Anaphylatoxins

Small proteins released through limited proteolysis from larger precursors during activation of the complement system. In a narrower sense, the cleavage products of the complement system, C3a (C4a) and C5a, are referred to as anaphylatoxins (C3a and C5a have, in principle, a similar spectrum of action). They are misnamed, since classic anaphylactic shock is an IgE-mediated reaction. In contrast, anaphylatoxins exert their effects directly through receptor-mediated degranulation of certain cells. Anaphylatoxins are highly potent inflammatory mediators and trigger a variety of proinflammatory reactions in various target cells and tissues (e.g., smooth muscle contraction, chemotaxis and degranulation of leukocytes, as well as edema of the skin and mucous membranes (see below : hereditary angioedema). They are rapidly inactivated in the bloodstream by carboxypeptidase N, which removes the C-terminal arginine residue, causing C3a to lose all of its activity and C5a to lose over 90% of its activity.

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