C3-deficient BM cells produce decreased amounts of M-CSF and failed to up-regulate RANKL during differentiation. (A) M-CSF levels were measured by ELISA in WT and C3^−/− BM cell-conditioned media during differentiation. (B) RANKL/OPG expression levels were quantified by qRT-PCR in WT and C3^−/− BM cells after 1,25(OH)₂ vitamin D₃ (VD) stimulation. Results are representative from 2 independent experiments performed in triplicates. Data are mean ± SD: *P < .05.