Hypersensitivity

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Type
Mediators
Timing
Examples
Type I Hypersensitivity
Allergy
Exogenous antigen binding to IgE bound to Mast cells leading to degranulation
Within minutes to an hour, rarely delayed onset (10-12 hours)
Asthma
Anaphylaxis
Hayfever
Type II Hypersensitivity
Cytotoxic
Caused by endogenous antigens which bind to cells. Antibodies IgM and IgG bind to these cells causing apoptosis
Minutes to hours
Autoimmune haemolytic anaemia, thrombocytopenia, Goodpasture’s syndrome
Type III Hypersensitivity
Immune complex (autoimmune)
Caused by endogenous or exogenous antigens bound to IgG forming immune complexes which causes activation of the complement system and neutrophils causing systemic or organ specific damage.
3-8 hours
SLE, Aspergillosis, Rheumatoid arthritis,
Type IV Hypersensitivity
Delayed type
Caused by helper T cells and cytotoxic T cells which cause localized damage and recruits monocytes and macrophages.
48-72 hours
Contact dermatitis, Tuberculin test, granuloma in TB, toxoplasmosis

http://en.wikipedia.org/wiki/Hypersensitivity
http://pathmicro.med.sc.edu/ghaffar/hyper00.htm

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