Abstract

After ultracentrifugation of normal mouse serum, we found chemoattractant activity in the high molecular weight protein region at the bottom of the tube, which was comparable in amount and potency to the attractant in endotoxin-activated serum. This was not a pre-formed attractant, but was generated from serum reactants at least one of which was inactivated by heating at 56 degrees C. Analysis of sera from 10 different mouse strains for hemolytic C5 activity and for capacity to generate chemoattractant on ultracentrifugation showed that the 4 strains without C5 were the only strains that failed to generate the attractant. Thus, the attractant precursor is C5. Since the activity was generated in the presence of 0.01 M EDTA, classical or alternative complement activation was not required. The chemoattractant product had a mol. wt of approximately 170,000; it was therefore not free C5a. These results, and data recently published on digestion of purified human C5 by trypsin, suggest that limited proteolysis of C5 can produce a chemoattractant molecule without release of free C5a.