mosby items and derived items © 2007, 2003 by mosby, inc.slide 1 chapter 21 immune system

Mosby items and derived items © 2007, 2003 by Mosby, Inc.

Chapter 21Chapter 21Immune SystemImmune System


IntroductionIntroduction

The immune system protects against assaults The immune system protects against assaults on the bodyon the body

External assaults include microorganisms— External assaults include microorganisms— protozoans, bacteria, and virusesprotozoans, bacteria, and viruses

Internal assaults—abnormal cells reproduce and Internal assaults—abnormal cells reproduce and form tumors that may become cancerous and form tumors that may become cancerous and spreadspread


Organization of the Immune SystemOrganization of the Immune System The immune system is continually at work patrolling and The immune system is continually at work patrolling and

protecting the bodyprotecting the body

Identification of cells and other particlesIdentification of cells and other particles Self markers—molecules on the surface of human cells that are unique to Self markers—molecules on the surface of human cells that are unique to

an individual, thus identifying the cell as “self” to the immune systeman individual, thus identifying the cell as “self” to the immune system

Non–self markers—molecules on the surface of foreign or abnormal cells Non–self markers—molecules on the surface of foreign or abnormal cells or particles and identify the particle as “non–self” to the immune systemor particles and identify the particle as “non–self” to the immune system

Self-tolerance—the ability of our immune system to attack abnormal or Self-tolerance—the ability of our immune system to attack abnormal or foreign cells but spare our own normal cellsforeign cells but spare our own normal cells

Two major categories of immune mechanisms—innate Two major categories of immune mechanisms—innate immunity and adaptive immunity (Figure 21-1; Table 21-1)immunity and adaptive immunity (Figure 21-1; Table 21-1)

Innate immunity provides a general, nonspecific defense Innate immunity provides a general, nonspecific defense against anything that is not “self”against anything that is not “self”


Organization of the Immune SystemOrganization of the Immune System Adaptive immunity acts as a specific defense against specific Adaptive immunity acts as a specific defense against specific

threatening agentsthreatening agents Primary cells for innate immunity—epithelial barrier cells, Primary cells for innate immunity—epithelial barrier cells,

phagocytes (neutrophils, macrophages), and natural killer cells; phagocytes (neutrophils, macrophages), and natural killer cells; chemicals used in innate immunity—complement and interferonchemicals used in innate immunity—complement and interferon

Primary types of cells for adaptive immunity—lymphocytes called T Primary types of cells for adaptive immunity—lymphocytes called T cells and B cellscells and B cells

Cytokines—any of several kinds of chemical released by cells to Cytokines—any of several kinds of chemical released by cells to promote innate and adaptive immune responses (examples: promote innate and adaptive immune responses (examples: interleukin, interferon, leukotriene)interleukin, interferon, leukotriene)

Other chemicals (e.g., complement, other enzymes, and histamine) Other chemicals (e.g., complement, other enzymes, and histamine) also play regulatory roles in immunityalso play regulatory roles in immunity


Innate Immunity (Table 21-2)Innate Immunity (Table 21-2)

Species resistance—genetic characteristics of Species resistance—genetic characteristics of an organism or species defends against an organism or species defends against pathogenspathogens

Mechanical and chemical barriers—first line of Mechanical and chemical barriers—first line of defense (Figure 21-2)defense (Figure 21-2) The internal environment of the body is protected by The internal environment of the body is protected by

a barrier formed by skin and mucous membranesa barrier formed by skin and mucous membranes

Skin and mucous membranes provide additional Skin and mucous membranes provide additional immune mechanisms—sebum, mucus, enzymes, immune mechanisms—sebum, mucus, enzymes, and hydrochloric acid in the stomachand hydrochloric acid in the stomach


Innate ImmunityInnate Immunity

Inflammation—second line of defense Inflammation—second line of defense (Figure 21-3)(Figure 21-3)

Inflammatory response—tissue damage elicits responses Inflammatory response—tissue damage elicits responses to counteract injury and promote normalcyto counteract injury and promote normalcy

• Inflammation mediators include histamine, kinins, prostaglandins, Inflammation mediators include histamine, kinins, prostaglandins, and related compounds (Figure 21-4)and related compounds (Figure 21-4)

• Chemotactic factors—substances that attract white blood cells to Chemotactic factors—substances that attract white blood cells to the area in a process called chemotaxisthe area in a process called chemotaxis

• Characteristic signs of inflammation—heat, redness, pain, and Characteristic signs of inflammation—heat, redness, pain, and swellingswelling

• Systemic inflammation—occurs from a body-wide inflammatory Systemic inflammation—occurs from a body-wide inflammatory responseresponse


Innate ImmunityInnate Immunity Inflammation—second line of defense (cont.)Inflammation—second line of defense (cont.)

Phagocytosis—ingestion and destruction of Phagocytosis—ingestion and destruction of microorganisms or other small particles by microorganisms or other small particles by phagocytes (Figure 21-7)phagocytes (Figure 21-7)

• Antigen-presenting cells (APCs)—phagocytes that ingest Antigen-presenting cells (APCs)—phagocytes that ingest foreign particles, isolate protein segments (peptides), and foreign particles, isolate protein segments (peptides), and display them as antigens on their surfaces to trigger an display them as antigens on their surfaces to trigger an immune response when recognized by a specific (adaptive) immune response when recognized by a specific (adaptive) immune cellimmune cell

• Chemotaxis—chemical attraction of cells to the source of Chemotaxis—chemical attraction of cells to the source of the chemical attractant (Figure 21-6)the chemical attractant (Figure 21-6)

• Diapedesis—process by which immune cells squeeze Diapedesis—process by which immune cells squeeze through the wall of a blood vessel to get to the site of through the wall of a blood vessel to get to the site of injury/infection (Figure 21-5)injury/infection (Figure 21-5)


Innate ImmunityInnate Immunity

Phagocytosis (cont.)Phagocytosis (cont.)

• Neutrophil—most numerous type of phagocyte; usually Neutrophil—most numerous type of phagocyte; usually first to arrive at site of injury; migrates out of bloodstream first to arrive at site of injury; migrates out of bloodstream during diapedesis; forms pusduring diapedesis; forms pus

• Macrophages (Table 21-3)Macrophages (Table 21-3)

Phagocytic monocytes grow larger after migrating from Phagocytic monocytes grow larger after migrating from bloodstreambloodstream

Dendritic cell (DC)—type of macrophage with long Dendritic cell (DC)—type of macrophage with long branches or extensions (Figure 21-8)branches or extensions (Figure 21-8)

Examples are histiocytes in connective tissue, microglia in Examples are histiocytes in connective tissue, microglia in nervous system, and Kupffer cells in livernervous system, and Kupffer cells in liver


Innate ImmunityInnate Immunity Natural killer cells—lymphocytes that kill tumor cells and cells Natural killer cells—lymphocytes that kill tumor cells and cells

infected by viruses (Figure 21-9)infected by viruses (Figure 21-9) Method of recognizing abnormal or non–self cells—target cell is killed if Method of recognizing abnormal or non–self cells—target cell is killed if

killer-inhibiting receptor on NK cell does not bind to a proper MHC killer-inhibiting receptor on NK cell does not bind to a proper MHC surface proteinsurface protein

Method of killing cells—lysing cells by damaging plasma membranesMethod of killing cells—lysing cells by damaging plasma membranes Interferon (INF)—protein synthesized and released into the Interferon (INF)—protein synthesized and released into the

circulation by certain cells if invaded by viruses to signal other, circulation by certain cells if invaded by viruses to signal other, nearby cells to enter a protective antiviral statenearby cells to enter a protective antiviral state

Complement—group of enzymes that produce a cascade Complement—group of enzymes that produce a cascade of reactions resulting in a variety of immune responses of reactions resulting in a variety of immune responses (Figure 21-10)(Figure 21-10) Lyse cells when activated by either adaptive or innate mechanismsLyse cells when activated by either adaptive or innate mechanisms Opsinization—mark cells for destruction by phagocytesOpsinization—mark cells for destruction by phagocytes Variety of other immune responsesVariety of other immune responses


Overview of Adaptive Immunity Overview of Adaptive Immunity Adaptive immunity is part of the third line of defense consisting of Adaptive immunity is part of the third line of defense consisting of

lymphocytes—two different classes of a type of white blood cell lymphocytes—two different classes of a type of white blood cell (Figure 21-11)(Figure 21-11)

Two classes of lymphocytes (Figure 21-12)—B lymphocytes Two classes of lymphocytes (Figure 21-12)—B lymphocytes (B cells) and T lymphocytes (T cells)(B cells) and T lymphocytes (T cells)

Subsets of lymphocytes are defined by the cluster designation Subsets of lymphocytes are defined by the cluster designation (CD) surface markers that the cells carry, for example, CD4 and (CD) surface markers that the cells carry, for example, CD4 and CD8 cellsCD8 cells

Lymphocytes flow through the bloodstream, become distributed in Lymphocytes flow through the bloodstream, become distributed in tissues, and return to the bloodstream in a continuous recirculationtissues, and return to the bloodstream in a continuous recirculation

B-cell mechanisms—antibody-mediated immunity (humoral B-cell mechanisms—antibody-mediated immunity (humoral immunity); produce antibodies that attack pathogens immunity); produce antibodies that attack pathogens (Figure 21-13)(Figure 21-13)


Overview of Adaptive ImmunityOverview of Adaptive Immunity

T cells attack pathogens more directly—classified T cells attack pathogens more directly—classified as cell-mediated immunity (cellular immunity)as cell-mediated immunity (cellular immunity)

Lymphocytes have protein markers on their Lymphocytes have protein markers on their surfaces that are named using the CD systemsurfaces that are named using the CD system

Activation of lymphocytes requires two stimuli: Activation of lymphocytes requires two stimuli: a specific antigen and activating chemicals a specific antigen and activating chemicals (Figure 21-14)(Figure 21-14)

Lymphocytes are densest where they develop—in Lymphocytes are densest where they develop—in bone marrow, thymus gland, lymph nodes, bone marrow, thymus gland, lymph nodes, and spleen (Figure 21-15)and spleen (Figure 21-15)


B Cells and B Cells and Antibody-Mediated ImmunityAntibody-Mediated Immunity

B cells develop in two stages:B cells develop in two stages: Pre-B cells develop by a few months of agePre-B cells develop by a few months of age

The second stage occurs in lymph nodes and spleen—activation of a The second stage occurs in lymph nodes and spleen—activation of a naïve B cell after it binds a specific antigennaïve B cell after it binds a specific antigen

B cells serve as ancestors to antibody-secreting plasma cellsB cells serve as ancestors to antibody-secreting plasma cells

Antibodies—proteins (immunoglobulins) secreted by activated B cell Antibodies—proteins (immunoglobulins) secreted by activated B cell (Figure 21-16)(Figure 21-16)

An antibody molecule consists of two heavy and two light polypeptide An antibody molecule consists of two heavy and two light polypeptide chains; each molecule has two antigen-binding sites and two chains; each molecule has two antigen-binding sites and two complement-binding sites (Figure 21-17)complement-binding sites (Figure 21-17)

Babies are born with different clones of B cells in bone marrow, lymph Babies are born with different clones of B cells in bone marrow, lymph nodes, and spleen; cells of the clone synthesize a specific antibody nodes, and spleen; cells of the clone synthesize a specific antibody with a sequence of amino acids in its variable region that is different with a sequence of amino acids in its variable region that is different from the sequence synthesized by other clonesfrom the sequence synthesized by other clones



Five classes of antibodies (Figure 21-18)— immunoglobulins Five classes of antibodies (Figure 21-18)— immunoglobulins M, G, A, E, and DM, G, A, E, and D IgM—antibody that naïve B cells synthesize and insert into their own IgM—antibody that naïve B cells synthesize and insert into their own

plasma membranes; it is the predominant class produced after initial plasma membranes; it is the predominant class produced after initial contact with an antigencontact with an antigen

IgG—makes up 75% of antibodies in the blood; predominant antibody IgG—makes up 75% of antibodies in the blood; predominant antibody of the secondary antibody responseof the secondary antibody response

IgA—major class of antibody in the mucous membranes and in saliva IgA—major class of antibody in the mucous membranes and in saliva and tearsand tears

IgE—small amount; produces harmful effects such as allergiesIgE—small amount; produces harmful effects such as allergies

IgD—small amount in blood; precise function unknownIgD—small amount in blood; precise function unknown

Antibody molecules produce antibody-mediated immunity Antibody molecules produce antibody-mediated immunity (humoral immunity)—within plasma(humoral immunity)—within plasma



Antibodies resist disease first by recognizing foreign or abnormal Antibodies resist disease first by recognizing foreign or abnormal substances (Figure 21-19)substances (Figure 21-19) Epitopes bind to an antibody molecule’s antigen-binding sites, forming an Epitopes bind to an antibody molecule’s antigen-binding sites, forming an

antigen-antibody complex that may produce several effects antigen-antibody complex that may produce several effects (Figure 21-20)(Figure 21-20)

Complement—a component of blood plasma consisting of several Complement—a component of blood plasma consisting of several protein compoundsprotein compounds Complement kills foreign cells by cytolysis or apoptosis Complement kills foreign cells by cytolysis or apoptosis

(Figures 21-21 and 21-22)(Figures 21-21 and 21-22)

Complement causes vasodilation, enhances phagocytosis, and other Complement causes vasodilation, enhances phagocytosis, and other functionsfunctions

Complement activity can also be initiated by innate immune mechanismsComplement activity can also be initiated by innate immune mechanisms

• Formation by innate immunity is called the alternate pathwayFormation by innate immunity is called the alternate pathway

• Complement protein 3—activated without antigen stimulation—produces full Complement protein 3—activated without antigen stimulation—produces full complement effect by binding to bacteria or viruses in presence of properdincomplement effect by binding to bacteria or viruses in presence of properdin



Primary and secondary responses (Figure 21-23)Primary and secondary responses (Figure 21-23) Primary response—initial encounter with a specific antigen triggers the Primary response—initial encounter with a specific antigen triggers the

formation and release of specific antibodies that reaches its peak in a formation and release of specific antibodies that reaches its peak in a few daysfew days

Secondary response—a later encounter wit the same antigen triggers a Secondary response—a later encounter wit the same antigen triggers a much quicker response; B memory cells rapidly divide, producing more much quicker response; B memory cells rapidly divide, producing more plasma cells and thus more antibodiesplasma cells and thus more antibodies

Clonal selection theory (Figure 21-24)Clonal selection theory (Figure 21-24) The body contains many diverse clones of cells, each committed by its The body contains many diverse clones of cells, each committed by its

genes to synthesize a different antibodygenes to synthesize a different antibody When an antigen enters the body, it selects the clone whose cells are When an antigen enters the body, it selects the clone whose cells are

synthesizing its antibody and stimulates them to proliferate and create synthesizing its antibody and stimulates them to proliferate and create more antibodymore antibody

The clones selected by antigens consist of lymphocytes and are selected The clones selected by antigens consist of lymphocytes and are selected according to the shape of antigen receptors on the lymphocyte’s plasma according to the shape of antigen receptors on the lymphocyte’s plasma membranemembrane


T Cells and Cell-Mediated ImmunityT Cells and Cell-Mediated Immunity

T cells—lymphocytes that go through the thymus gland before T cells—lymphocytes that go through the thymus gland before migrating to the lymph nodes and spleenmigrating to the lymph nodes and spleen Pre-T cells develop into thymocytes while in thymusPre-T cells develop into thymocytes while in thymus

Thymocytes stream into blood and are carried to T-dependent zones in Thymocytes stream into blood and are carried to T-dependent zones in spleen and lymph nodesspleen and lymph nodes

Activation of T cellsActivation of T cells T cells display antigen receptors on their surface membranes that are T cells display antigen receptors on their surface membranes that are

similar to antibodiessimilar to antibodies

A T cell is activated when an antigen (presented by an APC) binds to A T cell is activated when an antigen (presented by an APC) binds to its receptors, causing it to divide repeatedly to form a clone of identical its receptors, causing it to divide repeatedly to form a clone of identical T cells (Figure 21-25)T cells (Figure 21-25)

• Cells of the clone differentiate into effector T cells and memory T cellsCells of the clone differentiate into effector T cells and memory T cells

• Effector T cells go to site where antigen entered, bind to antigens, and begin Effector T cells go to site where antigen entered, bind to antigens, and begin their attacktheir attack


T Cells and Cell-Mediated ImmunityT Cells and Cell-Mediated Immunity

Cytotoxic T cells—T cells release lymphotoxin to kill Cytotoxic T cells—T cells release lymphotoxin to kill cells (Figure 21-26)cells (Figure 21-26)

Helper T cells (TH cells) —regulate the function of Helper T cells (TH cells) —regulate the function of B cells, T cells, phagocytes, and other leukocytes B cells, T cells, phagocytes, and other leukocytes (Figure 21-27)(Figure 21-27)

Suppressor T cells—regulatory T cells that Suppressor T cells—regulatory T cells that suppress lymphocyte function, thus regulating suppress lymphocyte function, thus regulating immunity and promoting self-toleranceimmunity and promoting self-tolerance

T cells function to produce cell-mediated immunity T cells function to produce cell-mediated immunity and help to regulate adaptive immunity in general and help to regulate adaptive immunity in general


Types of Adaptive Immunity Types of Adaptive Immunity (Table 21-4)(Table 21-4)

Innate immunity (inborn or inherited immunity)—genetic Innate immunity (inborn or inherited immunity)—genetic mechanisms put innate immune mechanisms in place during mechanisms put innate immune mechanisms in place during development in the wombdevelopment in the womb

Adaptive or acquired immunity; resistance developed after birth; Adaptive or acquired immunity; resistance developed after birth; two types:two types: Natural immunity results from nondeliberate exposure to antigensNatural immunity results from nondeliberate exposure to antigens Artificial immunity results from deliberate exposure to antigens, called Artificial immunity results from deliberate exposure to antigens, called

immunizationimmunization Natural and artificial immunity may be active or passiveNatural and artificial immunity may be active or passive

Active immunity—when the immune system responds to a harmful agent Active immunity—when the immune system responds to a harmful agent regardless of whether it was natural or artificial; lasts longer than regardless of whether it was natural or artificial; lasts longer than passivepassive

Passive immunity—developed when immunity from another individual is Passive immunity—developed when immunity from another individual is transferred to an individual who was not previously immune; it is transferred to an individual who was not previously immune; it is temporary but provides immediate protectiontemporary but provides immediate protection


Summary of Adaptive ImmunitySummary of Adaptive Immunity Adaptive immunity is specific immunity—targeting specific Adaptive immunity is specific immunity—targeting specific

antigensantigens Adaptive immunity involves two classes of lymphocyte: B cells Adaptive immunity involves two classes of lymphocyte: B cells

and T cells (Figure 21-27)and T cells (Figure 21-27) B cells—antibody-mediated (humoral) immunityB cells—antibody-mediated (humoral) immunity T cells—cell-mediated (cellular) immunityT cells—cell-mediated (cellular) immunity

Adaptive immunity occurs in a series of stages (Figure 21-28)Adaptive immunity occurs in a series of stages (Figure 21-28) Recognition of antigenRecognition of antigen Activation of lymphocytesActivation of lymphocytes Effector phase (immune attack)Effector phase (immune attack) Decline of antigen causes lymphocyte death (homeostatic balance)Decline of antigen causes lymphocyte death (homeostatic balance) Memory cells remain for later response if neededMemory cells remain for later response if needed

B cells and T cells work together in a coordinated system of B cells and T cells work together in a coordinated system of adaptive immunity (Figure 21-29)adaptive immunity (Figure 21-29)


The Big Picture: The Big Picture: Immune System and the Whole BodyImmune System and the Whole Body

Immune system regulated to some degree by Immune system regulated to some degree by the nervous and endocrine systemsthe nervous and endocrine systems

Agents of the immune system include blood Agents of the immune system include blood cells, skin cells, mucosal cells, brain cells, cells, skin cells, mucosal cells, brain cells, liver cells, and other types of cells and their liver cells, and other types of cells and their secretions secretions

mosby items and derived items © 2007, 2003 by mosby, inc.slide 1 chapter 21 immune system

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