Anaphylatoxins inhibit C2 production.

Anaphylatoxins C5a and C3a and their des Arg derivatives inhibited C2 production by mononuclear phagocytes. C5a and C5adesArg which were approximately equipotent (IC50 = 10(-10) mol/l) were more effective than C3a (IC50 = 5 X 10(-8) mol/l) which was approximately 10-20-fold more potent than C3adesArg IC50 = 5 X 10(-6) mol/l). Inhibition of C2 production was only reversed slightly by the addition of either indomethacin or ETYA to the cultures. Intracellular levels of cAMP, were increased by anaphylatoxins. The level of cAMP showed a good inverse correlation with C2 levels in the culture supernatants. The data suggest that the reduction in C2 production produced by anaphylatoxins may be mediated by an increase in intracellular cAMP.