Osteoclast precursors in the BM cells are enriched by culturing with M-CSF.

Freshly prepared BM cells were cultured with M-CSF (50 ng/mL) for 2, 4, or 6 days, and 10³ adherent or nonadherent cells were inoculated into each well of 24-well plates and treated with M-CSF (50 ng/mL) and RANKL (25 ng/mL). After a further 6 days of culturing, the number of TRAP⁺-MNCs was counted. Bars indicate means ± SD of triplicate cultures. The results obtained with adherent (▪) and nonadherent (■) cells were significantly different on each day of culturing (adherent versus nonadherent cells on days 2, 4, and 6,P < .01; day 2 versus 4 and 6, day 4 versus 6 for both adherent and nonadherent cells, P < .01).