, agrowing number of medical practitioners are drawingconclusions regarding the immunotoxicity of chemicalsin the environment that other practitioners and researchersbelieve to be unjustiled on the basis of current knowledge.This disagreement has had at least two interesting effectson governance in the past few years.

One effect is the increasing public demand forgovernmental attention to a problem frequently identifiedas multiple chemical sensitivity (MCS) but also called en-vironmental illness and several other names. MCSremains a poorly defined problem — experts disagree onwhat causes the problem and whether it is physical ormental—but sufferers generally exhibit symptoms thatthey attribute to immune system dysfunction when ex-posed to very low levels of common industrial, environ-mental, and household chemicals. Two States, Marylandand New Jersey, commissioned studies of MCS as apublic health problem but have not proceeded withscreening or regulatory programs. California has con-sidered (but not passed) legislation that would encourageresearch and education regarding environmental illnessand MCS. Within the Federal Government, EPA is fund-ing a study by the National Academy of Sciences that willassess the type of research needed to determine whetherMCS exists and its possible causes. Constituents at theState and Federal level are appearing before their electedrepresentatives to demand attention to this problem,which some medical practitioners attribute to im-munotoxicity. This background paper does not attemptto weigh the merits of arguments supporting or denyingthe existence of MCS or of claims that MCS is an immunesystem dysfunction. The analysis examines state-of-the-art methods for identifying substances that may damagethe immune system but does not evaluate diseases of orinvolving the immune system.

A second effect is the introduction of immunotoxico-logical test results to support claims of disability. Individuals

with diseases they believe to be linked to immune systemimpairment are making claims against Social Security,workers’ compensation programs, and in tort suits forinjuries caused by chemicals frequently used in com-merce. Here, too, experts disagree on whether availableevidence supports these claims. However, most of theexperts contacted by OTA believe that data currentlyavailable from immunotoxicological testing are limited inthe support they provide to plaintiffs’ claims of immunesystem injury from toxic substances. Appendix A providesa brief description of the compensation programs and asynopsis of a few claims based on immune system injuryfrom toxic chemicals.

SUMMARY

immunotoxicology has advanced rapidly as a distinctfield of study over the last several years. Scientists nowrecognize the immune system as an important targetorgan for toxicity. Tests to determine whether a sub-stance can suppress the immune system or induce hyper-sensitivity or autoimmunity have been developed andapplied by manufacturers and by regulatory agencies.Yet the growing database of immunotoxicological infor-mation remains insufficient for most regulatory purposes.

immunotoxicology is complicated by several factors:the complex nature of the immune system, limited (his-torically) attention to immunotoxicity research, and lack ofhuman exposure data stand out among them. Regulators atthe FDA have the opportunity to observe the effects ofdrugs on humans in clinical trials before they are marketed.However, when FDA, EPA, OSHA, or the other regu-latory agencies try to decide whether a food additive orpesticide, for instance, poses an undue risk to humanhealth, they face the problem of trying to extrapolatefrom animal test results to the likely consequences ofhuman exposure to immunotoxic substances. Very fewuseful human data are available to support these attempts.

The science of immunotoxicology is sufficiently ad-vanced for regulators to begin to consider use of itsresults in the decisionmaking process, but much researchremains to be done. Current law permits Federal agenciesto require immunotoxicological testing-either by thegovernment or by industry-on substances suspected ofposing a potential threat to the human immune system.The agencies are devoting resources to developing andapplying immunotoxicological tests in areas where thepotential for human exposure is thought to be significant,

Chapter 2

The Immune System and immunotoxicity

Chapter 2

The Immune System and immunotoxicity

INTRODUCTION

Each day, the human body must defend itself againsta battery of foreign substances (e.g., bacteria andviruses), as well as against elements from within (e.g.,cancer cells). This protective capacity arises, for the mostpart, from our immune system, which can generally dis-tinguish what is “self’ from what is “nonself,” or foreign.The stark statistics of acquired immune deficiencysyndrome (AIDS), for example, demonstrate the impor-tance to human health of an appropriately functioningimmune system.

The immune system is a complex, highly regulated,cooperative effort among several types of cells, cellproducts, tissues, and organs. It is not an isolated system,but operates in concert with other systems within thebody (e.g., endocrine, central nervous, and cardiovas-cular). Any particular stimulus to the immune systemresults in a complex series of events, and any singleresponse can have a number of consequences. Similarly,perturbations that primarily affect other body systemscan cascade, resulting in an effect on the immune system.

This chapter briefly describes the principal com-ponents of the immune system and the general conse-quences that stem from perturbations to it. This chapteralso briefly explores one of the practical considerationsof immunotoxic substances and humans: Who is at risk?

Only the most basic and broad concepts of immunol-ogy are presented in this chapter. Current knowledgeabout the immune system is presented in several sources(4,19,22). Similarly, a detailed description of toxicologi-cal effects on the immune system is beyond the scope ofthis report but is presented elsewhere (7,10,11,18,27,28).

COMPONENTS OF THE IMMUNESYSTEM

Cells are the basic structural unit of living organisms.They are the smallest components of plants and animalsthat are capable of carrying on all essential life processes.

A single cell is a complex collection of molecules withmany different activities, all integrated to form a func-tional, self-assembling, self-regulating entity, althoughcells in different organs carry out different functions.

Several types of cells comprise the human immunesystem, as do units of cells and tissue, i.e., organs.Together these cells, tissues, and organs respond to chal-lenges to the immune system. This section brieflydescribes the major components of the immune system;a later section examines how these elements coordinateto mount an immune response.

Antigens and Antibodies

Elements that are capable of eliciting an immuneresponse are called antigens. Humans are exposed toantigens primarily through inhalation, direct skin con-tact, or ingestion. Antigens include, but are not limitedto, chemical compounds and micro-organisms. And,while antigens are generally substances “foreign” to – i.e.,originating outside — the human body, in some instances,the immune system will perceive a normal, self com-ponent of the body as foreign and mount an immunereaction against it. Several types of cells can react withantigens, depending on the exact nature of the particularantigen.

One response to antigen stimulation results in theproduction of proteins called immunoglobulins, or an-tibodies. Antibodies have binding sites that are specificfor, and complementary to, the structural features of theantigen that stimulated their formation. Antibodiesformed by a sheep, for example, in response to injectionof human hemoglobin (the antigen) will combine withhuman hemoglobin and not an unrelated protein such ashuman growth hormone.

By combining specifically with antigens, antibodiescan neutralize substances, such as toxins. Antibodies alsofacilitate the elimination of bacteria and viruses to whichthey are bound by recruiting other components of theimmune system (e.g., macrophages and complement).

13


(Complement activation is a rapid, complex process thatis activated by antigen-antibody complexes to destroycells, bacteria, or viruses, or cause inflammation.)

The basic unit comprising antibodies consists of fourprotein chains– two identical light chains and two iden-tical heavy chains. Heavy chains can vary in type, and thetype of heavy chain in a particular antibody determinesthe subclass– i.e., IgM, IgA, IgD, IgG, or IgE–of an-tibody. These protein subunits are linked in a fixed andprecise orientation to forma “Y’’-shaped molecule (fig-ure 2-l). The forked end of the antibody contains twovariable regions, the sites of the molecule that recognizeand bind with the specific antigen. To accommodate themany antigens that exist, these variable regions differfrom molecule to molecule. The other end is nearlyidentical among all antibodies and is known as the con-stant, or effecter, region. The constant region is notresponsible for antibody binding specificity, but hasother functions, including promoting efficient attach-ment of the antigen-antibody complex by certain cellsand activation of the complement cascade.

Cells

In recognizing and reacting to substances it perceivesas foreign, the immune system, or lymphoid system, in-volves several different cell types. Most of these cells arecommonly referred to as white cells, or leukocytes. Fig-

Figure 2-1 – Structure of an Antibody Molecule


ure 2-2 presents one simple classification scheme forwhite cells.

An exhaustive description of each type of cell involvedin an immune response is beyond the scope of this report.Rather, this section provides short descriptions of onlythe principal cell types –lymphocytes and macro-phages-to serve as background for the following sec-tion, which describes the interaction of these cell types,and for chapter 3, which discusses how scientists test forimmunotoxicity by measuring perturbations in these cellpopulations. Table 2-1 lists additional cell types that haveimmunological importance.

B Cells

A particular subclass of lymphocytes, called B lym-phocytes or B cells, recognizes antigens as foreign sub-stances and responds by producing antibodies specificfor a given antigen. Antigen-antibody mediated reactionsare known as humoral immunity. Once a B cell has beenactivated by an antigen, it is committed to producingantibodies that bind to the specific antigen. B cells arisefrom precursors in the bone marrow (as do all otherlymphoid and blood cells) . These cells, like macrophages(described in following section), play important roles inantigen processing, one sequence of events necessary totrigger antibody production and other immune re-sponses.

A distinguishing feature of the outer surface of B cellsis the presence of surface antibodies. These surface markers,along with surface markers on other cells of the immunesystem (box 2-A), play critical roles in the activation and

Table 2-l—Major Cells Classes of ImmunologicalImportance

Primary effecter cellsB lymphocytesT lymphocytesNK cells

Antigen presenting cellsB lymphocytesMacrophages/monocytesFollicular dendritic cellsInterdigitating dendritic cellsLangerhans cellsEndothelial cells

Accessory cellsNeutrophilsBasophils and mast cellsEosinophilsPlatelets


Chapter 2—The Immune System and immunotoxicity ● 15

Figure 2-2-White Cells

White

@

,,. : ‘ 4: -.. .0 .

‘t-t?,,. : f) 0;8f ,. ● . . . . “.:: . ” s e e b . .

a . . . . . .. . , ● *

.: . .“. .“9 ● .:*

@

. . . . ~.. ...-., . . . . . . . . .. . . . ::..:.. . . . . . .;. . . >.~: ..” .. . . . . .“.:::.. “. & . .. . .

. * .:.. . . . . . . . . . . ,. ..,. . . . - . . .

. . . . . .7* :...‘.. b. a. . AC.<.(jj( .:.’

. .. . . .- :....:.’..:; :...;;;.. :...:.” I.:.l.

Polymorphonuclearcells

@c, . . . . . . . . . . .

,,1. . . .-~.:..:: . . . .. . .. . . . , , . . .+

. . . .. . .. . .. . .. .

y . . : ? 2 . .i $k b? :. :j~ .:;y’m‘ qfl... . ,<: .~ .<;”.: .:.;.,, . . . . . .. . .. . . . . . . . . . . ..:.:. ... 4 , . . . .

. . .

Mononuclearcells

@

. . . . ..,:f ..O:::,

,:J+:?. j 0 ::,‘. + , . *!. Neutrophils. .. . . . . . . . .. . . ● .? g ,

..0 .“

1

Mast cells(tissue)

Lymphocytes

Plasma

Macrophages Histiocytes(monocyte) (tissue)

SOURCE: Office of Technology Assessment, 1991, adapted from S. Sell, Basic Immunology: Immune Mechanisms in Health andDisease (New York, NY: Elsevier, 1987),

regulation of the immune system. Surface immunoglobulinsdefine the specificity of the response for that B cell and helptrigger the production of antibodies by that cell.

T Cells

A second broad group of lymphocytes are T cells. LikeB cells, T cells arise from precursors in the bone marrow,but must circulate to the thymus for maturation. Similar-y, they have characteristic cell surface markers and can

specifically recognize antigen if it has been processedand presented to them by other cells of the immunesystem. Based on functional and other criteria, T cellscan be divided into several major subpopulations (table2-2).

T cells can be viewed as the “master regulators” of theimmune system (22). In addition to their required inter-action with B cells to produce antibody, various T celltypes are responsible for cell-mediated immunity, a class


of immune responses that does not depend on antibodyproduction. T cells can be cytotoxic, i.e., directly kill cellsthat are expressing a specific antigen. T cells (and mac-rophages and natural killer (NK) cells) produce a varietyof protein molecules, called cytokines, but they do notproduce antibodies.

Cytokines serve as messengers that transmit signalsbetween cells to control and modulate an immuneresponse. For example, some cytokines recruit othercells to participate in and augment an immune response.Some stimulate B cells to produce antibodies. Otherssuppress the immune reaction or ensure that the systemfocuses on the antigen and does not run rampant in anonspecific attack that would damage host tissue.Cytokines are produced in extremely small amounts – onthe order of parts per billion – and act locally at the siteof their release. The interferon are examples ofcytokines. \

M a c r o p h a g e s

Macrophages (literally “large eaters”) are the largestcell type in the immune system and play a central role inthe immune system’s response to a foreign agent. Mac-rophages invade sites of inflammation and serve to clearthe sites of cellular debris; they are also particularlyeffective in phagocytizing, or ingesting, infecting or-ganisms.

Macrophages do not produce antibodies. Instead,they are involved in the first step leading to induction ofan immune response. A microphage ingests and non-specifically processes antigen, and then presents theprocessed antigen on its cell surface so that it can berecognized by specific antigen reactive cells. Such an-tigen presentation and processing-which is linked togenetic elements (3,12,17,24,29) – is a critical part of theinduction of both humoral and certain cell-mediated

Chapter 2—The Immune System and Immunotoxicity ● 17

Table 2-2—Major Functions of T Cells

Abbreviation Function

TD~ . . . . . . . . . . .

TH~ . . . . . . . . . . .

TK~ . . . . . . . . . . .

TS~ . . . . . . . . . . .

T cells responsible for ’’delayed-type hyper-sensitivity y.’’ After reacting with antigen, TDcellsrelease cytokines that can kill target cells invitro (cytotoxins) and activate macrophages,inducing inflammation.T helper cells assist in humoral immunity, i.e.,antibody production. They are required if a Bcell is to produce antibody. One characteristicfeature of helper T cells is a surface markercalled CD4.Often referred to as killer T cells, or cytotoxiclymphocytes, this subclass of T cells, afterbeing specifically sensitized, directly interactswith target cells to kill them in vitro. They aredistinguished from NK cells by the requirementfor sensitization and cell surface markers.T cells that serve to control immune responsesby producing factors that can act on both Bcells and TH cells. Suppressor T cells can bedis-tinguished from helper T cells becausethey exhibit a signature molecule referred to asCD8.


immune responses. (B cells also process antigens.) Mac-rophages also produce important cytokines that regulateoverall immune responsiveness.

NK Cells

Another lymphocyte subclass is natural killer cells, orNK cells. NK cells derive from the bone marrow, but theirexact relationship to B cell and T cell precursors remainsto be elucidated. NK cells share some properties of Tcells and macrophages, but also share several surfacecharacteristics with B cells.

NK cells do not play a central role in antigen-specificantibody responses, but are critical components ofgeneral, nonspecific immune defenses. In vitro, NK cellslyse, i.e., kill, several types of tumor cells and virus-in-fected cells, and thus are believed to be important in thebody’s defense against viruses or cancer. Additionally,these cells likely play an important role in immunity tocertain bacterial and parasitic infections.

Organs

Several organs are responsible for the developmentand maintenance of a functioning immune system (fig-ure 2-3), which complicates making assessments ofimmunotoxicity. Changes in the circulatory or lymphatic

systems, for example, can affect any number of organs.Strictly speaking, however, lymphoid organs are the prin-cipal organs of the immune system (22). A lymphoidorgan is a compartmentalized collection of lymphocytes,macrophages, and other immune cells. It maybe part of,or mixed among, cells of another organ. Lymphocytesalso circulate freely through the blood and lymphaticvessel network.

Bone marrow, the thymus, and even the fetal liver, inpart, are lymphoid organs. In humans (and most otherspecies), bone marrow is the predominant organ fromwhich lymphoid cells originate. Some of the cells thatdevelop in the bone marrow complete their maturationbefore entering circulation. Others, however, must un-dergo further differentiation in other organs (e.g., thethymus).

The spleen and lymph nodes are lymphoid organs thatclear the blood of infectious organisms and serve asrepositories for antibody-producing cells. Tonsils, theappendix, and Peyer’s patches (small aggregates of cellsin the intestine) are also lymphoid organs. Local collec-tions of tissue within both the gastrointestinal tract andbronchus play a role in certain immune responses–gastrointestinal lymphoid tissue is thought to play animportant role in immunity to infectious agents enteringthe body through the mouth, for example.

I M M U N E R E S P O N S E S

Immune responses can be divided into two categories:nonspecific and acquired. Nonspecific, or innate, im-munity involves those cells (e.g, macrophages andnatural killer cells) and processes (e.g., complementactivation) that do not depend on exposure, followed byreexposure, to antigen. Generally, nonspecific immuneresponses represent the body's first line of defense andinvolve a generic, innate reaction to foreign substances.Acquired, or adaptive, immunity is characterized by an-tigen specific processes.

There are two broad classifications of acquired im-munity that are commonly referred to as humoral im-munity and cell-mediated immunity. Both require thecoordination of multiple cell-types of the immune sys-tem. And, while one type of immune response can some-times dominate after exposure to a particular antigen, forthe most part, both play roles when foreign substancesare presented. This section briefly describes the interac-


Figure 2-3 –Major Organs and Tissues of the Immune System

Lymph

L

I

Thymus

des

er's patches

K’JW)AL’11 I \ 1/:’/ II Bone marrow

SOURCE: Office of Technology Assessment, 1991, adapted from S. Sell, Basic Immunology Immune Mechanisms in Health andDisease (New York, NY: Elsevier, 1987).

tions involved in the two classes of acquired immuneresponses to provide a background for how perturba-tions in immune responses can be measured.

As mentioned previously, the immune system func-tions principally to protect the body. Under some circum-stances, however, control mechanisms can be compromisedand the immune system turned against the body, causingharm. Conditions that arise when this occurs vary frommild discomfort to fatal disorders. Thus, this section alsoexamines pathological immune responses.

h u m o r a l I m m u n i t y

The production of specific antibodies in response toexposure to a foreign substance is called humoral im-munity. humoral immunity can be particularly importantin protecting the body against certain biological agents.

As illustrated by figure 2-4, three types of immune cellstypically interact during optimum immunoglobulin produc-tion. A toxic substance that blocks any step can disruptthis response in a measurable fashion.

First, an antigen presenting cell, often a microphage,must process the foreign substance. Macrophages per-form this reaction nonspecifically, and in doing so con-centrate the antigen as well as release factors thatfacilitate subsequent B and T cell cooperation. Second,T helper cells interact with the antigen-presenting cell toproduce chemical signals, cytokines (interleukins), thatstimulate B cells and additional T cells. Finally, the B cellcan mature into an antibody producing cell, also called aplasma cell.

This series of reactions is antigen-specific. Each dif-ferent antigen elicits a unique antibody and there are a


Figure 2-4 – Generation of Antibody Forming Cells

Activation Proliferation

\

J JBcellDifferentiation

Antibodiessecreted

./ + .

. n t i g e n ~ ~ m ~ ’ ; : : ; : ; : : o f

TH activation and proliferation

T-helper ( TH ) cells

Antigenprocessing cells

SOURCE: Office of Technology Assessment, 1991, adapted from K. White, Medical College of Virginia, Richmond, VA, 1990.

large number of antigens against which antibodies can beproduced. Additionally, the immune system has a“memory" whereby re-presentation of a familiar antigenresults in a slightly different, accelerated immune response.Both B and T cells are involved in immune memory.

In some cases, B cells can be stimulated, by certainantigens called T cell-independent antigens, to produceantibodies without the involvement of T cells. B cells canalso be stimulated to proliferate in vitro by mitogens.Mitogen assays are used as a measure of immunotoxicityand are discussed in chapter 3.

One potentially adverse consequence involving an-tibody production is immediate-type hypersensitivity, atype of allergy response. (Some use the term allergy torefer only to immediate-type hypersensitivity, and not asecond reaction, delayed-type hypersensitivity. Thisbackground paper uses allergy to denote both re-sponses.) When immediate-type, or anaphylactic, reac-tions are initiated by certain antigens– e.g., pollens oranimal dander– in certain individuals, mast cells (table2-1, figure 2-2) release pharmacologically active substan-ces (e.g., histamine, serotonin). These substances caninduce a range of problems, including inflammatorychanges in many tissues that result in hives and wheezing,or even abrupt changes in blood pressure. In some cir-cumstances, such reactions can be life-threatening. The

predominant immunoglobulin involved in immediate-type hypersensitivity in humans is called IgE.

Ce l l -Med ia t ed Immuni ty

As described previously in table 2-2, several sub-populations of T cells can be recognized physically andfunctionally. T cells, NK cells, and activated macrophagescarry out the functions of the second broad category ofacquired immune responsiveness, cell-mediated im-munity. Again, the interaction of cells in cell-mediatedimmunity forms the basis for tests developed to assesspotential immunotoxicants. Cell-mediated immuneresponses require antigen processing to specifically sen-sitize T cells. Table 2-3 summarizes the general types ofcell-mediated immunity. Cell-mediated immunity is par-ticularly important to transplantation rejection, tumorsurveillance, and for protection against infectious agents.

Several different types of cell-mediated immune responsesexist (8). One potentially adverse consequence of cell-mediated immunity is delayed-type hypersensitivity(DTH). Contact sensitization, such as poison ivy andother skin allergies resulting in inflammation and tissuedamage, is a classic example of DTH. Another delayed-type hypersensitivity called cutaneous basophil sensitivityalso involves the skin, but the predominant cell typeinvolved differs from that for classic contact sensitivity


Table 2-3-Mechanisms of Cell-mediated Immunity

Direct killing by sensitized TK cells; the cells react directly withthe target cells to Iyse them (cytotoxic T lymphocyte activity).Indirect killing by sensitized TD cells in combination withcytokines.Antibody-dependent cell-mediated cytotoxicity (ADCC) in-volves a type of lymphocyte without characteristic cell sur-face markers (“null cells”) in combination with specific anti-body.Direct killing by nonsensitized NK cells; the cells react directlywith the target cells.Phagocytosis, i.e., digestion, of substances by macrophages.Release of cytokines.

SOURCE: Office of Technology Assessment, 1991; based on S. Sell, Basiclmmunology:lmmune Mechanisms in Health and Disease (NewYork, NY: Elsevier, 1987).

and the time lag between exposure and the reaction isshorter (1,8).

Autoimmunity

“Tolerance” is the term applied to the mechanisms thatprevent the immune system from responding to its own–i.e., self or auto — antigens. Sometimes, however,tolerance to self antigens is lost, resulting in autoimmunereactions (table 2-4). When such situations occur,humoral immunity, cell-mediated immunity, or both canturn their destructive capabilities against the body, lead-ing to tissue damage and/or inflammation. The presenceof antibodies that react against self antigens (auto-antibodies) can sometimes be demonstrated in severalautoimmune diseases (e.g., systemic lupus erythematosus,rheumatoid arthritis, diabetes). But, the presence ofautoantibodies is not inevitably associated with diseaseand, in fact, autoantibodies normally increase with age.

Autoimmune pathologies can be difficult to assess, butcertain features are thought to be indicative of autoim-mune phenomena. The induction of autoimmune eventsin a few discrete populations have been attributed toexposure of the individuals to certain toxicants (5,14,15).

WHAT IS immunotoxicITY?

As mentioned, immune responses are complex, multi-factorial interactions with different consequences depend-ing on the situation. In some instances, the immuneresponse will be depressed or suppressed (table 2-5),

which can result in increased susceptibility to disease ortumor formation. Conversely, the immune system some-times hyperreacts when presented with certain foreignsubstances, which can result in an allergic response, i.e.,immunologic hypersensitivity, wherein the response isout of proportion to and more harmful than the initialthreat of the substance. In some of these cases, theresponse can be the source of tissue damage, so thatsuppressing certain immune reactions actually reducestissue injury. Finally, the immune system can becomeconfused and fail to recognize the body’s own com-ponents as “self’ – i.e., the immune system treats a “self’substance as foreign and mounts an autoimmuneresponse, which can result in certain characteristicpathologies.

For the purposes of this study, OTA defines immu-notoxicity as an adverse or inappropriate change in thestructure or function of the immune system after ex-posure to a foreign substance. Adverse effects can bemanifest as immunosuppression, hypersensitivity, orautoimmunity.

In any of these reactions, the cells, tissues, and organsof the immune system can be activated, inhibited,destroyed, or their responses exaggerated. It is thedemonstrated involvement of at least one or more ofthese components that defines whether a consequenceresults from an actual immune response. For example,the term allergy should be used only to denote the in-volvement of immune responses, but is often mistakenlyused to describe other adverse reactions (box 2-B).

An array of biological, physical, and chemical sub-stances can perturb the intricate balance of the immunesystem, and this complex system provides several targetsites for immunotoxicants. OTA broadly defines immu-notixicant as a substance that leads to undesired effectson the immune system. The focus of this report is onimmunotoxicants that are chemicals, although impor-tant information has been, and continues to be, learnedfrom studies of biological substances.

Whether a substance causes an adverse effect on theimmune system, which could be permanent or reversible,depends on many factors, including the nature of thesubstance, dose and exposure, route and extent of ex-posure, the presence of other agents, and an individual’ssex, genetic predisposition, age, and state of health.


Table 2-4-Some Human Diseases in Which Autoantibodies Have Been Detected

Self-antigens (as defined by the autoantibodiesDisease involved or detected)

Guillan-Barré syndrome . . . . . . . . . . . . . . Myelin and other components of the peripheral nervesHashimoto’s thyroiditis . . . . . . . . . . . . . . Cytoplasmic or microsomal thyroid antigen, thyroglobulinMultiple sclerosis . . . . . . . . . . . , . . . . . . . Brain or white matterMyasthenia gravis . . . . . . . . . . . . . . . . . . Acetylcholine receptor at the neuromuscular synapsisProgressive systemic sclerosis

(scleroderma) . . . . . . . . . . . . . . . . . . . Various antigens in cell nuclei, especially nucleoliRheumatoid arthritis . . . . . . . . . . . . . . . . Heart, muscle, joint, subcutaneous nodules, aggregated

gamma-globulinSystemic lupus

erythmatosus (SLE) . . . . . . . . . . . . . . Various nuclear antigens, especially double-strandedDNA, antigens on leucocytes and erythrocytes, liver,spleen, kidney, muscle

SOURCE: Office of Technology Assessment, 1991; adapted from E. Gleichmann, I. Kimber, and I.F.H. Purchase,“lmmunotoxicology: Suppressive and Stimulator Effects of Drugs and Environmental Chemicals on theImmune System,” Archives of Toxicology 63:257-273, 1989; and S. Sell, Basic Immunology: ImmuneMechanisms in Health and Disease (New York, NY: Elsevier, 1987).

Table 2-5-Some Immunodeficiency Disorders

Disorder Immunological defect

Acquired immune deficiency syndrome (AIDS) . . Viral infection of certain T ceils

Congenital thymic aplasia (DiGeorgesyndrome) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thymus absent or small; T cells absent or reduced

Severe combined immune deficiency disease(SCID; “Bubble Boy” disease) . . . . . . . . . . . . . Lack of T and B ceils

X-linked hypogammaglobulinaemia(Bruton’s disease) . . . . . . . . . . . . . . . . . . . . . . . . Absence of B cells

SOURCE: Office of Technology Assessment, 1991; adapted from E. Gleichmann, I. Kimber, and I.F.H. Purchase,“lmmunotoxicology: Suppressive and Stimulator Effects of Drugs and Environmental Chemicals on theImmune System,” Archives of Toxicology63:257-273, 1989.

Chapter 3 discusses what tests are currently employed todetermine whether a substance is immunotoxic anddescribes immunotoxic substances and their effects.

immunotoxicANTS: WHO IS AT RISK?

While exposure to immunotoxic substances can occuranywhere to anyone, the opportunity to be exposed isgreater for some populations of individuals than forothers. Since immunotoxic effects have been describedfor some ambient and indoor air pollutants, some pointout that the magnitude of individuals at risk could betremendous (21). Yet others argue that while such effectshave been described for indoor air pollutants, the levelsof these chemicals would generally be low– probablybelow the threshold for response (2).

Nevertheless, certain discrete populations areprobably at increased likelihood of exposure, moreamenable for scientific research, or both. For example,observations of occupational exposures to toxic sub-

stances have contributed much of the data pertinent toimmunotoxicological effects — i.e., hypersensitivity,autoimmunity, and immunosuppression. Similarly, im-munosuppressive drugs can be viewed as prototype im-munotoxicants, and so patients receiving such drugs toprevent transplant rejection can be observed. Con-sumers of cosmetics have also been examined to detecthypersensitivity to various agents.

Yet even among populations of individuals, not all ofthose exposed are affected. Certain individuals may bemore susceptible to developing adverse reactions for avariety of reasons separate from mere exposure to thetoxicant – even when dose and duration of exposure aresimilar for different individuals. For example, the personcould be innately susceptible, i.e., be geneticallypredisposed. Age is another important factor in im-munotoxicology, since the immune system is not com-pletely functional at birth and might be more vulnerableto damage then. It also changes appreciably in olderpopulations–generally to a less responsive level (26).

22 . Identifying and Controlling Immunotoxic Substances

Box 2-B –"Allergy": Some Common Misperceptions

From an immunological standpoint, the term allergy refers to a normal immune response with deleteriousconsequences, such as allergic rhinitis, or hay fever (e.g., to grass pollen), or contact sensitivity (e.g., to poisonivy). True “allergies’’ occur when a human comes in contact with a substance that triggers a predictable responsethat involves certain compon-ents of the immune system. Immunological hypersensitivity, or allergy, is not dueto an alteration of the immune system by a foreign substance per se, but is an inappropriate activation of theimmune system. Two exposures, the first involving sensitization to the substance, are needed to demonstrateallergy.

“Allergy," however, is often improperly used to denote generic adverse reactions or susceptibilities. Forinstance, some persons develop, or are born with, an inability to produce the intestinal enzyme lactase. Theselactase-deficient individuals are unable to breakdown the sugar lactose. For them, digestion and absorptionofordinarylactose-containing milk is quite troublesome and results in gastrointestinal distress. The symptoms,however, do not arise as a result of perturbations to the immune system. Rather, the problems stem from anintolerance, not an allergy, to the milk sugar lactose.

In contrast, some problems previously thought to be intolerances might be true immune reactions, orallergies —e.g., example the condition known as celiac sprue, where an individual has an adverse reaction towheat. In this syndrome, the soluble protein of wheat flour, A-gliadin, induces a damaging inflammatory reactionto the epithelial layer of the gut leading to a malabsorption syndrome. Although once believed to be due to anotherenzyme deficiency, growing evidence indicates that A-gliadin shares significant structural homology with anadenovirus protein. AS a result of earlier presensitization to the adenovirus protein, epithelial lymphocytes respond tothe gliadin with subsequent adverse inflammatory effects — a true immune response, and hence a true allergicresponse.


Finally, the overall state of health is also important indetermining immunotoxicity.

Genetic background, in particular, is an importantconsideration in evaluating both potential immu-notoxicity and variation in toxic effects. For example,genetic bases could account for the differential ability ofindividuals to produce anti-inflammatory factors, whichin turn would influence how a person would be able tomount and modulate an immune response to an offend-ing agent (8). Likewise, although almost anyone candevelop an allergy to a given substance, a distinct seg-ment (15 to 20 percent (23)) of the population is clinicallyatopic, i.e., individuals who are unusually reactive to avariety of substances. Several genes have been identifiedthat could influence this hyperreactivity (16), althoughspecifics remain to be elucidated.

Not only is there a genetic basis for controlling theimmune response to a particular antigen (as determinedby histocompatibility or human leukocyte antigens (HLA),which present processed antigens (3,12,17,24,29)), butother genes are responsible for certain pharmacologicabnormalities that can predispose an individual to immune

dysfunctions, e.g., hyperreactivity to histamine or acetyl-methylcholine. The latter substance is used to detectpeople with hyperreactive airways that constrict andcause wheezing when exposed to antigen. Total IgEproduction–central to immediate-type allergic reac-tions– is regulated by genes (16). Persons could havegenetic differences —singular or in combination— thatmight predispose them to allergies to certain environ-mental and occupational antigens (30). Certain HLAgenes also are associated with increased risk of autoim-mune diseases (13,20).

Finally, in addition to intrinsic factors, external riskfactors are critical. Smoking and exposure to tobaccosmoke, for example, are important external risk factorsthat must be accounted for in assessing potential im-munotoxicity in humans (6). Another potential externalrisk factor is the presence of coincidental pulmonaryinfection at the time of exposure. The association of viral(but not bacterial) infection with triggering attacks ofboth childhood and adult onset asthma has been docu-mented (9). Such infections can cause bronchial hyper-reactivity that may even become permanent. It has beenhypothesized that such an infection occurring in a worker


simultaneous with exposure to an industrial substance orenvironmental pollutant could result in an enhancedsensitivity to that substance. A different external factor,house dust mites, is a precondition for certain childhoodasthmas (25).

SUMMARY AND CONCLUSIONS

A functioning immune system helps protect thehuman body from a vast array of chemical, physical, andbiological foreign substances, as well as from problemsthat arise from within (e.g., tumor cells). proper reactionto a stimulus requires the cooperation of several types ofcells and organs, as well as feedback from other systemsin the body.

Two broad types of immune responses exist: non-specific and acquired. The latter response involves twodifferent types of reactions: humoral immunity and cell-mediated immunity. humoral immunity is characterizedby the production of antibodies that circulate in bloodand lymph fluid. Cell-mediated immunity encompassesan array of responses that involve different cell types, butdoes not involve antibody production.

The complexity of the immune system makes it vul-nerable to the effects of toxic substances on many fronts.immunotoxicity, then, is any alteration in an immuneresponse — suppression, hypersensitivity, or autoim-munity-- resulting from exposure to a toxic substance.

The science of immunotoxicity, i.e., immunotoxicol-ogy, is complicated by several elements: the complexnature of the immune system, age of subject, geneticbackground, and external risk factors, such as smoking.Genetic factors account, in some instances, for variationin immune responsiveness to an antigen, and hence needto be assessed when evaluating potential immunotoxicaffects of a substance.

1.

2.

3.

4.

CHAPTER 2 REFERENCES

Askenase, P., “Basophil Arrival and Function in Tis-sue Hypersensitivity Reactions;’ Journal of AZZer~and Clinical Immunology 64:79-89, 1979.Axelra~ B., U.S. Environmental Protection Agency,Washington, DC, personal communication,November 1990.Barinag~ M., “Immune Mystery Revealed: HowMHC Meets Antige~” Science 250:1657-1658, 1990.Bic~ P.H., ‘The Immune System: Organization andFunction,” Immunotom”cologY and Immunophar-

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

macology, J.H. Dea~ M.I. Luster, A.E. MunsoE etal. (eds.) (New Yor~ NY: Raven Press, 1985).Bigazz~ P.E., “Autoirnmunity Induced by Chemi-cals~’ Clinical Toxkology 26(3&4) :U5-156, 1988.Burchlle~ C.M., Higgins, M.W., Keller, J.B., et al.,“Passive Smoking in Childhood: Respiratory Condi-tions and PulrnonaxyFunction inTecumse~ Michigan,”American Review ofRespirato~Dtiease 133%6-973,1986.Burger, EJ., Tardiff, R.G., and Belkmt~ J.A. (eds.),Environmental Chemical Exposures and ImmuneSystem Integrity, Volume XIII: Advances in i14bakmEnvkmnw@ Ta”d~ (l%nceto~ NJ: PrincetonScientific Publishing Co., 1990).Burrell, R., “Identifying and Controlling Im-munotoxic Substances,” contract paper prepared forthe Office of Technology Assessment, U.S. Con-gress, April 1990.Busse, W.W., ‘The Relationship Between Viral In-fections and Onset of Allergic Diseases and Asth~”ChicalandEqenhumtil Imnumolqg 19:1-9, 1989.Dean, J. H., Cornacoff, J.B., and Luster, M.I.,‘Toxicity to the Immune System: A Review~’ Im-munophamzacolopReviews, vol. I, J.W. Hadden andA. Szentivanyi (eds.) (New York, NY: PlenumPublishing Corp., 1990).De~ J.H., Murray, M.J., and Ward, E. C., ‘ToxicResponses of the Immune System” Casm-ett andDoull’s Toxicology. T~Le Basic Science ofPobons, 3rdcd., C.D. Klaassen, M.O. Amdur, and J. Doull (eds.)(NewYor~ NY: MacMill~ 1986).Deverso~ E.V., Gow, I.R., Coadwel~ WJ., et al.,“MHC Class II Region Encoding Proteins Relatedto the Multidrug Resistance Family of Trans-membrane Transporters,” Nature 348:738-740.Erlich, HA., and Bugawa~ T.L., “HLA Class IIGene Polymorphism: DNA Typing, Evolutio~ andRelationship to Disease Susceptibility,” PCR Tech-nology: Principles and Applications for DNAAmplijicatwn, H.A. Erlich (cd.) (New York NY:Stockton Press, 1989).Gleichmann, E., Kimber, I., and Purchase, I. F.H.,“Imrnunotoxicology Suppressive and StirnulatoryEffects of Drugs on the Immune Systeq’’Archives ofTOXiCOIOQ 63257-273,1989.Kamrnuller, MEv Bloksm~ N., and Seine~ Wq’’Chemi-cal-inducedAutoimmune Reactions and Spanish ToxicOil Syndrome: Focus on Hydantoins and RelatedCompounds,” Clinical Toxicology 26(3&4):157-174,1988.Mar~ D.GV and Bi~ W.B., ‘The Genetics of AtopicAllergy~’ Immunological Dkeases, 4th cd., M. Sarn-

24 ● Identifying and ControllingImmunotoxic Substances

17.

18.

19.

20.

21.

22.

23.

24.

ter, D.W. Talrnage, M.M. Fra~ et al. (eds.) (Bosto~MA: Little, Brown & Co., 1988).Monaco, JJ., Cho, S., and Attaya, M., ‘TransportProtein Genes in the Murine MHC: Possible Im-placations for Antigen Processing’’ Science 250:1723-1726,1990.Norbury, KCV “Irnmunotoxicological EvaluatioIx AnOvemiew~’JoumaloftheArnAcan Ch%geof Toxicology4(4)279-289, 1987.Roitt, I.M., EssentiulImmunology, 6th cd., (Chicago,IL: Year Book Medical Publisher% Inc., 1988).Scharf,SJ., FriedmarqA.,Brautbar, C., et al., ’’HLAClass II Allelic Variation and Susceptibility to Pem-phigus vulgaris, ” Proceedings of the NationalAcaakmy of Sciences (USA) 85:3504-3508, 1988.Selgrade, M., U.S. Environmental Protection Agen-cy, Research Triangle Park, NC, personal com-munication, September 1990.Se~ S., Basic Immunology: Immune iklechanisms inHealth andDkease (New Yor~ NY: Elsevier, 1987).Smith J.S., “Epidemiololgy and Natural History ofAsthma, Allergic Rhinitis, and Atopic Dermatitis(Ecmma)~’AlleW, l?rinc@es and Practice, E. Mid-dleton,Jr., C.E.Ree~ and E.E.El~ (eds.) (St. Louis,MO: C.V. Mosby, 1978).Spies T., Bresnah~ M., Bahrmq S., et al., “A Genein the Human Major Histocompatibility Complex

25.

26.

27.

28.

29.

30.

Class I Region Controlling the Class I AntigenPresentation Pathway,” Nature 348:744-747, 1990.Sporik, R., Holgate, S.T., Platts-Mills, T.A.E, et al.,“Exposure to House-dust Mite Allergen (DerpI) andthe Development of Asthma in Childhood” lheNewEngland Journal of Medicine 323(3)502-506, 1990.Thoman, M.L., and Wiegle, W.O., ‘The Cellular andSubcellular Bases of Immunosenescence, ’’Advancesin Immunolqy 46:221-261, 1989.Thomas, P.T., BusSe, W.W., Kerkvliet, N.I., et al.,“Immunologic Effects of Pesticides;’ The Eflects ofPesticides on Human Health S.R. Baker and C.F.Wilkinson (eds.) (Princeto~ NJ: Prin~ton ScientificPublishing Co., 1990).Trizio, D., Basketter, D.A., Both~ P.A., et al.,“Identification of Irnmunotoxic Effects of Chemicalsand Assessment of Their Relevance to M~’’Food andChemical Toxicology 26(6):527-539, 1988.Trowsdale, J., Hanso~ I., Mockridge, I., et al., “Se-quences Encoded in the Class II Region of the MHCRelated to the ‘ABC’ Superfamily of Transporter%”Nature 348:741-744, 1990.U.S. Congress, Office of Technology Assessment,Genetic i140nitoring and Screening in the Workplace,OTA-BA-455 (Washington DC: U.S. GovernmentPrinting Office, October 1990).

Chapter 3

Immunotoxicological Tests

Chapter 3

Immunotoxicological Tests

INTRODUCTION

This study defines immunotoxicity as an adverse orinappropriate change in the structure or function of theimmune system after exposure to a foreign substance. Anoverreactive or a suppressed immune system can lead tocertain health effects commonly associated with immunedysfunction. Skin and respiratory allergies indicate thatthe immune system has become overreactive–hypersen-sitive-to a foreign substance. Increased rates of certaintypes of infection or incidence of certain tumors indicatethat parts of the immune system have become sup-pressed. For example, researchers received an importantclue regarding human immunodeficiency virus whenphysicians reported more frequent diagnoses of a rareinfection, Pneumocystis carinii, and a rare tumor,Kaposi’s sarcoma, in the same individual. Similarly, cer-tain fungal or viral infections point to a suppressed im-mune system, for these ubiquitous infectious agents rarelysurmount the body’s defense systems.

Evidence accumulated over time indicates that somechemicals encountered in commerce can alter the struc-ture or function of the immune system. Occupational andconsumer experiences have identified several allergens.Clinical experience with certain drugs and studies ofaccidental exposure to certain industrial substances in-dicate that some chemicals can lead to disease by sup-pressing various immune functions or can causeautoimmune reactions.

Rather than wait for adverse effects to manifest them-selves, chemical manufacturers and regulators now seekmeans to predict immunotoxicity prior to human ex-posure. immunotoxicologists have developed in vivo andin vitro tests, often used in combination, to analyze theeffects of substances on various components and proces-ses of the immune system. This chapter describes methodsfor evaluating chemical immunotoxicity. It also provides abrief explanation of the difficulties entailed in interpret-ing currently available tests and using their results to

predict immunotoxicity in humans. Finally, it reports onsome known or suspected immunotoxicants.

TEST METHODS

The purpose of toxicity testing is to ascertain thepotential for a substance to adversely affect the structureor function of an organ system. Toxicological tests mustbe valid, i.e., they must actually measure the effect ofinterest. They must also be reliable, i.e., it must be pos-sible to duplicate the test in different laboratories with aminimal number of inaccurate results. Importantly, sincethe test results may be used as the basis of regulation, itmust be possible to extrapolate the likely results ofhuman exposure from data garnered from toxicologicaltests on experimental animals.

An immunotoxicity assessment measures quantitativeand functional changes in the immune system followingexposure to the test substance. It measures whether achemical alters lymphoid organ weights or histology,causes qualitative or quantitative changes in humoral,cell-mediated, and nonspecific immunity, or modifiessusceptibility to infectious agents or tumors. (Ch. 2details the various functions of the immune system andits components.) Most tests used in immunotoxicologicalassessments are performed on experimental animals,usually rodents. In the best experiments, animals areexposed to a putative toxicant in a manner that mimicshuman exposure conditions as closely as possible. Inmany of the tests, tissue or fluids removed from an animalthat has been killed (sacrificed) are examined in vitro todetect evidence of toxicity. Some tests, primarily the hostresistance assays, are performed in vivo, but have diseaseor death as the endpoint measured.

Because of the harm that most current tests can do tothe test subject, predictive testing for immunotoxicityusing human subjects is quite rare. It is possible to per-form some of the common predictive tests on humanperipheral blood, bronchoalveolar lavage fluid, or nasal

27


lavage fluid since removal of these fluids does no harm.Tests similar to those used to predict hypersensitivity areused on humans in a clinical setting-to determine thecause of allergic symptoms—but clinical testing isbeyond the scope of this report.

A basic list of immunotoxicity tests and what theymeasure is provided in the following sections. The list isillustrative rather than comprehensive. Descriptions ofbasic tests and specific methodology can be found inseveral sources (3$8,75).

Pathology

Pathology– the science of disease– is a basic tool oftoxicology. Examination of the organs and cells of theimmune system using routine pathologic tests can yieldevidence of immunotoxicity. Many of the following testsare applied routinely to new chemicals, and can be inter-preted to suggest the need for further study of immunesystem effects.

Hematology--A complete blood cell count measuresthe total number of blood cells. A differential blood cellcount discriminates between the red blood cells and thetypes of white cells (e.g., lymphocytes, monocytes,neutrophils, basophils, and eosinophils) in the blood.Alterations in cell counts can indicate potential im-munotoxic effects.

Histology-The lymphoid organs – the thymus,spleen, lymph nodes, and bone marrow — provide infor-mation about possible immune alterations when ex-amined at the cellular level. Changes in the thymus mayindicate T cell alterations; B and T cell accumulations inspecific areas of the spleen and the lymph nodes suggesta potential change in either humoral immunity (B cells)or cell-mediated immunity (T cells). Bone marrowevaluation can yield information about pluripotentialstem cells (immune cell progenitors).

Organ weights –T cells complete their maturation inthe thymus. The spleen contains B and T cells. Thymusor spleen weights outside normal reference ranges areviewed as important indicators of potential im-munotoxicity.

Cellularity– Counts of certain cells in the tissues of thethymus, spleen, bone marrow, and peripheral lymphnodes can be used to determine potential immune altera-

ions, since a change in cell number suggests an im-munotoxic effect on that organ.

Quantitation of splenic B and T cells–B and T cellscannot be distinguished by size or shape, but they do havedistinct surface markers. A variety of specializedmarkers can be used to identify cell types and subsetswithin type. Marked cells can be counted manually or byusing automated cell counters. Alterations in cell countssuggest possible immunotoxic effects.

humoral Immunity

humoral immunity involves the production of specificantibodies by B cells following exposure and sensitizationto a specific antigen (see ch. 2). The following tests ofhumoral immunity call for quantitation in vitro of celltypes following exposure in vivo to a test agent. The testsare performed on organ cells (which come only fromexperimental animals) or on peripheral blood (which cancome from animals or humans).

Antibody plaque forming cell (PFC) response–Thistest measures the number of B cells capable of producingantibodies following exposure to an antigen. The testcommonly employs a T-cdl-dependent antigen, such assheep red blood cells (SRBC), and can reveal whether Bcells, T helper cells, and macrophages are functioningproperly. This test cannot identify the cell type (or types)responsible for the abnormal result. This assay can alsobe performed following immunization with T-cell-inde-pendent antigens to exclude the possibility that altera-

Photo credit: American Type Culture Collection, Rockville, MD

Human T cells surrounded by sheep red blood cells in a PFC assay.

Chapter 3—Immunotoxicological Tests . 29

tions in antibody production to T-dependent antigensare due to T helper cell dysfunction.

B cell mitogen response –This test measures the abilityof B cells to proliferate (undergo mitogenesis) afterstimulation by a bacterial mitogen. Analysts measure theamount of DNA synthesis by B cells from the spleen orperipheral blood after exposure to the suspect chemical.Reference values are determined in unexposed cells,and a decrease in synthesis or proliferation below thosevalues may indicate that the B cells did not respond tostimulation.

Immunoglobulin (Ig) levels in serum –Severalmethods exist to measure serum or body fluid Ig levels.Changes in a given Ig level are proportional to the num-ber of B cells secreting that particular class of antibody.The most common techniques for measuring serum Igcan identify class (e.g., IgG, IgA, or IgE) and subclass(e.g., IgG has four major subclasses, each of which canbe associated with specific disorders). In the case of IgE,the radioallergosorbent test (RAST) can be used toidentify antigen specific antibody.

Ce l l -Med ia t ed Immuni ty

Cell-mediated immunity describes any immuneresponse in which antibody plays a subordinate, ratherthan a dominant, role (see ch. 2). Most immune respon-ses involve both humoral and cell-mediated immunity,but the responses can be measured separately.

The test for delayed hypersensitivity response is car-ried out in vivo. Other tests for cell-mediated immunityare evaluated in vitro after exposure in vivo. Humantesting is possible if peripheral blood is to be evaluated,and in some cases human skin testing can be done.

T cell mitogen response –This test measures the abilityof T cells to proliferate after stimulation by mitogenssuch as plant lectins. As with the B cell mitogen assay,analysts measure the amount of DNA synthesis in T cellsfrom the spleen or peripheral blood. A decrease in syn-thesis or proliferation (below reference values) may in-dicate that the T cells did not respond to stimulation.

Cytotoxic T lymphocyte (CTL) assay–This assaymeasures the ability of certain T cells, those induced todifferentiate into cytotoxic T cells, to lyse (destroy) cells

of the type with which they were immunized. Thecytolytic activity of these activated cells is assessed bymeasuring the amount of radioactivity released fromradiolabeled target cells of the same type used to im-munize the animal. Cytolytic activity below referencevalues established in the test indicates a possible im-munotoxic effect.

Delayed hypersensitivity response– This assaymeasures the ability of the immune system to mount adelayed hypersensitivity response after injection with anantigen. Measurement of swelling and redness at the siteof antigen injection can be used to evaluate the response,as can other types of assays using radioisotopic proceduresthat measure the influx of macrophages or serum al-bumin.

Mixed leukocyte response (MLR)—The MLR is ageneral test of cell-mediated immunocompetence. Thetest measures T cells’ ability to recognize foreign lym-phocytes, to transform and proliferate into various effec-tor T cells, and to release cytokines.

Nonspecif ic immunity

Immunity is considered nonspecific when it developswithout prior contact with antigens. Tests for nonspecificimmunity are most often performed on experimentalanimals. However, tests of natural killer (NK) cell activitycan be performed using peripheral blood, and the testsmeasuring microphage numbers and functions can bedone using human lavage fluids.

Natural killer (NK) cell activity – NK cells are thoughtto lyse (kill) several types of tumor cells and virus-in-fected cells. The cytotoxic activity of NK cells can bemeasured by the amount of radioactivity released fromlabeled NK-sensitive targets when they are incubatedtogether with the NK cells. The release of radioactivity isan indication that the tumor cells have been attacked anddamaged in a way that would ultimately lead to theirdeath.

Macrophages– Microphage functions commonlymeasured include antigen presentation and cytokineproduction (mechanisms used by the microphage forcell-to-cell communication), phagocytosis (consumptionof debris and invading organisms), intracellular produc-tion of oxygen free radicals (substances to kill the or-


Photo credit: Medical College of Virginia, Richmond, VA

Flow cytometers are used to count cellsin various immunotoxicity assays.

ganisms the cell consumes), and direct tumor-killingactivities. Macrophages can also be counted in the man-ner described for B and T cells.

Host Resistance

Assays of host resistance – ability to fight infections ortumors–are performed on experimental animals. Theytest overall immunocompetence. In host resistance as-says, animals are first exposed to a potential im-munotoxicant and then exposed to — challenged with – atumor, bacterium, virus, or parasite. Different com-ponents of the immune system can be evaluated by select-ing specific challenge agents.

Challenge with one type of tumor cell, a PYB6 sar-coma, assesses the cytolytic activity of T cells (cell-mediated immunity) and NK cells (nonspecificimmunity); challenge with cells from another tumor, theB16F10 melanoma, mainly permits evaluation of the non-specific immunity afforded by NK cells and macro-phages. Influenza virus and Streptococcus bacteriaprovoke antibody production and are used generally totest humoral immunity, though some scientists believethat no adequate host resistance assay of humoral im-unity has been developed. Antibody apparently playsno role in resistance to Listeria bacteria, which dependson T cells and macrophages, thus Listeria challengemeasures cell-mediated immunity. These challengeagents are illustrative and do not represent a completelist of tests in use.

Hypersensitivity

The assays described above generally test for a sup-pressed immune system. Tests for hypersensitivity canalso be performed on laboratory animals to screen for asubstance’s allergic potential (or in an allergist’s office todiscern the reasons for an individual’s allergicsymptoms). Several types of tests have been developedto measure whether chemicals can produce an allergicresponse directly or by bonding with proteins in the body.Tests of skin and respiratory reactions can be performedin experimental animals and humans.

Skin reactions: Guinea pig sensitization tests-Tests todetermine a substance’s potential to induce delayed-typehypersensitivity – usually manifest as allergic contactdermatitis–are conducted most often in guinea pigs.The tests measure erythema and edema (redness andswelling). Common tests include the Draize test, theopen epicutaneous test, the Buehler test, the Freund’scomplete adjuvant test, the optimization test, the splitadjuvant test, and the guinea pig maximization test. Theessential difference among these tests is the manner inwhich the animal is exposed to the test substance (3,64).

Skin reactions: Mouse tests—In addition to the guineapig tests, a mouse ear swelling test (MEST) has recentlybeen developed and validated. Some researchers believethe MEST is a sensitive, efficient, and cost-effectivealternative to the guinea pig tests (26). More recently, amurine (mouse) local lymph node assay has beendeveloped to identify chemicals that are contact aller-gens. This test assesses proliferation of T cells in the

Photo credit: Medical College of Virginia, Richmond, VA

The mouse ear swelling test.

Chapter 3—Immunotoxicological Tests ● 31

draining lymph node of the ear after application of thechemical to the ear. The test developers find the resultsof the lymph node assay to be as reliable as results fromguinea pig tests (47,79).

Skin reactions: Human sensitization assays-Skintests can also be conducted in humans– either ex-perimentally, to predict sensitization potential (on in-formed volunteers), or clinically, to determine the causeof an allergic reaction. Four basic types of predictive testsare used: a single induction/single challenge patch test;a repeated insult patch test; a repeated insult patch testwith continuous exposure; and a maximization test. Aswith the animal tests, erythema and edema are measured(64). [Clinical test methods are beyond the scope of thisstudy.]

Respiratory reactions—Experimental animals, oftenguinea pigs, can be tested for pulmonary hypersensitivityby measuring certain types of pulmonary function afterinhalation exposure (43). Carefully controlled, clinicalstudies of human respiratory responses have also beenundertaken (63,67,68,78).

Serum IgE levels--Total IgE levels and IgE levelsspecific for a particular antigen can be measured in theperipheral blood of both humans and experimentalanimals.

Test Selection

The time and resources available for testing new andexisting chemicals generally preclude application of alltests to all chemicals. Therefore researchers try todevelop screening processes that reserve the most com-prehensive tests for the chemicals considered most likelyto engender problems. Toxicologists often examine achemical’s structure-activity relationship to known toxicantsas a preliminary step. They compare the test chemical’smolecular structure to previously studied substances. Ifa chemically analogous substance is identified, its effectson the body– its activity-will be presumed for the testsubstance, to the extent the substances are similar. Anevaluation of the structure-activity relationship of a newchemical can indicate whether it might affect the immunesystem and whether an immunotoxicity assessment isdesirable. Determinations based on structure-activityrelationships are not fool-proof, however, since struc-

turally similar compounds can have quite different levelsof toxicity.

Pathologic tests of immune system organs are fairlystandard in general toxicologic testing. These tests canreveal structural changes in immune system organs,which can be used to determine whether additional im-munotoxicity testing is warranted. The main drawback tothese tests is that they assess only structure, not immunefunction.

Interest in screening chemicals for possible im-munotoxic effects has led some chemical manufacturersand regulatory agencies to develop standardized testingtiers. Testing regimes for possible immunosuppressantsare generally divided into two or more tiers. The first tieris limited to a screening-type effort intended to assess, asefficiently as possible, the integrity of the major com-ponents of the immune system. Subsequent tiers repre-sent more in depth evaluation of those responses and alsoinclude assays that evaluate host ‘resistance to challengewith infectious agents or transplantable tumors.

There is also some interest in developing a tier testingmethod for hypersensitivity assessment. One approachto assessing the potential for low molecular weight com-pounds to act as respiratory allergens calls for a literaturesearch on the compound, followed by an evaluation of itsability to bind with serum proteins (required for aller-genicity), followed in turn by skin tests, and, if warranted,respiratory tests (77).

Tier testing is not appropriate for all needs. FDA, forinstance, eschews standardized tests in favor of a case-specific evaluation of substances intended for humanconsumption.

immunotoxicology is still a developing field. Selection ofimmunotoxicological tests for chemicals remains discre-tionary. The tests applied to a particular substance arethose considered most efficacious in a particular instanceby the manufacturer and the regulator.

E P I D E M I O L O G I C E V A L U A T I O N O Fi m m u n o t o x i c I T Y

Environmental epidemiology, which attempts to as-sociate disease or other adverse outcomes with an en-


vironmental exposure, measures health effects inhumans at exposure conditions that are by definitionrealistic (4). Epidemiologic studies can identify possibleassociations that should be tested in laboratory environ-ments and can be used to evaluate human health riskssuggested by laboratory exposures (17).

Some epidemiologic studies of suspected im-munotoxicants have been performed. Contact hypersen-sitivity and asthma are known hazards of manyoccupations because of the experience of exposedworkers (29,42,57). Accidental exposure to industrialchemicals outside the workplace has occasionallyyielded opportunities to study health effects in humans,as with polybrominated biphenyls (PBBs) (see box 3-A),polychlorinated biphenyls (PCBs) (see box 3-B), anddioxin (36). Some of the studies on PBBs, PCBs, anddioxin have shown evidence of quantitative immunosup-pression, but none has shown evidence of actual healtheffects, and followup studies have sometimes con-tradicted the original studies. A recent study of the ef-fects of passive smoking on children did reveal animmune-mediated effect on lung function correspondingto elevated prevalence of asthma and chest colds (12).Current epidemiologic research on immunotoxicity in-cludes examination of the correlations between asbestosexposure and the development of immune system dys-function (30,54,97). Some experts believe that increasedimmunological evaluation of asbestos workers may even-tually explain the long latency between asbestos exposureand disease (14).

Epidemiologic research on any substance is compli-cated by the lack of good exposure data (4). Efforts toimprove this situation are underway, however. In May1990, the Board on Environmental Studies and Toxicol-ogy of the NAS and the Agency for Toxic Substances andDisease Registry cosponsored a meeting on Frontiers inAssessing Human Exposures to EnvironmentalToxicants. This meeting signaled increased emphasis ondeveloping improved epidemiologic evaluationmeasures and increased coordination of Federal,academic, and industrial research efforts in this area.Confounding factors, such as diet and exposure to chemi-cals other than the one under study, make epidemiologya challenging field for researchers.

Idiosyncrasies of the immune system compound thedifficulties for epidemiologic studies of immunotoxicants.The range of “normal” immune responses and “normal”conditions of immune system components varies greatlywithin the population, thus it is hard to define a “sup-

pressed” human immune system in the absence of disease(18). Since epidemiologic studies do not permit chal-lenging the study population with infectious agents, satis-factory evidence of immunosuppression may not beavailable during the study period, particularly if im-munosuppression is transient.

Epidemiologic investigations of immunotoxicity arecomplex undertakings that require much time and manyresources. Few epidemiologic studies have specificallyexamined environmental or occupational exposure toimmunotoxic substances (33,49). They are likely, how-ever, to be the only means of gaining realistic data on thehuman health effects of nontherapeutic substances.

PROBLEMS WITH PREDICTING ANDI N T E R P R E T I N G I M M U N O T O X I C I T Y

The immune system is a complex toxicological target.As with other organ systems, its response to chemicalinsults has features that complicate the interpretation ofexperimental findings. For instance, test agents com-monly show variations in impact on test subjects that canbe attributed to species, strain, or sex differences (e.g.,hexachlorobenzene stimulates the immune system in ratsbut suppresses the immune system in mice (103); chloralhydrate in drinking water significantly depressedhumoral immune function in female mice, but male miceshowed no alterations (45,108)).

immunotoxicological studies often reveal complexdose-response relationships as well. A specific test agentcan stimulate the immune system at one dose and sup-press the immune system at another. Problems with in-terpreting dose-response relationships also manifest asproblems with evaluating the immune system’s reserve orredundant capacity. Scientists cannot accurately predictwhether exposure to a test agent that reduces one celltype will impair immune function or whether that sametest agent will stimulate another component of the im-mune system, which will then compensate for the irn-paired component (e.g., dimethylnitrosamine (DMN)reduced B and T cell function in mice, but susceptibilityto Listeria was reduced because DMN stimulated mac-rophage function (37,108)).

Experimental conditions also influence immuneresponse. Reaction to exposure in vivo often differs sig-nificantly from reaction to exposure in vitro (e.g.,estradiol benzoate decreased NK cell activity in mice invivo, but not in vitro (39)). Acute and chronic doses canrender different results (e.g., acute doses of dichloroethane

Chapter 3-Immunotoxicological T e s t s . 3 3

Box 3-A– Polybrominated Biphenyls: The Michigan CaseIndustrial incidents allow scientists to examine human immunotoxicity in “real-life” situations. One incident

involving polybrominated biphenyls (PBBs) in Michigan “frustrates some of the problems in assessing im-munotoxicity in humans.

In the 1970s, a commercial preparation of PBB was accidentally used in place of an inorganic ingredient inpreparing a feed supplement for lactating cows, and the supplement was subsequently used throughoutMichigan in 1973 and 1974. Toxic manifestations in the cattle included reduced milk production, joint swelling,hyperkeratosis, persistent mastitis, cutaneous and subcutaneous infections, abscess formation on back legs andudder-, and various reproductive anomalies, but did not involve indications necessarily related to infection. Ittook 9 months from initial contamination to identify the toxicant.

Many people consumed the contaminated products-– milk, milk products, meat, eggs, and poultry— andPBB was found in serum and adipose tissues of individuals at least through 1980, Clinical symptoms included I

fatigue, a striking decrease in the ability to do physical or mental work, and an unusual requirement for sleep.Reduced memory and energy were also noted. Arthritic changes and other symptoms affecting the liver,neurological, and musculoskeletal systems were detailed. Increased susceptibility to infections or tumors,however, was not described.

Two studies, in 1977 and 1980, of farm residents exposed to PBB examined immunological parameters.These individuals were compared to age-matched controls: dairy farm residents living in nearby Wisconsin,who had not been exposed to the contaminated products, and New York City residents. Total B and T cellcounts, functional mitogenic assays, immunoglobulin content, and NK cell abnormalities were studied. For atleast 18 of 45 Michigan residents examined, a statistically significant decrease in the absolute number of T cells(about 60 percent of the amount in nonexposed control subjects) and a decreased mitogenic response to bothT and B cell mitogens. The absolute number of B cells was unchanged. In a follow-up study, the researchersconcluded that the immunological dysfunction reported in the first study had persisted, lasting at least 5 years.Elevated levels of IgG, IgA and IgM were also reported.

Two other studies of a different, larger cohort of exposed Michigan residents, however, found no significantdifferences in an array of immune parameters. The first found significantly higher levels of circulatinglymphocytes in the PBB-exposed group when tested in 1976 to 1977, but found no decrease in the absolutenumbers of T or B cells. The second study reported no significant differences in B or T cells among exposedMichigan residents, PBB workers, and unexposed individuals. The researchers reported depressed mitogenicresponses to certain mitogens in PBB-exposed individuals v. unexposed persons, but considered the valueswithin the normal range of their laboratory, and thus did not attach any significance to the finding.

In all studies, the individuals exposed had not exhibited an unusual increase in infections or tumors, twowidely accepted and applied indicators of suppression-type immunotoxicity. Although the lack of clinicalmanifestations might indicate that it was and is too early to predict or extrapolate immunotoxicit y of PBB basedon the Michigan accident, the conflicting laboratory values and conclusions of these studies, derived withdifferent methods on different populations, underscore the problems associated with evaluating humanepidemiologic studies, Clearly PBB affected many organ systems, but its immunotoxicological significance isdifficult to discern.

SOURCE-S: Office of Technology Assessment, 1990 based on J.G. Bekcsi, J.F. I Iolland, I I.A. Anderson, et al., “Lymphocyte Functionof Michigan DaiV Farmers Exposed to Polybrominated Biphenyls,” Science 199:1207-1209, 1978; J.(3. Bckesi, J. Roboz,A. Fisehbein, et al., “Immunological, Biochemical, and Cl inical Consequences of Exposure to Polybrominated Bipheny]s,”Immunoto.nscology and I)nmnop)lanmco[og), J. I 1. Dean, M.I. Luster, A.E. Munson, et al., (eds.) (NewYork, NY: RavenPress, 1985); J.G. 13ekesi, J.P. Roboz, S. Solomon, et al., “Altered Immune Function in Michigan Residents Exposed toPolybrominated Biphenyls,” Immunolo.xicolcyy, G.G. Gibson, R. IIubbard, and D.V. Parke (eds.) (New York, NY:Academic Press, 1983); R. Burrcll, “Identifying and Controlling Irnmunotoxic Substances,” contract paper prepared forthe Office of Technology Assessment, U.S. Congress, April 1990; PJ. L,andrigan, K.R. Wilcox, Jr., J. Silva, Jr., et al.,“Cohort Study of Michigan Residents Exposed to Polybrominated Iliphenyls: Epidemiologic and Immunologic Findings,”Annab of the New York Acu&wy of Scknccs 320:284-294, 1979; J. Roboz, J. Grcavcs, and J.G. Bekesi, “PolybrominatedBiphenyls in Model and Environmentally Ccmtaminatcd Iluman Blood: I’rotcin 13inding and immunotoxicologicalStudies,” Ent’ironmmuai }lealdl Pwspcc[hics 60:107-1 13, 1985; and J.K. St ross, LA. Smokier, J. Isbistcr, et al., “The I IumanIIealth Effects of Exposure to Polybrominated Biphenyls,” Toxicology and Applied Pharmdcolqy 58;145-150, 1981.


Box 3-B – Polychlorinated Biphenyls: The Taiwan Case

In February 1979, rice bran oil poisoned over 2,000 people in Taiwan. The oil had been accidentallycontaminated by polychlorinated biphenyls (PCBs), which were detectable in oil samples at concentrations offrom 4.8 to 204.9 ppm, and in the blood of poisoned patients from 3 to 1,156 ppb. Subsequent analysesconvinced most scientists that the toxic effects were associated with the chlorinated dibenzofurans (chemicalsclosely related to dioxin) that contaminated the PCBs. Patients experienced headaches, ocular disturbances,diarrhea, mylagia, arthritis, and general malaise.

The syndrome, which was first seen in Japan in 1%8, where it is called the “Yusho Syndrome;" is oftenreferred to as "Yu-Cheng,” literally “oil disease.” Yu-Cheng is characterized mostly by distinctive acneiformeruptions and pigmentation, as well as other symptoms involving nonimmune organ systems. An increase in

Iinfections per se was not detailed, and infections that were reported seemed to be largely confined to superficialskin infections not usually associated with immunodeficiency.

For the most part, in vitro lymphocyte mitogen assays of patient lymphocytes showed enhanced stimulation.T cell loss was reported, particularly helper cells, and increased skin reactivity (delayed-type hypersensitivity)to tuberculin and streptococcal enzymes was also documented. Tuberculin reactivity seemed to persist intothe fourth year. These people were probably tuberculin sensitive before the accident and carried the bacteriain an inactive state. One possible future consequence of the PCB and furan exposure could be reactivation oftuberculosis, although to date this has not been reported.

SOURCE: Office of Technology Assessment, 1991; based on R. 13urreli, “Identifying and Controlling immunotoxic Substances,”contract paper prepared for the Office of Technology Assessment, L’.S. Ckmgre.ss, June 1990; Y.-C. Lu, Y.-C. Wu, “ClinicalFindings and Imml~nologic Abnormalities in Yu-Cheng Patients,” Environrnentul Ifeuhh Perspectives 59:17-29, 1985; andWilson, J. D., “A Dose-Response Curve for Yusho Syndrome,” Rebwla[oy Toxicolog and Phannacolog 7:364-369, 1987.

suppressed the mouse immune system, but chronic ad- clusion that many results can be extrapolated fromministration in drinking water had no effect (62)). Anoral dose can have no effect while injection of the samesubstance provokes a response. Thus the route of ex-posure can affect the tests results (e.g., as with chlor-dimeform exposure in mice (81)). The age ormaturational status of the test animal may also affectresults. with prenatal or neonatal exposure to im-munotoxicants often provoking a much stronger reactionthan adult exposure (e.g., as with DES (38)). Non-specific environmental factors can also affect the im-mune system. For instance, even moderate dietaryrestrictions in mice can reduce spleen cellularity. How-ever, the effects of cell reduction are unpredictable (e.g.,the reduction in spleen cellularity was accompanied byan increase in PFC response (66,108)).

Even when toxicologists overcome the difficulties ininterpreting results from tests on laboratory animals, thequestion remains as to whether animal responses cor-respond to human responses. Experience withtherapeutic drugs provides evidence to support a con-

laboratory animals to humans. However, little directevidence exists with regard to industrial or environmen-tal exposures to immunotoxicants. Purposely exposinghumans to suspected toxicants generally is consideredunethical clinical practice. Epidemiologic studies haveposed serious problems for researchers since reliableexposure data have usually been lacking, though therehas been some improvement in this area (102).

Perhaps the greatest problem with extrapolating testresults from animals to humans is evaluating the clinicalsignificance of altered immune responses, particularlythe significance of suppressing humoral, cell-mediated,or nonspecific immunity. Observational experience isbased mainly on severe and long-lasting immunosup-pression resulting from therapeutic drug treatments, andscientists do not know the clinical relevance of moderateand transient perturbations of the immune system. Con-versely, changes in the immune system may not be imme-diately apparent, i.e., biologically significant changes inimmune function could occur with few morphological


correlates and remain subclinical until the animal orhuman is subjected to a particular stress or insult.

Comprehensive and reproducible testing schemesexist to evaluate immunotoxicological potential ofchemicals in experimental animals. However, few chemi-cals have been tested in this manner, and the im-munotoxicological findings in experimental animals canonly serve as indicators of concern in humans. Histori-cally, the immune system has received little attention asa target organ for toxicity, and immunology has not beenan integral part of the toxicology curriculum (61). In-creased education and research integrating immunologyand toxicology would benefit scientists and policymakersinterested in identifying and controlling immunotoxi-cants.

EXISTING DATA ON immunotoxicITY

Few of the chemical substances now marketed haveundergone immunotoxicological testing. This sectiondescribes some of the research that has been done onsubstances or classes of substances to determine whetherthey can suppress the immune system or cause hypersen-sitivity or autoimmune reactions. Most of the referencedstudies have been performed on laboratory animals sincehuman studies on nontherapeutic substances arenotoriously difficult. Specific note is made of the origin —animal or human— of the data.

Immune Suppression

Several substances clearly exhibit a toxic effect on theimmune system by suppressing normal immune respon-siveness. Table 3-1 lists several substances and classes ofsubstances thought to be immunosuppressive toxicants.This subsection further analyzes the effects of some ofthese substances.

Therapeutic Drugs

Therapeutic drugs designed to prevent transplantrejection or to treat autoimmune disorders and cancerare the most thoroughly studied immunosuppressivesubstances. They are listed here as immunotoxicantsbecause of the clearly demonstrated association betweenthe therapeutic use of immunosuppressants and the in-creased incidence of infections and cancer (59). Forinstance, 50 percent of transplant patients get cancerwithin 10 years (65).

Table 3-l—Known or Suspected Immunosuppressants

Halogenated aromatic hydrocarbons (HAHs)PCBsPBBsDioxins

Immunosuppressive drugsAzathioprineGlucocorticosteroidsCyclophosphamideCyclosporin A

PesticidesOrganophosphates (e.g., malathion)Organochlorides (e.g., DDT)Carbamates (e.g., aldicarb)

Polycyclic aromatic hydrocarbons (PAHs)3-methylcholanthraceneBenzo[a]pyrenes

BenzeneIllegal drugs

Cannibinoids (e.g., marijuana)Phencyclidine (PCP)Opiates (e.g., heroin)

Heavy metalsLeadNickelCadmiumMercuryOrganotins

Air pollutantsNitrogen dioxideOzoneCigarette smoke


The most frequently used immunosuppressive drugsfall into four basic categories –alkylating agents,glucocorticosteroids, antimetabolites, and naturalproducts. Research remains to be done on exactly howthese drugs produce immunosuppression, but each ap-pears to act through a different mechanism. Alkylatingagents disrupt cell functions, particularly mitosis. Theyare, therefore, highly toxic to rapidly proliferating cells,such as lymphoid cells. Cyclophosphamide is repre-sentative of this type of drug, and is used as a pretreat-ment in bone marrow transplant recipients to preventgraft rejection and is also used as a cancer treatment andto reduce symptoms of certain autoimmune diseases (91).Treatment with cyclophosphamide, while very effective, car-ries with it an increased risk of certain cancers (95).

Glucocorticosteroids alter phagocytosis and depressT and B lymphocyte function, though the exact mechanismsfor these immunosuppressive effects remain un-known. Prednisolone and methylprednisolone,glucocorticosteroids, are therapeutic for transplantrecipients and for individuals suffering from extremeallergic reactions (91). Glucocorticosteroids are as-


sociated with enhanced susceptibility to infection (95).Azathioprine is a widely used antimetabolite and actschiefly by inhibiting protein synthesis (71). It is usedclinically in transplant patients and also as an anti-inflam-matory agent. A common side effect of azathioprine treat-ment is bone marrow suppression (95). Cyclosporin A,a natural product derived from fermentation products oftwo fungi, appears to act through modulation of mechanismsregulating immune responsiveness. Cyclosporin A sup-presses cell function but spares B cell function, and hasproved successful with transplant patients, though long-term use has been shown to lead to higher infection ratesand incidence of non-Hodgkins lymphoma (55).

Benzene

Benzene, a basic industrial chemical, serves as a sol-vent or feedstock in the synthetic chemical, printing,lithograph, rubber cement, rubber fabricating, paint, var-nish, stain remover, adhesive, and petroleum industries.Benzene has been causally linked to several healthproblems, including immune dysfunction, and it is sub-ject to stringent workplace regulations because of itsproven carcinogenicity (1 ppm TWA; 5 ppm STEL (29CFR 1910)). High dose exposure to benzene results indecreased immune cell function and increased lethalityof infections. Acute exposure studies in rats havedemonstrated bone marrow toxicity and depressed im-mune function. Benzene metabolizes remain in bonemarrow after exposure ceases, and may lead to long-termimmunotoxic effects.

Workers chronically exposed to benzene ( >100 ppm)experienced increased rates of agranulocytosis andmyelogenous leukemia, accompanied by an increasedrisk of infection (22). Depressed levels of some im-munoglobulins in humans exposed to benzene have beenreported (21), but a 1988 study showed no change inlymphocyte function in workers exposed for long periodsto benzene concentrations of 1 to 5 ppm with peaks upto 100 ppm (107). There have been major disparitiesbetween studies of individuals that experienced short-term, high dose exposure, and studies of individualssubjected to long-term, low dose exposure. Benzene is,therefore, considered immunotoxic, but the magnitude ofeffect and the exposure threshold remain to be estab-lished.

Pesticides

Pesticides have been the subject of numerous animalstudies of immunosuppression in recent years. Rodent

studies of organophosphates, such as malathion; or-ganochlorides, such as DDT; and carbamates, such ascarbofuran, showed evidence of immunosuppression(93). However, none of these pesticides has been sub-mitted to a systematic evaluation for immunotoxicity. Inaddition, it appears that intentionally added inert in-gredients or other contaminants maybe responsible forthe observed suppressive effects (83,93). Many expertsconsider the animal studies indicative of potential im-munotoxicity in humans, though certainly not conclusiveevidence, and recommend prudence when dealing withpesticides, particularly the organochlorides, whichremain stable in the environment and become con-centrated in the food chain.

Most studies of the immunosuppressive effects of pes-ticides in workers indicate no decrease in resistance todisease even where changes in immune system com-ponents were measurable (43,48,106). However, onestudy of workers handling organophosphate pesticidesdid find an increase in upper respiratory tract infection(35). Epidemiologic evidence of the effects of pesticideexposure outside the workplace is quite sparse (23). Astudy of women who drank aldicarb-contaminatedgroundwater showed altered numbers of T cells, but thebiological significance of the alteration was notdemonstrated (25,93).

Halogenated Aromatic Hydrocarbons

Among the most infamous halogenated aromatichydrocarbons (HAHs) are polybrominated biphenyls(PBB), polychlorinated biphenyl (PCBs), and dioxins.PCBs (now banned) has been used as plasticizers and asa heat transfer medium; PBB as a fire retardant. Dioxinappears as a contaminant in some commercial sub-stances. Studies of the effects of HAHs on experimentalanimals indicate that they can have adverse effects on theimmune system (94). Findings in laboratory animals ex-posed to PCBs or PBB at levels higher than most humanexposures include severe atrophy of primary and sec-ondary lymphoid organs, lower circulating im-munoglobulin levels, and decreased specific antibodyresponse (85,%). Evidence from epidemiologic studies isinconclusive regarding immunotoxicity of these sub-stances in humans. Studies of human exposure haveshown abnormal laboratory values for immuneparameters, but no conclusive clinical evidence of im-mune aberration (see boxes 3-A and 3-B).

The name dioxin is assigned to 75 chemicals withsimilar composition. The most widely studied dioxin,


2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), affectsyoung animals more severely than adults and leads tosevere thymic atrophy and moderate atrophy of theperipheral lymph nodes at doses that cause other toxiceffects as well (94). Recent animal research indicates thatgenetic predisposition plays a major role in susceptibilityto the effects of dioxin (76,82). A study of mobile homepark residents exposed to TCDD yielded abnormal invitro test results in about 25 percent of the exposedpopulation, but uncovered no reports of clinical diseasedue to demonstrated cellular immunity (36). These ef-fects were not detectable upon reexamination of thesame population, and the authors of the second paperconsider the possibility that the first paper was in error(24). Some data on children accidentally exposed toTCDD show normal immunoglobulin levels and elevatedlymphocyte responsiveness, but the only clinicalevidence of disease is chloracne (70). The position of themajority of scientists who have examined human healtheffects of dioxin is that little or no harm has been doneby its dissemination in the environment (31,73).

Polycyclic Aromatic Hydrocarbons

Fossil fuel combustion produces polycyclic aromatichydrocarbons (PAHs), and distillates from these productsare widespread in the chemical industry. Exposure oc-curs in the workplace and in the environment generally.Many PAHs are carcinogenic, and a growing body ofevidence indicates that they may also be immunotoxic. A1980 study showed that mice exposed in utero tobenzo[a]pyrene (BaP), a PAH, experienced significant,persistent suppression of humoral immunity(99). A laterstudy by the same author showed inhibition of the PFCresponse and the MLR when spleen cells were exposedto concentrations of BaP (100). Another PAH, 7,12-dimethylbenz[a]anthracene (DMBA), significantly in-creased susceptibility to murine cytomegalovirus (80).Noncarcinogenic PAHs do not appear to produce im-mune alterations (104). The immunotoxic effects of PAHshave not been widely studied in humans.

Oxidant Gases

The transportation system and many industrial pro-cesses produce airborne pollutants. Two air pollutants thathave been studied for their immunotoxic effects areozone and nitrogen dioxide, oxidant gases regulatedunder the Clean Air Act (CAA). Studies on experimen-tal animals reveal increased susceptibility to infectionafter exposure to low levels of ozone and nitrogendioxide. Pulmonary NK cell activity in rats was sig-

nificantly suppressed following continuous exposure toozone, but after 10 days, NK cell activity returned tonormal, even in the continued presence of ozone (13).Dutch researchers found that ozone suppressed or en-hanced pulmonary NK cell activity in the rat dependingon the exposure level (101). Mice exposed to 2.5 to 5.0ppm of nitrogen dioxide showed increased susceptibilityto bacterial infection (40).

Ozone has been shown to cause immediate short-termchanges in lung function and increased respiratorysymptoms among healthy adults and children who exer-cise moderately or heavily during periods of elevatedozone concentrations. Some studies suggest that theremay be some persistent effects associated with long-termexposure to ozone, although understanding of such ef-fects, including whether they are immune-mediated, iscurrently limited (98). Government researchers recentlysummarized the results of several epidemiologic studiesof nitrogen dioxide exposure (32). The studies reveal anincreased prevalence of respiratory infections amongindividuals, particularly children, exposed to nitrogendioxide, but small sample sizes and poor exposure datatend to lessen the significance of the findings. EPA hasset national primary ambient air quality standards forozone (0.12 ppm) and nitrogen dioxide (0.053 ppm)based on health effects other than immunotoxicity (40CFR 50).

Indoor Air Pol lutants

Some air pollutants become particularly concentratedindoors. Some of the epidemiologic evidence of thehealth effects of nitrogen dioxide comes from studies ofindividuals in homes with gas stoves. Sidestream cigarettesmoke, in one study of children, increased the incidenceof respiratory infections through immune-mediatedmechanisms (12). Concerns have been raised about off-gassing from products containing formaldehyde, butanimal (20) and human (69) studies of immune functionsfollowing inhalation of formaldehyde indicate that it isnot immunosuppressive.

Metals

Heavy metals are ubiquitous – in the air and water, atwork and at home — and a few of them have been studiedfor immunotoxicity. A 1982 study of the effects of lead onmacrophage function in mice indicated a significant im-munosuppressive effect (46). A more recent study oflead’s effects on host resistance in mice yielded conflict-ing results depending on time and amount of exposure,

38 . Identifying and ControllingImmunotoxic Substances

making it difficult to draw any conclusions about lead’simmunotoxicity (50). The latter study also evaluated theeffects of nickel and selenium. Nickel’s effects on hostresistance varied significantly with time and amount ofexposure; selenium uniformly increased resistance toinfection. Other studies of nickel indicate that it sup-presses NK activity in mice and rats (86,87,89) but thatnickel chloride does not adversely affect the immunesystem of the developing mouse (88). One study of cad-mium showed that it significantly depressed NK cellactivity in mice but had no effect on mortality due toinfection (19). A study of cadmium in aged mice showedno immunosuppressive effects (10). The evidence forimmunosuppressive effects of mercury on animals is con-flicting (52). Organotins, used as heat stabilizers, catalyticagents, and antifungal/antimicrobial compounds, havebeen widely studied, but show highly variable effectsdepending on the species, times. and amount of exposureinvolved in the test (11,84,85,90).

Hypersensitivity

This report defines immunologic hypersensitivity asallergic response (see ch. 2). Delayed-type hypersen-sitivity manifests as allergic contact dermatitis and is theresult of a T cell mediated inflammatory response. Im-mediate hypersensitivity is an antibody-mediatedresponse that manifests as allergic rhinitis, asthma, oranaphylaxis. This section describes some problems withhypersensitivity resulting from environmental exposures.

Contact Sensitivity and Skin Disorders

The skin is an excellent route for toxic agents to enterthe body. Workers engaged in leather tanning and finish-ing poultry/egg processing, manufacturing sealants, ad-hesives, or abrasives, fish packing, boat building andrepairing, and landscaping are at risk for skin manifesta-tions of immunotoxicity called occupational dermatoses.Cell-mediated hypersensitivity causes 20 to 30 percent ofoccupational dermatoses (14).

A number of therapeutic and cosmetic materialsprovoke various types of skin reactions. Oils used asbases in many ointments for either medical or cosmeticpurposes can induce contact sensitivity. If substances(e.g., perfumes) are dissolved in solvents, cutaneous ab-sorption is greatly facilitated. One type of immunologichypersensitivity, “underarm anti-perspirant granuloma,"occurred when compounds containing the element zir-conium were introduced. Although excellent anti-perspirants they induced cell-mediated hypersensitivity,which over along period of application led to pathologi-cal manifestations of granuloma formation. Once the keyingredient was identified, the compounds were eithereliminated or modified to avoid the condition.

Some common metals also cause hypersensitivityresponses. The nickel in costume jewelry can cause con-tact sensitivity 5 percent of all contact dermatitis can beattributed to nickel-containing compounds (14). Ex-posure to platinum, chromium, mercury, and gold canalso lead to skin sensitization. Table 3-2 lists a number ofagents known to induce types of contact sensitivity.

Respiratory Disorders

Numerous inhalants cause immune-mediated respiratorydisorders, including some types (but not all) of bronchialasthma, hypersensitivity pneumonitis, allergic rhinitis,bronchopulmonary aspergillosis, silicosis, asbestosis,coalworkers’ pneumoconiosis, and possibly byssinosis(60). Some of these conditions result from a humoralimmune response, as in the case of IgE-mediated,bronchial asthma, while others have cell-mediated im-mune involvement, as with the mineral pneumoconioses.

Hypersensitivity pneumonitis is a respiratory diseaseof immune origin. The exact mechanism of its pathogenesisis controversial, but the involvement of several immunecomponents, including nonspecific complement activa-

Table 3-2—Common Contact Sensitizers

Another skin disease of immunologic significance isatopic dermatitis (eczema). This condition is a chronic,periodic skin disorder, primarily of infants and children, thatdepends on a complex interrelationship of geneticpredisposition, and an imbalance of immunologic andpharmacologic mediators in the skin (53). Environmen-tal agents, including jewelry and cosmetics, may provokeinitial attacks or recurrences (14).

PlantPoison ivyEuropean primrose

Synthetic compoundsBenzocaineEpoxy resinsMercaptanPicric acid derivativesC-1 HydrocarbonsEthylenediamineParaphenylenediamineThimerosol

MineralsBerylliumNickelCadmiumChromatesSilverZirconiumCutting oils



tion, T and B lymphocyte stimulation, and microphageactivation, has been reported (15,72). Hypersensitivitypneumonitis is caused by allergy to specific microbial ororganic substances. However, the dusts that cause thecondition are sometimes mixtures of many potentiallyinflammatory or bio-active agents.

Asthma is the leading chronic disease of childhood(27). Occupational asthma is the most common occupa-tional respiratory ailments in the Western world (16).Numerous agents can induce asthma, and they are generallydivided into two groups: large molecular weight substan-ces, usually proteins, that cause classical, IgE-mediatedasthma; and low molecular weight materials that causenon-IgE-mediated, longer lasting types of asthma. Oc-cupational asthma is often of the non-IgE-mediated type;table 3-3 presents a list of the some common incitants foroccupational asthma.

Table 3-3—industrial Chemicals Associated WithOccupational Asthma

Platinum salts EthylenediamineNickel salts Phthalic anhydridesPyrethrum Colophony resinsDiisocyanates Exotic wood dustsSOURCE: Office of Technology Assessment, 1991.

Substances That Are Allergenic

Some commonly used drugs cause allergic reactionsin users. Penicillin produces an allergic reaction in 1 to10 percent of users (less than 1 percent are of the life-threatening anaphylactic variety) (l). Some drugs usedto treat hypertension are also suspected of producingallergic reactions in patients using the drug for extendedperiods (l), although the exact mechanism of the reac-tion remains unknown. Over-the-counter medicationsare also allergenic for some users and bear warnings tothat effect. It should be noted that not all adverse drugreactions are immune-mediated though the reaction maybe called “allergic” (see box 2-B). For instance, aspirinproduces an allergy-like reaction in some users, but theweight of the evidence now indicates a non-immunologicbasis for aspirin intolerance (21).

Formaldehyde has historically been used to increasewrinkle resistance and fabric durability, and many gar-ment industry workers were believed to develop an aller-gic reaction to free formaldehyde (21). However, recentchallenge studies on patients with asthma yielded noevidence that formaldehyde could cause or aggravatesymptoms, and attempts to measure serum antibody and

skin reactions yielded no adverse reactions (69). OSHAregulates formaldehyde as a carcinogen.

Toluene diisocyanate (TDI) is used in plastics manufac-ture and reportedly has induced asthma and contactdermatitis in occupationally exposed individuals. Somepatients with ‘I”DI-induced asthma remain symptomaticeven years after cessation of exposure, and some ob-servers believe that TDI may cause airways to becomehyperreactive to agents such as smoke or air pollutants.Most individuals with TDI-induced asthma react similar-ly to other diisocyanates (42). OSHA now regulates TDIat levels below those demonstrated to induce hypersen-sitivity in humans (0.005 ppm TWA; 0.002 ppm STEL).

Definitive data demonstrate that Occupational ex-posures to some pesticides (e.g., some carbamate andorganophosphorous esters) can induce contact hyper-sensitivity. While animal studies indicate that antibodyresponse to pesticide derivatives is possible (93), noreports of IgE sensitization of humans to pesticides havebeen confirmed. Some scientists believe reported reac-tions may be irritative rather than allergic in nature.

Autoimmunity

Autoimmune diseases are aberrations of the immunesystem resulting in an organism attacking a part of itselfas a foreign substance. Certain toxic substances that arebiological in nature can increase the risk of certainautoimmune conditions. For example, it is well knownthat certain streptococcal infections, when left untreated,may lead to rheumatic fever and post-streptococcalglomerulonephritis. However, the evidence for chemi-cal-induced autoimmune disorders is ambiguous(2,34,41).

A growing list of pharmaceuticals have been shown toinduce autoantibody formation (antibodies against selfantigens) or actual autoimmune pathologies (table 3-4;box 3-C; 9,28,41). Genetic susceptibility also plays an im-portant role in immunotoxicology and autoimmunity. Be-cause of the strong genetic component and a generallypoorer understanding of autoimmunity compared to otherimmune responses, deciphering the exact role of toxicchemicals in the induction of autoimmunity is difficult.

S U M M A R Y A N D C O N C L U S I O N S

Scientists have developed a number of tests that assessthe various components and processes of the immunesystem. Pathologic evaluations and certain assays of


Table 3-4-Substances Associated WithAutoimmune Responses

Antihypertensive drugsHydralazineMethyldopa

Anti-arrhythmia drugsProcainamidePractololQuinidine

Anticonvulsant drugsPhenytoinEthosuximidePrimidone

Antimicrobial drugsPenicillinSulfonamidesIsoniazidNitrofurantoin

MetalsLithiumGoldMercuryCadmium

Other substancesPenicillaminesChlorpromazinePropylthiouracilGriseofulvinOxyphenisatinVinyl chlorideMethylcholanthrene

SOURCE: Office of Technology Assessment, 1991; based on P.E. Bigazzi,“Mechanismsof Chemical-induced Autoimmunity,” Immunotox-icologyand Immunopharmacology J. H. Dean, Ml. Luster, A.E.Munson, et al. (eds.) (New York, NY: Raven Press, 1985).

humoral, cell-mediate~ and nonspecific immunity havebeen validated in one experimental animal, the mouse,and validation efforts are underway for other species.Tests that measure immune cell numbers have advancedmore quickly than tests that measure functional im-munity, but tests to evaluate specific immune functionsare available.

immunotoxicological testing–like all toxicology–presents an investigator with significant challenges. Theresults of tests on experimental animals often differdepending on the test subject’s age, species, or sex. En-vironmental factors, such as diet or smoking, also affectimmune system performance. Choosing the appropriatetest dose and the means and duration of exposure canprove difficult when resources are limited and the pointof the exercise is to extrapolate from the test to theconsequences of human exposure.

Scientists believe that the immune system has a reservecapacity, although the size of that reserve is as yet un-determined. Thus tests that measure impairment of oneimmune system component may not, in fact, indicateoverall immunotoxicity, since other immune componentsor processes may compensate for the impairment. Inseveral of the studies cited in the preceding text, a chemi-cal produced a discernible decrease in a specific immunefunction without producing a measurable decrease in host

Box3-C-Chemical-InducedAutoimmunitySpanish Toxic Oil Syndrome

Understanding of autoimmune responses tochemical exposure lags far behind hypersen-sitivity and immunosuppression. Following apoisoning episode in Spain, scientists made oneof the few attempts to examine whether anautoimmune mechanism could explain thesymptoms experienced after toxic exposure.

In May 1981, an unknown disease affectingapproximately 20,000 people was reported inMadrid and northwest of the city. About 3months after the acute phase of the outbreak, asubpopulation of individuals developed a severeneuromuscular and scleroderma-like syndrome,causing at least 350 deaths. Epidemiologic evidencesupported a conclusion that adulteratedrapeseed oil, sold as olive oil, was responsiblefor the disease.

Kammuller, et al., reported that a con-taminant, l-phenyl-5-vinyl-2-imidazolidine-thione (PVIZT), was isolated in certaincase-associated oil samples. Because the chemi-cal structure of PVIZT is closely related tohydantoins and thioureylenes, which can causeautoimmune-like disorders in man, the re-searchers conclude that PVIZT could accountfor the syndrome. Patients with toxic oilsyndrome presented symptoms similar to thosefound in known human autoimmune diseases.In addition, the researchers measured im-munological changes, including high nonspecificIgE antibody levels, marked eosinophilia,decreased T suppressor cells, and several typesof autoantibodies.

SOURCE: Office of Technology Assessment, 1991; basedon M.E. Kammuller, N. Bloksma, and W.Seinen, “Chemical-Induced AutoimmuneReactions and Spanish Toxic Oil Syndrome:Focus on Hydantoins and Related Compounds”Clinical Toxicology 26(3&4):157-174, 1988.

resistance to disease. Many scientists believe that withoutincreased incidence of infection or cancer, there is noevidence of immunotoxicity. There is still much to be


learned about the long-term consequences of weakeningindividual components of the immune system.

Immunotoxicologists have identified many substancesthat have demonstrable immunotoxic effects inlaboratory animals, and in a few instances, the effects ofthese substances have been observed in humans as well.Drugs developed to control graft rejections and cancerdefinitely suppress the human immune system, andpatients receiving these drugs provide good human dataon the consequences of prolonged immunosuppression.Occupational experience (see table 3-3) has providedsome evidence of substances’ inadvertent immunotoxiceffects in humans. Accidental exposures to suspectedimmunotoxicants have, in a few cases, provided the op-portunity for gathering human data (see boxes 3-A and3-B). For the most part, however, data are sparse on theeffects of general exposure to immunotoxicants in theenvironment. The scientific community recognizes thatthe immune system is an important target organ for toxicity.Most scientists agree that the lack of human test datashould not preclude efforts to control human exposuresto suspected immunotoxicants, but the absence of datawill ensure continued disagreement about suitablemeans and levels of control.

1.

2.

3.


Amos, H.E., and Park B.K, “Understanding Im-munotoxic Drug Reactions,” Immunotoxz”cology andImmunopharmacol~, J.H. Deaq et al. (eds.) (NewYorlq NY: Raven Press, 1985), pp. 207-228.Aueoin, D.P., Peterso~ M.E., Hurvitq A.I., et al.,“Propylthiouracil-Induced Immune-Mediated Dis-ease in the Cat,” Journal of Pharmacology and Ex-perimental Therapies 234:13-18, 1985.Bass, B. F., Muir, W. R., and Rose, N. R., “Im-munotoxicology Strategy-Review of Major ScientYlcconference% Federal Activities and Federal PoliciesRelating to immunotoxicology,” EPA contract No. 68-

4.

5.

6.

7.

8.

9.

10,

11.

12.

13.

22-4228 (Alexandria, VA: Hampshire ResearchAssociates, Inc., 1987).Beck B.D., Calabrese, EJ., and Anderson, P.D., ‘TheUse of Toxicology in the Regulatory Process;’ Rin-ziples and Methods of Tom”cology A.W. Hayes (cd.)(NewYor~ NY: Raven Press, 1989), pp. 1-28.Bekesi, J.G., Holland J.F., Anderso~ H.A., et al.,

“Lymphocyte Function of Michigan Dairy FarmersExposed to Polybrominated Biphenyls,” Science199:1207-1209, 1978.Bekesi, J.G., Robo~ J.P., Fischbe@ A. et al., “Im-munologica~ Biochemical, and Clinical Consequencesof Exposure to Polybrominated Biphenyls,” Im-~-~In~p~o@t .T.H. Dean etal. (eds.) (New York NY: Raven Press, 1985), pp. 393-%.Bekesi, J.G., Robo~ J.P., Solomon, S., et al., “AlteredImmune Function in Michigan Residents Exposed toPolybrominated Bipheny~” Inwnunotaxicolqy, G.G.Glbso~ et al. (eds.)(Londoq England Academic Press,1983) pp. 182-191.B@@ PQ’’Mechanisms ofChernical-IndumdAutoirn-

mmunotiol@y and Inmunophurmacology,munity,” 1J. H. Dean et al. (eds.) (New York NY: Raven Press,1985), pp. 277-290.Bigazz~ P.E., “Autoimmunity Induced by Chemicals~’Clinical Toxicology 26(3&4):125-156, 1988.Blakely, B.R., “humoral Immunity in Aged Mice Ex-posed to Cadmium” Canadian Journal of Veterina~Research 52(2):291-2, April 1988.BOyer, IJ., “TOxiCity of Dibutylt~ Tributyltin, andOther Organotin Compounds to Humans and to Ex-perimental Animals,” Toxicology 55:253-298, 1989.Burchtle~ C.M., Higgins, M.W., Keller, J.B., et al.,“Passive Smoking in Childhoo~’’Anzerican Review ofRespiratory Disease 133%6-973, 1986.Burleso~ G.R., Keyes, L.L., and Stutzm~ J.D., “Im-munosuppression of Pulmonary Natural Killer Ac-tivity by Exposure to Ozone,” Invnunophannacolovand immunotoxicology 11(4):715-735, 1989.


14.

15.

16.

17’.

18.

19.

20.

21.

22.

23.

24.

25.

26.

Burrel~ R., “Identi@ng and Controlling lmmunotoxicSubstanees~’ contract report prepared for the Officeof Technology Assessnxmt, U.S. Congre~ April 1990.Burrel~ R., and Rylander, R., “A Critical Review ofthe Role of Precipitins in HypersensitivityPneumon.itis,n European Journal of Respiratory Dk-ease 62;332-343, 1981.Cartier, A., Grarnmer, L., Malo, J., et al., “SpWificSerum Antibodies Against lsocyanates: AssociationWith Occupational Asthrn~” Journal of Aile~ andChMcallmmunolog Y, p p . 5 0 ’ 7 - 5 1 4 , O c t o b e r 1989.Cone, JEVReeve, (Ml, and Landrigaq PJV “CiinicalandEpidemiological Studi~” Zmic Subsumes and HunMwRlkk-Wlc@a @-llalzl lrlw?praalixl (New York, NY:Plenum Press, 198’/) pp. 95-120.Cornfel@ R.S., and Schlossman, S.F., “ImmunologicLabor atory”i’ests: A Critique of the Alcolac Decision,”Toxics Law l?eporw~ Sept. 6, 1!%9, pp. ‘381-390.L)aniel~ MJ’., Menache, M.G., Burleson, G.R., et al.,“E&cts of NW12 and CdU2 on Suscepuiility to MurineQtomegalovkus and Vnus-Augmen~ed Natural KdlerCell and interferon llespoifie~” Furuimnerual andAppltid Toxicoiog 8:443-453, 1987.De- J.H., I_auer, L.D., House, R. V., et al., “Studiesof immune Function and Host Resistance in J36C3F1Mice Exposed to Formaldehyde;’ Toxicology and Ap-phkd Pharmacology 72:519-529, 1984.D~J.H9 Mwray,MJ9 and Ward E.CV “I’oxicR~~pon-sesofthe lmmunebysle~’’<lzsmzu and flwlk T’a’qgyZ4eBa.we SiienceofPoi.ms, 3rd cd., CD. Klaasse~ et al.(eds.) (New Yor~NY: MacMdkq 1{%6).Decxmfle, P., Blatmer, W., and Blair, A., ‘MortalityAmong Chemical Workers Exposed to Benzene andOther Agents,” Envu-onrnerual Resewch ‘30:16-25,1983.EmE.F9“ACfi~~k at the Evidencellat Environ-mental Toxins Cause Damage to the lrnmunologic Systemin M~” Invnurmtoxicolqr From Lub to Law @ha~NY: CornellUniversity, 1988), pp. 37-45.Ev~ R.G., Webb, K.B., Krutsen, A.P., et al., “AMedical Followup of the Health Effects of Long-TermExposure to ~3,7,8-tetrachlorodlbtmzo-p-dioxin~’Ar-chives of EnvironnwualHeolth 43:2’13-2’78, 1988.Fiore, M. C., Anderso~ H.A., Hong, R., et al., “ChronicExposuretoAldicarb-Contaminated ChwundwaterandHuman Immune Functio~” Environnuvual Research41:633-645, 1986.Gad S.C., Dmq B.J., Dobbs, D.W., et al., “Develop-ment and Validation of an Alternative Dermal Sen-

2’7.

28.

29.

30.

31.

32.

33.

34.

35.

36.

37.

38.

sitization Test: The Mouse Ear Swelling Test(MEST),” Toxicology and Applied Pharrnacolou84:93-114, 1986.Gergen, PJ., and Weiss, KB., “Changing Patterns ofAsthma Hospitalization Among Children: 1979 to1987~’ Jourrud of the American Medical Association264(13):1688-16~ 1990.G~~ Kimber, ~ and Purchasej LFq ‘!lmrnunetoxicnlqy Suppressive and Stimulatory Effects of D~on the hnnmneSpte~’’Amh”ve$of l’lmkaQgy 6X257-273,1989.Goldste@ R.A., Sogq D. D., and Ayres, J., “Occupa-tional and Environmental Immunologic Lung Disease:A Persped.ive~’ hrnunotancolqgy and Invnunophar-rnacolo~, J. H. Dean et al. (eds.) (New York NY:Raven Press, 1985), pp. 489-496.Goo~ R. A., and Lindenlaub, E. (eds.), “The Nature,Cellular, and Biochemical Basis and Management ofImmunodeficiencies;’ Symposium held in Bernrie~West Germany, Sept. 21-25,1986, pp. 497-509.GOU& M., Diox@ Agent Orange (New York NY:Plenum Press, 1986).Graham, J.A., Grant, L.D., Folinsbee, L.G., et al.,Direct Health Effects ofAirPollutants Associated W&Acid fiewsorl+nissions (National Acid PrecipitationAssessment Program Report 22, Washingto~ DC,1991).Grufferrnan, S., University of Pittsburgh, Pittsburgh,PA, personal communication, May 1990.Hahn, B.I-I., “Animal Models of Systemic LupusErythematosus,” Dubois’ Lupus E@wnatosus, 3rdcd., D.J. Wallace and E.L. Dubois (eds.) (Philadel-phi~ PA: Lea& Febiger, 1987).Hermanowicz, A., and Kossman, S., “NeutrophilFunction and Infectious Disease in Workers Occupa-tionally Exposed to Phosphoorganic Pesticides: Roleof Mononuclear-Derived Chemotactic Factor forNeutrop~” ClinimlInwunol~ and Invnunopathol-OQ 33: 13-22, 1984.Hoffma~ R.E., Stehr-Green, P.A., Webb, KB., et al.,“Health Effects of Long-Term Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxi~’’Journal of theAnlericanMedicalAssociation 2.55:2031, 1986.Holsapple, M. P., Bic~ P.H., and Duke, S. C., “Effectsof N-nitrosodimethylarnine on Cell-Mediated Im-munity,” Journal of Leukocyte Biology 37567-381,1985.Holsapple, M.P., MUIISOW A.E., Munso~ HA., et al.,“Suppression of Cell-Mediated Immunocompetence


After SubChronic Exposure to Diethylstilbestrol inFemale B6C3FI Mice,” 17wJour@ ofPhannacolo~andi%pen”mental Theraptics 227:130-138, 1983.

39. Ho~J., and Zhe~W.F., ’’Effect of SexHormonesonNK and ADCC Activity of Mice,” InternutionulJour-nal of Ihrmurwphunnacology 10:15-22, 1988.

40. Jakab, G.J., “Modulation of Pulmonary DefenseMechanisms Against Viral and Bacterial Infections ByAcute Exposures to Nitrogen Dioxide,” ResearchRepotis of the Health Effects Institute 20:1-38, Novem-ber 1988.

41. Kammuller, ME7 BIo-NV andseine~ Wq’’Chemi-cal-induced Autoimmune Reactions and Spanish ToxicOil Syndrome: Focus on Hydantoins and RelatedCompounds,” Clinical Toxicology 26(3&4):157-174,1988.

42. Karo~ M.H., “Hypersensitivity to Isocyanates,” Zm-ml.uwtil@y andlhununqha.nnac oi@ J. H. Deanetal. (c&) (NewYor~NY:Rawm Prtx+ l%5),pp.47S488.

43. Karo~ M.H., Stadler, J., and Magre@ C., “Irnmu-notoxicologic Evaluation of the Respiratory SystenxAnimal Models for Immediate- and Delayed-Onselt Pul-monary Hypersensitivity,” Fundamental and AppliedToxicology 5:459-47~ 1985.

44. Kashyap, S.K., “Health Survelliance and BiologicalMonitoring of Pesticide Formulators in India,”Toxicology Letters 33,107-114,1986.

45. Kauffm~ B.M., White, KL., Sander% V.M., et al.,“humoral and Cell-Mediated Immune Status in MiceExposed to Chloral Hydrate,” Environmental HealthPerspectives 44147-151,1982.

46. Kerkvliet, N.I., and Baecher-Steppan, L., “Im-munotoxicolog Studies on Lead: Effect of Exposureon Tumor Growth and Cell-Mediated Immunity AfterSyngeneic or Allogeneic Stiiulator~’ Immunophar-macolo~ 4:213-24, 1982.

47. Kimber, I., HiltoL J., and Both~ P.A., “Identifka-tion of Contact Allergens Using the Murine LocalLymph Node Assay: Comparisons With the BuehlerOccluded Patch Test in Guinea Pigs,’’ Journal ofAp-phkd ToXiCOIO~ 10:173-180, 1990.

48. Kundiev, Y.I., Krasnyuk, E.P., and Viter, V.P.,“Specific Features of the Changes in the Health Statusof Female Workers Exposed to Pesticides in Green-houses;’ Toxicology Letters. 33:85-89, 1986.

49. Landrig~ PJ., The Mount Sinai Medical Center,New Yorlq NY, personal communicatio~ June 1990.

50. Landrigaq P.J., Wilco+ K,R., Jr., Silva, J., Jr., et al.,“Cohort Study of Michigan Residents Exposed to

Polybrorninated Biphenyls: Epidemiologic and Im-munologicFmding+” Annals of the New YorkAcademyof Sciences 320:284-294, 1979.

51. Laschi-Loquerie, A., Eyrau~ A., Morisse~ D., et al.,“Influence of Heavy Metals on the Resistance of MiceToward In faction,” Immunopharmacology andimmunotoxicology 9(2&3) :235-24~ 1987.

52. Lawrence, D.A., “Irnmunotoxicity of Heavy Metals;’Immurwtoxicolop and Immunophannacology, J. H.Dean et al. (eds.) (New York NY: Raven Press,1985), pp. 341-353.

53. hung D.Y.MV Rhoda AR. and Ge~ R.S. “AtopicDermat*” Dmrnu@@y in General Medicine, T. El.Fitzpatrick et al. (eds.) (New York NY: McGraw-Hi~ 1987).

54. Lew, F., Tsang, P., Holland, J.F., etal., ’’HighFrequen-ey of Immune Dysfunctions in Asbestos Workers and inPatients WM Malignant Mesotheliom~’’JoumalofCliu”-cal Inununol@gy6(3):225-233, 1986.

55. Lu, Y.-C, and W% Y.-C., “Clinical Findings and Im-munologic Abnormalities in Yu-Cheng Patients,” En-vironmental Hea[th Perspectives 59:17-29, 1985.

56. Luster, M.I., National Institute of EnvironmentalHealth Sciences, Research Triangle Park, NC, per-sonal cmnmunicatio~ September 1990.

57. Luster, M.I., and Dean, J.H., “ImmunologicalH yper-sensitivity y Resulting From Environmental or Occupa-tional Exposure to Chemical: A State-of-the-ArtWorkshop Summary~’Fiimakww ruz4andAppiled Toxicol-OQ 2:237-330, 1982.

58. Luster, M.I., Munso~ A.E., Thomas, P.T., et al.,“Methods Evaluation-Development of a Testing Bat-tery to Assess Chemical-Induced immunotoxicityNational Toxicology Program’s Guidelines for Im-munotoxicity Evaluation in Mice,” Fundamental andAppli~d Toxicology 10:2-19, 1988.

59. Luster, M.I., Wierda, D., and Rosenth~ GJ., “En-vironmentally Related Disorders of the Hematologicand Immune Systems,” Environmental Medicine74(2):425-440, March 1990.

60. Morgan, N.KC., and Seeto~ A, Occupational LungDiseases (Philadelphia, PA: W.B. Saunders Co.,19&l).

61. Mm~M.,tim~otiwl~Pr~~Mddbl-lege of Vigir@Richmon~V~ personal communicationJune 1990.

62. Munson, A.E., Sain, L.S., Sanders, V.M., et al.,‘Toxicology of Organic Drinking Water Contaminants:Trichloromethane, Bromodichloromethane, Dibrom~


63.

64,

65,

66.

6’7.

68.

69.

70.

71.

72.

73.

74.

chkxo- a n d Tribmmome&an@’ 13whvrm-kzlH&Perspectives 46:117-126, 1982.Orlando, G.S., House, D., Danie~ E.G., et al., “Effectof Ozone on T-cdl Proliferation and Serum Levels ofCmtisol and Beta-Endorphin in Exercising Males~’Inhalation Toxicology 1:53-63, 1988.Pat.riclq E.,and Maibach, H.I., “Dermatotoxicdogy~ti”nc@es and Methodk of Totiol@gY, A. WallaceHayes (cd.) (New York NY: Raven Pre~ 1989),pp. 383-406.Pew I., “Neoplastic Consequences of Immunosuppression,v immunotoxicology and Immunophar-macology J.H. Dean et al. (eds.) (New York NY:Raven Press, 1985), pp. 79-90.Pestka, JJ., T~ J.H., Witt, M.F., et al., “Suppressionof Immune Respone in the B6C3F1 Mouse AfterDietary Exposure to the Fusarium MycotoxinsDeoxyvalenol (Vornitoxin) and ZearaneloneJ’ Foodand Chemical Toxicology 25297-304,1987.Peterso~ M.L., Harder, S., Rummo, N., et al., ‘TheEffect of Ozone on Leukocyte Function in ExposedHuman Subjects;’ Environmental Research 15:485-493,1978.Peterso~ M.L., Smialowicq R., Harder, S., et al., ‘TheEffect of Controlled Ozone Exposure on HumanLymphocyte Function,” Environmental Research24:299-308, 1981.Press, H.F., Day, J.H., Clark, R.H., et al., “Im-munologic Studies of Subjects With Asthma Exposedto Formaldehyde and Urea-Formaldehyde Foam In-sulation (UFFI) Off Products,” Journal ofAllergy andClintialImmunology 79(5):797-810, 1987.Reggia@ G., “Acute Human Exposure to TCDD inSeveso, Raly,’’Joumalof Toxicology and Environmen-talHealth 6;27-43, 1983.Renowq G., “Immunomodulatory Agents,” Immuno-toxico[ogyandImmunopharmacology, J.H. Dean et al.(eds.) (New York NY: Raven Press, 1985), pp. 193-206.Richersoq H.B., “Hypersensitivity Pneumonitis–Pathology and Pathogenesis,” Clinical Reviews ofAllqy 1:469-483, 1983.Roberts, L., “DioxinRisksRevisited,” Science 251:624-626,1991.RoboqJV Greav~J9 and Bekes~J.G9 “PolybrominatedBiphenyls in Model and Environmentally Con-taminated Human Blood: Protein Binding and Im-munotoxicological Studies,” Environmental HealthPerspectives 60:107-113, 1985.

75.

76.

’77.

78.

79.

80.

81.

82.

83.

84.

85.

86.

Rose, N.R., Friedmaq H., and Fahey, J.L. (eds.),Manual of Clinical Laboratory Immunology, 3rd ed.(Washingto~ DC: American Society for Microbiol-ogy, 1986).Rosenth~ GJ., Lebetl@ E., Thigpen, J.E., et al.,“characteristics of ~,7,8-tetrachlorodibenzO-p-dioxinInduced Endotoxin Hypersensitivity Assoaa“ tion WithHepatotoxicity” Totik%y 56:239-254 1989,Sarlo, K,and Clarlq E., “ATierApproachf orEvaluat-ing Low Molecular Weight Chemicals (LMWC) asRespiratory Allergen~” The Toxicok@~ February1990.Savino, A., Peterso~ M.L., House, D., et al., ‘TheEffect of Ozone on Human Cellular and humoralImmunity Characterization of T and B Lymphocytesby Rosette Formation,” Environmental Research15:65-69, 1978.Selgrade, M.K., Environmental Protection Agency,Research Triangle Park, NC, personal communica-tio~ November 1990.Selgrade, M.K., Daniels, M.J., Burleso~ G.R., et al.,“Effects of 7,12 -Dimethylbenz[a] anthracene,Benzo[a]pyrene, and Cyclosporin A on MurineCytomegalovirus Infection: Studies, of Host Resis-tance Mechanisms,’’ IntemationalJoumal oflnvnuno-pharmacolo~ 10(7) ;811-818, 1988.Shopp, G.M., McCay, J.A., and Holsapple, M.P.,“Suppression of the Antibody Response by a For-mamidine Pesticide: Dependence on the Route ofExposure,” Journal of Tom”cology and EnvironmentalHealth 15:293-304 (1985).Silkworth, J.B., Cutler, D.S., and Sack, G., “Im-munotoxicity of 2,3,7,8-Tetrachlorodibenzo-p-dioxinin a Complex Environmental Mixture From the LoveCanal,” Fundamental and Applied Toxicology12(2):303-312, 1989.Sjobla~ R., Office of Pesticide Programs, Environ-mental Protection Agency, Washington, DC, personalecmmmnicatio~ November 1990.Smialowicz, RJ., Riddle, M.M., and Rogers, R.R.,“Immunologic Effects of Perinatal Exposure of Ratsto Dioctyltin Dichloride;’ Journal of Toxicology andEnvironmental Health 25:4Q3-422, 1988.Smialowicz, RJ., Riddle, M.M., Rogers, R.R., et al.,“immunotoxicit yof Tributyltin Oxide in Rats ExposedAs Adults or Pre-Weaklings,” Toxicology 57:97-111,1989.Smialowicz, RJ., Rogers, R.R., Riddle, M.M., et al.,“Immunologic Effects of Nickel, I: Suppression of


87.

88.

89.

90.

91.

92.

93.

94.

95.

96.

1.

I

A

1

1<,

3eJlu.lar and humoral Immunity,” Environmenta2Re-?eamh 33:4S427, 1984.hhlowicq RJ., Rogers, R.R., Riddle, M.M., et al.,‘Immunologic Effects of Nickel II: Suppression of!Jatural Killer Cell Activity;’ EnvtionmentalResearch%:5666, 1985.$mialowicq RJ., Rogers, R.R., Riddle, M.M., et al.,‘Immunological Studies in Mice Following In UteroExposure to NiCl~” Toxicology 38:293-303, 1986.hialowi~ RJ., Rogers, R.R., Rowe, D.G., et al.,The Effects of Nickel on Immune Function in thella~” Toxicology 44:271-281, 1987.hmeij, NJ., Penninks, A.H., Seine% W., “BiologicalActivity of Organotin Compounds: An Overview,wEn-?ironmentalResearch 44:335-353, 1987.3preafko, F., Massimo, A., Merendino, A., et al.,‘Chemical Immunodepressive Drugs: Their Actionm the Cells of the Immune System and Immunekfediators~’ immunotoxicology and Immunophar-vzacology, J.H. Dean et al. (eds.) (New Yorlq NY:Raven Press 1985), pp. 179-192.Strcx+ J= Smolder, 1A Isbister J. et al., ‘The HumanHealth E&xls of Expmure to Pdybdnated Biphen~”Tti@mdA@zi I%amacdqy58:145-150, 1981.Thomas, P.T., BusSe, W.W., Kerkvliet, N.I., et al.,“Immunologic Effects of Pestieide~” 7he Efiects ofF’estictis on Human Health S.Il. Baker and C.F.Wilkinson (eds.) (NewYor~ NY: Princeton ScientitlcPublishers, Inc., 1990), pp. 261-295.llho~ P.TV and Faifi RE., “Adult and Perinatal Im-munotoxiatyInduced by Halogpnated AromaticHydmcar-bo~” 1~ol@YandI~hamwco@y J. H.Dean et aL (eds.) (New York NY: Rawm Pr~ N85),pp.3os314.Treleave~ J.G., and Barret, AJ., “Immunosuppres-sive Agents in Current Use,’’ British Jouma1ofHospi-talMedicine 43(4):256-64, April 1990.Tryphonas, H., Haywar~ S., O’Grady, L., et al.,“hmmnotoxicity Studies of PCB (Aroclar 1254) inthe Adult Rhesus (Macaca Mulatta) Monkey Prelimi-nary Report,’’ International Journal of Imnwnophar-maco[ogy 11(2):199-206, 1989.

97.

98.

99.

100.

101.

102.

103.

104.

105.

106.

Tsang P.H., Chu, F.N., F~chbei~ A., et al., “Impair-ments in Functional Subsets of T-Suppressor (CD8)Lymphocyte Monocytes, and Natural Killer CellsAmong Asbestos-Exposed Workers; Clinical Imm-unology and Immunopathology 47:323-332, 1988.U. S. CmgreM Office of Technology Assessment,Catching ~rBreath: Next Steps forReducing UrbanOzoW OTA-O-412 (Washington, DC: U.S. Gover-nment Printing Offh, July 1989).Urso, P., and Gengozi~ N., “Depressed humoralImmunity and Increased Tumor Incidence in MiceFollowing In Utero Exposure to Benzo(a)pyrene~’Journal of Toxicology and Environmental Health6569-76,1980.Urso, P., Gengozizq N., Rossi, R.M., et al., ’’Supples-sion of humoral and Cell-Mediated ImmuneResponse In Mtro by Benzo[a]pyrene~’ Journal of1mmunopharmacologY 8(2):223-241, 1986.Van Lovere~ H., Krajanc, E.I., Rombout, PJ., et al.,“Effects of Ozone, Hexachlorobenzene, and Bis (bri-n-butyltin) Oxide on Natural Killer Activity in the RatLung,” Toxicology and Applied Pharmacology102(1):21-33, January 1990.Vogt, R., Centers for Disease Control, Atlant~ GApersonal communication, September 1990.Vos, J.G., Brouwer, G.M.J., van Leeuwen, F.X.R., etal., ‘Toxicity of Hexachlorobenzene in the Rat Fol-lowing Combined Pre- and Postnatal Exposure: Com-parison of Effects on Immune System Liver, andLung” International Symposium on immunotoxicol-o~, G. Gibson et al. (eds.) (London, England:Academic Press), pp. 221-235.War~E~Murray,MJ.pd ki~J.H5’%nrnunotoxiatyof Nonhalogenated po~cydic /irOITEitiC Hydrocarh~”Inmwnotoz”cologY and Irrmu.tnopharmacolon, J. H.Dean et al. (eds.) (New Yorlq NY: Raven Press,1985), pp. 291-313.Wilson, J.D., “A Dose-Response Curve for YushoSyndrome;’ Regulato~ Toxicology and Phamlacol-0~ 7364-369, 1987.Wysock~ J., Kalin~ Z., and Owczarzy, I., “SerumLevels of Immunoglobulins and C-3 Component of


Complement in Persons Occupationally Exposed to Maqn Bnli3h Journa1 of Ititrial Medicine 45:5M-Chlorinated Pestieide~”AfedkaZl?ractice 36: 11-117, 5281988.1985. 108. Zbindeq G., “The Relationship Between Clinical

107. Yardley-Jon~ A., Andersoq D., and Jenkinso~ P., Immunolq?y and Cla!xml“ ExperimentaUmnlunotoxicOl-“Effeets of Occupational Exposure to Benzene on ogy,’’Proceedings oftheIUTOXCongress in Brighto~Phytoherq@hin (PHA) Stimulated Lymphocytes m July 16-22,1989.

Pesticides,' Medical Practice

Yardley-Jones, Anderson, Jenkinson, 'Effects Ph}toltemagg!utinin (PHA)

Man,' British Jouma lndustrinl 45:516-

Zbinden, Innnuno1cgy CIa>sical Experimental Innnunotoxicology,' Proceedings ofthelUTOXCongress Brighton, July

Chapter 4

Federal Attention to Immunotoxicants

Chapter 4

Federal Attention to Immunotoxicants

INTRODUCTION

A diverse framework of laws authorizes several Federalagencies to control human exposure to toxic substances,including immunotoxicants. This chapter describesFederal research activities designed to enhance the baseof knowledge about immunotoxicology and to supportregulatory efforts. This chapter also provides a briefsummary of the power of the Federal regulatory agenciesto license, register, set standards, or otherwise controlimmunotoxic substances. Several previous OTA studies havedescribed Federal programs to regulate toxic substances inmuch greater detail (24,26,27,28,29,30,31,32). Finally, thischapter describes Federal programs that enable workersand the general public to obtain information about thepresence of toxic substances as a means to control ex-posure.

FEDERAL RESEARCH ACTIVITIES

Federal immunotoxicology programs focus on re-search, development, and validation of test methods toassess the impact of substances on the immune system.Researchers seek improved methods for assessing thetoxicological bases of hypersensitivity, autoimmunity, andimmune suppression. This section discusses Federal effortsto evaluate substances that may present immunotoxic healthrisks and to develop immunotoxicological tests for use inregulation.

The National Toxicology Program

The Secretary of the U.S. Department of Health andHuman Services(HHS) established the National ToxicologyProgram (NTP) in 1978 to coordinate and strengthen theDepartment’s activities in characterizing the toxicity ofchemicals. NTP is charged with:

● broadening the spectrum of toxicologic infor-mation obtained on selected chemicals;

● increasing the numbers of chemicals studied,within funding limits;

. developing and validating assays and protocolsresponsive to regulatory needs; and

● communicating NTP plans and results togovernmental agencies, the medical and scien-tific communities, and the public.

NTP consists of four charter agencies of HHS: theNational Cancer Institute (NCI), the National Instituteof Environmental Health Sciences (NIEHS), the Nation-al Center for Toxicological Research (NCTR), and theNational Institute for Occupational Safety and Health(NIOSH). NTP coordinates the relevant programs,staff, andresources from those Public Health Service agencies relatingto basic and applied toxicological research, An executivecommittee consisting of the heads of the EnvironmentalProtection Agency (EPA), the Food and Drug Administra-tion (FDA), the National Institutes of Health (NIH),NIEHS, the Agency for Toxic Substances and DiseaseRegistry (ATSDR), the Consumer Product Safety Com-mission (CPSC), NCI, NIOSH, and the Occupational Safetyand Health Administration (OSHA) oversees NTP.Nominations of chemicals for toxicology studies are made byall participating agencies and are encouraged from allsectors of the public.

The objectives of NTP’s immunotoxicology Programare to systematically: 1) evaluate and examine the in-fluence of selected chemicals on the immune response;2) relate alterations in immunologic functions to bothgeneral toxicity and specific organ toxicity; 3) relatechanges in immunologic functions to altered host resis-tance; and 4) refine and employ a panel of immune andhost resistance test procedures in order to better definein vitro and in vivo immunotoxicit y. The immunotoxicol-ogy Program seeks to correlate laboratory immunologicfindings with altered host susceptibility and to extrapo-late animal findings about chemically induced effects toestimates of human risk (17).

NTP researchers conceived a tier approach to testingfor immunosuppression (12; see ch. 3). Tier I (see table4-1) includes assays for pathology, humoral immunity,

49


Table 4-1—NTP’s Panel of Tests for Detecting immunotoxicity

Parameter Procedures

Screen (Tier 1)Immunopathology . . . . .

humoral-mediatedimmunity . . . . . . . . . .

Cell-mediatedimmunity . . . . . . . . . .

Nonspecific immunity . .

Comprehensive (Tier 11)Immunopathology . . . . .humoral-mediated

immunity . . . . . . . . . .Cell-mediated

immunity . . . . . . . . . .

Nonspecific immunity . .

Host resistancechallenge model(endpoints) . . . . . . . .

Hematology-complete blood count and differentialWeights-body, spleen, thymus, kidney, liverCellularity—spleenHistology-spleen, thymus, lymph node

Enumerate lgM antibody plaque forming cells to T-dependentantigen(SRBC)

LPS mitogen response

Lymphocyte blastogenesis to mitogens (Con A) and mixed Ieukocyteresponse against allogeneic leukocytes (MLR)

Natural killer (NK) cell activity

Quantitation of splenic B and T cell numbers

Enumeration of lgG antibody response to SRBCs

Cytotoxic T lymphocyte (CTL) cytolysis. Delayed hyper-sensitivityresponse (DHR)

Microphage function-quantitation of resident peritoneal cells, andphagocytic ability (basal and activated by MAF)

Syngeneic tumor cellsPYB6 sarcoma (tumor incidence)B16F1O melanoma (lung burden)

Bacterial modelsListeria monocytogenes (mortality)Streptococcus species (mortality)

Viral modelsInfluenza (mortality)

Parasite modelsPlasmodium yoelii (parasitemia)

SOURCE: Ml. Luster, A.E. Munson, P.T. Thomas, et al., “Methods Evaluation—Development of a Testing Battery toAssess Chemical-Induced immunotoxicity: National Toxicology Program’s Guidelines for immunotoxicityEvaluation in Mice,” Fundamental and Applied Toxicology 10:2-19, 1988.

cell-mediated immunity, and nonspecific immunity. Thetests included in Tier I function as a basic immunotoxicityscreening mechanism and cannot predict whether a sub-stance will reduce the immune system’s ability to fight disease.However, they can detect immune alterations that suggestthe need to evaluate the compound further, using one ormore of the specialized tests listed under Tier II. Tier IIassays include pathologic tests and measures of humoral,cell-mediated, and nonspecific immunity, and employhost resistance challenge models that test the ability ofan animal (usually a mouse) to prevent infection or tumorgrowth after exposure to a suspected immunotoxicant.NTP’s battery of tests does not include measures of asubstance’s potential to induce hypersensitivity. NTP’smethods cannot measure tolerance or reversibility ofeffect, since animals are evaluated at a single point in

time, or specific sites of immune responsiveness, such aslung or intestinal immunity.

Since 1985, when validation of the NTP tiers wascompleted, more than 50 chemicals have been evaluated forimmunosuppression (see table 4-2). NTP has also tested2 of those chemicals and 15 additional chemicals usingstandard hypersensitivity assays (see table 4-3). Amongthe agents tested by NTP are the AIDS treatment, AZT;nitrophenylpentadien — spy dust; methyl isocyanate, theprimary causative agent of the Bhopal disaster; and sili-cone fluid used in surgical implants.

The mouse has been the experimental animal ofchoice at NTP because its immune system is well charac-terized. Efforts are underway to validate immunotoxicity

Chapter 4-Federal Attention to Immunotoxicants . 51

Table 4-2—Substances Tested by NTP for Immunosuppression

Substance Use/Industry immunotoxicity

acetonitrile . . . . . . . . . . . . . . . . . . .aldicarb oxime . . . . . . . . . . . . . . .allyl isovalerate . . . . . . . . . . . . . . .arsine . . . . . . . . . . . . . . . . . . . . . .azathioprine. . . . . . . . . . . . . . . . . .benzidine . . . . . . . . . . . . . . . . . . . .benzo (a) pyrene . . . . . . . . . . . . . .benzo (e) pyrene . . . . . . . . . . . . . .o-benzyl- p-chlorophenol . . . . . . . .

ydt-butylhy roquinone . . . . . . . . . . .cadmium chloride . . . . . . . . . . . . .chemical mixture . . . . . . . . . . . . .4-chloro-o-phenylenediamine . . .cyclophosphamide . . . . . . . . . . . .2,4-diaminotoluene . . . . . . . . . . .dideoxyadenosine . . . . . . . . . . . . .diethylstilbestrol . . . . . . . . . . . . . .dimethylbenz(a) anthracene . . . . .dimethyl vinylchloride. . . . . . . . . .diphenylhydantoin . . . . . . . . . . . . .ethyl carbamate . . . . . . . . . . . . . .ethylene dibromide . . . . . . . . . . . .formaldehyde . . . . . . . . . . . . . . . .

gallium arsenide . . . . . . . . . . . . . .

ginseng . . . . . . . . . . . . . . . . . . . . .hexachlorobenzo-p-dioxin . . . . . .indomethacin . . . . . . . . . . . . . . . . .interferon-alpha . . . . . . . . . . . . . .lithium carbonate . . . . . . . . . . . . .methyl carbamate. . . . . . . . . . . , ,methyl isocyanate . . . . . . . . . . . . .nickel sulfate . . . . . . . . . . . . . . . . .nitrobenzene . . . . . . . . . . . . . . . . .nitrofurazone . . . . . . . . . . . . . . . . .n-nitrosodimethylamine . . . . . . . .m-nitrotoluene ... , . . . . . . . . . . . .p-nitrotoluene . . . . . . . . . . . . . . . .ochratoxin a . . . . . . . . . . . . . . . . .oxymetholone . . . . . . . . . . . . . . . .pentachlorophenol . . . . . . . . . . . .pentamidine isethionate. . . . . . . .o-phenylphenol . . . . . . . . . . . . . . .phorbol myristate acetate. . . . . . .ribavirin . . . . . . . . . . . . . . . . . . . . .silicone polymers . . . . . . . . . . . . .2,3,7,8 -tetrachlorodibenzo-

p-dioxintetraethyI lead-.- ~~~.’.’ ~.’ ~.’ ~ ~; ~; j

Jtetrahydrocannibinol. . . . . . . . . . .4,4-thiobis(6-t-butyl-m-cresol) . . .toluene . . . . . . . . . . . . . . . . . . . . . .tris(2,3-dichloropropyl) phosphate.vanadium pentoxide . . . . . . . . . . .4-vinyl-1- -cyclohexene diepoxide .

catalyst; solventinsecticidefragrance; flavoring agentdopant for microelectronicschemotherapeutic agentdrycleaning fluid; dye manufacturingfossil fuel combustion byproductveterinary antisepticgermicideantioxidant in cosmeticsphotography; dyes; lubricantsmix of 26 groundwater contaminantshair dyes; curing agentcancer therapeuticphotographypotential AIDS therapeuticformerly a hormone therapy; cattle growth promoterinduces malignant tumors (research)organic synthesisanticonvulsant therapeuticanesthetic; co-solvent; anti-neoplasticfumigant; gasoline additivedisinfectant; tissue fixative; textiles; photography;

wood productssemiconductors; electronics; microwave

generationmedicinal and research purposeschemical byproductanalgesic; anti-inflammatorycell product with antiviral activityglazes; antidepressant drugchemical intermediatesynthesis of pesticidesfabrics; plating; catalystdyes; shoe polish; leather; paint; soapsantibacterial agent; food additivesolvent; rocket fuels; antioxidantexplosives; dyesexplosives; dyesmetabolize from moldtherapeutic; synthetic androgenwood preservativeantiprotozoal used to treat pneumoniafungicide; cleaning; rubber; preservativetumor promoter (research)antiviral therapeuticsemiconductor manufacture; surgical implants

herbicide production byproductchemical intermediateconstituent of marijuanaantioxidant and stabilizersolvent; denaturantflame retardantcatalyst; glass; ceramics; photos; textilesresins

—++++—

—++

+++++++++—

++++++—

—+—++++—+

—++—

++—+———+

NOTE: Positive (+) compounds demonstrated a significant dose-response effect for any one parameter in the NTPTiers or showed significant effects in multiple parameters at a high dose level. The designation indicatespotential immunosuppresive chemicals, not definitive immunotoxicants.

SOURCE: Office of Technology Assessment, 1991; based on Ml. Luster, National Institute of Environmental HealthSciences, Research Triangle Park, NC, personal communication, July 1990.

testing in rats because they are used most frequently in to identify the most suitable test subjects for particulargeneral toxicological testing. The goal of toxicological immune functions.testing on experimental animals is to be able to extrapo-late from test results to human health effects. Thus re- in fiscal year 1990, NTP had a budget of almost $2.6searchers may proceed with testing and test validation in million for immunotoxicological research (19). NTP con-other species (e.g., dogs, swine, and primates) in order tinues to work on refining and improving the immu-


Table 4-3-Substances Tested by NTP for Hypersensitivity

Substance Use/industry immunotoxicity

benzothonium chloride . . . . . . . . . . . . . . .benzyl-p-chlorophenol . . . . . . . . . . . . . . .4-chloro-o-0-phenylenediamine . . . . . . .cobaltous sulfate . . . . . . . . . . . . . . . . . . .crotonaldehyde . . . . . . . . . . . . . . . . . . . . .2,4-diaminotoluene . . . . . . . . . . . . . . . . .dinitrofluorobenzene . . . . . . . . . . . . . . . .ethylene thiourea. . . . . . . . . . . . . . . . . . .glutaraldehyde. . . . . . . . . . . . . . . . . . . . .isobutyraldehyde . . . . . . . . . . . . . . . . . . .isophorone diisocyanate . . . . . . . . . . . . .2-mercaptobenzothiazole . . . . . . . . . . . .nitrophenylpentadien. . . . . . . . . . . . . . . .oleic acid diethanolamine . . . . . . . . . . . .polydimethylsiloxane fluid. . . . . . . . . . . .triethanolamine . . . . . . . . . . . . . . . . . . . . .xylenesulfonic acid . . . . . . . . . . . . . . . . .

veterinary medicinedisinfectant germicidehair dyes; curing agentelectroplating; glazessolvent; warfarephotographyreagantelectroplating; dyes; rubberdisinfectant; fixativeperfumes; rubber; antioxidantspolyurethanerubber; fungicide; oilspy dustsurfactantwater repellant; resin; surgical implantsdry cleaning; cosmetics; textilesshampoos;cleaning compounds

+++—

+++

++

. ,NOTE: Positive (+) indicates statistically significant contact hypersensitivity response observed in mice and/or guinea

pigs.SOURCE: Office of Technology Assessment, 1991; based on Ml. Luster, National Institute of Environmental Health

Sciences, Research Triangle Park, NC, personal communication, July 1990.

notoxicity test battery, and is currently engaged inreviewing data to determine whether the Tier I and TierII assays can predict the immunotoxicity of compoundsand the potential for use of the test data in risk assess-ment (34).

The Environmental Protection Agency

EPA’s primary immunotoxicological research effortsare located in the Office of Health Research (OHR). Infiscal year 1990, OHR had 6 principle investigatorsengaged in immunotoxicological research and funded$345,000 of intramural research and $324,000 of ex-tramural research (22).

EPA’s research program in immunotoxicology hasfour primary goals:

●

●

●

to develop tier testing methods in the rat similarto those used by NTP in the mouse. This effort,which is coordinated with NTP, supportsguideline development for the Office of Pes-ticide Programs and the Office of Toxic Sub-stances;to develop host resistance assays for both themouse and rat that can be included in testguidelines, which would facilitate use of immu-notoxicity testing data for risk assessment pur-poses;

to develop methods for assessing immuneresponses in the lung (including developmentof appropriate host resistance models) in order

to improve the ability to assess immunotoxiceffects of inhaled compounds. These methodsare used to evaluate National Ambient AirQuality Standard (NAAQS) pollutants as wellas other compounds covered by the Clean AirAct. Such methods are needed because of thediffuse nature of the immune system and be-cause many of the inhaled compounds assessedprimarily affect the lung rather than the spleenfrom which cells are usually obtained for im-mune function tests. Effects of certain air pol-lutants on markers of immune dysfunction inthe lung are also being assessed in human clini-cal studies; and

● to develop improved methods for assessing al-lergenic potential of compounds, includingmethods development in both contact sensitivityand pulmonary hypersensitivity (22).

In addition to work in the immunotoxicology programof OHR, EPA scientists have established an oral refer-ence dose for tributyltin oxide (an antimicrobial/antifungalpesticide) based on immunotoxic concerns. The refer-ence dose may eventually be used by regulatory officeswithin the agency to set exposure standards.

The Food and Drug Administration

FDA has contributed substantially to the field of im-munotoxicology and held one of the first scientific con-ferences on inadvertent modification of immuneresponse. Four centers of the FDA, the Center for Food

Chapter 4—Federal Attention to Immunotoxicants . 53

Safety and Applied Nutrition (CFSAN), the Center forDrug Evaluation and Research (CDER), and the Centerfor Biologics Evaluation and Research (CBER), andNCTR are currently engaged in basic immunotoxicityresearch and test development.

FDA uses different immunotoxic testing strategiesdepending on the substance tested and its intended uses,thus a standardized testing scheme is unsuited to FDA’sneeds. CFSAN has been involved in immunotoxicologi-cal research since the mid-1970s, when it began todevelop in vitro studies to screen for potentially im-munotoxic food constituents and contaminants. Currentresearch efforts involve methods development as well asactual studies of the immunotoxic potential of food ad-ditives and contaminants. CFSAN is trying to integrateimmunotoxicity with conventional toxicity testing andmay soon issue guidelines for evaluating the im-munotoxic potential of direct food additives (11).

immunotoxicology research efforts at CBER areaimed at better understanding the clinical relevance ofcompromised immune function (5). CDER evaluatesdrugs on a case-by-case basis and encourages im-munotoxicity testing by manufacturers where it is war-ranted (14). The NCTR initiated an immunotoxicityresearch program in 1975, and the major focus ofNCTR’S research program has been on development ofin vivo testing (2). FDA states that much of its workloadis directly related to identifying possible toxic effects onthe immune system, and the agency was unable torespond to OTA’s inquiry about budget and personneldevoted specifically to immunotoxicology (3).

Other Federal Research Efforts

The NIH allocated approximately $27 million to im-munotoxicological research in fiscal year 1989 (some ofwhich went to NTP) (16). Funds for intramural andextramural research have been available at varying levels ineach of the Institutes. Much of the immunotoxicity researchwas incidental to other research efforts, but im-munotoxicology received some direct attention. For in-stance, the National Institute of Allergy and InfectiousDiseases has supported dermatotoxicological studies ofallergenic plants, assessment of how chemical additivesin foods and medications can trigger asthmatic attacks,and animal studies on the causal role of workplacechemicals in asthma.

NIEHS spent approximately $7.5 million on im-munotoxicological research in fiscal year 1989. NIEHS isactively involved in developing and validating im-munotoxicological test methods, and provides fundingfor NTP’s immunotoxicity testing program. NIEHS,working independently and through NTP, also performsbasic research, seeking to better define the relationshipbetween immune function changes and altered hostresistance, particularly at the low end of the dose-response curve, as well as provide data that should sup-port a framework to allow better extrapolation fromanimal immunotoxicity data to human health risks.

The Centers for Disease Control (CDC) also conductimmunotoxicity research. The Center for EnvironmentalHealth and Injury Control allocated $175,000 and twofull-time equivalent staffers (FTEs) to a study of im-munology measurements for human exposure assess-ment in fiscal year 1990. NIOSH conducted anassessment of immunological markers of herbicide ex-posure in fiscal year 1990, and provided basic support toimmunotoxicological research for a total budget of over$300,000 and four FTEs. The Agency for Toxic Sub-stances and Disease Registry (ATSDR) also providesfinancial support to much of CDC’S immunotoxicologyresearch (8).

The Alcohol, Drug Abuse, and Mental Health Ad-ministration (ADAMHA) carries out research to deter-mine the effects of alcohol and abused drugs on theimmune system. ADAMHA has a particular interest inthe interaction between the nervous system and the im-mune system (6). The Department of Defense reportedthat it funded, in fiscal year 1990, one extramural im-munotoxicity research project designed to develop amodel for studying the toxicity of dioxin (15). TheDepartment of Agriculture reported that it does notsingle out immunotoxic substances for research, but in-dicated significant research attention to aflatoxin, whichhas shown evidence of immunotoxicity (21).

Because of significant differences in data collectionand reporting among the agencies, OTA could not arriveat an exact budget for federally supported im-munotoxicological research for this background paper.Most of the agencies charged with protecting humanhealth have some ongoing immunotoxicological researchactivities, much of it devoted to developing and validatingtests that can be applied to substances of concern to the


agencies. There is strong interest among the Federalagencies–particularly FDA, NIH, CDC, and EPA– toorganize a Federal interagency committee on im-munotoxicology to foster increased interaction amongthe agencies responsible for immunotoxicity researchprograms (4).

FEDERAL REGULATORY ACTIVITIES

OTA identified 12 laws with mandates broad enoughto encompass immunotoxicological concerns thatauthorize Federal agencies to regulate toxic substances(table 4-4). None of these laws spells out a specific dutyto regulate immunotoxicants, but the duty to protecthuman health included in each law places im-munotoxicants within the regulatory reach of the ad-ministering agencies.

The Occupational Safety and HealthAdministration

OSHA administers the Occupational Safety andHealth Act (OSH Act) of 1970 (29 U.S.C. 651 et seq.).The Act authorizes OSHA to promulgate new standardsfor toxic materials and to modify or revoke existing stand-ards. Section 655(b)(5) states that:

Table 4-4—Major Federal Laws ControllingToxic Substances

Agency primarilyAct responsible

Toxic Substances Control Act. . . . . . . . . . . .Federal Insecticide, Fungicide,

and Rodenticide Act . . . . . . . . . . . . . . . . .Federal Food, Drug, and Cosmetic Act . . . .

Occupational Safety and Health Act. . . . . .Comprehensive Environmental Response,

Compensation, and Liability Act. . . . . . . .

Clean Air Act . . . . . . . . . . . . . . . . . . . . . . . . .

Federal Water Pollution Control Act andClean Water Act.. . . . . . . . . . . . . . . . . . . .

Safe Drinking Water Act . . . . . . . . . . . . . . . .Resource Conservation and Recovery Act..

Consumer Product Safety Act . . . . . . . . . . .Federal Hazardous Substances Act. . . . . . .Federal Mine Safety and Health Act . . . . . .

EPA

EPAFDA

OSHA

EPA

EPA

EPA

EPAEPA

CPSCCPSCMSHA

KEY: CPSC-Consumer Product Safety Commission; EPA—Envi-ronmental Protection Agency; FDA—Food and Drug Administration;MSHA—Mine Safety and Health Administration; OSHA--Occu-pational Safety and Health Administration


The Secretary, in promulgating standards dealing withtoxic materials or harmful physical agents under this sub-section shall set the standard which most adequately as-sures, to the extent feasible on the basis of the best availableevidence, that no employee will suffer material impairmentof health or functional capacity even if such employee hasregular exposure to the hazard dealt with by such standardfor the period of his working life.

The Supreme Court has interpreted this language torequire OSHA to enact the most protective standardpossible to eliminate a significant risk of material impair-ment, subject to the constraints of technological andeconomic feasibility (American Textile Manufacturers In-stitute, Inc. v. Donovan, 452 U.S. 490 (1981)).

OSHA rulemaking can result in requirements formonitoring and medical surveillance, workplace proce-dures and practices, personal protective equipment, en-gineering controls, training, recordkeeping, and new ormodified permissible exposure limits (PELs). In 1987,OSHA adopted updated standards that had been set bythe American Conference of Government IndustrialHygienists (ACGIH), a voluntary organization, forworkplace exposure to 428 toxic substances (52 FR 2332;29 CFR Part 1910). Despite these new standards, OSHAlacks information on the effects of chronic exposure forover 90 percent of these substances. Most of the remain-ing 10 percent, which have been evaluated for chronictoxicity, have not been evaluated for immunotoxicity(36). However, an immunotoxic effect, sensitization, wasspecifically noted for eight of these substances (table4-5).

Photo credit: Environmental Protection Agency, Washington, DC

Special clothing, as well as exposure limits,can help protect workers.

Chapter 4--Federal Attention to Immunotoxicants . 55

Table 4-5-Sensitizers Regulated by OSHA

Substance Use/industry Health effects

Captafol . . . . . . . . . . . . . . . . . . . . fungicide Skin and respiratory sensitization

Cobalt (metal, dust, and fume) . . aircraft; automobile Pulmonary sensitization

Isophorone diisocyanate . . . . . . . housing; automobile Skin and respiratory sensitization

Phenothiazine . . . . . . . . . . . . . . . . veterinary insecticide Skin sensitization

Phenyl glycidyl ether . . . . . . . . . . monomer and surfactant Skin sensitizationproduction

Picric acid . . . . . . . . . . . . . . . . . . . rocket fuels; steel Skin sensitization

Subtilisins . . . . . . . . . . . . . . . . . . . laundry detergents Respiratory sensitization

Toluene-2,4-diisocyanate. . . . . . . rubber; paints; coal tar Pulmonary sensitizationSOURCE: Federal Register, vol. 53, No. 109, Tuesday, June 7, 1988.

The Food and Drug Administration

FDA regulates chemicals found in foods, drugs, andcosmetics under the Food, Drug, and Cosmetic Act of1938 (FDCA; 21 U.S.C. 301-392). FDCA encompassesseveral laws passed by Congress since the first Federalstatute regulating food safety, the Food and Drugs Actof 1906, including the Pesticide Chemical ResiduesAmendment of 1954, the Food Additives Amendment of1958, the Color Additive Amendments of 1960, the DrugAmendments of 1962, and the Animal Drug Amend-ments of 1%8.

F o o d s

FDCA declares it illegal to sell an adulterated food.A food is adulterated if:

. . . it bears or contains any poisonous or deleterioussubstance which may render it injurious to health; but incase the substance is not an added substance such food shallnot be considered adulterated under this clause if the quan-tity of such substance in such food does not ordinarilyrender it injurious to health (21 U.S.C. 342(a)).

FDA has authority to regulate unavoidable environ-mental contaminants, pesticide residues, and additivesthat appear in food. Added substances are governed bya stricter standard than naturally occurring substances.FDA has authority to require premarket submission ofspecific toxicity test data. FDA does not currently havetesting guidelines for immunotoxicity in foods, butCFSAN has proposed some guidelines that are currentlyunder review (11).

FDA regulates some substances studied as im-munotoxicants, such as mercury and polychlorinated

biphenyls (PCBs), based upon other adverse health ef-fects (21 CFR Part 189). FDA regulated Yellow Dye No.5 based on its association with hypersensitivity. FDA hasalso regulated the use of sulfites because they canprovoke life-threatening responses– often severeasthmatic attacks— in sensitive individuals. Sulfites areno longer generally recognized as safe for use on fruitsor vegetables intended to be served or sold raw orpresented as fresh to consumers, or on potatoes intendedto be served or sold unpackaged and unlabeled to con-sumers (21 CFR Part 182).

D r u g s

FDCA authorizes FDA to regulate new drugs forhumans and animals. The Public Health Service Actprovides similar authority for biologics (e.g., vaccines,monoclinal antibodies, cytokines, and growth factors).New drugs and biologics require pre-marketing ap-proval. In the approval process, applicants must submittwo kinds of applications: 1) an Investigative New Drug(IND) application, essentially a request to conduct aninvestigation; and 2) a New Drug Application (NDA) orProduct Licensing Application (PLA), essentially a re-quest for permission to conduct a more detailed inves-tigation adequate to achieve marketing approval.

The IND application must include chemical,manufacturing, and control information; pharmacologicand toxicologic information from animals and in vitrosystems; and a plan of clinical study. An NDA or PLA,submitted after the research period for the IND, mustinclude full reports of toxicological studies and clinicalinvestigations to show that the test agent is safe andeffective; a complete list of the test agent’s composition;samples of the test agent; information that may be re-


Photo credit: Julios, Washington, DC-- Onrubia

Federal regulations now prohibit the use of sulfites on saladbars because they evoke hypersensitivity reactions.

quired for monitoring; specimens of proposed labels;and information on the potential risks of inactive in-gredients.

The mechanisms of immunosuppression and its clini-cal consequences are better understood than those ofimmunostimulation, due largely to experience withimmunosuppressive drugs in clinical practice. FDA hasapproved the use of several drugs as immunosuppressiveagents, such as cyclosporin A. In addition, FDA hasapproved drugs whose known immunotoxic effects, par-ticularly sensitization, are outweighed by their benefits, butgenerally requires a warning of sensitization as a possibleside effect. In CDER, each division routinely evaluates im-munotoxicity as part of the total safety assessment. Many

of the tests for effects on the immune system are routinelyincorporated into the 28-day toxicity studies that areusually submitted as part of the IND (14). FDA’s drugtesting guidelines do not specifically require im-munotoxicity testing, but require that an applicant con-vince FDA that its test data are adequate. FDA can suggestor require immunotoxicity testing where appropriate.

Cosmet i c s

FDA cannot, under the law, require a manufacturerto perform toxicity testing of cosmetic ingredients, However,products that have not been tested for safety cannot bemarketed unless they bear a label reading “Warning. Thesafety of this product has not been determined” (21 CFR740.10).

FDA has restricted fewer than 20 cosmetic ingredients onthe finding that they were “poisonous or deleterious.”Among these restricted ingredients, however, are sub-stances known to affect the immune system, such asmercury and mercurial compounds, potent allergens andcontact sensitizers (21 CFR 700.13), and vinyl chloride, acontact sensitizer (21 CFR 700.14). Despite FDA’s inabilityto compel toxicity testing, the cosmetic and fragrance in-dustries do operate voluntary testing programs for poten-tial skin sensitizers (7).

The Environmental Protection Agency

EPA administers several laws that authorize regula-tion of toxic substances, including the Clean Air Act(CAA; 42 U.S.C. y 7401 et seq.), the Clean Water Act(CWA; 33 U.S.C. 1251 et seq.), the Safe Drinking WaterAct (SDWA; 42 U.S.C. 201, 300f et seq.), the FederalInsecticide, Fungicide, and Rodenticide Act (FIFRA; 7U.S.C. 136 et seq.), the Toxic Substances Control Act(TSCA; 15 U.S.C. 2601 et seq.), the Resource Conserva-tion and Recovery Act (RCRA; 42 U.S.C. 6901 et seq.),and the Comprehensive Environmental Response, Compen-sation, and Liability Act (CERCLA; 42 U.S.C. 9601 et seq.).

The Clean Air Act

Under the CAA, EPA regulates air pollutants bysetting National Primary and Secondary Ambient AirQuality Standards as necessary to protect the public

Chapter 4-Federal Attention to Immunotoxicants ● 57

health and welfare. EPA has promulgated primary Na-tional Ambient Air Quality Standards for sulfur oxides,particulate matter, carbon monoxide, ozone, nitrogendioxide, and lead (40 CFR 50). None of these standardswas based on consideration of immunotoxic effects, al-though ozone, nitrogen dioxide, and lead have all shownevidence of immunotoxicity in animal tests.

The 1970 amendments to the CAA also called forEPA to set standards limiting hazardous pollutants. Sec-tion 112 of the CAA authorizes EPA to set emissionsstandards for pollutants that may reasonably be an-ticipated to result in an increase in mortality or an in-crease in serious, irreversible, or incapacitatingreversible illness. The list of substances designated byEPA as hazardous air pollutants includes asbestos, ben-zene, beryllium, coke oven emissions, inorganic arsenic,mercury, radionuclides, and vinyl chloride (40 CFRPart 61). Several of time substances have shown evidence ofimmunotoxicity in the laboratory, but serious health effectsother than immunotoxicity served as the basis for thesestandards, which set exposure levels far below those usedin the tests.

Amendments to the CAA passed by the 10lst Con-gress (Public Law 101-549) establish a statutory list of 189hazardous substances or classes of substances. The EPAAdministrator may add or delete substances based onevidence of a pollutant’s potential to cause in humans:

(i) cancer or developmental effects, or

(ii) serious or irreversible–

Photo credit: Environmental Protection Agency, Washington, DC

Few data exist on the human health risks from transient,low-level chemical exposures.

(I) reproductive dysfunctions,

(II) neurological disorders,

(III) heritable gene mutations,

(IV) other chronic health effects, or

(V) adverse acute human health effects.

The 1990 amendments direct EPA to require applica-tion of the maximum achievable control technology(MACT) initially. Following implementation of MACT,EPA is required to evaluate residual risk from sources ofthese substances and decide whether public health isadequately protected; if not, stricter controls can be re-quired.

The Clean Water Act

Since the Federal Water Pollution Control Act wasfirst enacted in 1948, it has been amended nine times andis now generally referred to as the CWA. The 1972amendments set the goal of achieving “fishable, swim-mable” waters by 1983 and prohibiting the “discharge oftoxic pollutants in toxic amounts” by 1985. The 1977amendments endorsed anew method for regulating toxicpollutants, and the 1987 amendments continuedCongress’s emphasis on control of toxic pollutants.

The CWA authorizes the EPA administrator to estab-lish and revise a list of toxic water pollutants. EPA maythen issue effluent limitations or effluent standards toregulate discharges of these substances into the Nation’snavigable waters. Effluent limitations, established on anindustry-by-industry basis, impose technology-based re-strictions on the amount of a toxic substance that can bedirectly discharged from a point source. Effluent stand-ards are control requirements based on the relationshipbetween the discharge of a pollutant and the resultingwater quality in a receiving body of water. Effluent stand-ards can be imposed when, in the judgment of the Ad-ministrator, the effluent limitations affecting a particularsource are insufficient to protect the designated use of aparticular water body reflected in the water qualitystandard for that body established by the State. Thismore stringent effluent standard is employed much lessfrequently than the technology-based effluent limitations.

The CWA also requires that EPA establish pretreat-ment standards for toxic substances discharged fromprivate pollution sources into publicly owned water treat-ment facilities. In addition to these legally binding regula-tions, the CWA authorizes EPA to establish ambient


water quality criteria for all pollutants, including toxics,to be used as water quality goals.

EPA has published a list of hazardous substancesunder the CWA (40 CFR 116.4) and has establishedreportable quantities for each of these substances (40CFR 117.3). Under the CWA, EPA has also promul-gated toxic pollutant effluent standards for six substances(40 CFR Part 129), including PCBs (known to be im-munotoxic in laboratory animals). immunotoxicity wasnot the endpoint of concern in these rulemaking proce-dures, however.

The Safe Drinking Water Act

The SDWA regulates public waters systems and ad-dresses contaminants “which may have an adverse effecton the health of persons.” Under the SDWA, EPAestablishes maximum contaminant levels goals for con-taminants that may have an adverse effect on health.These are nonenforceable health goals, which are usedas guidelines for establishing enforceable drinking waterstandards. EPA then sets enforceable “maximum con-taminant levels” (MCL) that are as close to the goal asfeasible considering the best available technology andthe economic costs of complying with the standard.MCLs have been set for inorganic chemicals (40 CFR141.11 and 141.62) organic chemicals (40 CFR 141.12 and141.61). Immunotoxicity was not a noted consideration inthese actions.

T h e F e d e r a l I n s e c t i c i d e , F u n g i c i d e , a n dRodenticide A c t

FIFRA makes it unlawful to sell or distribute a pes-ticide that is not registered with EPA. An applicant forregistration of a pesticide must file the following infor-mation with EPA: a statement of all claims made for thepesticide; directions for its use; a description of testsmade upon it; and the test results used to support claimsmade for the substance. In addition, the applicant mustsupply appropriate health and safety data. EPA mustregister the pesticide if its composition warrants theproposed claims for it, if it will perform its intendedfunction without unreasonable adverse effects on theenvironment, and if, when used in accordance withwidespread and commonly recognized practice, it willnot generally cause unreasonable adverse effects on theenvironment. An “unreasonable adverse effect on theenvironment” is defined as “any unreasonable risk to manor the environment, taking into account the economic,social, and environmental costs and benefits of the use of

any pesticide.” The burden of proof regarding safety ison the manufacturer. If EPA finds that a pesticide meetsor exceeds any of its specified criteria for risk (40 CFR154.7), it must initiate a special review process. Thisprocess allows EPA to require additional toxicity testingincluding immunotoxicity, if warranted.

A pesticide may be registered for general or restricteduse, and EPA may conditionally register pesticides evenif some test data are unavailable. EPA has concentratedits attention to date on the active ingredients in pesticides,but expresses increasing concern about inert ingredients.EPA has issued no restrictions on pesticide use based solelyon immunotoxicity. The 1988 amendments to FIFRArequire EPA to review 600 active ingredients of existingpesticides by 1997, which requires reexamination of safety,including toxicity. The test guidelines for reregistration arethe same as for registration.

In 1982, EPA’s Office of Pesticide Programs (OPP),which administers FIFRA, published data requirements forthe toxicological evaluation of biochemical pesticidesand for microbial pesticides. Biochemical pesticides in-clude pheromones, hormones, natural insect and plantgrowth regulators, and enzymes. Microbial pesticides in-clude bacteria, fungi, protozoa, and viruses. OPP recentlyrevised the requirements to reflect advances in toxicology(23). The immunotoxicity study now required forbiochemical pesticides is designed to accommodateeither the rat or the mouse as the test animal. The tieredtesting scheme as revised is presented in table 4-6. The studyis required for biochemical pesticides where uses result insignificant human exposure (e.g., food uses, indooraerosols). Tier I tests serve as a screen for immunotoxicpotential, and Tier II tests are designed to provide infor-mation necessary to perform risk assessment. Tests todetermine whether biochemical pesticides can induce adelayed-type hypersensitivity reaction in guinea pigs arerequired and are set forth as a separate study in the datarequirements (40 CFR 158.690).

The revisions of the data requirements deleted therequirement for specific immunotoxicity testing ofmicrobial pesticides, but the ability of the test animals toclear the active microbial ingredient after dosing via oral,pulmonary, and intravenous routes is used as an indicatorof a properly functioning immune system. EPA reservesthe right to require an immunotoxicity study for certainmicrobial pesticides, but this study would be reserved forcertain viruses that are related to viruses known to impactadversely on the human immune system (23). The re-quirement for a hypersensitivity assessment of

Chapter 4--Federal Attention to Immunotoxicants . 59

Table 4-6-EPA Subdivision M Guidelines: ProposedRevised Requirements for immunotoxicity Testing of

Biochemical Pest Control Agents

Tier /A. Spleen, thymus, and bone marrow cellularityB. humoral immunity-do one of the following:

1. Primary and secondary immunoglogulin (lgG and lgM)responses to antigen

2. Antibody plaque forming cell assayC. Specific cell-mediated immunity—do one of the following:

1. One-way mixed Iymphocyte reaction (MLR) assay2. Effect of BPCA on normal delayed-type hypersensitivity3. Effect of BPCA on generation of cytotoxic T-lymphocyte

D. Nonspecific cell-mediated immunity:1. Natural killer cell activity2. Microphage function

Tier IIA. Tier II studies required if:

1. Dysfunction is observed in Tier I tests2. Tier I test results cannot be definitively interpreted3. Data from other sources indicate immunotoxicity

B, General testing features:1. Evaluate time-course for recovery from immunotoxic

effects2. Determine whether observed effects may impair host

resistance to infectious agents or to tumor cell challenge3. Perform additional specific, but appropriate, testing

essential for evaluation of potential risksSOURCE: Office of Technology Assessment, 1991.

microbial pesticides also has been dropped, with report-ing of any observations of allergic reactions being re-quired instead. This is because it is expected thatproteinaceous components of microbial pesticidepreparations (including fermentation byproduct in-gredients) would elicit a positive response in test guineapigs after subcutaneous induction and challenge; andwould most likely not give a positive response with topicalinduction and challenge.

OPP plans to revise its testing guidelines for chemicalpesticides to include immunotoxicity testing Laboratorystudies presently required for registration of chemicalpesticides include a battery of acute toxicity studies (oral,dermal, pulmonary, eye), subchronic studies, chronicstudies, developmental toxicity studies, reproduction ef-fects study, battery of mutagenicity studies, chronic car-cinogenicity study, and metabolism study (23).

The Toxic Substances Control Act

TSCA authorizes EPA to regulate chemicals (specifi-cally excluding pesticides; tobacco and tobacco

products; nuclear materials; foods, drugs, and cosmetics;pistols, firearms, revolvers, shells, and cartridges, which areregulated under other statutes) before and after theyreach the market. EPA’s first task under TSCA was tocompile an inventory of all existing chemical substancesthat would be subject to the provisions of TSCA that weremanufactured or imported into the United States in 1977.Any chemical not on that initial list is a “new” chemicaland subject to premanufacture notice (PMN) require-ments.

TSCA requires manufacturers to notify EPA in ad-vance of the intended introduction into commerce of anew chemical with a Premanufacture Notice (PMN).EPA must also be notified if a chemical is to be used inaway that differs significantly from that proposed in theoriginal PMN. The PMN contains data on a chemical’sidentity and structure, proposed use, manufacturingbyproducts, and impurities.

TSCA does not require that manufacturers carry outa specific program of toxicity testing before approval ofa new chemical, thus PMNs are rarely submitted withtoxicity data for each organ system. The extent of toxicitydata submitted with PMNs generally depends on theprojected annual production volume for the compound.If insufficient or incomplete toxicity data are provided tosupport a PMN, EPA requests additional information orissues a consent order in which the manufacturer agreesto provide the required information according to anestablished timetable.

EPA toxicologists evaluate PMNs by comparing newchemicals to structurally related existing chemicals. Iftoxicity is predicted on the basis of structural analogues,a chemical maybe subjected to a more detailed examina-tion. If during the detailed review EPA concludes that anew chemical may present an unreasonable risk of ad-verse effects on human health or the environment, addi-tional toxicity data can be required. Immunotoxicity has notbeen used as the basis for any regulatory action taken byEPA under the PMN provisions of TSCA.

TSCA also directs EPA to regulate existing chemicalsubstances that pose an unreasonable risk of injury tohuman health or the environment and to act promptly onsubstances that pose imminent hazards. An InteragencyTesting Committee reviews substances on the existingchemicals list and can recommend that EPA require


testing for these substances. In determining whether achemical presents or may present an unreasonable riskto human health or the environment, EPA considers:

●

●

●

●

the effects of a substance or mixture on humanhealth and the magnitude of the exposure ofhuman beings to it;

the effects of a substance or mixture on theenvironment and the magnitude of the ex-posure of the environment to such substance ormixture;

the benefits of such substance or mixture forvarious uses and the availability of substitutesfor such uses; andthe reasonably ascertainable economic conse-quences of the rules, after consideration of theeffect on the national economy, small business,technological innovation, the environment, andpublic health.

If EPA can show that there is inadequate informationon the effects of a chemical and that testing is necessaryto obtain that information, it may issue a test rule definingthe substances to be tested and how they should betested. EPA has developed general guidelines for toxicitytesting (40 CFR 796), but each test rule contains require-ments specific to the chemical under scrutiny. Chemicalmanufacturers and processors are responsible fordeveloping these test data, but EPA bears the burden ofproof in establishing that a substance is an unreasonablerisk to human health or the environment.

For either new or existing chemicals, EPA regulatoryefforts may include steps to: prohibit their manufacture,processing, or distribution in commerce; limit their usesor amounts; require certain labeling; require main-tenance of records and monitoring; prohibit or regulateany manner or method of commercial use; prohibit orregulate their disposal. Manufacturers or processors arerequired to notify EPA of any unreasonable risks posedby new or existing chemicals. immunotoxicity has been anoted concern in evaluations of chemicals under TSCA,but has not served as the health effect of primary concernin any regulatory action.

The Resource Conservation and Recovery Act

RCRA defines solid and hazardous wastes, authorizesEPA to set standards for facilities that generate ormanage hazardous waste, and mandates a permit pro-

gram for hazardous waste treatment, storage, and dis-posal facilities. Hazardous waste is defined as any solidwaste that may cause death or serious disease, or maypresent a substantial hazard to human health or theenvironment if it is improperly treated, stored, trans-ported, or disposed of. Lists of wastes subject to RCRAregulation can be found at 40 CFR 261.31, .32, and .33.The list contains known immunotoxicants, but im-munotoxicity has not been the basis for any chemical’sappearance on this list.

The Comprehensive Environmental Response,Compensation, and Liability Act

CERCLA (sometimes referred to as Superfund) re-quires anyone who releases significant amounts of haz-ardous substances into the environment to notify EPA.CERCLA defines hazardous substances as substancesidentified as toxic by the CWA, RCRA, CAA, or TSCA,and any substance which “when released into the en-vironment may present substantial danger to the publichealth or welfare or the environment.” CERCLA alsorequires that hazardous waste sites be cleaned up to astandard that ensures the protection of human healthand environment. Reportable quantities (RQ) were setfor each hazardous substance on the basis of aquatictoxicity, mammalian toxicity, ignitability, reactivity,chronic toxicity, and potential carcinogenicity. Im-munotoxicity has been a consideration but not a primaryfactor in setting RQ standards.

Other Federal Regulatory Activity

EPA, FDA, and OSHA exercise the main regulatoryauthority over toxic substances, including immunotoxicants.Other agencies also administer laws that could be usedto control these substances, however. The ConsumerProduct Safety Commission (CPSC), for instance, en-forces the Consumer Product Safety Act (CPSA) (15U.S.C. 2051 et seq.) and the Federal Hazardous Sub-stances Act (FHSA) (15 U.S.C. 1261 et seq.).

The CPSA authorizes regulation of consumerproducts (except for foods, drugs, and cosmetics; pes-ticides; tobacco and tobacco products; motor vehicles;aircraft and aircraft equipment; and boats and boat ac-cessories) that pose an “unreasonable risk” of injury orillness. CPSC may set safety standards that specify re-quirements for product performance or design, require-ments for consumer instructions or warnings, or both. A

Chapter 4--Federal Attention to Immunotoxicants ● 61

product c-an be banned if adequate safety standards arenot feasible. No products have been regulated underCPSA on the basis of immunotoxicity.

The FHSA covers hazardous substances (excludingpesticides, foods, drugs, cosmetics, certain radioactivematerials, and tobacco and tobacco products) in generaluse in the home, and is meant particularly to protectchildren from hazardous toys and products. A hazardoussubstance is a substance or mixture that may cause sub-stantial personal injury or substantial illness as aproximate result of any customary or reasonably foresee-able handling or use, including reasonably foreseeableingestion by children. A product can be required to beara hazard label or it can be banned if labeling is inade-quate to protect health. No products have been regulatedunder FHSA on the basis of immunotoxicity.

The Mine Safety and Health Administration (MSHA)regulates the exposure of miners to toxic substancesunder the Federal Mine Safety and Health Act Amend-ments of 1977 (30 U.S.C. 801 et seq.). Much of MSHA’sregulation of toxic exposures involves incorporating byreference the lists of ACGIH. Some observers questionuse of the standards set by ACGIH since they historicallyhave been set without reference to adequate research(36). On the other hand, as demonstrated by the very fewstandards that have been enacted by OSHA, hardly anyworkplace chemical exposures would be regulated if theACGIH standards were not adopted by MSHA andOSHA (28).

FEDERAL INFORMATION PROGRAMS

Some Federal programs incorporate the assumptionthat an informed public is one means to decrease toxicexposures. Worker Right-to-Know programs, estab-lished by OSHA’s hazard communication standard, andCommunity Right-to-Know programs, established by theEmergency Planning and Community Right-to-KnowAct of 1986 (EPCRA), require that workers and othercitizens be provided with knowledge about the toxicsubstances in their work or local environment. TheFederal Government funds a national database at theNational Library of Medicine that helps distribute infor-mation collected under EPCRA nationwide. Federal lawalso established the Agency for Toxic Substances andDisease Registry (ATSDR), which maintains a national-

ly available list of toxic substances and their health ef-fects. The following section briefly describes each ofthese programs.

Worker Right-to-Know

In 1983, OSHA first established its hazard com-munication standard (29 CFR 1910.1200). This standardrequires each employer to have a written hazard com-munication program for each workplace, including a listof all hazardous chemicals in the workplace. Theemployer is permitted to rely substantially on manufac-turers and importers of chemicals to prepare the neces-sary information.

There are four basic elements of a hazard communica-tion program. First, each manufacturer or importer of achemical must determine whether that chemical is haz-ardous. A health hazard is defined as a chemical for whichthere is “statistically significant evidence based on at leastone study conducted in accordance with scientific prin-ciples that acute or chronic health effects may occur.”Second, each manufacturer or importer must prepare amaterial safety data sheet (MSDS) containing comprehen-sive information on the chemical, including all itshazards, precautions for safe handling and use, and con-trol measures. These MSDS must be available toemployees and customers. Third, employers must labelcontainers to alert workers to the identity and significanthazards of the chemical. Finally, each employer mustprovide its workers with education and training in thehandling of hazardous chemicals (13,20).

The standard requires disclosure of immunotoxic ef-fects, where known. The standard does not permit OSHA tocompel testing to determine unknown health effects,however. It should be noted that many MSDS containvery limited information on known toxic hazards (32),and those hazards that are described may be expressedin terminology unintelligible to the lay public (10).

Community Right-to-Know

Congress enacted EPCRA (42 U.S.C. 110001-11050)in response to releases of chemicals at Bhopal, India.EPCRA requires EPA to establish and maintain a list of“extremely hazardous substances.” The current list in-cludes 420 substances set out in 40 CFR Part 355 Appen-

62 ● Identifyingand Controlling Immunotoxic Substances

dix A. EPA has developed a threshold planning quantity(TPQ) for each substance on the list.

This law requires owners and operators of facilitiesthat store, use, or release extremely hazardous sub-stances in amounts in excess of the TPQ to report to EPAinformation about those chemicals, their amounts, andtheir locations. EPCRA requires facility owners andoperators to report releases of these chemicals into theenvironment whether from accidental spills or normaloperations. The statute does not limit use or release of asubstance; it merely requires that the public be informed(9).

Local community organizations must be notified ofany offsite spills or any releases of a “reportable quantity"(RQ) of an extremely hazardous substance or a hazard-ous substance as defined in CERCLA. The RQ’s forextremely hazardous substances are set out in 40 CFRPart 355, Appendix A. The list of hazardous substancesand their RQ’s under CERCLA are set out at 40 CFR302.4. This emergency notification must include thechemical’s common name, the lists on which it appears,the quantity released, the time and duration of therelease, the media into which the release occurred, anyacute or chronic health risks presented by the release,precautions to be taken, and the persons to contact forfurther information (l).

EPCRA community right-to-know provisions also re-quire the public availability of material safety data sheetssimilar to those prepared under OSHA’s hazard com-munication standard. The MSDS must contain thechemical and common names of the chemical, thechemical’s physical and chemical characteristics, itsphysical and health hazards, its routes of exposure,precautions and emergency response procedures, ex-posure limits, and possible carcinogenic effects. If im-munotoxic effects are among the known health hazards,they must be listed (35). Some research indicates that theMSDS, which were developed to convey informationabout workplace exposures, are unsuited to a communityinformation program and that better means to communi-

cate information about risk to the general public areneeded (10).

National Library of Medicine: ToxicologyInformation Program

The National Library of Medicine (NLM) is theNation’s principal resource for the collection, organiza-tion, and retrieval of scientific literature in the health andbiomedical fields (25). It has provided data about toxicchemicals and their hazards to the public for over 20years. To enhance the accessibility of this information,NLM established the Toxicology Data Network (TOX-NET). This database contains several files, including theToxic Chemicals Release Inventory (TRI), which con-tains data on the estimated releases of toxic chemicals tothe air, water, or land, as well as amounts transferred towaste sites. Current law requires U.S. industrial facilitiesto report the TRI information to EPA, which in turnprovides it to NLM for public access. Searches of this filecan be performed by region, company, chemical, but thefile does not contain information on the health effects of,or human exposure to, these chemicals.

Another TOXNET file, the Hazardous SubstancesData Bank (HSDB), covers chemical toxicity, as well asemergency handling procedures, environmental fate,human exposure, detection methods, and regulatory re-quirements. This file contains information on 4,200chemicals. Most of the data in this file is taken frompeer-reviewed journals. TOXNET also includes theRegistry of Toxic Effects of Chemical Substances(RTECS), which covers 100,000 chemicals, and containsinformation on their acute and chronic effects, car-cinogenicity, mutagenicity, and reproductive conse-quences. This file is not peer reviewed.

NLM also maintains the TOXLINE group ofdatabases, outside TOXNET, which contains referencesto journal articles dealing with hazardous chemicals andother areas of toxicology and environmental health. Atpresent, interested parties must contact a health sciencelibrary or information center to request a TOXLINE

Chapter 4-Federal Attention to Immunotoxicants ● 63

search. In the future, more public libraries may tie in toNLM. Individuals can request an application form to useNLM’s system on a personal computer (33,18).

The Agency for Toxic Substances andDisease Registry

Congress created ATSDR in 1980, and its mission isto prevent or mitigate adverse human health effects anddiminished quality of life resulting from exposure tohazardous substances in the environment. As part of itsmission, ATSDR prepares toxicological profiles for haz-ardous substances which are most commonly found atfacilities on the CERCLA National Priorities List andwhich pose the most significant potential threat to humanhealth.

Each toxicological profile must include:

●

●

●

an examination, summary, and interpretationof available toxicological information andepidemiological evaluations on the hazardoussubstance;a determination of whether adequate informa-tion on the health effects of each substance isavailable or in the process of development; andan identification of toxicological testingneeded to identify the types or-leve ls of ex-posure that may present significant risk of ad-verse health effects in humans.

ATSDR also has a Division of Health Educationwhich coordinates health communication and educationactivities for the Agency; coordinates development andeducational activities for emergency response personnel;develops and disseminates to physicians and the healthcare providers materials on the health effects of toxicsubstances; establishes and maintains a list of areasclosed or restricted to the public because of contamina-tion with toxic substances; and initiates research. In ad-dition, ATSDR has regional staff, located throughout theUnited States, who offer consultation on environmentalhealth issues, including emergency response.

S U M M A R Y A N D C O N C L U S I O N S

The Federal Government is actively involved in ad-vancing the state-of-the-art of immunotoxicology. EPA,FDA, and NIH have immunotoxicological researchprograms, and each of these agencies contributes to thework of the NTP. Much of the ongoing Federal researchis directed toward developing and validating tests for

evaluating substances for immunotoxic potential. NTP

has published a panel of tests for immunotoxicity testingthat has been validated in the mouse. NTP continues towork on validating immunotoxicity tests in other speciesand on improving its current panel of tests. NTP is alsoapplying the tests to various substances. EPA is workingon developing and validating immunotoxicity tests usingthe rat as the test species, and has published im-munotoxicity testing guidelines for certain pesticides.Immunotoxicity is a major concern of FDA researcherswhen evaluating new products for human and animalconsumption.

Few substances have been regulated by the FederalGovernment on the basis of immunotoxicity. OSHA hasissued regulations for eight substances on the basis oftheir ability to provoke hypersensitivity. FDA hasrestricted the use of Yellow Dye No. 5 and sulfites infoods because of their association with hypersensitivity.These agencies and EPA regulate other substances thathave shown evidence of immunotoxicity in a few animaltests, but other health effects serve as the basis for thoseregulations.

Several Federal activities are designed to enhancepublic awareness of the hazards of toxic substances,including immunotoxicants. OSHA’s hazard com-munication standard requires that workers be providedwith information about known health hazards in theirjobs. However, since so little information is availableregarding immunotoxic effects, and since the standardcannot be used to compel testing, the standard does littleat present to protect workers from immunotoxic hazards.Community right-to-know legislation requires EPA tocollect information about substances that pose potentialtoxic hazards to local communities and make that infor-

mation available to the public. As with the OSHA stand-ard, however, this program does not permit EPA torequire that health effects information be developed,therefore available information on immunotoxicity isvery limited. ATSDR is disseminating information abouthealth risks, including immunotoxicity, to the public.


1. Abrams, R., and War~ D.H., “Prospects for SaferCanrnunitk Emergency Response, Community Right-to-Know, and Prevention of Chemical Accidents,”Hm-vardEnvironmentalL awReview 14:135-188, 1990.

2. Bass, B.F., Muir, W. R., and Rose, N.R., “Irnmu-notoxieology Strategy— Review of Major ScientificConferences, Federal Activities and Federal Policies


3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

Relating to immunotoxicology~ EPA contract No.68-02-4228 (Alexandri~ VA: Hampshire Research As-soeiat~ Inc., 198’7).

Cannon, H. C., Food and Drug Administration,Washington, DC, personal communieatio~ Oc-tober 1990.Cavagnaro,J.A., Center for BiologiesEvaluation andResearch Food and Drug Adrninistratio~ Rock-ville, MD, personal communicatio~ May 1990.Cavagnaro,JA., Center for BiologiesEvaluation andResearch Food and Drug Administratio~ Rock-ville, MD, personal ammmnieatio~ July 1990.Condon, T.P., Alcoho~ Drug Abuse, and MentalHealthAdminis@atioq Washingto~ ~personalcom-munication, May 1990.Domans~ JJ., Lehn & Fink Products TechnicalCenter, MontVale, NJ, personal communication, July1990.Dowdle, W.R., Centers for Disease Contro~Atkmt~GA, personal communication, February 1990.Finto, KJ., “Regulation by Information ThroughEpm” N~id h~~ and EntiOnmenl 4(3):13-48, Winter 1990.Hadden, S. G., “Providing Citizens With InformationAbout Health Effects of Hazardous Chemi~’’Joumalof &cupationdMdiche 31(6):528-535, June 1989.Hinton, D.M., Center for Food Safety and AppliedNutritio~FoodandDrugAdministratio~ Washingto~DC, personal communication, August 1990.Luster, M.I., National Institute of EnvironmentalHealth Sciences Research Triangle Park NC, per-sonal cmmnunicatio~ July 1990.Mar% Dv “OSHA’S Expanding Hazard cOITUIWl&

tion Requirement~’’NaturalResources and Environ-ment 4(3):19-50, Winter 1990.Mielac~ F.A., Center for Drug Evaluation and Re-search, Food and Drug Administratio~ Washingto~DC, personal communication, September 1990.

15.

16.

17.

18.

19.

20.

21.

22.

23.

24.

25.

26.

Millburq G.P., Office of Defense Research and En-gineering Department of Defense, Washingto~ DC,personal communication, March 1990.Moskow@JqNationalInstitutes ofHeal@ Washingto~DC, personal communication, March 1990.National Toxicology Program Annual Plan for FiscalYear 1989, NTP-89-167, June 1989.OMB Watch “TRI Gains in Use and Popularity;lhe OMB Watcher 8(1):10-11, 1990.Phelps, B., National Toxicology Program, ResearchTriangle Par~NC, personal communicatio~ August1990.Piecio@ R., “Indust@s Response to OSHA’S Haz-ardous Communication Standard: Is the LawWork-ing as Intended?” Chemical Times and Trends, pp.31-36, April 1990.Plowma~ R. D., Agricultural Research Serviee, U.S.Department of Agriculture, Washingto~ DC, per-sonal communicatio~ February 1990.Selgrade, M., Health Effects Research Laboratory,Environmental Protection Agency, Research Tri-angle Park NC, personal communicatio~ July 1990.Sjobla~ R.D., Office of Pesticides and Toxic Sub-stan~Environmental ProtectionAgeney, Washingto~DC, personal cmmm.micatio~ July 1990.U.S. Congress, Office of Technology Assessment,Assessment of Technologies for Determining CancerRisks From the Environment, OTA-H-138(Washingto~DC: U.S. Government Printing Office,June 1981).U.S. Congress, Office of Technology Assessment,MEDLARS and Health Information Po!iqy, OTA-TM-H-11 (Washington, DC: Government PrintingOffice, September 1982).U.S. Congress, Office of Technology Assessment,Acid Rain and TrampotiedAirPollutants: InlplicationsfmPubh2Policy OTA-O-204 (Washingto~ DC: U.S.Government Printing Office, June 1984).

Chapter 4—Federal Attention to Immunotoxicants . 65

27.

28.

29.

30.

31.

U.S. Congress Offke of Technolog Assessment,%tectigti Ntils Groundw@rFm Con@ruka-ti@ OTA-O-233 (Washingto~ DC: U.S. Gover-nment Printing Office, October 1984).U.S. Congress Offke of Technology Assessment,PreventingIlihm andInjuyh the Wix@~ OTA-H-256 (Washingto~ DC: U.S. Government PrintingOffi~ April 1985).U.S. Congress, Oflke of Technology AssessmentSuperjimd Strate~, OTA-ITE-252 (Washington,DC: U.S. Government Printing Office, April 1985).U.S. Congress, Offke of Technology Assessment,Identi~gandRegulating Carcinogens, OTA-BP-H-42 (Washington, DC: U.S. Government Printing Of-fice, November 1987).U.S. Congress, Office of Technology Assessment,Catching Our Breath: Next Steps for Reducing Urban

32.

33.

34.

35.

36.

Ozone, OTA-O-412 (Washington, DC: U.S. Govern-ment Printing Offke, July 1989).U.S. congress Offke of Technology Assessment,Neurotoxicity: Identifying and Controlling Poisons ofthe Nervous Systerq OTA-BA-436 (Washingto~DC:U.S. Government Printing Office, April 1990).Wexler, P., “Finding and Using Toxics Information;’J7?mle Earth Review, pp. 120-121, Spring 1990.White, KL., Jr., Medical College of Virgini~ Rich-mon~ VA personal communicatio~ July 1990.Y@ N.C. and Sehul@ JAI. ‘The Chemicals AmongUS” The Whgton Lawyr 4:(4):24-57, March/April1990.Zie~ G. Baltimore, MD, personal communicatio~July 1990.

Appendices

Appendix A

Income Replacement for Individuals Disabledby Immunotoxicants

INTRODUCTION

Even the best efforts to prevent harmful exposures totoxic substances are imperfect. When regulations orother precautions fail to prevent toxic exposure, per-manently or temporarily disabling illnesses sometimesresult. Federal and State level programs have evolved toprovide a continuing source of income for disabled in-dividuals. This appendix presents a brief overview ofSocial Security, State workers’ compensation programs,and toxic tort. The initiatives described in this appendixwere not specifically designed to compensate individuals forexposure to toxic substances, but they are available, withincertain limits, to immunotoxicant exposure victims.

SOCIAL SECURITY BENEFITS

If an illness or injury interferes with a person’s abilityto work and lasts, or is expected to last, for more than a12-month period, it can give rise to full Social Securitybenefits, either disability benefits (SSDI; 42 U.S.C. 423)or Supplemental Security Income (SSI; 42 U.S.C. 1381-1383a). To secure these benefits, a claimant must proveinability to work. It is not necessary for a Social Securityclaimant to prove that illness or injury occurred becauseof a work-related incident.

SSDI benefits are available to persons who wouldotherwise be qualified for Social Security benefits hadthey paid into the system for the requisite number ofquarters (as established by 20 CFR 404.130). The SSIprogram guarantees a minimum level of cash income toneedy aged, blind, and disabled persons who may nototherwise be eligible for Social Security.

A Social Security claimant files an application with theSocial Security Administration (SSA), which then turnsit over to the State administering agency. The State as-sesses the claim and medical evidence presented against astandard set by law, which defines disability as the in-ability to do any substantial gainful activity by reason ofany medically determinable physical or mental impair-

ment which can be expected to result in death or whichhas lasted or can be expected to last for a continuousperiod of not less than 12 months (4).

For purposes of SSDI and SSI benefits, a medicallydeterminable diagnosis of an immune-system injury– in-cluding an injury or illness caused by an immu-notoxicant – would be compensable. A diagnosis shouldbe supported by a medical history, clinical findings,laboratory findings, and information regarding treat-ment and prognosis. Well known immune system disor-ders, such as a severe allergy, asthma, or autoimmunedisease (e.g., rheumatoid arthritis) could be medicallydeterminable to result in a disability.

More problematic for Social Security claimants andthe SSA is the issue of environmental illness. In its Pro-gram Operations Manual System (POMS), SSA now recog-nizes the claim of some medical practitioners thatexposure to toxic substances can damage the immunesystem, and the SSA identifies this claim as environmen-tal illness (POMS 24515.065, Evaluation of Specific Is-sues-Environmental Illness). In the POMS, the SSAstates that while there is no evidence that claimants withthis type of claim have immune deficiency, immune com-plex disease, autoimmunity, or abnormal functioning oftheir immune systems, evaluation should be made on anindividual case-by-case basis to determine if the impair-ment, whether or not immune system related, preventssubstantial gainful activity. Some legal and medical prac-titioners claim that this standard should increaseclaimants’ success in obtaining Federal benefits after ex-posure to immunotoxic substances.

WORKERS’ COMPENSATION

Workers’ compensation laws vary among the States,but all laws share the requirement that the injury orillness occur on the job and that the claimant be tem-porarily or permanently disabled as a result. This sectionbriefly describes worker’s compensation programs andconcludes with a short summary of some workers’ com-

69


pensation claims based on damage to the immune sys-tem, and a synopsis of recent congressional interest inworkers’ compensation.

Basic Workers’ Compensat ion Law

State workers’ compensation programs represent acompromise reached 80 years ago between labor andbusiness, before many of the chemicals in common usetoday were developed or their hazards understood.Under the common law, the basic duty of employers wasto act with due care for employee safety, as a reasonablyprudent person would, and to furnish a sufficient numberof safe tools and equipment, as well as a sufficient numberof qualified employees to do the work. Employers wereresponsible for issuing and enforcing rules for workplacesafety, rules that with ordinary care would preventreasonably foreseeable accidents. Finally, employers had aduty to warn workers of unusual hazards.

In theory, if the employer failed to live up to thisstandard of conduct, an injured employee could sue fordamages under the common law. This was seldom easy,however. The first difficulty was simply proving theemployee’s case. Other employees might be crucial wit-nesses, but when few governmental or union job protec-tions existed, anyone who testified against an employerrisked being fired. The common law also established threepowerful defenses that employers could use against lawsuitsbrought by employees: negligence of other servants orco-workers; knowledgeable assumption of risk by theemployee; and cent.tlmtory negligence by the injuredemployee. Just prior to enactment of the workers’ com-pensation statutes, however, some States began to easethe claimant’s burden of proving employer negligence,and a few workers began to win sizable judgments (16).

Workers’ compensation substituted a regular, fixed,and predictable compensation payment, previously un-available to most workers, for uncertain, potentiallyruinous liability judgments, which were becoming un-comfortably frequent for employers. The first State lawto withstand challenge passed in the State of Wisconsinin 1911; all States had worker compensation laws by 1948.Initially workers’ compensation laws only covered acci-

dental injury and excluded occupational disease. How-ever, all States covered occupational disease by 1%7.

Three basic approaches to occupational disease coveragehave been adopted. States generally elect either to:

● establish a schedule of covered diseases (whichminimizes problems of proof but excludes un-listed diseases);

● establish a schedule and a residual clause thatallows claims for unlisted disease to be made,with the burden of proof on the claimant; or

● cover diseases “peculiar to” or “characteristicof” relevant trades.

Most States exclude coverage of the ordinary diseasesof life (even where risk of ordinary disease maybe nota-bly increased by an occupation) and require that aworker face a hazard greater than that to which thegeneral public is exposed.

Disease claims that are readily connected to workplaceexposure and are relatively inexpensive (e.g., acute der-matoses) are compensated like accidental injuries. Dis-ease claims involving serious disabilities that are lessclearly linked to workplace exposures (e.g., chronicrespiratory disease) are marked by extended controversyand long waiting periods between the time a claim is filedand a decision on that claim. For these claims, the systemretains many of the undesirable features of the tort sys-tem that workers’ compensation was supposed to sup-plant.

Some observers believe that workers’ compensationsystems have failed to keep pace with knowledge of thehazards of chemical agents (9,11). According to OSHA,occupational diseases from chemical exposures repre-sent a continuing complex problem for workers’ compensa-tion programs. Disabilities resulting from occupationallyinduced illness often are less clearly defined than those fromoccupationally induced injury. As a result, OSHA findsthat workers’ compensation is often a weak remedy in thecase of occupational disease (52 FR 26843). This findingis used as partial justification for OSHA’s decisions toregulate certain chemical exposures rather than rely on

Appendix A-Income Replacement for Disabled Individuals . 71

market-based incentives or other Federal programs toensure worker health and safety.

Table A-l-State Workers’ Compensation DisabilityBenefits, 1989

Disease claimants face extended conflict over the issue ofcausality, in part due to meager scientific evidence to showa relationship between exposure and disease. The factthat many years often intervene between exposure anddisease also plays a role (19). In addition, proof ofcausality may be ambiguous where cases are aggravatedby lifestyle choices (e.g., smoking) or other non-workplace exposures to hazardous substances. SomeStates have opted for a statutory presumption that aclaimant’s disease is work-related, but that is not theprevalent approach. One study found that 60 percent ofoccupational disease claims are contested, and 15 per-cent of challenged claims result in an award for theworker (9).

Occupational disease now accounts for about 1 per-cent of all workers’ compensation claims. The insuranceindustry expects the number of occupational diseaseclaims to rise significantly during the 1990s if medicalresearch more clearly shows a link between illness andworkplace exposure to harmful substances (18). Thus theresults of future research on immunotoxicity could great-ly affect the number and success of workers’ compensa-tion claims based on exposure to immunotoxicants.

Even if a claimant establishes a right to workers’ com-pensation, the amount collected may not be perceived asadequate recompense for the illness. In a majority ofStates, the maximum amount paid a temporarily disabledworker is at least 100 percent of the State’s average wage,but 22 States pay less than that. Table A-1 shows themaximum weekly benefits paid by each State and thepercentage of the State’s average wage this amount rep-resents. These temporary disability benefits are paid inaddition to medical expenses, but obviously represent asubstantial decline in income for many workers (18). Whilethis problem is not peculiar to claims based on exposureto toxic substances, it may serve to discourage claims thathave less than a certainty of success, like toxicant-causedillnesses, since the rewards for the claimant and a legalrepresentative are relatively low.

immunotoxicity Claims

The legal literature includes some published eases ofworkers’ compensation awards to individuals claiming animmune system disorder following exposure to a toxicsubstance. In Grayson v. Gulf Oil Company, 357 S.E. 2d

The first column shows the maximum weekly benefit paid toworkers whose disability is total but temporary. The secondcolumn shows that payment as a percentage of the State’saverage weekly wage.

Maximum Maximum benefit asweekly percentage of State’sbenefit average weekly wage

Alabama . . . . . . . . . . . . . . .Alaska. . . . . . . . . . . . . . . . .Arizona . . . . . . . . . . . . . . . .Arkansas . . . . . . . . . . . . . .California . . . . . . . . . . . . . .Colorado . . . . . . . . . . . . . . .Connecticut . . . . . . . . . . . .Delaware . . . . . . . . . . . . . .District of Columbia. . . . . .Florida . . . . . . . . . . . . . . . .Georgia . . . . . . . . . . . . . . . .Hawaii . . . . . . . . . . . . . . . . .Idaho . . . . . . . . . . . . . . . . . .Illinois. . . . . . . . . . . . . . . . .Indiana . . . . . . . . . . . . . . . .Iowa . . . . . . . . . . . . . . . . . .Kansas . . . . . . . . . . . . . . . .Kentucky . . . . . . . . . . . . . .Louisiana . . . . . . . . . . . . . .Maine . . . . . . . . . . . . . . . . .Maryland .., , . . . . . . . . . .Massachusetts . . . . . . . . .Michigan . . . . . . . . . . . . . . .Minnesota . . . . . . . . . . . . .Mississippi . . . . . . . . . . . . .Missouri . . . . . . . . . . . . . . .Montana . . . . . . . . . . . . . . .Nebraska . . . . . . . . . . . . . .Nevada . . . . . . . . . . . . . . . .New Hampshire. . . . . . . . .New Jersey . . . . . . . . . . . .New Mexico . . . . . . . . . . . .New York . . . . . . . . . . . . . .North Carolina. . . . . . . . . .North Dakota. . . . . . . . . . .Ohio . . . . . . . . . . . . . . . . . .Oklahoma . . . . . . . . . . . . . .Oregon . . . . . . . . . . . . . . . .Pennsylvania . . . . . . . . . . .Rhode Island . . . . . , . . . . .South Carolina. . . . . . . . . .South Dakota. . . . . . . . . . .Tennessee . . . . . . . . . . . . .Texas . . . . . . . . . . . . . . . . .Utah . . . . . . . . . . . . . . . . . .Vermont . . . . . . . . . . . . . . .Virginia . . . . . . . . . . . . . . . .Washington . . . . . . . . . . . .West Virginia . . . . . . . . . . .Wisconsin . . . . . . . . . . . . . .Wyoming . . . . . . . . . . . . . .

357.98700.00276.15209.08224.00371.28671.00280.64513.00362.00175.00358.00193.80604.73274.00684.00271.00343.02267.00471.83407.00444.21409.00391.00206.60289.75318.00245.00368.82600.00342.00283.70300.00376.00313.00400.00231.00388.99399.00360.00334.87289.00252.00238.00347.00544.00393.00389.32367.89363.00354.00

10413074675194

14471

10210247

10160

14273

20777

10075

14310210392

1006878

1037899

162758563

11010210266

108103100102103

7261

101161105102103100

99SOURCE: U.S. Department of Labor, based on laws in effect on July 1,

1989.

479 (South Carolina Court of Appeals, 1987) total dis-ability benefits were awarded under south Carolina’s workers’

72. Identifyingand Controlling Immunotoxic Substances

compensation statute on the basis of petrochemical hy-persensitivity, which led, according to the claimant's physician,to a cascade of dysfunction of the claimant's immune system..The treating physician wrote that,"... the constant exposureover 19 years to the petrochemicals in her workplace dysregu-lated [the claimant’s] immune system resulting in an allergicor hypersensitivity cascade to her total environment, in-cluding all foods, chemicals, and her own microbiologicalflora.’’ The court found that the plaintiff’s hypersensitivity wascreated by her workplace and left her unable to functionproperly in any environment.

A Florida appeals court also upheld a workers’ com-pensation award based on an immune injury. In DayronCorporation v. Morehead 509 So. 2d 930 (Florida 1987),the claimant developed a permanent sensitivity to acoolant used in his workplace. Although the claimantshowed no signs of illness when outside of the workplace,the sensitivity was deemed a permanent disability forpurposes of entitlement to workers’ compensation.Workers’ compensation benefits were also awarded inKyles v. Workers' Compensation Appeals Board (Califor-nia Court of Appeals, 1st Appellate District, Division 4,1st Civil No. A037375, Oct. 21, 1987), where long-termPCB exposure was found to have led to chemical hyper-sensitivity.

These cases indicate that courts will entertain a claimfor workers’ compensation based on an immune injury ifthe claimant establishes a work-related cause. SomeStates, most notably California, are considering an in-surance system that would compensate employeesregardless of the work-relatedness of their illness orinjury, but such plans remain in a very preliminary stageat this time.

The cases also indicate, however, that such claimsoften proceed to court after they fail to be settled at theadministrative level. This increases the costs of the sys-tem and delays workers’ receipt of benefits. If the in-ability to work extends for a prolonged period, workerscan quickly become impoverished. Most State workers’compensation statutes also foreclose a worker’s ability tobring a tort case against the employer unless the workercan reasonably claim that the employer intentionallycaused the injury or illness.

Congressional Interest in Workers’Compensation

Congress has been concerned with the workers’ com-pensation system for many years. In 1970 Congresscreated a National Commission on State Workmen’sCompensation Laws, which concluded, in a 1972 report,that State laws in general were “inadequate and inequi-table.” The Commission urged Congress to impose na-tional standards if the States did not act quickly on theCommission’s key recommendations. On average, Statesnow comply with just over 12 (out of 19) of these recom-mendations (18). No Federal standards have beenenacted.

Hearings were held in 1979 on the National Workers’Compensation Standards Act, which would have guaran-teed minimum compensation levels nationwide andcreated an advisory panel to look at causation issues.Then Secretary of Labor Raymond Marshall, and severalother witnesses, testified to the peculiar problems ofcompensating occupational disease, especially issues ofcausation and long latency (24). Hearings were also heldin 1981 and 1983 on bills that would have created Federalstandards of compensation for work-related exposure totoxic substances (21,22). None of those bills was enacted.No bills introduced in the 101st Congress attempted toreform the workers’ compensation system as it relates totoxic exposures.

TORT CLAIMS

This section briefly describes how tort law providescompensation for injuries due to exposure to toxic sub-stances. It also summarizes a few cases based on evidenceof immune system damage, and briefly discusses recentcongressional activity related to tort law.

Basic Tort Law

Tort law is part of the common law system. Its purposeis to compensate persons injured as the result of theconduct of another. In order to receive compensation foran injury through the tort system, a claimant, or plaintiff,files suit alleging tortious (wrongful) conduct on the partof the defendant. To prove a case, the plaintiff must show

Appendix A-Income Replacement for Disabled Individuals .73

that he or she has suffered damage, that the damage wascaused by the defendant, and that the defendant had nosufficient justification or legal right to cause this damage(13). If the plaintiff convinces the jury (or the judge in anon-jury trial) that the defendant was more likely thannot the cause of the plaintiff’s damages, compensation isawarded to the plaintiff.

Claims for damages based on exposure to hazardoussubstances are called toxic torts. As part of the requiredproof, the plaintiff must show that the defendant causedhim or her to be exposed to a toxic substance, that thesubstance is capable of causing the type of damage suf-fered by the plaintiff, and that the particular exposurecaused by the defendant was, more likely than not, thecause of plaintiff’s damage. Toxic tort cases are difficultto prove in general, and present special difficulties whenimmune-system impairment is claimed since im-munotoxicology has only recently been developed, someof its methods remain controversial, and agreement hasnot been reached about what constitutes immune systemdamage.

immunotoxicity Claims

Cases involving damage to the immune system beganappearing in the early 1980s and have increased in theintervening years. Some attorneys now estimate thathundreds, and perhaps thousands, of cases incorporat-ing claims of immune system damage now stand in Stateand Federal court systems. Since the immune system isintimately connected with the body’s capacity to respondto foreign substances, a large range of cases exist forwhich a claim of immune damage maybe relevant.

Despite the difficulties of proving a case, several tortsuits have claimed damages from exposure to im-munotoxicants. OTA found the following cases in pub-lished databases. These cases are not presented as anexhaustive listing of immunotoxicity case law, but asillustrative of the circumstances in which individuals canbe exposed, the damages alleged, and the compensationrecovered.

It should be noted that many of the plaintiffs in thesecases claim to have a disease or syndrome commonlyreferred to as multiple chemical sensitivity (MCS). MCS is apoorly understood and controversial phenomenon. Itsproponents claim that exposure to certain chemicals, even at

very low levels, can create immunological, neurological,and other problems for its sufferers. Its opponents arguethat no scientific evidence supports such claims.Proponents and opponents agree that additional re-search will be required to prove or disprove the existenceof MCS and its cause or causes. This background paperdoes not attempt to weigh the merits of claims by MCSproponents or opponents and presents these cases solelybecause of their use of immune system evidence.

CASE: Woodrow Sterling et al. v. Velsicol ChemicalCorp., 647 Fed. Supp. 303 (W.D. Term. 1986); affirmedin part, reversed in part, 855 F 2d 1188.

Claim: Plaintiffs (community residents) claimed thatimmune system injury accounted for present disorders(including pulmonary disease, respiratory problems,seizures, and learning disabilities) and increased thefuture risk of developing disease. Immune system injurywas claimed to have been caused by exposure to variouschemicals, including carbon tetrachloride and chloro-form, in well water contaminated by Velsicol.

Evidence: Immunological tests consisted of a whiteblood cell count, a lymphocyte count, a total T cell count,a B cell count, a null cell count, and a breakdown of theT cell count into T helper and T suppressor cell counts.(See chapters 2 and 3 for descriptions of the immune systemand immunotoxicological tests.) Plaintiffs’ experts testifiedthat the data was consistent with a diagnosis of chemical-ly induced immune dysregulation.

Outcome: The trial court awarded damages of $75,000to four of the five plaintiffs for impairment of the immunesystem and $500,000 to the fifth plaintiff, a child. Theappeals court reversed the district court’s award ofdamages for immune system impairment, finding that theplaintiffs’ experts’ opinions were insufficient to sustainthe burden of proof. The award for immune systemdamage constituted only a portion of the total award($5,273,492 in compensatory damages; $7,500,000 in puni-tive damages; interest on compensatory damages at 8 per-cent annually). The case has now been settled (5).

CASE: Elam v. Alcolac, 765 S.W. 2d 42,4 TXLR 167(W.D. Mo. Ct. of Appeals)

Claim: The plaintiffs (community residents) claimedthat immune system injury was partially responsible for

74. Identifyingand Controlling Immunotoxic Substances

numerous adverse health conditions. Injuries were at-tributed to exposure to toxic waste originating in anAlcolac chemical plant.

Evidence: Tests of immunological parameters in-cluded a mitogen challenge, total T cell counts, total Thelper and T suppressor cell counts, and natural killercell counts. The plaintiffs’ expert witness testified thateach of the 31 plaintiffs was suffering from immunosup-pression.

Outcome: The jury awarded a $49 million verdict tothe plaintiff for claims including immunotoxicity. Thetrial court judge set aside this verdict; an action affirmedby the appeals emu-t (which found that the term “chemicalAIDS” used in association with the plaintiffs’ conditionwas inflammatory). The case was then settled out of courtfor an undisclosed amount (25).

CASE: Barth v. Firestone Tire and Rubber Co. ,673 F.Supp. 1466 (N.D. Cal. 1987).

Claim: The plaintiff (a worker at the Firestone plant)claimed that he suffered injury to his immune system andonset of diseases in their latency stage as a result ofFirestone’s fraudulent concealment of hazardous sub-stances at the workplace and lack of required safetydevices and protective clothing. He also claimed emo-tional distress. The plaintiff alleged exposure to benzene,heavy metal compounds, and other industrial chemicals usedin the manufacturing of tires. Plaintiff sought creation of amedical monitoring fund as remedy for the class.

Evidence: The case has not reached the trial stage andno evidence has been presented.

Outcome: The Federal district court denied a motionby defendant to dismiss the claim on grounds that therewas no legally cognizable the injury. The California Su-perior Court has ruled that the class is unascertainable(17).

CASE: Moore v. Polish Power, Inc., 720 S.W. 2d 183(Tex. Ct. App. 1986).

Claim: The plaintiff (who purchased a carpet from thedefendant) claimed neurological and muscular problemsas a result of exposure to formaldehyde off-gassing fromPolish Power’s carpet.

Evidence: The plaintiff’s expert witness testified thatthe plaintiff suffered from damage to her immune systemfrom exposure to formaldehyde, which led to theneurological and muscular problems.

Outcome: The trial court excluded evidence from themedical expert witness relating to characteristics, for-maldehyde content, formaldehyde emission rate, anddangerousness of carpet and carpet pad based on his lackof expertise on the chemistry of carpets. The court al-lowed the expert’s opinion that formaldehyde was causeof carpet buyer’s physical problems. The jury brought ina verdict for Polish Power. The Court of Appealsreversed the trial court’s exclusion of the carpetevidence, and the case was sent for a new trial on themerits.

CASE: Higgens v. Aerojet-General Corp., 1986 Env’tRep. (BNA) 1183 /Nos. 287147, 290449, 290450 (Cal.super. Ct. 1986).

Claim: The plaintiff alleged immune system damage,among other injuries, resulting from defendantcompany’s disposal of tricholoroethylene (TCE) andother solvents in unlined ditches on his property.

Evidence: Plaintiff’s experts testified that the plaintiffsuffered from immune system damage, basing their find-dings on a blood sample from the plaintiff. Defendant’s ex-pert countered that since there was no base linemeasurement, the blood tests were inconclusive. Twoimmunologists testified for the defendant that the medi-cal community had not accepted the immune dysfunctiontheory as valid. The defendant’s experts also testifiedthat, according to the immune dysfunction theory, theplaintiff was constantly being exposed to immunotoxicsubstances and that it was impossible to say that a par-ticular exposure was “more probable than not” to be thecause of a given injury (12).


Outcome: Aerojet received a jury verdict in its favor.The ease was not appealed, and the parties reached asettlement (8).

CASE: Stites v. Sudstrand, 660 F. Supp. 1516 (W.D.Mich. 1987).

Claim: Plaintiffs (community residents) claimed in-creased risk of cancer and emotional distress, partiallysupported by evidence of immune system injury, due toimproper disposal of TCE, which was claimed to haveentered drinking water.

Evidence: The plaintiffs’ expert testified that the plain-tiffs suffered damage to their immune systems and dys-functions of a major enzyme system, and to his belief thatthose two problems resulted in a “greatly increased sus-ceptibility to a number of future illnesses, particularlycancer." Defendants countered with an affidavit from 9experts in immunology, stating that they could not showto a reasonable certainty that the plaintiffs would developcancer.

Outcome: The court issued a summary judgment forthe defendants on the claim for increased risk of cancer,finding that none of the plaintiff’s experts were able toquantify enhanced cancer risk. The court also ruled,however, that claims for damages for fear of cancer couldgo to the jury. The case was eventually settled for anundisclosed amount (6).

CASE: Lowe v. Norfolk& Western Railway Company,463 N.E. 2d, 792.

Claim: Forty-seven plaintiffs (railroad employees) al-leged various physical ailments, including immunologicaldamage, arising from exposure to dioxin contained in achemical, or thochlorophenol, which was spilled whilebeing transported by the defendant.

Evidence: The plaintiffs’ expert testified that testsperformed on blood samples to evaluate the body’s im-mune system indicated that each plaintiff showed someabnormality of the immune system.

Outcome: The jury returned a verdict in favor of theplaintiffs totaling $57,965,000. The appeals courtreversed the verdict on the basis of errors in trial proce-dure and remanded the case for anew trial. The case wasthen settled for an undisclosed amount (15).

Congressional Interest in Toxic Tort

Congress has occasionally considered enacting legis-lation directed specifically to compensating victims ofnon-work-related toxic exposures. The Toxic Tort Act of1979 would have created an independent agency withinthe EPA to compensate victims of pollution related in-juries regardless of fault (in addition to creating aFederal cause of action for victims of toxic substances)(24). During the 98th Congress, legislation was con-sidered in the House of Representatives that would haveprovided compensation for injury, illness, or deathresulting from exposure to hazardous substances (23).Some Members of Congress have argued that such legis-lation was an implicit promise of the Superfund legisla-tion, which requires environmental cleanup, but no billshave been enacted and none was considered in the 101stCongress, though general product liability reform legis-lation was proposed and debated.

DIFFICULTIES COMMON TO PROVINGWORKERS’ COMPENSATION OR TOXIC

TORT CLAIMS

Workers’ compensation was intended to be a no-faultsystem of compensation — if employment causes an ill-ness or injury, the worker should recover. Tort is a systemlargely based on fault, where it generally must be provedthat the defendant breached a duty owed to the plaintiff.Only employees can collect workers’ compensation; tortis available to everyone except employees covered by aworkers’ compensation system. Despite these significantdissimilarities, claimants under either system share thecommon burden of proving causation. It is not sufficientfor claimants to show that they have suffered an injury,they must show that the workplace or defendant causedthe injury in order to collect compensation or damages.This section discusses some of the difficulties entailed inproving that exposure to an immunotoxicant caused aparticular disorder.

Scientific Uncertainty

A commonly made claim of immunotoxicity, which issometimes referred to as “chemically induced immunedysregulation, " is that exposure to a chemical or sub-stance impairs the body’s immune system, therebyrendering an individual hypersensitive to chemicalsand/or more susceptible to many ailments, includingcancer. Many scientists doubt whether state-of-the-art

76. Identifying and Controlling Immunotoxic Substances

immunotoxicology can actually establish immune systemdysfunction as a result of chemical exposure. For in-stance, there is no agreed upon definition of “normal”immunological parameters. As discussed in chapter 3,scientists do not know how great a quantity of any par-ticular cell type is required for proper immune function.Cell counts can vary greatly among individuals that ap-pear to have functional immune systems.

It is also the case that various environmental and hostfactors, such as exposure to other toxic and nontoxicchemicals, tobacco, alcohol, drugs, or radiation, cookinghabits, bacteria, viruses, nutritional imbalances, obesity,and existing medical conditions, may provide alternativeexplanations for plaintiffs’ conditions. The illnesses fromwhich immunotoxicity plaintiffs allegedly suffer general-ly do not have chemical-specific pathologies and occurin the general population. It is, therefore, difficult toisolate the specific cause of such alleged findings andillnesses in light of the panoply of environmental and hostfactors, and to prove causation with the degree of cer-tainty required bylaw (3,14).

Warring Experts

The plaintiff must rely on scientific and medical ex-perts to establish that he or she has suffered some typeof physical damage and that the toxic substance is capable ofcausing that damage. Experts may also be required toprove that the defendant caused the plaintiff to be ex-posed to the toxic substance and to attest to the extent ofthe plaintiff’s damages. These expert witnesses must con-vey their highly specialized knowledge to the trier of fact(the judge or jury) who generally has little scientifictraining.

Most often experts who present evidence of immunotoxicityfor the plaintiff are clinical ecologists. These medical prac-titioners are at odds with much of the established medicaland scientific community. The American Academy of Allergyand Immunology has published position statements refut-ing the theory that any valid scientific evidence supports thetheory that exposure to chemicals or pollutants in the en-vironment adversely affects the function of T cells andrejecting the medical effectiveness of treatments prescribedby clinical ecologists (1,2). This disagreement among ex-

perts adds to the difficulty of trying immunotoxicityclaims since judges and juries have difficulty sorting outthe scientific evidence.

Continuing Debate Over Animal Testing

Very few substances have been tested to determinewhether they are immunotoxic. Where testing has beendone, it has generally been done on animals. Humanevidence is available from clinical trials or case reportsconcerning immunosuppressive therapeutics.Very fewepidemiologic studies have been conducted on im-munotoxicants, and the results have been inconclusive.Recent court cases, however, have found plaintiffs' experts’opinions regarding immunotoxicity based on animal dataunsupported by epidemiologic data to be inadequate tosustain the burden of proof (7,10). This absence of datapresents a serious dilemma for plaintiffs.

Further scientific developments in the field of im-munotoxicology should eliminate much of the scientificuncertainty and, presumably, end many of the disagree-ments between clinical ecologists and the rest of themedical and scientific community. The necessity ofanimal testing is an ongoing debate in U.S. society, andresolution lies well outside the field of immunotoxicology(20).

APPENDIX A REFERENCES

1.

2.

3.

4 .

5 .

6 .

American Academy of Allergy and Immunolog,“Position Statements: Clinial Ecology,” Journal ofA2-lew and Clinical Invnunology 78:269, August 1986.American Academy of Allergy and Immunolo~,“PositionStatements: Controversial Techniqu~’’JoumalofAllew and Clinical Imnwnolo~ 67:333, 1981.Comfel~ R. S., and Schlossman, S.F., “ImmunologicIAorato~ Tests: A Critique of the Alcolac Decision;’Toxics Law Reporter, Sept. 6,1989, pp. 381-390.Comaghie, C.A., “Evidena in Disability Claims Underthe Social Security Act,” Federal Bar News & Report37(8):464-467, 1 9 9 0 .Gilreath, S., Attorney, Knoxville, TN, personal com-munication, November 1990.Gleicher, E. , Attorney, Detroi t , MI, personal com-munication, July 1990.


7.

8.

9.

10.

11.

12

13.

14.

15.

16.

17.

18.

In re Paoti Railroad Yard PCB Litigation, 3 TXLR843, No. 8&2229, Slip Op. (E.D. PA NOV. 29, 1988).Kanner, A., Attorney, Philadelphi~ PA personalcommunicatio~ November 1990.Locke, L., “Adapting Workers’ Compensation to theSpecial Problems of Occupational Disease~’ % Har-vard Environmental Law Review, vol. 9, No. ~ 1985,pp. 249-282.Lych V. Merrell-NW Laboratmiq 830 FM 1190(lstcir. 1987).Mallino, D.L.,”Workers’ Compensation and Preven-tion of Occupational Disease,” Annals of the NewYorkAcademyofSctinces, 1987.Maskin, A., “Overview and Update of EmergingDamage Theories in Toxic Tort Litigation,” paperpresented July 14-16, 1988, Snowmass, CO, ALI-ABA Course of Study.ProsserandKeeton, Presser and Keeton on Torts,5thed. (St. Pad MN: West Publishing Co., 1984).Rothma~ R.A., and Maskin, A., “Defending Im-munotoxicity Cla@” TtiLuwRepmtq Mar. ~1989,pp. 1219-lZ3LSchoenbeck,S.M., Attorney, St. Lo@ MO,personalcommunicatio~ December 1990.Shor, G.M., “Workers’ Compensation: Subsidies forOccupational Disease,” Journal of Public HealthPohky, December 1980, pp. 328-340.Stemple, G., Attorney, Century City, CA personalcommunicatio~ October 1990.Thompso~ R., “Reforming Workers’ Compensa-tio~” Eal”torialResearch Repo~, Apr. 13,1990.

19.

20.

21.

22.

23.

24.

25.

U.S. Congres~ Office of Technology Assessment,Genedc Monitmkg and Screening it the W*lhcCOTA-BA-455 (Washingto~ DC: U.S. GovernmentPrinting Office, September 1990).U.S. Congress Office of Technology Assessmen~Alternatives to Anima[ Use in Research Testing andEducatio~ OTA-BA-273 (Washingto~ DC: U.S.Government Printing Office, February 1986).U.S. House of Representatives, Hearings before theSubcommittee on Labor Standards of the Committ-ee on Education and Labor, 97th Cong., 1st sess.,Oct.6,1981,0nOmupational “kmebnpensdonandSociaJ %curity.U.S. House of Representatives Hearings before theSubcommittee on Labor Standards of the Committ-ee on Education and Labor, 98th Cong., 1st sess., onH.R. 3175, the Occupational Disease CompensationAct of 1983, June 13,14,27 and July 27,1983.U.S. House of Representatives, Hearings before theSubcommittee on Commeree, Transportation andTourism of the Committee on Energy and Com-merce, 98th Cong., 1st sess., on H.R. 2582, the Haz-ardous Substance Victims’ Compensation Act, June29,1983 (Serial No. 98-45).U.S. Senate, Hearings before the Committee onLabor and Human Resourees, %th Cong., 1st sess.,on S. 420, the National Workers’ CompensationStandards Act of 1979, Mar. 28 and Apr. 2-3,1979.Welch L., Attorney, Kansas City, MO, personalcommunication, June 1990.

Appendix B

Reviewers and Contributors

In addition to the workshop participant% OTA acknowledges the following individuals who reviewed drafts orotherwise contributed to this study:

Joseph F. AlbrightChief, Basic Immunology BranchDivision of Allergy, Immunology,

and TransplantationNational Institute of Allergy and Infectious DiseaseBethesda, MD

Nicholas A. AshfordAssociate Professor of Technology and PolicyCenter for Technology, Policy, andIndustrial Development

Massachusetts Institute of TechnologyCambridge, MA

Robert AxelradDirectorIndoor Air DivisionOffice of Air and RadiationU.S. Environmental Protection AgencyWashington, DC

Thomas BurkeJohns Hopkins School of Hygiene

and Public HealthBaltimore, MD

Gary R. BurlesonPulmonary ImmunologyHealth Effects Research LaboratoryU.S. Environmental Protection AgencyResearch Triangle Park, NC

Dorothy A. CanterScience AdvisorOffice of Solid Waste andEmergency Response

U.S. Environmental Protection AgencyWashington, DC

Richard CornfeldCoburn, Croft, and PutzellSt. Louis, MO

Mark CullenYale-New Haven Occupational Medicine ProgramSchool of MedicineYale UniversityNew Haven, CT

John J. DomanskiLehn & Fink Products GroupSterling Drug, Inc.Montvale, NJ

Richard N. HillSenior Science AdvisorOffice of Pesticides and Toxic SubstancesU.S. Environmental Protection AgencyWashington, DC

Dennis M. HintonResearch ChemistGeneral & Molecular Toxicology BranchCenter for Food Safety and NutritionU.S. Food and Drug AdministrationWashington, DC

Meryl H. KarolIEHS DepartmentUniversity of PittsburghPittsburgh, PA

Mary LamielleNational Center for Environmental Health StrategiesVoorhees, NJ

Sheryl LardDivision of Anti-Viral Drug ProductsU.S. Food and Drug AdministrationRockville, MD

Marie Ann LeykoStaff ScientistCytokine/immunotoxicOlog LaboratoryHazleton Laboratories America, Inc.Vienna, VA

78

Appendix B-Reviewers and Contributors . 79

Robert W. Luebkeimmunotoxicolofzy SectionU.S. Environmental Protection AgencyResearch Triangle Park, NC

Anne McCayMedical College of VirginiaRichmond, VA

Frances A. MielachReviewing PharmacologistDivision of Antiviral Drug ProductsU.S. Food and Drug AdministrationWashington, DC

Claudia MillerDepartment of PediatricsUniversity of Texas Health Science CenterSan Antonio, TX

Albert E. MunsonDepartment of Pharmacology and ToxicologyMedical College of VirginiaRichmond VA

Charles NobleResearch LaboratoriesMerck Sharp and DohmeWest Point, PA

Helen North-RootDial CorporationScottsdale, AZ

Tara O'TooleOceans and Environment ProgramOffice of TechnologyAssessmentWashington, DC

David P. RailDirector, National Institute

of Environmental and Health SciencesResearch Triangle Park, NC

Anthony RoismanCohen, Milstein, Hausfeld, and TollWashington, DC

Noel R. RoseDepartment of Immunology and

Infectious DiseasesJohns Hopkins UniversityBaltimore, MD

William G. RosenbergAssistant Administrator for

Air and RadiationU.S. Environmental Protection AgencyWashington, DC

J. Harold SaylarProcter & Gamble CompanyCincinatti, OH

Mark SchaeferSenior Staff AssociateCarnegie Commission on Science,

Technology, and GovernmentWashington, DC

Paul A. SchulteChief, Screening & Notification Div. of Surveillance,

Hazard Evaluations and Field StudiesNational Institute for Occupational Safety and HealthCincinatti, OH

John C. SelnerDenver, CO

Roy D. SjobladHealth Effects DivisionOffice of Pesticide ProgramsU.S. Environmental Protection AgencyWashington, DC

Ralph Smialowiczimmunotoxicology SectionU.S. Environmental Protection AgencyResearch Triangle Park, NC

Bob SonawaneOffice of Research and DevelopmentU.S. Environmental Protection AgencyWashington, DC


Robert S. SpeirsBrooks, CA

Robert StewartS.C. Johnson& Son, Inc.Racine, WI

Peter T. ThomasManagerMicrobiology/ImmunologyIIT Research InstituteChicago, IL

R.S. TomarG Project ENTOXUniversity of CaliforniaRiverside, CA

Mark J. UtellDepartment of MedicineUniversity of Rochester Medical CenterRochester, NY

Kimber L. White, Jr.Department of BiostatisticsMedical College of VirginiaRichmond, VA

LuJuana WilcherAssistant Administrator for WaterU.S. Environmental Protection AgencyWashington, DC

Grace ZiemBaltimore, MD

NOTE: OTAisgrateful forthevaluable assistance and thoughtful critiques provided bythereviewers and contributors. Theviewsexpressedin this background paper, however, are the sole responsibility of the Office of Technolo~ Assessment.

Appendix C

Glossary of Terms and Acronyms

Glossary of Terms

Acquired immunity Disease resistance acquired afterbirth and characterized by antigen-specific promises. Seeh u m o r a l I M M U N I T Y and CELL-MEDIATED IM-MUNITY; Compare NONSPECIFIC IMMUNITY.

Adaptive immunity: See ACQUIRED IMMUNITY.Agranulocytosis: Absence of granulocytes in the

blood.Allergen: A substance known to be an agent con-

tributing to hypersensitivity.Allergy: Immunologic hypersensitivity. See HYPER-

SENSITIVITY.Anaphylaxis: Acute reaction that follows rapid intro-

duction of an antigen into an individual having preexistingIgE antibodies. Systemic anaphylaxis develops withinseconds and is characterized by constriction of the larynx andbronchi and falling blood pressure. Local anaphylacticreactions are acute inflammatory reactions caused bylocal contact with antigen. See IMMEDIATE HYPER-SENSITIVITY.

Antibody: A protein produced by B cells in responseto stimulation by an antigen and that reacts specificallywith that antigen. Antibodies are immunoglobulins.

Antigen: A substance that brings about an immuneresponse when introduced into the body. Antigens areusually high molecular weight compounds, such as proteins.However, low molecular weight compounds (e.g., drugs orindustrial chemicals) can bind to serum proteins andbecome antigenic.

Asbestosis: Fibrosis of the lungs resulting from in-halation of asbestos fibers.

Asthma: A usually chronic condition characterizedby episodes of labored breathing.

Atopic: Having a tendency toward immediate hyper-sensitivity reactions due to IgE antibodies. Approximately10 percent of the population manifest one or more formsof atopy. See IMMEDIATE HYPERSENSITIVITY;ANTIBODY.

Autoantibody: An antibody against a self antigen. SeeANTIBODY.

Autoimmunity A condition characterized by cell-mediated or humoral immunologic response to antigensof one’s own body. This occasional departure from theusual recognition of self and nonself contributes to avariety of diseases.

B cell: A lymphocyte that produces antibodies. SeeLYMPHOCYTE; ANTIBODY.

Bronchoalveolar lavage fluid: The fluid obtainedfrom the lungs by lavage. Lavage is a technique in whichan organ is flushed with water in order to analyzematerial in the drainage fluid (in this case, cells from thebronchioles and alveoli).

Bronchopulmonary aspergillosis: Infection of thebronchi and lungs by the species Aspergillus, charac-terized by inflammatory lesions.

Bronchus: One of the large conducting air passagesof the lung.

Byssinosis: An occupational respiratory disease as-sociated with inhalation of cotton, flax, or hemp dust. Itis characterized initially by chest tightness, shortness ofbreath, and cough but may lead to permanent lungdamage.

Carcinogen: A substance that causes cancer.Cell-Mediated immunity: Immunological reactions

initiated and mediated by T cells. See T CELL. Compareh u m o r a l I M M U N I T Y .

Challenge: Administration of an antigen to assess thestate of immunity. In immunotoxicological testing, anexperimental animal is challenged with an infectiousagent or tumor cells to determine whether exposure to achemical decreased the animal’s ability to fight infection orcancer. See ANTIGEN.

Complement: A series of reactions involving ap-proximately 20 proteins that circulate in the blood in aninactive form. When the first complement substance is trig-gered – usually by an antibody locked to an antigen– it setsin motion a ripple effect. As each component is activated, itacts upon the next in a precise sequence of carefully regulatedsteps. This phenomenon, known as the complement cascade,causes release of the chemicals that produce the redness,warmth, and swelling of the inflammatory response. It canalso bring rapid death to bacteria and other cells by punctur-ing their cell membranes. See ANTIBODY; ANTIGEN.

Contact sensitization: To stimulate an immuneresponse upon initial skin contact with an antigen withthe consequence of preparing the body for a strongerresponse upon reexposure to the antigen.

Cytokine: A substance produced by cells, includingcells, that transmits messages between cells to controland modulate immune response.

Cytotoxic: Lethal to cells.

81


Delayed-type hypersensitivity: An inflammatoryreaction that occurs 24 to 48 hours after challenge withantigen and is a result of cell-mediated immunity. SeeHYPERSENSITIVITY.

Dermatitis: An inflammatory skin condition.Dose-response: The quantitative relationship be-

tween exposure to a substance, usually expressed as adose, and the extent of toxic injury or disease.

Edema: Swelling.Endpoint: The disease, condition, or adverse effect

resulting from exposure to a toxic substance (e.g., im-munosuppression, infection, cancer, death).

Epidemiology: The scientific study of the distributionand occurrence of human diseases and health condi-tions and their determinants.

Erythema: Redness.Hematology: The science of blood and its nature,

function, and diseases.Histocompatibility: The extent to which individuals

or their tissues are immunologically similar.Histology: The study of the minute structure, com-

position, and function of body tissues.Host resistance: The ability of an organism to mount

a successful immune response against disease-causingantigens.

humoral immunity: Immunity associated with an-tibodies that circulate in the blood. See ANTIBODY.Compare CELL-MEDIATED IMMUNITY.

Hypersensitivity: A state of heightened reactivity toa previously encountered antigen.

Immediate hypersensitivity: Immune responsemediated by antibodies, characterized by hives, wheez-ing, and/or abrupt changes in blood pressure, and oc-curring with a few minutes or hours after exposure to anantigen.

Immune system: A specialized group of body cells,cell products, tissues, and organs that respond to foreignorganisms and substances in the body.

Immunize: To deliberately introduce an antigenicsubstance (vaccination, or active immunization) or an-tibodies (passive immunization) into an individual, withthe aim of producing immunity to a disease. Im-munotoxicologists sometimes refer to the process ofexposing an animal to an antigen in order to test theanimal’s ability to mount, at some later point, an immunereaction to the antigen as immunization.

Immunocompetence: The capacity to respond im-munologically to an antigen.

Immunoglobulin. Protein that has antibody activityor that is antigenically related to an antibody. They aregrouped into five categories based on structural dif-ferences: IgG, IgM, IgA, IgD, IgE. See ANTIBODY.

Immunology. The science concerned with thephenomena that allow an animal to respond to a sub-sequent exposure to a foreign substance in a way that isdistinct from the way it responds to the initial exposureto that same substance.

Immunologic: Pertaining to immunology.Immunosuppression: Suppression of immune re-

sponse.immunotoxic. Having the potential to adversely af-

fect immune response or damage components of theimmune system.

immunotoxicant: A substance that elicits an adverseimmune response or damages the immune system.

immunotoxicity: An adverse or inappropriatechange in the structure or function of the immune sys-tem after exposure to a foreign substance.

Inhalant: A substance that may be taken into thebody through the respiratory system.

Innate immunity See NONSPECIFIC IMMUNITY.In vitro: Literally, in glass; pertaining to a biological

process taking place in an artificial environment, usuallya laboratory.

In vivo: Literally, in the living; pertaining to a biologi-cal process or reaction taking place in a living organism.

Latent effect: A reaction to a toxic substance that isnot immediately evident but that appears later in life;also referred to as a silent effect.

Leukocyte: A white cell. Major classes of leukocytesare granulocytes, lymphocytes, and monocytes.

Lymphocyte: A specialized leukocyte involved in theimmune response. B-lymphocytes originate in the bonemarrow and when stimulated by an antigen producecirculating antibodies; See humoral IMMUNITY.T-lymphocytes are produced in the bone marrow andmature in the thymus gland and engage in a type ofdefense that does not depend directly on antibody at-tack; See CELL-MEDIATED IMMUNITY. See BCELL; T CELL.

Lymphoid organs: The principal organs of the im-mune system, including bone marrow, thymus, spleen,and lymph nodes. They produce, store, and distributethe immune system cells.

Lymphokine. A protein that mediates interactionsamong lymphocytes and is vital to proper immune func-

Appendix C-G1ossary of Terms and Acronyms ● 83

tion. Interleukins and interferon are lymphokines.Lymphokines are cytokines.

Lyse: To break up or rupture a cell membrane.Microphage: A type of large, amoeba-like cell, found

in the blood and lymph, which ingests dead tissue, tumorcells, and foreign particles such as bacteria andparasites. The microphage also plays an important rolein antigen processing and presentation.

Mitogenesis: The initiation of cell division, or mitosis.Monocyte: Phagocytic, large leukocytes containing

one nucleus.Myelogenous leukemia: A cancer of the blood

granulocytes that usually occurs in persons of age 30-50.Nasal lavage fluid: The fluid obtained from the nasal

passages by lavage. See BRONCHOALVEOLARLAVAGE FLUID.

Natural killer cell: A type of lymphocyte that attackscancerous or virus-infected cells without previous ex-posure to the antigen. Also called NK cell.

NK cell: See NATURAL KILLER CELL.Nonself: That which is not recognized by an individual’s

immune system as being a natural constituent of thatindividual’s body.

Nonspecific immunity: Immunity that exists frombirth and that occurs without prior exposure to an an-tigen; also called innate immunity. C o m p a r eAQUIRED IMMUNITY.

Pathology: The scientific study of the cause of diseaseand of the associated structural and functional changesthat are the result of disease.

Peripheral blood: Blood in the circulation remotefrom the heart.

Pesticide: A generic term referring to toxic substan-ces developed to control pests; they include insecticides,fungicides, rodenticides, and herbicides.

Phagocytosis: Consumption of foreign particles (e.g.,bacteria) by cells that use ameboid movement to sur-round the particle and then ingest it. Macrophages arephagocytes.

Pneumoconiosis: A condition characterized by thedeposition of mineral dust in the lungs as a result ofoccupational or environmental exposure.

Pneumonitis: Inflammation of the lungs.Reference dose (IUD): A term used to characterize

risk and derived by applying safety factors to the highestlevel at which a substance produces no effect. If humanexposure to a substance is below the RfD, no risk isassumed to exist; if exposure exceeds the RfD, risk isassumed to exist. The term maybe used interchangeablywith acceptable daily intake.

Rhinitis: Inflammation of the lining of the nose.Right-to-know laws: State and local laws requiring

companies to inform workers and communities of thechemical names and hazards of their products.

Self: That which is recognized by an individual’s im-mune system as being a natural constituent of thatindividual’s body.

Silicosis: A condition of lung fibrosis which isbrought about by prolonged inhalation of silica dust.

Structure-activity relationship: The relationship be-tween a chemical’s structure and the biochemical changesit induces.

T cell: A lymphocyte produced in the bone marrowthat matures in the thymus and is integral to cell-mediated immunity. T cells regulate the growth anddifferentiation of other lymphocytes and are involved inantibody production. See LYMPHOCYTE.

Teratogen: A substance that causes physical defectsin offspring by adversely affecting developing embryos.

Toxicity: The quality of being poisonous or the degreeto which a substance is poisonous.

White cell: A colorless cell in the blood, lymph, ortissues that is an important component of the immunesystem. See LEUKOCYTE.

ACGIH

ADAMHA

AIDSATSDR

AZT

CAACBER

CDCCDER

CERCLA

CFSAN

CPSACPSCCTLCWA

Acronyms

–American Conference ofGovernmental Industrial Hygienists

–Alcohol, Drug Abuse, and MentalHealth Administration

–Acquired Immune Deficiency Syndrome–Agency for Toxic Substances and

Disease Registry–Azidothymidine, now known as

zidovudine–Clean Air Act– Center for Biologics Evaluation and

Research (FDA)– Centers for Disease Control– Center for Drug Evaluation and Re-

search (FDA)– Comprehensive Environmental Response,

Compensation and Liability Act– Center for Food Safety and Nutrition

(FDA)–Consumer Product Safety Act– Consumer Product Safety Commission– cytotoxic T lymphocyte– Clean Water Act


DESDHHS

DMNDNADTHEPAEPCRA

FDAFDCAFHSAFIFRA

FTEHAHHLAHSDBIgINDLPSMCLMCSMESTMLRMSHA

NAAQS

NCINCTR

NDANIEHS

NIHNIOSH

–Diethylstilbestrol–Department of Health and Human

Services–Dimethylnitrosamine–Deoxyribonucleic acid–Delayed-type hypersensitivity–Environmental Protection Agency–Emergency Planning and Community

Right-to-Know Act–Food and Drug Administration–Food, Drug, and Cosmetic Act–Federal Hazardous Substances Act–Federal Insecticide, Fungicide, and

Rodenticide Act–full-time equivalent–halogenated aromatic hydrocarbon–human leukocyte antigen–Hazardous Substances Data Bank– immunoglobulin–Investigative New Drug–lipopolysaccharide— maximum contaminant level— multiple chemical sensitivity— mouse ear swelling test— mixed leukocyte response–Mine Safety and Health

Administration–National Ambient Air Quality

Standards–National Cancer Institute–National Center for Toxicological

Research (FDA)–New Drug Application–National Institute of Environmental

Health Sciences–National Institutes of Health–National Institute for Occupational

Safety and Health

NKNLMNTPOHROPPOSHA

OTAOTSPAHPBBPCBPELPFCPLAPMNPOMSPPBPPMPVIZTRCRA

RQRTECS

SRBCSDWASSASSDISSISTELTCDDTDITPQTRITSCATWA

– natural killer–National Library of Medicine–National Toxicology Program–Office of Health Research (EPA)–Office of Pesticide Programs (EPA)–Occupational Safety and Health

Administration– Office of Technology Assessment–Office of Toxic Substances (EPA)– polycyclic aromatic hydrocarbons–polybrominated biphenyls–polychlorinated biphenyl–permissible exposure limit–plaque forming cell–Product Licensing Application–Premanufacture Notice– Program Operations Manual System– parts per billion– parts per million– l-phenyl-5-vinyl-2-imidazolidine-thione–Resource Conservation and Recovery

Act— reportable quantity– Registry of Toxic Effects of Chemical

Substances– sheep red blood cell–Safe Drinking Water Act–Social Security Administration–Social Security Disability Income–Supplemental Security Income– short-term exposure limit–2,3,7,8-tetrachlorodibenzo-p-dioxin– toluene diisocyanate–threshold planning quantity–Toxic Release Inventory–Toxic Substances Control Act– time weighted average

Index

Acetonitrile, 51Acquired Immune Deficiency Syndrome (AIDS), 5,13,

50Acquired immunity, 4-5,17-18

Adaptive immunity. See Acquired immunityAflatoxin, 53Agency for Toxic Substances and Disease Registry

(ATSDR)meeting on human exposure data sponsored by, 32information programs of, 61,63research by, 9,49,53

Airborne pollutantsEPA studies on, 52immunosuppression and, 7,37

Alcohol, Drug Abuse, and Mental Health Administra-tion (ADAMHA), research by, 8,53

Aldicarb oxime, 51Alkylating agents, 35

Allergydefinition used in OTA background paper, 4,19,20disability claims and, 69genetic component of, 22misperceptions about, 22substances that induce, 38-39see also Contact sensitivity; Delayed-type hypersen-

sitivity; Hypersensitivity; Immediate-type hyper-sensitivity

Allyl isovalerate, 51American Academy of Allergy and Immunology, 76

American Conference of Governmental IndustrialHygienists (ACGIH), 54,61

Anaphylaxis. See Immediate-type hypersensitivity; Hy-persensitivity; Allergy

Antibodyclasses of (immunoglobulin), 14humoral immunity and, 18-19plaque forming cell response test, 28production by B cells of, 4,14role in immune responsiveness of, 4, 14-15structure, 14test to measure levels of, 5,29

Antigenacquired immunity and, 17binding to antibody of, 13-14definition of, 4,13humoral immunity and, 18-19processing of, 16self, 20

Antimetabolites, 35

Arsine, 51

Asthma, 8,22,39,69

Autoimmune disease. See AutoimmunityAutoimmunity

as a response of the immune system, 4,20difficulty in assessing, 20,40disability claims and, 69epidemiologic studies of humans for, 6,40genetic role in, 40Spanish Toxic Oil Syndrome and, 40substances inducing, 40

Azathioprine, immunosuppression and, 6,35,51

Azidothymidine (AZT), 50

B cellshumoral immunity and 18-19quantitation of as a measure of immunotoxicity, 28role in antibody production of, 4, 14, 18-19suppression by glucocorticosteroids on, 35test to assess antibody production capability of, 28test to assess mitogen response of, 29

Barth v. Firestone Tire and Rubber Co., 74Benzene, 6,36,57

Benzidine, 51

Benzo(a)pyrene, 51

Benzo(e)pyrene, 51

Benzothonium chloride, 52Benzyl-p-chlorophenol, 52

o-benzyl-p-chlorophenol, 51Buehler test, 30

t-butylhydroquinone, 51Cadmium, immunosuppression and, 7,38

Cadmium chloride, 51

87


Californialegislation related to MCS, 9workers’ compensation, 72

Captafol, 55

Carcinogenshistorical interest in, 3

Cell-mediated immunitydescription of, 5,19,23immunotoxicological tests for, 5,27,29importance to normal immune function of, 19-20occupational dermatoses and, 38potential adverse consequences due to, 19-20see also Allergy; Contact sensitivity; Delayed-type

hypersensitivity

Cells, immune system, 14-17

Cellularity, as a test for immune pathology, 28

Center for Biologics Evaluation and Research(CBER)–FDA, 53

Center for Drug Evaluation and Research (CDER) –FDA, 53,56

Center for Environmental Health and Injury Control –CDC, 53

Center for Food Safety and Nutrition (CFSAN) – FDA,52-53

Centers for Disease Control (CDC), research in im-munotoxicology by, 8,53

Chloral hydrate, 32Chlordimeform, 344-chloro-o-phenylenediamine, 51,52

Cigarette smokeas a confounding factor in immuntoxicity assessment,

22immunosuppressive potential of, 7,37

Clean Air Act (CAA), 8,37,52,54,56-57

Clean Water Act (CWA), 54,56,57-58

Cobalt, 55

Cobaltous sulfate, 54Community Right-to-Know, 8,61-62,63

Complement activation, 14

Comprehensive Environmental Response, Compensa-tion, and Liability Act (CERCLA), 54,56,60,62

Consumer Product Safety Act (CPSA), 54,60-61

Consumer Product Safety Commission (CPSC), re-search or regulation by, 8,60-61

Contact sensitivitycosmetics and regulation by FDA of substances caus-

ing, 55-56description of, 19EPA research in, 52substances causing, 38see also Cell-mediated immunity; Delayed-type hy-

persensitivity; Hypersensitivity

Cosmeticshypersensitivity and, 8,21,38regulation of, 56

Crotonaldehyde, 52

Cyclophosphomide, immunosuppression and, 6,35,51Cyclosporin A, immunosuppression and, 6,36,56Cytokines, 4,16

Cytotoxic T lymphocyte (CTL) assay, 29Dayron Corporation v. Morehead, 72Definitions. See TerminologyDelayed-type hypersensitivity (DTH)

description of, 19EPA requirements to assess biochemical pesticides

for, 58-59substances inducing, 38-39test to measure, 29see also Cell-mediated immunity; Contact sensitivity;

Hypersensitivity

Department of Agriculture, research or regulation by,8,53

Department of Defense, research or regulation by, 8,53Department of Health and Human Services, research

by, 8,49Department of Labor, research or regulation by, 8

2,4-diaminotoluene, 51,52

Dichloroethane, 32

Dideoxyadenosine, 51

Diethylstilbestrol (DES), 34,51

Dimethyl vinyl chloride, 51Dimethylbenz(a)anthracene (DMBA), 37,51

Dimethylnitrosamine (DMN), 32

Dinitrofluorobenzene, 52Dioxin

Department of Defense study of, 53immunosuppression and, 7,32,36-37see also TCDD

Index ● 89

Diphenylhydantoin, 51

Disability, income replacement for immunotoxicity-re-lated, 69-76

Draize test, 30Drugs

autoimmunity and, 40hypersensitivity and, 8,38,39immunotoxic effects of illegal, 35immunosuppression and, 6,39,41regulation of, 55-56see also Therapeutic drugs

Elam v. Alcolac, 73-74Emergency Planning and Community Right-to-Know

Act (EPCRA), 61-62

Environmental Protection Agency (EPA)community right-to-know and, 8,61-62coordination about TRI with NLM, 62funding of study on multiple chemical sensitivity by,

9immunotoxicity testing of biochemical pest control

agents and, 58regulation by, 56-60regulation of oxidant gases based on health effects

other than immunotoxicity by, 37research in immunotoxicology by, 8,52,63role in NTP of, 49tier testing and, 52,58-59

Epidemiologydifficulties in obtaining human immunotoxicity data,

5-6,31-32studies of autoimmunity in humans, 5-6, 40studies of hypersensitivity in humans, 5-6,31-32studies of immunosuppression in humans, 5-6,31-32

Estradiol benzoate, 32Ethyl carbamate, 51

Ethylene dibromide, 51

Ethylene thiourea, 52

Federal Hazardous Substances Act (FHSA), 54,60-61

Federal Insecticide, Fungicide, and Rodenticide Act(FIFRA), 54,56,58-59

Florida, workers’ compensation, 72

Food and Drug Administration (FDA)regulation by, 55-56research in immunotoxicology by, 8,52-53,63restriction of sulfites by, 8,55,63

role in NTP of, 49view on tier testing, 31,53

Food, Drug, and Cosmetic Act (FDCA), 55Foods, regulation of, 55

Formaldehyde, 37,39,51

Freund’s complete adjuvant test, 30

Fundinglevels for irnmunotoxicological research by CDC, 53levels for immunotoxicological research by EPA, 52levels for immunotoxicological research by NIEHS,

53levels for immunotox.ecological research by NIH, 53levels for immunotoxicologicd research by NIOSH,

53levels for immunotoxicological research by NTP, 51

Gallium arsenide, 51

Geneticsrole in autoimmunity, 8,40role in evaluating immunotoxicity of populations, 22

Ginseng, 51

Glucocorticosteroids, immunosuppression and, 35

Glutaraldehyde, 52Grayson v. Gulf Oil Company, 71-72Halogenated aromatic hydrocarbon (HAH)

immunosuppression and, 6,36-37see also Polybrominated biphenyls; Polychlorinated

biphenyl; DioxinHazardous Substances Data Bank (HSDB) –NLM, 62Hematology, as a test for immune pathology, 28Hexachlorobenzo-p-dioxin, 51

Higgens v. Aerojet-General Corp., 74-75Histology, as a test for immune pathology, 28Host resistance, immunotoxicological tests for, 5,30,50,

52

Human leukocyte antigen (HLA), 22

humoral immunitydescription of, 5,18-19,23immunotoxicologal tests for, 5,27,28-29importance to normal immune function of, 18-19potential adverse consequences due to, 19see also Allergy; Antibody; Hypersensitivity

Hypersensitivitydefinition, 4EPA efforts in methods development for lung, 52


epidemiologic studies of humans for, 6genetic component of, 22,23immunotoxicity and, 19-20immunotoxicological tests for, 5,30-31pesticides and, 8,39respiratory disorders and, 38-39substances causing contact sensitivity and skin disor-

ders, 38substances tested by NTP for, 52see also Allergy; Contact sensitivity; Delayed-type

hypersensitivity; Immediate-type hypersensitivityImmediate-type hypersensitivity

allergy and, 19potential adverse consequences due to, 19see also Allergy; humoral immunity; Hypersen-

sitivityImmune suppression. See ImmunosuppressionImmune system, 13

cell surface receptors of, 14, 16cells of, 4, 14-17organs of, 4, 16-17reserve capacity of, 5,40responses of, 4, 17-20tests to analyze effects of substances on 5,27-31

Immunity. See Acquired immunity; Cell-mediated im-munity; humoral immunity; Nonspecific immunity

Immunoglobulin. See Antibody

Immunosuppressiondefinition, 3-4halogenated aromatic hydrocarbons and, 36-37immunotoxicity and, 20indoor air pollutants and, 37lack of data on human studies, 34metals and, 37-38oxidant gases and, 37pesticides and, 6,36polycyclic aromatic hydrocarbons and, 7,37substances tested by NTP for, 51tests for, 5therapeutic drugs and, 6,35-36

immunotoxicantexamples of substances that are, 6-8,35-40OTA definition of, 4,20populations at risk to effects of, 22-23see also immunotoxicity

immunotoxicitychallenges in studying, 5,20-23,32-35,40-41difficulties in proving claims for, 75-76disability and, 69-76

epidemiologic evaluation of, 31-32existing data on, 5,35-40terminology used in OTA background paper, 3-4,

20-21tests for, 27-31tort claims and, 73-75workers’ compensation and, 71-72see also immunotoxicant

Indomethacin, 51Indoor air pollutants, 21,37

InhalantsEPA development of methods to assess, 52hypersensitivity induced by, 8

Innate immunity. See Nonspecific immunityInterferon-alpha, 51

Isocyanates, hypersensitivity and, 8Isobutyraldehyde, 52

Isophorone diisocyanate, 52,55Jewelry, hypersensitivity to, 8,38Kyles v. Workers’ Compensation Appeals Board, 72Lead, 7,37,57Lithium carbonate, 51Lowe v. Norfolk & Western Railway Company, 75Lymphocytes. See B cells; T cells; Natural killer cells

Lymphoid organs. See Organs

Macrophagescell-mediated immunity and, 19humoral immunity and, 18nonspecific immunity and, 17role in immune responsiveness of, 4, 13, 16, 18test to assess activity of, 29,30test to assess functional capability of in antibody

production, 28

Maryland, study related to environmental illness andmultiple chemical sensitivity, 9

Material safety data sheets, 61,62

2-mercaptobenzothiazole, 52

Mercury, 7,38,57

Metalsimmunosuppression and, 7,37role in autoimmune processes, 8role in hypersensitivity, 8see also Cadmium; Lead; Mercury; Nickel; Or-

ganotinsMethyl carbamate, 51

Methyl isocyanate, 50,51

Index ● 91

Michigan, polybrominated biphenyl exposure case in,33

Mine Safety and Health Act, 54,61Mine Safety and Health Administration (MSHA), re-

search or regulation by, 8,61Mixed leukocyte response (MLR), 29

Moore v. Polish Power, Inc., 74Mouse ear swelling test (MEST), 30-31Multiple chemical sensitivity, 9,73

Murine local lymph node assay, 30-31NK cells. See Natural killer cells

National Academy of Sciencesmeeting on human exposure data sponsored by, 32study of multiple chemical sensitivity by, 9

National Ambient Air Quality Standards (NAAQS), 52,57

National Cancer Institute (NCI), 49National Center for Toxicological Research (NCTR) –

FDA, 49

National Commission on State Workmen’s Compensa-tion Laws, 72

National Institute for Occupational Safety and Health(NIOSH), 49

National Institute of Allergy and Infectious Diseases, 53

National Institute of Environmental Health Sciences(NIEHS), 49,53

National Institutes of Health (NIH), research in im-munotoxicology by, 8,49,53

National Library of Medicine (NLM), 9,62-63National Toxicology Program (NTP)

agencies comprising, 49funding for immunotoxicological research by, 51,63objectives of, 49research in immunotoxicology by, 8,49-52substances tested for hypersensitivity by, 52substances tested for immunosuppression by, 51testing approach developed by, 8,49-52

Natural killer cellscell-mediated immunity and, 19nonspecific immunity and, 17role in immune responsiveness of, 4, 17test to assess activity of, 29,30

New Jersey, study related to environmental illness andmultiple chemical sensitivity, 9

Nickelhypersensitivity and, 8,38immunosuppression and, 37-38

Nickel chloride, 38Nickel sulfate, 51

Nitrobenzene, 51

Nitrofurazone, 51Nitrogen dioxide,7, 37,59n-nitrosodimethylamine, 51

m-nitrotoluene, 51p-nitrotoluene, 51

Nitrophenylpentadien, 50,52

Nonspecific immunitydescription of, 4,17immunotoxicological tests for, 5,27,29-30,50role of NK cells in, 17tests for host resistance as a measure of, 30

Ochratoxin A, 51Occupational Safety and Health Act (OSH Act), 54

Occupational Safety and Health Administration(OSHA)regulation by, 8,54,63role in NTP of, 49substances regulated as sensitizers by, 8,54-55worker right-to-know and, 8,61,63workers’ compensation and, 70-71

Office of Health Research (OHR) –EPA, 52Office of Pesticide Programs (OPP) –EPA, 52,58-59

Office of Technology Assessment (OTA)evaluation of environmental noncancer health risks

by, 3organization of report by, 3previous studies on regulation of toxic substances by,

49

Office of Toxic Substances (OTS) –EPA, 52Oleic acid diethanolamine, 52

Organotins, 7,38

Organsimmunotoxicity testing of, 28of the immune system, 4, 17

Oxidant gases, 37. See also Immunosuppression;Nitrogen dioxide; Ozone

Oxymetholone, 51

Ozone, immunosuppression and, 7,37,57


Pathology, immunotoxicological tests for, 5,28Penicillin, hypersensitivity and 8,39

Pentachlorophenol, 51

Pentamidine isethionate, 51

PesticidesEPA testing guidelines for immunotoxicity of, 8,58-

59hypersensitivity and, 8,39immunosuppression and, 7,38

Pharmaceuticals. See Drugs

Phenothiazine, 55

Phenyl glycidyl ether, 55

l-phenyl-5-vinyl-2-imidazolidine-thione (PVIZT), 40

o-phenylphenol, 51Phorbol myristate acetate, 51

Picric acid, 55

Plaque forming cells (PFC), test to assess, 28Polybrominated biphenyls (PBBs)

immunosuppression and, 6,32,36Michigan exposure case, 33

Polychlorinated biphenyl (PCB)immunosuppression and, 6,32,36regulation by EPA under CWA of, 58regulation by FDA of, 55Taiwan exposure case, 34

Polycyclic aromatic hydrocarbons (PAH), immunosup-pression and, 7,37

Polydimethylsiloxane fluid, 52

Prednisolone, immunosuppression and, 6,35

Registry of Toxic Effects of Chemical Substances(RTECS)–NLM, 62

Regulationby OSHA of substances as sensitizers, 54-55major Federal laws controlling toxic substances, 54-

61of sulfites based on immunotoxic criteria, 8,55of Yellow Dye No. 5 based on immunotoxic criteria,

55

ResearchFederal agencies involved in, 8,49-54interest in Federal interagency coordination commit-

tee, 54need for integration of immunology and toxicology,

35see also Funding

Resource Conservation and Recovery Act (RCRA), 56,60

Respiratory disorders and hypersensitivity, 7-8,38-39

Ribavirin, 51

Safe Drinking Water Act (SDWA), 56,58

Selenium, immunosuppression and, 37-38Senate Committee on Environment and Public Works,

Subcommittee on Toxic Substances, EnvironmentalOversight, Research and Developmentinterest in noncancer health risks by, 3request for this OTA background paper by, 3

Silicone, 50,51

Social Security Administration (SSA), 69

Social Security Disability Income (SSDI), immune sys-tem injury and, 69

South Carolina, workers’ compensation and immunesystem injury, 71-72

Spain, toxic oil exposure case in, 40Stiles v. Sudstrand, 75Subtilisins, 55

Sulfites, role in hypersensitivity and restriction by FDAof, 8,55,63

Supplemental Security Income (SSI), 69

Suppression of immune responsiveness. See Im-munosuppression

T cellscell-mediated immunity and, 19-20humoral immunity and, 18-19mixed lymphocyte response as a measure of, 29quantitation of as a measure of immunotoxicity, 28role in immune responsiveness, 4, 15-16, 18, 19suppression by cyclosporin A on, 36suppression by glucocorticosteroids on, 35test to assess cytotoxic, 29test to assess functional capability of antibody

production, 28test to assess host resistance activity of, 30test to assess mitogen response of, 29

Taiwan, polychlorinated biphenyl exposure case in, 34

Terminology, 3-4

Testingchallenges and difficulties of, 5-6,32-35methods of, 27-31

Testsfor cell-mediated immunity, 29for host resistance, 30for humoral immunity, 28-29for nonspecific immunity, 29-30for pathology, 28

Index .93

for potential to induce hypersensitivity, 30-31selection of, 31see also Testing; Tier testing

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 36, 51See also Dioxin

Tetraethyl lead, 51Tetrahydrocannibinol, 51

Therapeutic drugs. See Drugs

4,4-thiobis (6-t-butyl-m-cresol), 51

Tier testingEPA approach for biochemical pesticides and, 58-59EPA efforts to develop, 52,63FDA perspective on appropriateness of, 31for possible immunotoxicants, 31interest in developing for hypersensitivity assess-

ment, 31NTP approach to, 49-52

Toluene, 51

Toluene-2,3-diisocyanate (TDI)hypersensitivity and, 39regulation by OSHA as sensitizer, 39,55

Tort lawcongressional interest in, 75description of, 72-73difficulties in proving immune system injury under,

75-76immune system injury and, 73-75

Toxic Release Inventory (TRI) – NLM, 62

Toxic Substances Control Act (TSCA), 54,56,59-60Toxic torts. See Tort law

Toxicology, general principles of, 7,21-23

Toxicology Data Network (TOXNET) – NLM, 62TOXLINE-NLM, 62-63

Tributyltin oxide, 52

Triethanolamine, 52Tris (2,3-dichloropropyl) phosphate, 51

Vanadium pentoxide, 51

Vinyl chloride, 57

4-vinyl-l-cyclohexene diepoxide, 51White cells, 4, 15

Wisconsin, workers’ compensation and, 70Woodrow Sterling et al. v. Velsicol Chemical Corp., 73Worker Right-to-Know, 8,61,63

Workers’ compensationcongressional interest in, 72description of, 69-71difficulties in proving immune system injury under,

75-76immune system injury and, 71-72OSHA and, 70-71

Xylenesulfonic acid, 52

Yellow Dye No. 5,55,63

Zirconium, hypersensitivity and, 38

Other Related OTA Reports

Neurotoxicity: Identifying and Controlling Poisons of the Nervous System--SpecialReport. Describes the scope of the public health threat posed by neurotoxic substances;Federal research, testing, monitoring, and regulatory programs to address it; and theeconomic considerations associated with testing and regulatory programs. BA-436, 4/90;350 p.

GPO stock #052-003-01184-1; $15.00 per copy

Summary—Neurotoxicity: Identifying and Controlling Poisons of the NervousSystem. BA-437, 4/90; 48 p.

GPO stock #052-003-01185-9; $2.25 per copy

Genetic Monitoring and Screening in the Workplace. Examines efficacy, accuracy, andcost of technologies used by employers for genetic screening and monitoring; and the legaland ethical issues pertinent to employer testing. BA-455, 10/90; 270p.

Free summary available from OTA.GPO stock #052-003-01217-l; $12.00 per copyNTIS order #PB 91-105 940/AS

Identifying and Regulating Carcinogens (BP-H-42)NTIS order #PB 88-136999

Preventing Illness and Injury in the Workplace (H-256)NTIS order #PB 86-115 334/AS

Assessment of Technologies for Determining Cancer Risks From the Environment(H-138)

NTIS order #PB 81-235400

Catching Our Breath: Next Steps for Reducing Urban Ozone. Focuses on thehealth-based air quality standards for ozone; addresses the problem of regional oxidants;evaluates the cost-effectiveness of controlling various sources of hydrocarbon emissions forlowering ozone levels. 0-412, 7/89; 252 p.

GPO stock #052-003-01158-l; $10.00 per copyNTIS order #PB 90-130 451/AS

Superfund Strategy. Examines future Superfund needs and how permanent cleanups canbe accomplished in a cost-effective manner for diverse types of sites; describes theinteractions among many components of the complex Super-fund system; and analyzes theconsequences of pursuing different strategies for implementing the program. ITE-252, 4/85;292 p.

Free summary available from OTA.GPO stock #052-003-00994-3; $10.00 per copyNTIS order #PB 86-120 425/AS

Protecting the Nation’s Groundwater From Contamination: Volume I (O-233)NTIS order #PB 85-154 201/AS

Acid Rain and Transported Air Pollutants: Implications for Public Policy. Character-izes the potential benefits of acting now to abate long-range transported air pollution andthe potential costs of premature action. 0-204, 6/84; 324p.

NTIS order #PB 84-222 967/AS

MEDLARS and Health Information Policy (TM-H-11)NTIS order #PB 83-168658

NOTE: Reports are available from the U.S. Government Printing O&Ice, Superintendent of Documents,Washington, DC 20402-9325, (202) 783-3238; and/or the National Technical Information Service, 5285Port Royal Road, Springfield, VA 22161-0001, (703) 487-4650.