LEC 16: immune system

• Phagocytosis

  Digestion of foreign particles
• Phagocytosis

  • Eliminate pathogens
  • Clean up cellular debris
  • Activate immune response
  • Inflammation regulation
• Natural killer cells

  Kill cancer cells and virus infected cells before adaptive immune response is activated
• Inflammation


  Occurs when body tissues are injured
• Signs of inflammation

  • Redness
  • Heat
  • Swelling
  • Pain
• Inflammation response

  1. Immune cells recognise harmful stimulus

  2. Vasodilation and increased permeability

  3. Damaged cells release proinflammatory chemicals that causes vasodilation and increased cap. Permeability

  4. Chemotaxis - immune cells attracted to site of injury by chemical signals released by chemokines

  5. Phagocytosis - phagocytic cells digest pathogens and eliminate causes of inflammation and contribute to tissue cleanup

  6. Release of inflammatory mediators - enhances vasodilation, increase permeability, amplify inflammatory responses

  7. Formation of fibrin clot - forms a mesh that helps localize inflammation and provide network for tissue repair, blood clotting system activated to present excessive bleeding

  8. Tissue repair and healing - tissue regeneration or scar formation
• Antimicrobial proteins

  Enhances innate defences by attacking microorganisms directly
• Interferons (IFN)

  Proteins produced by virus infected cells that help protect surrounding healthy cells
• Complement cascade

  Group of plasma proteins that assembles a membrane attack complex to kill a cell by punching a hole in plasma membrane making cell leak
• Adaptive defences

  Recognize and destroy specific antigens that initiated the response, a systemic response; not limited to initial infection
• Adaptive immune response

  1. Antigen binding with a lymphocyte for further development

  2. Lymphocyte divides (clonal expansion) - produces a group of cells with an ability to bind this antigen

  3. Effector cells - actively fights infection

  4. Memory cells - respond quickly to future encounters with antigen
• Lymphocytes

  • T lymphocytes
  • B lymphocytes
• CD4+ cells (helper T cells)

  Activates B cells, T cells, macrophages, some are regulatory T cells that inhibit aggressive responses
• CD8+ cells (cytotoxic T lymphocytes)

  Destroys cells or foreign substances
• Th1 cells

  Work with macrophages and CD8+ cytotoxic T lymphocytes to activate cell-mediated immune responses against intracellular threats
• Th2 cells

  Work with B cells, eosinophils and mast cells to stimulate B proliferation and increase antibody production against extracellular threats
• Antibodies


  Proteins that target and bind to extracellular antigens
• B cell activation and antibody production

  1. Specific B lymphocyte becomes activated when antigen binds to surface receptors

  2. Activated B lymphocyte begins clonal expansion

  3. Most clones develop into plasma cells - antibody secreting cells

  4. Remaining develop into memory B cells
• Primary immune response

  Occurs on first exposure to particular antigen
• Secondary immune response

  Occurs when someone is exposed to the same antigen for a second time, produces antibodies with higher affinity for antigen