12.6 Specific immune system

    Cards (14)

    • Antigens trigger immune response, involves the production of polypeptides called antibodies
    • Antibodies:
      • antibodies are Y-shaped glycoproteins called immunoglobulins
      • antibodies are made up of two identical long polypeptides chains called the heavy chains and two shorter chains called the light chains
      • chains held together by disulfide bridges
    • Antibodies bind to antigens with a protein-based 'lock-and-key' mechanism
      • binding site known as variable region, different shape on each antibody and give the antibody its specificity
      • rest of antibody molecule is the same so called constant region
    • When antibody binds to antigen it forms a antigen-antibody complex
    • How antibodies defend the body:
      1. antibody of the antigen-antibody complex acts as opsonins so that complex can be easily engulfed by phagocyte
      2. most pathogens can no longer effectively invade host cell once part of antigen-antibody complex
      3. antibodies act as agglutinins causing pathogens carrying antigen-antibody complex to clump together = prevent spreading around body, allow phagocyte to engulf at same time
      4. antibodies act as anti-toxins, bind to toxin produce by pathogen making them harmless
    • Lymphocyte and the immune response:
      white blood cells called lymphocytes
      T lymphocyte mature in thymus gland
      • T helper cells, produce interleukins, type of cytokine (cell-signalling molecule)
      • interleukins stimulate activity of B cells = increase antibody production
      • T killer cells, destroy pathogen carrying antigen
      produce chemical = perforin, kills pathogen by making holes in the cell membrane
      • T memory cells - part of immunological memory
      if meet antigen second time, rapidly form huge number of clones of T killer cells
    • T regulator cells - stop immune response once pathogen has been eliminated
      • make sure body recognise self antigens and does not set up autoimmune response
    • B lymphocyte mature in bone marrow
      • Plasma cells - produce antibodies to particular antigen and release them into circulation
      • B effector cells - divide to form the plasma cell clones
      • B memory cells - programmed to remember a specific antigen and enable body to make rapid response when pathogen carrying antibody is encountered again
    • Cell-mediated immunity is the immune response that involves the activation of T cells.
      • T lymphocytes respond to the cells of an organism that have been changed in some way e.g. from a virus infection/mutation
      1. in non-specific defence system, macrophages engulf + digest pathogens by phagocytosis, process antigens on surface of pathogen to form antigen-presenting cells (APCs)
      2. receptors on some of the T helper cells fit the antigen, T helper cells become activated + produce interleukins = stimulate more T cells to divide rapidly by mitosis
    • Cloned T cells may -
      • develop into T memory cells = give rapid response if pathogen comes again
      • produce interleukins that stimulate phagocytosis
      • produce interleukins that stimulate B cells to divide
      • stimulate development of clone killer T cells that are specific for presented antigen + destroy infected cell
    • Humoral immunity:
      body responds to antigen found outside the cells e.g. bacteria
      • produces antibodies that are soluble in he blood + tissue fluid and not attached to cell
    • Humoral immunity:
      • activated T helper cells bind to the B cell APC this is clonal selection
      clonal selection - point at which B cells with correct antibody is selected for cloning
      • interleukins produced by activated T helper cell activate B cells
      • activated B cells divide by mitosis to give clones of plasma cells + B memory cells = clonal expansion
      • cloned plasma cells produce antibodies that fit antigen on surface of pathogen, bind to antigen and disable them or act as opsonins/agglutinins = primary immune response
      take up to days to become fully effective = result of ill symptoms
      • some cloned B cells develop into B memory cells
      if body infected again by pathogen, B memory cells divide rapidly to form plasma cell clones
      produce right antibody and wipe out pathogen very quickly before causing symptoms of disease = secondary immune response
    • Autoimmune disease:
      Autoimmune disease - when body does not recognise its self cells and starts attacking healthy body tissue
      • reason could be from genetics or T regulator cells not working effectively
      • immunosuppressants drugs prevent immune system working but deprive body of its natural defences against communicable disease