A C5a inhibitor in peritoneal fluid.

Peritoneal fluid was found to contain an inhibitor of neutrophil chemotaxis. The inhibitor was effective only against the chemotactic activity of zymosan-activated serum (including purified C5a) and had no effect when f-met-leu-phe served as chemoattractant. Inhibition was not the result of a direct effect on the neutrophils, since incubation of cells with the peritoneal fluid did not alter their chemotactic response. The inhibitor was found to be a protein with a molecular weight of approximately 40,000 dalton by gel filtration. It resembles the inhibitor previously described by us in synovial fluids, and thus it is proposed to play a role in the regulation of inflammation in serosal tissues.