Complement component 5a

C5a is a protein fragment released from complement component C5. In humans, the polypeptide contains 74 amino acids but is rapidly meatbolised by a serum enzyme, carboxypeptidase B to a 73 amino acid form, C5a des-Arg. C5a is an anaphylatoxin, caausing the release of histamine from mast cells; C5a des-Arg is a much less potent anaphylatoxin. However, both forms are effective leucocyte chemoattractants, casuing the accumulation of white blood cells, especially neutrophils, at sites of complement activation.