Figure. Concentration-dependent activation of C3AR1 by C3a. Reporter cells were transfected with either the expression plasmid for com­ple­ment C3a receptor 1 (C3AR1) or the mock plasmid and treated with various concentrations of C3a. Data points shown are the mean ± SEM of an experiment performed in triplicate, and the curve is a fit to Hill equation with an EC50 of 3.7 nM.