Hypersensitivity reactions

 

Type I
  • Immediate / Anaphylactic
    IgE linkage by an antigen leads to release of mast cell contents (histamine, 5HT, heparin, PAF, chemokines)
  • Minutes
  • Eg. eczema, asthma, allergic rhinitis
Type II
  • Cytotoxic
    Antibody in serum reacts against tissue components resulting in cell death from (1) complement action (2) destruction by killer T-cells (3) phagocytosis by macrophages
  • Minutes-hours
  • Eg. transfusion reactions
Type III
  • Immune complex
    Immune complex formed that activates complement/platelets - cause damage by formation of membrane attack complex (MAC) and enzyme release from inflammatory cells
  • Hours
  • Eg.
Type IV
  • Delayed
    Mediated by sensitised T-lymphocytes
  • Days TB, organ transplants