Hypersensitivity reaction
Hypersensitivity Reaction
Hypersensitivity reaction (pronunciation: /ˌhaɪpərsɛnsɪˈtɪvɪti rɪˈækʃən/) refers to an exaggerated or inappropriate immune response to an antigen, including allergens, autoantigens, and infectious agents. The term is derived from the Greek words "hyper" (meaning over or above) and "sensitivity" (from the Latin "sensitivus", meaning easily affected).
Hypersensitivity reactions are classified into four types: Type I, Type II, Type III, and Type IV. Each type is distinguished by the immune mechanism involved and the time course of the reaction.
Type I Hypersensitivity
Type I hypersensitivity, also known as immediate hypersensitivity, is mediated by IgE antibodies. It is characterized by an immediate response, usually within minutes, following exposure to an antigen. Common examples include allergic reactions to pollen, food, and insect stings.
Type II Hypersensitivity
Type II hypersensitivity, or cytotoxic hypersensitivity, involves IgG and IgM antibodies directed against antigens on the surface of cells or other tissue components. This can lead to cell damage and disease. Examples include hemolytic anemia and Goodpasture's syndrome.
Type III Hypersensitivity
Type III hypersensitivity, or immune complex-mediated hypersensitivity, involves the formation of immune complexes that deposit in tissues and trigger inflammation. This can result in conditions such as serum sickness and vasculitis.
Type IV Hypersensitivity
Type IV hypersensitivity, also known as delayed-type hypersensitivity, is mediated by T cells rather than antibodies. It typically takes 48-72 hours to develop after exposure to an antigen. Examples include contact dermatitis and tuberculosis.
See Also
References
External links
- Medical encyclopedia article on Hypersensitivity reaction
- Wikipedia's article - Hypersensitivity reaction
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