Regulation of monocyte function by complement activation products

Normal human monocytes, obtained at a mean purity of 60% by Percoll density gradient centrifugation, were found to be chemotactically deactivated to C5a by exposure to low, and biologically significant, concentrations of zymosan-activated serum (ZAS), while retaining their full response to FMLP. C5a was found to be 40X more potent than its metabolite C5a desArg in reducing chemotaxis to activated pooled serum. Conversely, exposure of monocytes to varying concentrations of N-formyl-methionyl-leucyl-phenylalanine (FMLP) decreased chemotaxis to that attractant, though had no effect on chemotaxis to activated serum. Monocytes were also found to actively absorb C5a from solutions of ZAS, rich in C5a. Our data support the concept that monocytes are specifically regulated by C5a and C5a desArg.