Chap 4

• Cytokines


  Soluble proteins synthesized and secreted by the cells associated with innate and adaptive immunity, in response to foreign substances like microbes and antigens, as mediators of immunity and inflammation
• General functions of cytokines


  • Cell to cell communication
  • Inducing cell growth and differentiation
  • Chemotaxis
  • Activation and/or enhanced cytotoxicity
  • Control regulation of immunity
  • Regulation of hematopoiesis

  
• Cytokines


  • Secretion is self-limited
  • Not stored
  • Synthesized only when required
  • Secreted immediately after synthesized
  • Synthesis is temporary
  • The action of cytokines are pleiotropic and redundant
• Pleiotropic


  One cytokine can act on different cell types
• Redundant


  Few cytokines have the same function
• Cytokine action


  1. Cytokines start their actions by binding to specific membrane receptors on target cells

  2. After cytokines bind to receptor on cells, they stimulate an action

  3. The cellular responses to most cytokines by performing new function

  
• Family of cytokines


  • Interleukins (ILs)
  • Interferons (IFNs)
  • Tumor necrosis factor
  • Chemokines
  • Transforming growth factors (TGF)

  
• Interleukins (ILs)


  Made by leukocytes and act on other leukocytes, do not bind antigen, modulate inflammation and immunity by regulating growth, mobility and differentiation of lymphoid cells

  
• Interferons (IFNs)


  Synthesized by cells in response to viral infection, act as antiviral, immunomodulators and antineoplastic agents
• Tumor necrosis factor


  Principles mediator of the acute inflammatory response to gram-negative bacteria and other infectious microbes, induces apoptosis in a variety of cells
• Chemokines


  Stimulate leukocytes movement from the blood to tissue site of infection
• Transforming growth factors (TGF)


  Product of virally transformed cells, inhibit the proliferation and differentiation of T cells and the activation of macrophage

  
• Examples of cytokines of innate and adaptive immunity


  • Innate immunity: Chemokines, Interferon gamma (IFN-γ), Interferons type 1 (IFN-α, IFN-β), Interleukin-1 (IL-1), Interleukin-6 (IL-6), Interleukin-10 (IL-10), Interleukin-12 (IL-12), Lymphotoxin (Lt), Tumor necrosis factor (TNF)
  • Adaptive immunity: Interleukin-2 (IL-2), Interleukin-4 (IL-4), Interleukin-5 (IL-5), Interleukin-13 (IL-13), Interleukin-15 (IL-15), Interleukin-18 (IL-18), Transforming growth factor beta (TGF-β)

  
• Cytokines are involved in host defense, mediating early inflammatory reactions to microbial organisms and stimulating adaptive immune response in innate immunity, and stimulating proliferation and differentiation of antigen-stimulated lymphocytes and activating specialized effector cells in adaptive immunity

  
• Cytokines are a family of proteins that are synthesized and secreted by immune cells in response to antigen exposure
• By the end of this topic, student should be able to: i. Define cytokines, ii. State the general functions of cytokines, iii. Explain the family of cytokines