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a substance produced by complement activation that causes the release of histamine and other mediators of immediate hypersensitivity from basophils and mast cells, thereby producing signs and symptoms of immediate hypersensitivity (anaphylaxis) without involvement of IgE.
Low molecular weight cleavage products (C3a, C4a, and C5a); generated by the activation of the complement cascade. They are proinflammatory; can cause permeability, smooth muscle contraction, and mask cell degranulation.
[anaphylaxis + toxin]
anaphylatoxin(1) Any antigen that reacts with an IgE and precipitates an anaphylactic reaction by stimulating histamine release.
(2) Activated complement fragments (C3a, C4a and C5a) that bind to mast cells and basophils and trigger the release of inflammatory mediators.
an·a·phyl·a·tox·in, anaphylotoxin (an'ă-fil'ă-tok'sin, an'ă-fil'ō-tok'sin)
1. A substance postulated to be the immediate cause of anaphylactic shock and that is assumed to result from the in vivo combination of specific antibody and the specific sensitizing material.
2. The small fragment (C3a) split from the third component (C3) of complement, which produces a local wheal following intracutaneous injection.