An induced systemic or generalized sensitivity; at times the term a. is used for anaphylactic shock. The term is commonly used to denote the immediate, transient kind of immunologic (allergic) reaction characterized by contraction of smooth muscle and dilation of capillaries due to release of pharmacologically active substances (histamine, bradykinin, serotonin, and slow-reacting substance), classically initiated by the combination of antigen (allergen) with mast-cell–fixed, cytophilic antibody (chiefly IgE); the reaction can be initiated, also, by relatively large quantities of serum aggregates (antigen-antibody complexes, and others) that seemingly activate complement leading to production of anaphylatoxins. SYN: anaphylactic reaction. [G. ana, away from, back from, + phylaxis, protection]
- active a. reaction following inoculation of antigen in a subject previously sensitized to the specific antigen, in contrast to passive a..
- aggregate a. an anaphylactic reaction initiated by the formation of antigen-antibody complexes that activate complement.
- antiserum a. SYN: passive a..
- chronic a. SYN: enteritis anaphylactica.
- generalized a. the immediate response, involving smooth muscles and capillaries throughout the body of a sensitized individual, that follows intravenous (and occasionally intracutaneous) injection of antigen (allergen). SEE ALSO: anaphylactic shock. SYN: systemic a..
- inverse a. anaphylactic shock in an animal ( e.g., guinea pig) whose tissues contain Forssman antigen, resulting from an intravenous injection of serum that contains Forssman antibody.
- local a. the immediate, transient kind of response that follows the injection of antigen (allergen) into the skin of a sensitized individual and is limited to the area surrounding the site of inoculation. SEE ALSO: skin test.
- passive a. a reaction resulting from inoculation of antigen in an animal previously inoculated intravenously with specific antiserum from another animal, a latent period being required between the two inoculations. SYN: antiserum a..
- passive cutaneous a. (PCA) a reaction that occurs in the guinea pig when antiserum is injected into the skin and, 6–24 hours later, specific antigen and a dye such as Pontamine blue or Evans blue are inoculated intravenously; the size of the blue areas at the sites of the antibody injections is a measure of the degree of altered permeability to dye-bound albumin.
- reversed a. SYN: reversed passive a..
- reversed passive a. an anaphylactic reaction induced in an animal injected with a specific antigen, which will bind to reactive tissue, and then, after a latent period, with serum from another animal previously sensitized to the identical antigen. SYN: reversed a..
- systemic a. SYN: generalized a..

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ana·phy·lax·is .an-ə-fə-'lak-səs n, pl -lax·es -.sēz
1) hypersensitivity (as to foreign proteins or drugs) resulting from sensitization following prior contact with the causative agent

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an emergency condition resulting from an abnormal and immediate allergic response to a substance to which the body has become intensely sensitized. It results in flushing, itching, nausea and vomiting, swelling of the mouth and tongue and airway enough to often cause obstruction, wheezing, a sudden drop in blood pressure, and even sudden death. In this extreme form it is called anaphylactic shock. Common causes are peanuts, latex, and wasp or bee stings. Treatment, which must be given immediately, consists of adrenaline (epinephrine) injection, oxygen with possible advanced support of the airway, intravenous fluids, intravenous corticosteroids, and antihistamines.
anaphylactic adj.

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ana·phy·lax·is (an″ə-fə-lakґsis) [ana- + phylaxis] 1. systemic or generalized anaphylaxis; a type I hypersensitivity reaction (see under hypersenstivity reaction) in which exposure of a sensitized individual to a specific antigen or hapten results in urticaria, pruritus, and angioedema, followed by vascular collapse and shock and often accompanied by life-threatening respiratory distress. Common agents causing anaphylaxis include Hymenoptera venom, pollen extracts, certain foods, horse and rabbit sera, heterologous enzymes and hormones, and certain drugs, such as penicillin and lidocaine. 2. a general term originally applied to the situation in which exposure to a toxin resulted not in development of immunity (prophylaxis) but in hypersensitivity. The term was extended to include all cases of systemic anaphylaxis in response to foreign antigens, as well as a variety of experimental models, such as e.g., passive cutaneous anaphylaxis. Anaphylaxis has now been subsumed under the more general concept of type I (immediate) hypersensitivity. anaphylactic adj

Medical dictionary. 2011.

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