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Anaphylatoxins, or complement peptides, are fragments (C3a, C4a and C5a) that are produced as part of the activation of the complement system. Complement components C3, C4 and C5 are large glycoproteins that have important functions in the immune response and host defense. They have a wide variety of biological activities and are proteolytically activated by cleavage at a specific site, forming a- and b-fragments. A-fragments form distinct structural domains of approximately 76 amino acids, coded for by a single exon within the complement protein gene. The C3a, C4a and C5a components are referred to as anaphylatoxins:〔 they cause smooth muscle contraction, histamine release from mast cells, and enhanced vascular permeability.〔 They also mediate chemotaxis, inflammation, and generation of cytotoxic oxygen radicals.〔 The proteins are highly hydrophilic, with a mainly alpha-helical structure held together by 3 disulfide bridges.〔 == Function == Anaphylatoxins are able to trigger degranulation (release of substances) of endothelial cells, mast cells or phagocytes, which produce a local inflammatory response. If the degranulation is widespread, it can cause a shock-like syndrome similar to that of an allergic reaction. Anaphylatoxins indirectly mediate: * smooth muscle cells contraction, for example bronchospasms * increase in the permeability of blood capillaries * chemotaxis — receptor-mediated movement of leukocytes in the direction of the increasing concentration of anaphylatoxins 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「anaphylatoxin」の詳細全文を読む スポンサード リンク
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