Natural Immunity

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  • Created by: gsemma
  • Created on: 30-04-19 16:39
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  • Natural Immunity
    • defence mechanisms
      • specific
        • cell-mediated response
          • T-lymphocytes
            • recognise antigens presented on plasma membrane of foreign cells
            • 1. pathogen invades cell or phagocytes takes it up
              • 2. antigens presented on cell or phagocyte
                • 3. receptors on specific T-helper cells fit the antigens which activates them to undergo rapid mitosis to produce lots of clones.
                  • 4. these then activate
                    • cytotoxic t-cells
                      • kill abnormal cells by producing a protein called perforin which makes holes in membrane so cell dies.
                    • develop into memory cells
                    • stimulate b-cells to divide or phagocytosis in phagocytes
        • humoral response
          • B-lymphocytes
            • complementary to antigen on pathogen
              • clonal selection
                • 1. antigen enters B-cell by endocytosis
                  • 2. B presnts antigen
                    • t binds and simulates b to undergo rapid mitosis
                      • large number of B clones with same shaped antibody
            • cells produced from clonal selection
              • plasma cells- shorted lived and produced by antibodies (2000 per sec). primary response
              • memory cells- long lived and remain dormant until next invasion. rapidly divide in secondary response.
      • non-specific
        • physical barriers
        • phagocytosis
          • phagocytes
            • WBCs that engulf pathogens and kill them
          • 1. phagocyte engulfs the pathogen and membrane folds inwards- phagocytosis
            • 2. pathogen trapped in phagocyte
              • 3. lysosomes bind and release lytic enzymes to digest the pathogen
                • 4. now harmless, absorbed/released
      • antigens
        • proteins on membrane
        • used to identify foreign cells form self-cells
        • foreign? immune response
      • antibodies
        • structure
          • diagram
        • function
          • form antibody-antigen complexes
            • opsonisation
              • act as binding site for phagocytes
              • binding can prevent pathogen entering cells.
              • less specific opsonin's stick to molecules not found in host
            • agglutination
              • each molecule has to bonding sites so can crosslink by binding to two different pathogens.
                • leads to clumping which impedes the pathogen making it easier for phagocytosis
              • particularly effective against viruses.


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