The Immune System 1

Innate Immunity
1. Vertebrates
  1. Barrier Defences
    1. Epithelial tissues
    2. Body secretions
  2. Cellular Innate Defences
    1. Phagocytic cells
      1. Toll-like receptors (TLR)
        Bind to fragments of molecules characteristic of pathogens (which are normally absent from vertebrates)
        Engulf and destroy pathogens w/ gases & lysozymes
      2. Neutrophils
        Attracted by signals from infected tissues
      3. Macrophages
        Large phagocytic cells
      4. Dendritic Cells
        Stimulate adaptive immunity
      5. Eosinophils
        Defence against multicellular invaders
    2. Natural Killer Cells
      1. Detect abnormal surface proteins of virus-infected and cancerous cells
        Release chemicals
    3. Interferons
      1. Proteins secreted by virus-infected cells which induce nearby unaffected cells to inhibit viral reproductiion
    4. Complement System
      1. Proteins that are activated by microbe surface components, resulting in lysis of invading cells
    5. Inflammatory Response
      1. Mast Cells
        Histomenes
        Vasodialation and more permeable blood vessels
        Delivers anti-microbial peptides
2. Invertebrates
  1. Exoskeleton as a first line of defence
  2. Lysozymes - break down bacterial cell walls
  3. Haemocytes
    1. Phagocytosis - the cellular ingestion and digestion of foreign substances
    2. Antimicrobial peptides
      1. Disrupt plasma membranes
Adaptive Immunity
1. Lymphocytes
  1. T Cells
    1. Mature in thymus
    2. Receptors
      1. Alpha and Beta chains
      2. Bind only to antigen fragments presented on the surface of host cells
        Antigen fragments presented by MHC (Major histocompatibility complex) molecules
  2. B Cells
    1. Mature in bone marrow
    2. Receptors
      1. Light chains and heavy chains
      2. B cell antigen recptors (surface-bound) and antibodies
        Antibodies - same Y-shape, but secreted rather than surface bound
  3. Antigen
    1. Ellicits response from B & T cells
    2. Antigen receptors
      1. Binds to the antigen
      2. Highly specific - binds to one part of one molecule of a particular pathogen
      3. Variable regions and constant regions
        Allows for great diversity
    3. Epitope
      1. Accesible portion of of antigen that binds to receptor
2. Self-tolerance
  1. Distinguish from self and non-self
  2. As lymphocytes mature, they are tested for self-reactivity
  3. Defective cells undergo apoptosis
3. Proliferation
  1. Clonal Selection
    1. An encounter with an antigen selects which lymphocytes (and hence receptor) will divide to produce clones
    2. Effector cells
      1. Short-lived clones that immediately defend against the antigen/pathogen
    3. Memory Cells
      1. Long-lived clones that give rise to effector cells if the same antigen is encountered again later
4. Immunological Memory
  1. Primary immune response
    1. Production of effector cells during first exposure
  2. Secondary immune response
    1. Immune response produced upon 2nd exposure
    2. Relies on memory cells
      1. Upon 2nd exposure, memory cells specific for that antigen enable rapid formation of clones of effector cells

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The Immune System 1

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