A New Role of the Complement System: C3 Provides Protection in a Mouse Model of Lung Infection with Intracellular Chlamydia psittaci

1. C3 is deleterious during early C. psittaci lung infection, but protective in the late phase. C3^−/− and the corresponding BL/6J wild-type (WT) mice were either intranasally infected with 10⁴ IFU of C. psittaci DC15 (cps; filled symbols) or mock-infected (mock; open symbols) (Fig. 1a and b). In panel c, varying amounts of C. psitttaci (10⁴, 2000 or 200 IFU per mouse) were applied as indicated. Body weight (a), clinical score (b) and survival rates (c) were determined for up to 21 days post-infection. Depicted are the means ± SEM. * indicates significant differences (p<0.05) between infected C3^−/− as compared to the corresponding infected BL/6J WT mice, and ** or *** p<0.01 and p<0.001, respectively.