PMA inhibits the suppressive effect of IL-10 on osteoclast formation. RAW264.7 cells were incubated with RANKL, IL-10 or PMA for 3 days. Cultures were washed to remove PMA and then incubated for a further two days with RANKL or RANKL + IL-10. Cells were fixed and stained for TRAP and the number of TRAP-positive mono and multinuclear osteoclasts quantified. IL-10 suppressed the number of TRAP positive cells and this was prevented by PMA. Results are expressed as the mean ± SEM for each group from three separate experiments n = 9. * p < 0.05 versus all other groups.