- Low molecular weight substances generated by the activation of complement; the biologically active complement components are derived from C3, C4, and C5 and lead to increased vascular permeability as a result of the degranulation of primarily mast cells; release of mediators of immediate hypersensitivity (Type I), i.e., histamine, follows mast cell degranulation. SYN: anaphylotoxin. [anaphylaxis + toxin]
* * *an·a·phyl·a·tox·in .an-ə-.fil-ə-'täk-sən n a toxic substance postulated to be formed in blood serum treated with some bacterial polysaccharides in order to explain the anaphylaxis that results when the treated and modified serum is injected into experimental animals
* * *ana·phyl·a·tox·in (an″ə-filґə-tok″sin) 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. The anaphylatoxins are low-molecular-weight complement cleavage products, C3a, C4a, and C5a, which bind to specific receptors on mast cells and basophils; C4a has comparatively weak anaphylatoxin activity; C5a is also a chemotactic factor for granulocytes and macrophages.
Medical dictionary. 2011.