**Understanding Cytokines: Communication Between Cells** Explore the roles, nomenclature, and effects of cytokines in im

1. Lecture 17Cytokines

2. What are cytokines? • A collection of polypeptides used for communications between cells • Play role similar to hormones (messengers of the endocrine system) • Hormones usually act at a distance • Cytokines act locally • Differ from growth factors that are produced constitutively, while cytokine production is carefully regulated • Play an important role in both innate and adaptive immunity

3. Cytokine nomenclature • Interleukins (1-18) • Interferons (a,b,g) • Others (common names)

4. Cytokine -mediated effects • Cell growth • Cell differentiation • Cell death • Induce non-responsiveness to other cytokines/cells • Induce responsiveness to other cytokines/cells • Induce secretion of other cytokines

5. How do cytokines tell cells what to do? • Produced by cells as part of normal cellular activity and/or the result of environmental trigger • Bind to receptors on cells • Trigger signal transduction pathways • Initiate synthesis of new proteins

6. Properties of cytokines • Proteins • Low molecular weight • Bind to receptor on either cell which produced it or another cell • Receptor binding triggers a signal • Signal results in altered pattern of gene expression

7. Cytokines can act in three different manners • Autocrine • Cytokine binds to receptor on cell that secreted it • Paracrine • Cytokine binds to receptors on near by cells • Endocrine • Cytokine binds cells in distant parts of the body

8. Cytokine Actions • Pleiotropy • Act on more than one cell type (INFa/b) • Redundancy • More than one cytokine can do the same thing (IFNa/b and IFN) • Synergy • Two or more cytokines cooperate to produce an effect that is different or greater than the combined effect of the two cytokines when functioning separately (IL-12 and IL-8) • Antagonism • Two or more cytokines work against each other (IL-4 and IL-12)

9. How can non-specific cytokines act specifically? • Only cells expressing receptors for specific cytokines can be activated by them • Many cytokines have very short half-lives • Only cells in close proximity will be activated • High concentrations of cytokines are needed for activation • Only cells in close proximity will be activated • May require cell-to cell contact

10. Five cytokine receptor families • Immunoglobulin superfamily receptors • Class I cytokine receptor family (hematopoietin receptors) • Binds most of the cytokines in the immune and hematopoietin systems • Class II cytokine receptor family • TNF receptor family • Chemokine receptor family

11. Cytokines regulate the immune response • Cells with the appropriate receptors become activated • To differentiate • To express receptors which will make them receptive to other cytokines • To secrete other cytokines

12. Signal Transduction by cytokine receptors • Cytokine receptors on different cell types trigger different events • How do you get the message from the outside of the cell to the machinery inside?

13. Cytokines, growth factors and hormone signal transduction pathways

14. The Jak/Stat Signaling Pathway

15. Alert to infection.tumor/etc. Recruit cells to site Specify type of immune response Immune effector phase Immune down-regulation Immune memory and resetting the system Early mediators (IFNa/b) Chemokines (MIP-1a) Early & late mediators (IL-2, IFNg, IL-4, IL-5) Down-regulators (IL-10, TNFg) Maintenance of cytokines, etc. (GM-CSF, IL-3, IL-7, etc.) Involvement of cytokines in the immune response

16. Early mediators • Interferons a/b • Induced by dsRNA, etc. • Induced by CD40/CD40L pathway • IFNs can induce more of themselves • Directly interferes with viral replication • Activation of T and NK cells

17. Chemokines • Recruit to sites of infection • MIP-1a (NK and T cells) • MIG, RANTES (CD4+T cells) • IL-8 (neutrophils) • Eotaxin (eosinophils)

18. Early mediators • IL-12, IL-15, 1l-18, IFN-g (from NK cells), IL-10 • Proinflammatory mediators • Produced by cell associated with innate immunity (macrophages, NK, etc.) • Mediate direct effects • Promote inflammation • Shape downstream responses

19. Late mediators • IL-2, IL-4, IL-5, IFN-g, TNF, IL-6, IL-10 • Produced by cells of the adaptive immune response (T and B cells) • Direct effects • More immunoregulatory functions

20. Cytokine secretion and biological activities of TH1 and TH2 Subsets Type 1 Type 2 Cell-mediated Immune response (intracellular Organisms) Humoral response (parasites) T cell IL-2 IFN-g TNF IL-4 IL-5

21. Down regulators • IL-10, IL-11, TGF-b • Inhibit proliferation, cytokine production • Produced by both innate and adaptive cells

22. Maintenance cytokines • GM-CSF, IL-3, IL-7, IL-9, etc. • Induce cell differentiation, cell growth

23. Cytokine cross-regulation • In a a given immune response, either TH1 or TH2 response dominates • Cytokines of one response tend to down-regulate the other type of response • Example: TH1 cells secrete IFN-g, which inhibits proliferation of TH2 subset

24. Role of TH1/TH2 balance in determining disease outcomes • Balance of two subset determines response to disease • Leprosy • Tuberculoid (TH1, CMI response, patient lives) • Lepromatous (TH2, humoral response, patient dies)

25. Cytokine-related diseases • Bacterial septic shock • Blood pressure drops, clots form, hypoglycemia ensues, patient dies • LPS triggers results in TNF release • TNF induces IL-1 which induces IL-6 and IL-8 • Bacterial toxic shock and related diseases • Superantigens trigger large numbers of T cells which release massive amounts of cytokines (Super antigens are bacterial toxins that bridge CD4 T cell receptors and the MHC class II molecules on APC’s, bypassing the need for antigen) • Lymphoid and myeloid cancers • Some cancer cells secrete cytokines • Chagas’ disease • Trypanosoma cruzi infection results in sever immune suppression • Depression of IL-2 receptor production

26. Intra- and Extracellular Inflammatory Mechanisms to Destroy or Inactivate Pathogens Components of the immune system Help  T cell CD4  T cell CD8  T cell B cell Inflammatory cytokines Cytotoxic T cells ? Antibody Interferon & Non-lymphoid Cytokines Macro- phages Complement Granulo- cytes Adapted from Marrack and Kappler, 1994

27. Infectious agents that target cytokines • Epstein-Barr virus foster the generation of T helper cells that do not produce IL-2. • EBV produces an analog of IL-10 that favors TH2 cells, rather than TH1. • Parasites such as tape worms induce high levels of IgE, an immunoglobulin induced by TH2 cells. • Since TH1 cells mediate inflammation, this may be a protective ploy to avoid destructive inflammatory processes.

28. Immunosuppressive effects of oral bacteria on immune function • Impairment of B and T cell function (P. intermedia, P. asaccharolytica, P. endodontalis, P. melaninogenica) • Production of specific toxins that kill monocytes (A. actinomycetemcomitans) • Provoke the release of peroxide, prostaglandins and other mediators capable of inhibiting lymphocyte function (T. denticola) • Modulate expression of cytokines

29. Cytokine-inducing components of Periodontopathogens • Taken from Wilson, M., Reddi, K., Henderson, B. 1996. Cytokine-inducing components of periodontopathogenic bacteria. J. Periodont. Res.31:393-407. • Pro-inflammatory cytokines such as interleukin (IL)-1, IL-6, IL-8 and tumor necrosis factor (TNF) are believed to be the major pathological mediators of inflammatory diseases ranging from arthritis to periodontal diseases. • It is believed that components of microorganisms have the capacity to induce cytokine synthesis in host cells.

30. Cytokine-inducing components of Gram-positive bacteria

31. Cytokine-inducing components of Gram-negative bacteria

32. Cytokine-induction by LPS from periodontopathogens other than P. gingivalis

33. Cytokines produced by host cells in response to components/products from periodontopathogens

34. Interferon Action • Viral replication stimulates the infected host cell to produce interferon. • Interferon induces uninfected cells to • produce antiviral proteins that prevent translation of viral mRNA • degrade viral nucleic acid • Viral replication is blocked in uninfected cells

35. Therapeutic uses of cytokines • Modulation of TH activation • Interfere with receptor function • Interfere with cytokine • Make it unable to bind to receptor • Make it unable to act

36. Examples of therapeutic uses • Soluble T-cell receptor • Anti-IL-2R • Interleukin analogs which bind receptor, but do not trigger activation (ties up receptor) • Toxins conjugated to cytokines which kill activated T-cells • Administration of cytokines to enhance immunity (side effects/ short half lives) • Allergies