CYTOKINES BY DR.RAHULMD (Final year) PHYSIOLOGYSMS Medical College,Jaipur

CYTOKINES

Cytokines (Greek cyto – cell ; and kinos- movement)

Cytokines are soluble proteins that interact with specific cellular receptors that are involved in the regulation of the growth and activation of immune cells and

mediate normal and pathological inflammatory and immune responses. [1]

In early attempts to classify cytokines immunologists began to name them as INTERLEUKINS that is communicate between (inter) WBC (leukocytes) [2]

Cytokines are extremely potent ,acting at picomolar and even femtomolor levels[5]

Cytokines act only on cellsbearing specific receptors.

Expression of cytokines andtheir receptors is highlyregulated.

Autocrine (same cell), eg.IL-2Paracrine (close proximity) eg.

IL-7 Endocrine (long distance) eg. IL-

1 & TNF

Cytokines can act in an:. [6]

1. Pleiotropic- phenomenon of different actions produced by same cytokine on different targets [4]

General Properties of cytokines

2. redundancy- different cytokines can have the same effects on same targets. [4]

3. Cytokines can synergize with each other.

4. Cytokines can antagonize each other.

5. Cascade effect --- cytokines can stimulate the production of other cytokines.

6. Cytokines play key roles in regulating hematopoiesis,innate immunity and acquired immunity.

Haematopoiesis in Bone marrow

[1,4]CLASSIFICATION OF CYTOKINSSTRUCTURAL CLASSIFICATION

1. Four α-helix bundle family :-includes 3 subsets

IL-2 Subfamily:-IL-2,IL-3,IL-4,IL-5,IL-6,IL-7,IL-9,IL-13,IL-15,CSF-1,GMCSF-2,EPO,LIF

INF Subfamily:- INF –α , INF-β

IL-10 Subfamily:-IL-10,IL-19,IL-20,IL-22,IL-24,IL-26

Majority of cytokines have 4 α-helical structural regions termed as A,B,C,D of which A & C run roughly parallel to B & D. and less or no β-sheet.

Helical regions

β-strand

Loops

NH2 COOH

NH2COOH

(a) Interleukin-2

FIG:14.3,Pg.166-STRUCTURE OF CYTOKINES OF HAEMOPOIETIN FAMILY[4]

2. IL-1 Family:- IL-1α, IL-1β, IL-1

3.Chemokine:- act through G protein –coupled receptors have distinctive 3D structure and regulates cell movement and are chemoattractants. IL-8 RANTES,MIG .

FUNCTIONAL CLASSIFICATION can prove cytokines clinical and experimental usefulness - •Type 1 (IFN-γ, TGF-β, etc.), enhance cellular immune response

• Type 2 (IL-4, IL-10,IL-13 etc.), which favor antibody responses.

Role of Cytokines in Haematopoiesis

CYTOKINE RECEPTOR FAMILIES :[2]

•Interleukin 1 family - IL-1, IL-1, IL-1Ra, IL-18, IL-33

•Hematopoietin (Class I cytokine) family-IL-2, IL-3,IL-4,IL-5,IL-6,IL-7,IL-12,IL-13,IL-15,IL-21, IL-23 ,GM–CSF, G-CSF, GH,EPO

•Interferon (Class II cytokine) family-IFN-α, IFN-β, IFN-γ, IL-10, IL-19, IL-20,IL-22

•Tumor Necrosis Factor Family-TNF-α, TNF-β, CD40L •Chemokines- IL-8, CCL19, CCL21, RANTES,

Five Receptor Families have been recognized namely:

Cytokines act on their target cells by binding specific membrane receptors.

. Hematopoietin familyreceptors are dimers or trimers with 4 positionally conserved cysteines in their extracellular domains and a conserved Trp-Ser-X-Trp-Ser sequence where X can be any amino acid.

Interferon family receptors have the conserved cysteine residues but not the Trp-Ser-X-Trp-Ser sequence, and include the receptors for IFN-α, IFN-β, and IFN-γ.

. Tumor Necrosis Factor family receptors have four extracellular domains; they include receptors for soluble TNF-α and TNF-β as well as membrane-bound CD40 (important for B cell and macrophage activation) and Fas (which signals the cell to undergo apoptosis).

Fig.14.4: Diagram showing comparative structural features of cytokine receptors of different families

[4].

Different receptors associate with differentJAK/STAT combinations

Role of Cytokines in development of TH-1 & TH-2 Subsets & their functions

[4] The differentiation of TH cells into TH-1 and TH-2 depend

upon the interleukin environment in which antigen primed TH cells develop.

IL-12 predominantly influence in differentiation of TH-1 and IL-4 influence into TH-2 cells.

TH-1 cells : INF-γ ,TNF-β ,IL-2TH-2 cells: IL-4,IL-5,IL-6,IL-10,IL-13

TH-1 is responsible for the cell mediated immune function enhancing phagocytosis ,inflammation. INF-γ inhibits TH-2 cells.

TH-2 cells causes activation of B-cells leading to humoral response.TH-2 cells support Eosinophil activation and synthesis of IgM, IgE . IL-10 supress the expansion of TH-1 cells and promotes Humoral response.

cytokines GM-CSF and IL-3 produced by both TH-1 and TH-2 cells – acts on bone marrow to increase leukocytes production - so they are needed no matter what type of pathogen is present

FIG: Cytokine mediated differentiation of TH cells into TH-1 &TH-2 and their functionscontinous. Stimulatory influence related to TH-2 and ----- shows inhibitory effects. Black arrows indicate TH-1 related effects. [4]

Cytokine antagonists [4,7]

A number of proteins that inhibit the biological activity of cytokines have been identified. These proteins can act in either of two ways:1) bind directly to a cytokine receptor and blocking the cytokine binding

to them 2) bind directly to the cytokine and inhibiting its activity.

IL1 R antagonist (IL1Ra) binds IL1 receptor but has no activity but blocks binding of IL1. Production of IL1Ra appears to play a role in regulating the intensity of the inflammatory response .

Cytokine inhibitors are found in blood and ECF. These soluble antagonist are proteins which arise from partial cleavage of extracellular domain of cytokine receptors.

Some Viruses produce cytokine binding proteins. These proteins bind cytokines diminish the inflammatory effects of the cytokine thus conferring virus a selective advantage. Thus acting as antagonist to escape the host defense mechanism.

Viral proteins acting as cytokine antagonist VIRUS PRODUCT FUNCTION

E.B Virus VIL-10 IL-10 HOMOLOGY

Small Pox SIL-1B TNF RECEPTOR

Myxoma Virus SIFN-γ INF RECEPTOR

HERPES HUMAN VIRUS- 3 IL-6 HOMOLOGY

Soluble IL-2 receptor (SIL-2R) consists of N-terminal 192 amino acids of α-subunits of IL-2R .The shed receptor binds to IL-2 and prevents its action SIL-2R is used as a chemical marker of chronic T-cell activation seen in transplant rejection and AIDS.

“good cytokine vs bad cytokine” [8]

Interferon (IFN)-γ, essential for defense against several intracellular microorganisms such as Mycobacterium tuberculosis, is also a major cytokine in the pathogenesis of several autoimmune diseases.

IL-2 is needed for the generation of cytotoxic T cells (CTL) and forms the basis for several vaccines but the same cytokine drives graft-versus-host disease and limits the success of bone marrow transplantation.

IL-6 increased production causes proliferation of cancer cells in autocrine manner seen in cervical cancers and bladder cancers.

FIGURE:- CHRONOLOGY OF EVENTS FOR INDUCTION OF FEVERSOURCE:-HARRISON’S PRINCIPLES OF MEDICINE VOL-1,FIGURE:16-1; 17th edition

Cytokines association with pyrexia

CYTOKINES AS DRUGS [4,9]

INF –α has been tried in Hepatitis B and C ,β-cell leukemia, AIDS, multiple myeloma

INF – β is used in multiple sclerosis

INF-γ has been tried in chronic granulomatous diseases

Recombinant human IL-11 (oprelvekin) stimulate bone marrow to induce platelet production in nonmyeloid malignancies in patients undergoing chemotherapy.

Recombinant human G-CSF (filgrastim) is used after autologous stem cell transplantation to treat neutropenia. It reduces the duration of neutropenia and lessens morbidity secondary to bacterial and fungal infections.

Etanercept is soluble TNF- receptor.. It binds to TNF-α. It is used for the treatment of rheumatoid arthritis, juvenile rheumatoid arthritis, ankylosing spondylitis and psoriaticarthritis.

Enbrel Chimeric TNF-receptor/IgGconstant region

Rheumatoid arthritis

Remicade or Humira Monoclonal antibody againstTNF- receptor

Rheumatoid arthritis, Crohn’s disease

Roferon Interferon -2a* Hepatitis B, Hairy-cell leukemia, Kaposi’s sarcoma, Hepatitis C†

Epogen Erythropoietin (hematopoieticcytokine)

Stimulates red-blood-cell production

Neumega or Neulasta Interleukin 11 (IL-11), ahematopoietic cytokine

Stimulates production of platelets

Ankinra (kineret) Recombinant IL-1Ra Rheumatoid arthritis

Avonex Interferon-–1a Multiple sclerosis

AGENT NATURE OF AGENT CLINICAL APPLICATIONS

TABLE :- Cytokine-based therapies in clinical use

Reference- Kuby immunology ,7th edition chapter 4,pg.121

Alopecia, Psoriasis, is common complication of INF-α

INF-β injection has been associated with local necrosis of the skin

G-CSF may induce neutrophilic dermatosis or sweet syndrome, pyoderma gangrenosum .

IL-2 associated with facial edema, xerosis, pruritis, pemphigus vulgaris , intravascular volume depletion , capillary leak syndrome,hypotension , impaired renal and liver function .

fluid retention, tachycardia, edema, nausea, vomiting, diarrhoea, shortness of breath and mouth sores. Other side effects include rash at the injection site, blurred vision, headache, fever, cough .

Few Complications to List of Cytokine Therapy [1,6]

BRIEF DESCRIPTION OF SOME IMPORTANT CYTOKINES [10]

INTERLEUKIN-1(IL-1):-•Known as Leucocytic activating factor(LAF) in 1972 & BAF in 1974. Renamed IL-1 in 1979.•IL-1 is stable poly peptide retaining its activity at 56 degree centigrade and pH3-11•IL-1 occurs in 2 molecular forms alpha and beta .•IL-1 is secreted by macrophages and monocytes•Immunological effects of IL-1 includes stimulation of T-cells, B cell proliferation ,neutrophil chemotaxis, phagocytosis•IL-1 together with TNF is responsible for hematological changes in septic shock and also enhances initial meningeal inflammation in Bacterial meningitis•Cytokine inhibitors like Dexamethasone protect against excessive meningeal inflammation

INTERLEUKIN -2:•Major activator of T and B cells and stimulate cytotoxic Tcells and NK cells•It converts null cells into lymphokine activated killer cells which can destroy NK-resistant tumour cells

INTERLEUKIN -3:is a growth factor for bone marrow stem cells.also known as multi CSF

INTERLEUKIN -4:•Formerly known as B cell growth factor-1•Act on B cell and induces its proliferation and antibody synthesis•Plays a key role in haematopoiesis by stimulating colony formation by precursors of erythroid cells,megakaryocytes ,granulocyte cell lineage•It augments IgE synthesis•It enhances action of cytotoxic T cells

INTERLEUKIN -6 :• Produced by stimulated T and B cells,macrophages and fibroblasts•It has stimulatory effect on hepatocytes,nerve cell,hematopoietic cells.•It act as an inflammatory response mediator in host defense against infections.

TUMOUR NECROSIS FACTOR:• Occurs in two forms –Alpha, Beta•TNF along with IL-1 play critical role in initiation of inflammatory response to infection and to cancerous cells•They directly kill tumour cells•Cause activation of other cells like macrophages , monocytes to produce IL-1 •TNF activity is enhanced by INF-γ. • In high concentration ,TNF has some endocrine function – Production of fever (TNF acts as endogenous pyrogen Increased protein synthesis including acute phase proteins in the liver

OTHER CYTOKINES TRANSFORMING GROWTH FACTOR (TGF-β)

•Named so because of the ability to transform fibroblasts •It promotes wound healing

LEUKEMIA INHIBITORY FACTOR (LIF)•Produced by T-cells, help in stem cell proliferation and eosinophil chemotaxis

Cytokine storm[7,8]

K/a hypercytokinemia is a fatal immune reaction consisting of a positive feedback B/W cytokine and immune cells with highly elevated levels of various cytokine Symptoms.

If a cytokine storm occurs in the lungs , for example, fluids and immune cells such as macrophages may accumulate and eventually block off the airways, potentially resulting in death

symptoms includes high fever ,swelling and redness, extreme fatigue and nausea. In some cases the immune reaction may be fatal.

The first reference to the term cytokine storm in the published in medical literature appears to be by Ferrara et al. in GVHD in FEB.1993.

infectious and non-infectious diseases including graft versus host disease (GVHD), acute respiratory distress syndrome (ARDS), sepsis, avian influenza, smallpox, and systemic inflammatory response syndrome (SIRS).

Cytokine storm may also be induced by certain medications like experimental drug TGN1412 .

cytokine storms were responsible for many deaths during 1918 influenza pandemic, which killed a disproportionate number of young adults.

Results from Hong Kong indicated this as the probable reason for many deaths during the SARS epidemic in 2003

Human deaths from the bird flu H5N1 may involve cytokine storms .Recent reports of high mortality among healthy young adults in the 2009 swine flu outbreak has led to speculation that cytokine storms could be responsible for these deaths, since the Swine Flu results from the same influenza strain as the Spanish Flu of 1918

but the Centers for Disease Control and Prevention (CDC) shows that symptoms reported from this strain so far are similar to those of normal seasonal flu,with the CDC stating that there is "insufficient information to date about clinical complications of this variant of swine-origin influenza A (H1N1) virus infection.”

Cytokine storm has also been implicated in hantavirus pulmonary syndrome.

Role in pandemic deaths[2, 7]

CYTOKINES and OBESITY RELATED DISEASES [8]

Clinical focus

Adipokines are a recent grouping of cytokines based on their production from white adipose tissue, including resident macrophages in fat, and their role in the metabolic syndrome, particularly in insulin resistance.

Various Adipokines, such as IL-1a and TNF-α, are known for their pro-inflammatory role in the atherosclerotic processes

Leptin ,is naturally occurring suppressor of appetite, appears to function primarily as a mediator of cytokine-induced inflammation and immune functions .

The ability of IL-1β to kill the b-cell, first reported in 1986 opened the field of cytokines to diabetologists. In response to glucose challenge, the b-cell produces IL-1β in a suicidal process The importance of IL-1 in type 2 diabetes has been demonstrated in a placebo-controlled trial of IL-1Ra, in which blocking IL-1 prevented the loss in b-cell function.

Adiponectin is an anti-inflammatory adipokine inhibiting macrophage functions.

Resistin increases insulin resistance in muscle and liver tissue but also induces chemokine and vascular adhesion molecules.

Adipokines have a role in obesity-related diseases .For example, in type 2 diabetes, fatty tissue-derived cytokines likely account for the progressive loss of the insulin-producing b-cells in the pancreatic islets.

Refernces:-[1] HARRISON’S PRINCIPLES OF INTERNAL MEDICINE ;TMH;16TH Edition ;Vol 1 : Pg-106-107 ;Vol2:Pg-1907,1915-17

[2] KUBY IMMUNOLOGY; W. H. Freeman &Company , New York; 7TH Edition ;

Judith A. Owen; Chap-4 ;Pg-105-140

[3] Clinical Immunology Principles and Practices ; Mosby International Ltd ; 2nd Edition; Robert.R.Rich et.al ;Volume1: Chap-12 : Pg-12.1-12.22

[4] Essentials of Immunology ;Arya Publications 2004 ; Dr.S.K.Gupta ;Chap-14 :Pg-164-181

[5] Immunology ; Mosby International Ltd ;6th Edition ; Roitt , Brostoff ,Male Chap-7:Pg-119-129

[6] Robbins and Cotran Pathological basis of Disease ; Elsevier ltd ;7th Edition ;Kumar et al

[7] INTERNET REFERENCE (en.wikipedia.org/wiki/Cytokine)

[8] Historical insights into cytokines,Charles A. Dinarello,University of Colorado Health Sciences Center, Denver, USA; Eur. J. Immunol. 2007. 37: S34–45

[9] Role of cytokines; M.M. KhanImmunopharmacology;Springer2008 chap-2 ;pg:33-59.

[10] Textbook of Microbiology ; Panicker; 8th edition ;pg-146-148 universities press

THANXDR.RAHUL