The alternative pathway of complement activation primarily underlies the complement-dependent enhancement of DC function in allostimulation in vitro. Irradiated BM DCs (LPS stimulated) from C3^−/− or fB^−/− or C4^−/− mice and WT control mice (C57BL/6) were cocultured with naive alloreactive CD4 T cells (BALB/c) in T cell culture medium. (A) IFN-γ production. (B) ³H-thymidine uptake. Data are shown as mean plus or minus SEM (n = 6, for ELISA; or n = 8, for thymidine uptake). Data were analyzed by Student t test (**P < .007; ***P < .001; ns, no significant difference). A representative of 4 independent experiments is shown.