- Abnormal sensitivity, a condition in which there is an exaggerated response by the body to the stimulus of a foreign agent. See allergy.- delayed h. 1. SYN: cell-mediated immunity. 2. SYN: delayed reaction. 3. a cell-mediated response that occurs in immune individuals peaking at 24–48 hours after challenge with the same antigen used in an initial challenge. The interaction of T-helper I lymphocytes with MHC class II positive antigen-presenting cells initiates the response. This interaction induces the T helper 1 and macrophages at the site to secrete cytokines, which are the major players in the reaction. Called tuberculin-type h..- immediate h. an exaggerated immune response mediated by antibodies occurring within minutes after exposing a sensitized individual to the approximate antigen; also called Type I h.. Clinical symptoms include atopic allergy and systemic anaphylaxis. The antigen induces IgE antibodies, which bind to most cells and basophils. Subsequent exposure to antigen causes binding with the cytophilic IgE resulting in the release of mediators. See allergy.- tuberculin-type h. SYN: delayed reaction.
* * *hy·per·sen·si·tiv·i·ty (hi″pər-sen″sĭ-tivґĭ-te) a state of altered reactivity in which the body reacts with an exaggerated or inappropriate immune response to what is perceived to be a foreign substance. The resulting hypersensitivity reactions are usually subclassified as types Iâ€“IV on the basis of the Gell and Coombs classification of immune responses; see individual types under hypersensitivity reaction at reaction.
Medical dictionary. 2011.