Infection and Response - Key Concepts

• Describe the process of phagocytosis.

  1. Chemotaxis- macrophage moves towards toxins that are released by the pathogen.
  2. Macrophage engulfs the pathogen.
  3. Fusion of phagosome and lysosome to form a phagolysosome which releases hydrolytic enzymes to destroy the pathogen.
  4. Hydrolysed products are absorbed by the phagocyte.
  5. Pathogen is presented on the surface of the phagocyte, forming an antigen presenting cell (APC).
• • Receptors on T cells bind to antigens on antigen-presenting cells. This is an example of clonal selection as the T cell becomes activated.
  • Activated T cells:
  • divide by mitosis to produce T helper-cell clones.
  • release cytokines to activate killer T cells.
  • activate B cells through release of interleukins.
  • stimulate phagocytosis.
  • This is the cell mediated response.
• • T helper cells bind to antigens on the antigen-presenting B cells (clonal selection).
  • Interleukins produced by T helper cells activate other B cells.
  • The B cells divide rapidly by mitosis to produce different B cells (plasma and memory) (clonal expansion).
  • Cloned plasma cells produce specific complementary antibodies to bind to the pathogens antigen, disabling them or can cause neutralisation and agglutination.