Activation of Human C3 by Living and Heat-killed Human Cells after Treatment with Trypsin.
Living and heat-killed, cultured human fibroblasts treated with 0.1% trypsin were found to activate the alternative complement pathway in human serum. The extent of C3 activation measured by conversion of C3 was dependent on the concentration of cells and associated with loss of hemolytic activity of complement. Complement activation by heat-killed cells was significantly enhanced compared with that observed in viable cells. C3 conversion was detected in normal serum chelated with EGTA-Mg++, but not in serum heated at 50℃ for 30 min to inactivate factor B or in EDTA-chelated serum. These data suggest that fibroblasts with modified membranes or killed by injury could induce antibody-independent activation of the complement system through the alternative pathway.