Anti-complement activity of oleanolic acid: an inhibitor of C3-convertase of the classical complement pathway.

Oleanolic acid is a naturally occurring compound, isolated from Luffa cylindrica, which inhibits the in-vitro immunohaemolysis of antibody-coated sheep erythrocytes by guinea-pig serum. In further experiments this reduced immunohaemolysis was found to be due to inhibition of the C3-convertase of the classical complement pathway. The threshold concentration for inhibition of C3-convertase was 100 micrograms mL-1. However, higher concentrations of oleanolic acid showed constant inhibitory effects on immunohaemolysis. Oleanolic acid also exhibited weak inhibitory effects on individual components of the complement system.