The Immune System 1

The Immune System 1

1. Innate Immunity

   • Vertebrates
     • Barrier Defences
       • Epithelial tissues
       • Body secretions
     • Cellular Innate Defences
       • Phagocytic cells
         • 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
         • Neutrophils
           • Attracted by signals from infected tissues
         • Macrophages
           • Large phagocytic cells
         • Dendritic Cells
           • Stimulate adaptive immunity
         • Eosinophils
           • Defence against multicellular invaders
       • Natural Killer Cells
         • Detect abnormal surface proteins of virus-infected and cancerous cells
           • Release chemicals
       • Interferons
         • Proteins secreted by virus-infected cells which induce nearby unaffected cells to inhibit viral reproductiion
       • Complement System
         • Proteins that are activated by microbe surface components, resulting in lysis of invading cells
       • Inflammatory Response
         • Mast Cells
           • Histomenes
             • Vasodialation and more permeable blood vessels
               • Delivers anti-microbial peptides
   • Invertebrates
     • Exoskeleton as a first line of defence
     • Lysozymes - break down bacterial cell walls
     • Haemocytes
       • Phagocytosis - the cellular ingestion and digestion of foreign substances
       • Antimicrobial peptides
         • Disrupt plasma membranes

2. Adaptive Immunity

   • Lymphocytes
     • T Cells
       • Mature in thymus
       • Receptors
         • Alpha and Beta chains
         • Bind only to antigen fragments presented on the surface of host cells
           • Antigen fragments presented by MHC (Major histocompatibility complex) molecules
     • B Cells
       • Mature in bone marrow
       • Receptors
         • Light chains and heavy chains
         • B cell antigen recptors (surface-bound) and antibodies
           • Antibodies - same Y-shape, but secreted rather than surface bound
     • Antigen
       • Ellicits response from B & T cells
       • Antigen receptors
         • Binds to the antigen
         • Highly specific - binds to one part of one molecule of a particular pathogen
         • Variable regions and constant regions
           • Allows for great diversity
       • Epitope
         • Accesible portion of of antigen that binds to receptor
   • Self-tolerance
     • Distinguish from self and non-self
     • As lymphocytes mature, they are tested for self-reactivity
     • Defective cells undergo apoptosis
   • Proliferation
     • Clonal Selection
       • An encounter with an antigen selects which lymphocytes (and hence receptor) will divide to produce clones
       • Effector cells
         • Short-lived clones that immediately defend against the antigen/pathogen
       • Memory Cells
         • Long-lived clones that give rise to effector cells if the same antigen is encountered again later
   • Immunological Memory
     • Primary immune response
       • Production of effector cells during first exposure
     • Secondary immune response
       • Immune response produced upon 2nd exposure
       • Relies on memory cells
         • Upon 2nd exposure, memory cells specific for that antigen enable rapid formation of clones of effector cells

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