C5a enhances TLR2- and TLR9-dependent serum IL-6 production and Th17 cell–promoting activity. (A) WT mice were treated intraperitoneally with zymosan (1 g/kg), CPG1826 (20 mg/kg), and polyI:C (15 mg/kg) alone or in combination with C5a (0.2 μg per mouse). Sera were collected after 3 hours (6 hours for polyI:C), and IL-6 levels were determined by ELISA. Values shown are the mean ± SEM, n = 3 for each group, *P < .01 by Student t test; ns indicates not statistically significant. (B) Naive mouse CD4⁺ T cells were activated by plate-bound anti-CD3/CD28 for 3 days in the presence of 5% serum from mice in panel A, and production of IFN-γ and IL-17 by the activated T cells was assessed by intracellular staining and flow cytometry. Plots are representative of 2 independent experiments.