Acquisition of higher T-cell stimulating activities by Daf^−/− macrophages and DCs in vivo requires C3 and C5aR. (A) Thioglycollate-elicited peritoneal macrophages from Daf^−/− mice, but not Daf^−/−/C3^−/− or Daf^−/−/C5aR^−/− mice, were more potent than similarly harvested WT macrophages in stimulating OT-II CD4⁺ T cells as measured by IFN-γ production. *P < .05 comparing with the Daf^−/− group. (B) Splenic DCs from LPS-treated Daf^−/− mice, but not similarly treated Daf^−/−/C3^−/− or Daf^−/−/C5aR^−/− mice or Daf^−/− mice pre-treated with a C5aR antagonist (C5a-ant in vivo), were more potent than WT mouse DCs in stimulating OT-II CD4⁺ T cells as measured by IFN-γ production. *P < .05 comparing with the Daf^−/− group. In contrast, addition of the C5aR antagonist to the cell culture of Daf^−/− DCs and OT-II CD4⁺ T cells (C5a-ant in vitro) had no effect. NS indicates not significant. P > .05 comparing with the Daf^−/− group.