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C3a, one of the cleavage products of complement component C3, has the following actions:

  • anaphylatoxin: it stimulates mast cells and basophils to release histamine, so increasing vascular permeability
  • contraction of smooth muscle: particularly of gastrointestinal tract and bronchi

As well as production by the classical and alternative pathways, it can be produced by the action of a variety of C3 cleaving enzymes e.g. bacterial proteases, plasmin.

Last reviewed 01/2018