HYPERSENSITIVITY REACTIONS

Immediate (type I) hypersensitivity
Anaphylaxis; allergies; bronchial asthma (atopic forms)
Production of IgE antibody ➙ immediate release of vasoactive amines and other mediators from mast cells; later recruitment of inflammatory cells
Vascular dilation, edema, smooth muscle contraction, mucus production, tissue injury, inflammation


Antibody-mediated (type II) hypersensitivity
Autoimmune hemolytic anemia; Goodpasture syndrome
Production of IgG, IgM ➙ binds to antigen on target cell or tissue ➙ phagocytosis or lysis of target cell by activated complement or Fc receptors; recruitment of leukocytes
Phagocytosis and lysis of cells; inflammation; in some diseases, functional derangements without cell or tissue injury


Immune complex–mediated (type III) hypersensitivity
Systemic lupus erythematosus; some forms of glomer-ulonephritis; serum sickness; Arthus reaction
Deposition of antigen-antibody complexes ➙ complement activation ➙ recruitment of leukocytes by complement products and Fc receptors ➙ release of enzymes and other toxic molecules
Inflammation, necrotizing vasculitis (fibrinoid necrosis)


Cell-mediated (type IV) hypersensitivity
Contact dermatitis; multiple sclerosis; type I diabetes; rheumatoid arthritis; inflammatory bowel disease; tuberculosis
Activated T lymphocytes ➙
(i)
release of cytokines ➙ inflammation and macrophage activation;
(ii)
T cell–mediated cytotoxicity
Perivascular cellular infiltrates; edema; granuloma formation; cell destruction
IMMUNE