CYTOKINES

1. M.Prasad Naidu MSc Medical Biochemistry, Ph.D.Research Scholar CYTOKINES

2. CYTOKINES Cytokines are small secreted proteins which mediate and regulate immunity, inflammation, and hematopoiesis. They are produced in response to an immune stimulus. Cytokine is the general term for a large group of molecules involved in signaling between cells during immune responses. All cytokines are proteins, some with sugar molecules attached (glycoproteines). They are synthesized and released by white blood cells and tissue macrophages.

3. They are proteins, peptides or glycoproteins in nature. Cytokines stimulate or suppress the functional activity of lymphocytes, monocytes, neutrophils, fibroblast and endothelial cells. They modulate the function of other cell types. Long known to be involved in cellular immune response, these products have additional effects that play important roles in both acute and chronic inflammation. 200 different human cytokines was have been identified

4. TERMS AND DEFINITIONS: Cytokines generated by mononuclear phagocytes are often called ‘Monokines’ and those by activated lymphocytes are reffered to as ‘Lymphokines’. Additionally, both monocytes and macrophages produce cytokines such as CSF’s, which stimulate the growth of immature leukocytes in the bone marrow.

5. GENERAL PROPERTIES Cytokines are produced during immune and inflammatory responses and secretion of these mediators is transient and closely regulated. Cytokine effects are often redundant and these proteins can influence the synthesis or action of other cytokines. Cytokines mediate their effects by binding to specific receptors on target cells and the expression of cytokine receptors can be regulated by a variety of exogenous and endogenous signals.

6. Cytokines induce their effects in two ways 1) they act on the same cell that produces them (autocrine effect) e.g: IL-2 produced by activated T cells promotes T- cell growth 2) they affect other cells in their vicinity (paracrine effect) e.g: IL-7 produced by marrow stromal cells promotes the differentiation of B- cell progenitors in the marrow Many classic growth factors act as cytokines and conversely many cytokines have growth promoting properties.

7. The main sets of cytokines are Interleukins Interferons Tumour necrosis factors Growth factors Colony stimulating factors Chemokines

8. INTERFERONS (IFNs) Interferons (IFNs) are proteins made and released by helper CD4+ T lymphocytes, as well as through monocytes, macrophages, and endothelial cells in response to the presence of pathogens — such as viruses, bacteria or parasites — or tumor cells. IFNs belong to the large class of glycoproteins known as cytokines. Although they are named after their ability to "interfere" with viral replication within host cells

9. They are produced very early in infection and are the first line of resistance to a great many viruses These are particularly important in limiting the spread of certain viral infections. One group of interferons (IFNα and IFNβ) is produced by cells which have become virally infected

10. Types of interferon Based on the type of receptor human interferons have been classified into two major types. Interferon type I: All type I IFNs bind to a specific cell surface receptor complex known as the IFN-α receptor. The type I interferons present in humans are IFN-α, IFN-β and IFN-ω. Interferon type II: In humans this is IFN-γ

11. FUNCTIONS they activate immune cells, such as natural killer cells and macrophages they increase recognition of infection or tumor cells by up-regulating antigen presentation to T lymphocytes and they increase the ability of uninfected host cells to resist new infection by virus. Certain host symptoms, such as aching muscles and fever, are related to the production of IFNs during infection.

13. INTERLEUKINS (ILs) These are a large group of cytokines produced mainly by T cells, although some are also produced by mononuclear phagocytes (or) by tissue cells. The interleukins were first described as signals for communication between white blood cells (leuk- from leukocytes). Currently, it is well-known that these molecules are produced and used as signalling molecules in many cells of the body, in addition to immune cells.

14. They have a variety of functions, but most of them are involved in directing there cells to divide and differentiate Interleukins represent a broad family of cytokines that are made by hematopoietic cells and act primarily on leukocytes There are currently 35 well-known interleukins, however, there are many more to be found and characterized.

15. TUMOUR NECROSIS FACTORS (TNF) Tumor necrosis factors (or the TNF-family) refers to a group of cytokines family that can cause cell death. TNF acts via the TNF Receptor (TNF-R) and is part of the extrinsic pathway for triggering apoptosis. TNF interacts with tumor cells to trigger cytolysis or cell death.

16. Types: Tumor necrosis factor-alpha (TNF-α) is the most well-known member of this class, and sometimes referred to when the term "tumor necrosis factor" is used. Tumor necrosis factor-beta (TNF-β), also known as lymphotoxin is a cytokine that is induced by interleukin 10

17. COLONY STIMULATING FACTORS (CSFs) Colony-stimulating factors (CSFs) are secreted glycoproteins which bind to receptor proteins on the surfaces of hemopoietic stem cells and thereby activate intracellular signaling pathways which can cause the cells to proliferate and differentiate into a specific kind of blood cell These are primarily involved in directing the division and differentiation of bone marrow stem cells, and the precursors of blood leucocytes

18. TYPES: CSF1 - macrophage colony-stimulating factor CSF2 - Granulocyte macrophage colony-stimulating factors (also called GM-CSF and sargramostim) CSF3 - Granulocyte colony-stimulating factors (also called G-CSF and filgrastim)

19. GROWTH FACTROS (GF) A growth factor is a naturally occurring substance capable of stimulating cellular growth, proliferation and cellular differentiation. Growth factors typically act as signaling molecules between cells and they are important for regulating a variety of cellular processes. e.g: Epidermal growth factor (EGF) Fibroblast growth factor (FGF) Granulocyte-colony stimulating factor (G-CSF) Nerve growth factor (NGF)

20. CHEMOKINES: This large group of chemotactic cytokines direct movement of cells around the body, from the blood stream into tissues and to the appropriate location within each tissue. Some of the chemokines also activate cells to carry out particular functions. Chemokines are cytokines that share the ability to stimulate leukocyte movement (chemokinesis) and directed movement (chemotaxis) and are particularly important in inflammation.

21. CYTOKINE RECEPTORS Cytokine receptors fall into four families 1) Type I receptors 2) Type II receptors 3) Type III receptors 4) Type IV receptors

22. TYPE I RECEPTORS: The largest family of cytokine receptors is Type I receptor superfamily. It is characterized by an extracellular region of structural homology approximately 200 amino acids long. Receptors for cytokines such as IL-2, IL-3, IL-4, IL-5, IL-6, IL-7, IL-9, IL-12, G-CSF and GM-CSF belong to this family.

23. TYPE II RECEPTORS: The Type II family of related cytokine receptors can be considered part of the immunoglobulin superfamily and contains receptors for all IFN types as well as IL-10 and M-CSF TYPE III RECEPTORS: TNF family cytokines bind to Type III cytokine receptors which all have multiple cysteine-rich repeats of about 40 amino acids in the extracellular domain.

24. TYPE IV: Receptors for IL-1α and β are representative of the Type IV cytokine receptor family. Regardless of these subtypes, cytokine receptors have several common characteristics. They usually consist of two or more subunits, and receptors for different cytokines may even share common subunits.

26. MECHANISMS OF CELL ACTIVATION The binding of a cytokine to its appropriate receptor sets off a cascade that leads to induction or inhibition of transcription of a number of cytokine regulated genes. This occurs via a chain of protein-protein recognition events leading to binding of diverse trancription factors to DNA . Cytokines initiate intracellular signals through ligand-induced aggregation of receptor components. Cytokine binding can cause hetero or homo-dimerization of receptors or trimerization depend on particular family.

29. Rheumatoid Arthritis • RA is a chronic systemic inflammatory disorder that may affect many tissues and organs but principally attacks the joints. • An auto immune reaction in which T cells play the pivotal role is widely held to be responsible for the chronic destructive nature of RA. • Once an inflammatory synovitis has been initiated by an exogenous agent.

30. T- cells, mainly CD4+ memory cells appear within the affected joints early early in the development of RA Soon the endothelial cells of synovial capillaries are activated with the expression of ICAM-1 Leading to further attachment and transmigration of other inflammatory cells This sequence is further enhanced by release of IL-1, TNF-α and IFN-γ Activated CD4+ cells simultaneously activate monocytes, macrophages and promote the release of monokines and activated B cells with antibody production in affected joints

31. TNF- α and have induces resorption of cartilage and bone bystimulating release of collagenases from synovial cells. Up regulates expression of adhesion molecules (ICAM-1) which inhibits synthesis of proteoglycans in cartilage Stimulates fibroblasts via platelet derived growth factor.

32. MULTIPLE MYELOMA Multiple myeloma is a plasma cell cancer that originates in the bone marrow and is characterized by involvement of the skeleton at multiple sites. • The proliferation and differentiation of myeloma cells seem to be dependent on several cytokines most notably ‘IL-6’ • Serum levels of this cytokine are increased in patients with active disease.

33. IL-6 seems to be produced by tumorous plasma cells themselves as well as by fibroblasts and macrophages in the surrounding stroma. • In addition to causing the growth of myeloma cells, cytokines also mediate bone destruction by acting as osteoclast activating factors. (TNF-β, IL-1, IL-6 and M-CSF)

34. CYTOKINE THERAPY

35. Non specific stimulation or inhibition of particular components of the immune system may sometimes be of benefit. • The best results have been obtained with cytokines and among these interferon-α (IFN- α) is the most widely used mainly for it’s antiviral properties. • The most striking clinical effect of a cytokine has been that of G-CSF in restoring bone marrow function after anti cancer therapy.

36. Interferon beta-1a and interferon beta-1b are used to treat and control multiple sclerosis, an autoimmune disorder. • Interferon therapy is used (in combination with chemotherapy and radiation) as a treatment for many cancers. This treatment is most effective for treating hematological malignancy; leukemia and lymphomas including hairy cell leukemia, chronic myeloid leukemia, nodular lymphoma, cutaneous T-cell lymphoma. • Both hepatitis B and hepatitis C are treated with IFN-α, often in combination with other antiviral drugs

37. Administered intranasally in very low doses, interferon is extensively used in Eastern Europe and Russia as a method to prevent and treat viral respiratory diseases such as cold and flu. IFN therapy causes immunosuppression, in particular through neutropenia and can result in some infections manifesting in unusual ways. The discovery that the β chemokines RANTES, MIP (macrophage inflammatory proteins) suppress HIV-1.

38. CYTOKINE INHIBITORS Cytokine inhibitors can be used for severe or chronic inflammatory conditions. Various ways of inhibiting TNF and IL-1 have proved valuable in rheumatoid arthritis and more controversially in septic shock and severe malaria. e.g: Cyclosporin A; Pentamidine.

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