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Structure and Function of MHC

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Topic updated on 11/19/16 4:05am

MHC Class I 
  • Found on all nucleated cells EXCEPT RBCS
  • HLA-A, B, C
    • disease associations
      • A3
        • hemochromatosis
      • B27 
        • psoriasis
        • ankylosing spondylitis
        • inflammatory bowel disease
        • reactive arthritis (reiter's syndrome)
  • Contain a β2 microglobulin (see figure)
    • β2 helps move MHC molecule from endoplasmic reticulum to surface
  • Presents intracellular peptides 
    • primary function is for self-surveillance 
    • aids in immune response to intracellular pathogens (e.g. viruses)
    • antigens presented to CD8+ T-cell receptor
  • Mechanism of loading
    • degradation of protein
    • peptides transported from cytosol into ER via TAP complex
    • combine with newly made class I MHC
    • transport to cell surface for presentation
MHC Class II
  • Found on all antigen presenting cells
    • Macrophages, B cells, dendritic cells, thymic epithelial cells
    • HLA-DP, DQ, DR
      • disease associations
        • DQ2/DQ8
          • celiac disease
        • DR2
          • multiple sclerosis
          • hay fever
          • SLE
          • Goodpasture's syndrome
        • DR3
          • diabetes mellitus type I
          • Graves' disease
        • DR4
          • rheumatoid arthritis
          • diabetes mellitus type I
        • DR5
          • pernicious anemia
          • Hashimoto's thyroiditis
  • Presents phagocytosed antigens
    • extracellular pathogens (e.g. bacteria)
  • Endosomal (exogenous) antigen processing
    • antigen presentation to CD4+ T lymphocytes
  • Mechanism of loading
    • phagosome digested
    • fusion of phagosome with endosome containing newly synthesized class II MHC
      • class II MHC has antigen binding site covered with invariant chain to prevent "self-presentation"
    • invariant chain degraded and antigen is loaded
    • transport to cell surface for presentation

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