Osteoclast formation is suppressed by IL-10. RAW264.7 cells were incubated with RANKL or RANKL plus IL-10 for 5 days. All cytokine concentrations were 50 ng/ml. Cells were fixed and stained for TRAP and the number of TRAP-positive mono and multinuclear osteoclasts quantified. Results are expressed as the mean ± SEM for each group from three separate experiments. IL-10 significantly suppressed osteoclast formation. * p < 0.05 versus control, ** p < 0.05 versus RANKL-treated group.