module 4

• pathogen associated molecular patterns


  molecules that are unique to microbes but are shared within discrete taxonomic groups
• PRR


  recognised PAMPs
• complement step 1


  immune cell recruitment: antibody/lectin bind, C2a and C4b bind
• complement step 2


  opsonisation: lysis of C3, C3b binds
• complement step 3


  bacterial lysis (MAC)
• cytokine


  secreted protein that affects behaviour of nearby cells with appropriate receptor
• chemokine


  secreted protein that attracts cells bearing the appropriate receptors
• neutrophil migration 1: bacteria trigger

  macrophages to release cytokines and chemokines
• neutrophil migration 2: redness, heat and swelling


  due to vasodilation and increased vascular permeability
• neutrophil migration 3: inflammatory cells


  migrate into tissue, releasing inflammatory mediators that cause pain
• neutrophils


  normally in blood
• macrophages


  normally in tissue
• phagocytosis 1: phagocyte binds

  opsonised organism, form pseudopod
• phagocytosis 2: recruit


  lysosomes
• phagocytosis 3: fusion to form

  phagolysosome
• phagocytosis 4: final step


  damage and digestion and release of microbial products
• B lymphocyte


  specific antigen binds causing proliferation and differentiation into plasma cells and memory B cells
• Fc


  constant region of antibody
• Fab


  variable region of antibody
• constant region


  can take on one of 5 isotypes
• variable region


  can take on almost infinite variety of forms
• single B cell


  makes an antibody of single specificity
• antibody isotypes


  IgM, IgD, IgG, IgE, IgA
• IgM


  on membrane of naive B cells, secreted into plasma as a pentamer
• IgG


  high concentrations in plasma and tissue fluids
• IgA


  high concentrations in mucosal secretions (often a dimer)
• IgE


  low levels in plasma, tissue fluids (bound to mast cells)
• isotype switching


  after B cells have been stimulated by antigens to make IgM
• variable region of heavy chain

  encoded by V,D, J segments
• variable region of light chain


  encoded by V, J segments
• B cell development


  immature B cells may display auto-reactive antibodies, these are deleted
• isotype switching mechanism


  DNA deletion by cutting and rejoining of DNA in switch sequences
• antibody structure


  two identical light chains and heavy chains
• TCR structure


  two chains (alpha and beta) with variable and constant regions
• TCR-aplha


  V, J and C region gene segments
• TCR-beta


  V, D, J and C region gene segments
• B cell antigen recognition

  antigen recognised by specific antibody
• T cell antigen recognition


  antigen peptide presented on MHC marker recognised by TCR
• MHC alleles


  inherited
• endosomal processing of protein antigens


  MHC II markers