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Acquired Immuno Deficiency

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Topic updated on 03/20/15 5:37pm

Overview
  • Initiation 
    • HIV binds to CD4 receptors on T cells and macrophages
      • early in infection
        • co-binding with CCR5 chemokine receptor
          • mostly on macrophages
        • mutation in CCR5
          • homozygous is immune to HIV
          • heterozygote slows course of disease (AKA long term non-progressors)
        • late in infection
          • co-binding with CXCR4 chemokine receptor
          • mostly on T cells
  • Host defense
    • virus taken up into macrophages and dendritic cells
      • does not kill these cells but can divide inside
    • cell mediated response
      • Activated CD8+ cells kill infected CD4+ cells
    • humoral mediated response
      • antibodies generated
        • present after 6-9 weeks
        • can only test if HIV positive after this time
  • Immune evasion
    • antigenic drift of HIV gp120
      • evades immune system
      • gp120 also heavily glycosylated
    • inhibits cytokine synthesis by immune cells
      • via Tat
    • proliferation of Th2 cells inhibits Th1 cells
  • Disease progression
    • CD4+ count falls
      • normal = 1000
      • AIDS definition
        • CD4 < 200
        • HIV positive with AIDS defining illness (e.g. pneumocystis)
        • CD4/CD8 ratio < 1.5
    • CD4:8 ratio
      • 2:1 at beginning of infection
      • 1:1 in middle of infection
      • 1:2 in AIDS


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