Enhancement of the chemotactic activity of human C5a des Arg by an anionic polypeptide ("cochemotaxin") in normal serum and plasma.

The potent chemoattractant, C5a is converted rapidly to C5a des Arg by a carboxypeptidase-like enzyme in normal human serum and plasma. Highly purified human C5a des Arg, at concentrations less than 120 ng/ml, is devoid of chemotactic activity for polymorphonuclear leukocytes. We have found that normal human serum and plasma contain a heat-stable (56 degrees C for 30 min), anionic polypeptide ("cochemotaxin") that permits low concentrations of C5a des Arg (20 to 160 ng/ml) to exhibit significant chemotactic activity. The "cochemotaxin" was isolated from serum and plasma by ammonium sulfate fractionation, molecular sieve chromatography, and anion-exchange chromatography. It was purified by high-performance liquid chromatography and was found to have an Mr of approximately 60,000 (determined by sodium dodecylsulfate polyacrylamide gel electrophoresis). The concentration of "cochemotaxin" in normal serum and plasma was estimated to be 4.0 microgram/ml. Purified "cochemotaxin" acted in a concentration-dependent fashion to permit low concentrations (20 to 160 ng/ml) of C5a des Arg to attract polymorphonuclear leukocytes. Chemotactic activity varied with the input of C5a des Arg and "cochemotaxin" and was maximal when the 2 polypeptides were combined at equal protein concentrations. The profile of chemotactic activity exhibited by C5a des Arg and its "cochemotaxin" very closely resembled that exhibited by dilutions of activated serum and by highly purified C5a. These data suggest that the bulk of chemotactic activity generated in whole serum after complement activation can be accounted for by C5a des Arg and its "cochemotaxin".