FIG. 4.

Effect of LPS on H regulation of ACP C3 convertase activity. Liposomes with equal amounts of bound C3b were incubated with ¹²⁵I-C3, B, D, and NiCl₂ to form the ACP C3 convertase in the presence and absence of H. Inhibition of convertase activity by H was determined as the percent decrease in bound ¹²⁵I-C3b observed in the presence of H. Results are the means ± SEM from two or more experiments with triplicate samples. t tests on the 2.4-μg/ml H values indicate that H inhibition of the C3 convertase was significantly greater for PC or Re595 LPS liposomes than for SM LPS liposomes (P < 0.05). H inhibition of liposomes prepared with R5 and R7 LPS was intermediate and not significantly different from H inhibition of either PC or SM LPS liposomes.