LPS-induced osteoclast formation is dependent on TNF-α. A, levels of IL-1β and TNF-α released in the cell culture supernatant at day 8 in untreated (open area) and LPS-treated (filled bar) cultures. B and C, number of osteoclast-like cells generated in response to LPS, TNF-α, and LPS/anti-TNF-α in untreated (B) and sRANKL-primed cultures (C). **, p < 0.01 compared with untreated cells; ##, p < 0.01 compared with LPS-treated cultures; $$, p < 0.01 compared with cells pretreated with sRANKL. Error bars = S.E.