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Hypersensitivity reactions.




Immediate (type I) hypersensitivity

Eg, Anaphylaxis; allergies; bronchial asthma(atopic forms)
Production of IgE antibody
immediate release of vasoactive amines and other mediators from mast cells
recruitment of inflammatory cells (late-phase reaction)
Vascular dilation, edema,smooth muscle contraction,mucus production,

Antibody-mediated (type II)hypersensitivity

Eg Autoimmune hemolytic anemia; Goodpasture syndrome
Production of IgG, IgM which binds to antigen on target cell or tissue
phagocytosis or lysis of target cell by activated complement or Fc receptors causing recruitment of leukocytes

Immune complex-mediated(type III) hypersensitivity

Systemic lupus erythematosus; some forms of glomerulonephritis; serum sickness; Arthus reaction
Deposition of antigen-antibody complexes causing complement activation
Recruitment of leukocytes by complement products and Fc receptors
Release of enzymes and other toxic molecules
Necrotizing vasculitis
Fibrinoid necrosis

Cell-mediated (type IV)hypersensitivity

Contact dermatitis; multiple sclerosis; type I diabetes; transplant rejection; tuberculosis
Activated T lymphocytes release cytokines causing macrophage activation
T cell-mediated cytotoxicity
Granuloma formation