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 ?
Macrophage are responsive to a number of lymphokines that induce their growth differentiation and activation; since lymphokines are released by primed lymphocytes, produced chiefly by T-lymphocytes, on contact with an antigen [21], and the demonstration of a lymphookine mediated reaction in this study strongly supported the existence of T like lymphocytes in Tilapias and that the fish is capable of delayed hypersensitivity reactions.
Mantoux testing elicits a delayed hypersensitivity reaction to a previously sensitized antigen (a T-lymphocyte function), and it is generally accepted as a valid in vivo indicator of a patient's level of cell-mediated immunity.
1 ml of PPD antigen was injected with needle bevel upwards intradermally, and examined after 48 hours for the delayed hypersensitivity reaction.
Delayed hypersensitivity reactions to subcutaneously injected heparin are relatively common and present as eczematous plaques at injection sites (Anders & Trautmann, 2013).

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