FIG 1.

Activation of human complement by CHIKV is concentration and time dependent. Complement activation and subsequent generation of C3a upon incubation of CHIKV with NHS are shown. Serum treated with zymosan served as a positive control, while the negative control was set up by incubating serum with PBS. (A) Levels of C3a generated in the serum when incubated with various concentrations of CHIKV for 45 min. CHIKV activated complement in a concentration-dependent manner. (B) Levels of C3a generated in the serum at different time points (1, 5, 10, 20, 30, and 45 min) when incubated with a set concentration of CHIKV. A gradual increase in the levels of C3a occurred with the increase in time (lanes 8–13); background levels of C3a were detected at 1 min, with marked saturation occurring midway. The serum-only control incubated for the indicated time period showed only basal levels of C3a (lanes 2–7), which were significantly lower than for the samples containing both CHIKV and NHS. The Western blots are representative of three independent experiments.