High dose of GL-2045 partially inhibits the alternative form of C3 convertase. C3a production was examined in the alternative C3 convertase assembly system, generated by incubation of C3b and factors D and B with GL-2045, HAGG, or IVIG for 15 minutes at 37°C. This was followed by the addition of C3 (A) or C3b; factors D and B were incubated for 15 minutes at 37°C followed by addition of C3 preincubated with GL-2045, HAGG, or IVIG (B). For classical C3 convertase assembly, C4, C2, and C1s enzymes were incubated with GL-2045, HAGG, or IVIG followed by the addition of C3 (C). Alternatively, C4, C2, and C1s were incubated with drugs pretreated C3 (D). The results are least squares mean ± SE estimated by ANCOVA. Natural log variance stabilizing transformation and Tukey procedure for multiple comparisons adjustment were used to test the differences. *P < .05, **P < .01, ***P < .001 compared with no-treatment control.