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hypersensitivity reaction
the exaggerated or inappropriate immune response occurring in hypersensitivity, in response to a substance either foreign or perceived as foreign and resulting in local or general tissue damage. Such
reactions are usually classified as types I–IV on the basis of the Gell and Coombs classification.
delayed hypersensitivity reaction
, delayed-type hypersensitivity reaction
a hypersensitivity reaction that takes 24 to 72 hours to develop and is mediated by T lymphocytes rather than by antibodies; usually denoting the subset of type IV hypersensitivity reactions involving cytokine release and
macrophage activation, as opposed to direct cell breakdown, but sometimes used more broadly for any type IV hypersensitivity reaction.
immediate hypersensitivity reaction
type I hypersensitivity reaction; a hypersensitivity reaction mediated by interaction of immunoglobulin E (IgE) antibody and antigen and release of histamine and other mediators
occasionally, any hypersensitivity reaction mediated by antibodies and developing rapidly, generally in minutes to hours (that
is, a type I, II, or III hypersensitivity reaction), as distinguished from those mediated by T lymphocytes and macrophages and generally requiring 24 to 72 hours to develop
(type IV hypersensitivity reactions).
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