delayed hypersensitivity reaction


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delayed hypersensitivity reaction

a reaction of cellular immunity, named in contrast to immediate hypersensitivity reactions because its onset is 24 to 72 hours after the antigenic challenge. The term is usually used to denote the subset of type IV hypersensitivity reactions involving cytokine release and macrophage activation, as opposed to direct cytolysis, but can be used more broadly, sometimes even as a synonym for type IV hypersensitivity reaction. The classic delayed hypersensitivity reaction is the tuberculin reaction observed in skin testing. See also hypersensitivity reaction.

delayed hypersensitivity reaction

A localized skin response mediated by T cells, which occurs 24 to 72 hr after injection of a specific antigen to which the person has been previously sensitized. It is used routinely to screen for tuberculosis infection through injection of purified protein derivative of Mycobacterium tuberculosis. In patients with immunodeficiency, common microbial antigens to which most people have been exposed, such as diphtheria, tetanus, measles, or Candida, are used to determine the presence of defects in T-cell–mediated immunity (CMI). If patients do not develop induration at the site, indicating a positive response to the antigen, a CMI defect is present. Delayed hypersensitivity is a type IV hypersensitivity reaction mediated by cytokines released by macrophages and helper T cells.
Synonym: nonimmediate allergic reaction
References in periodicals archive ?
Type IV reactions may also be involved in some delayed hypersensitivity reactions, such as celiac disease, in which there is a reaction to the gliadin fraction of grains and wheat gluten.
A diagnosis of a type IV delayed hypersensitivity reaction was made.
Non-IgE-mediated inflammatory responses to food antigens that are driven by T cells and other immune cell types have been implicated in delayed hypersensitivity reactions affecting both babies and adults (1,4).

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