IFN-γ dominantly inhibits receptor-activator of NFκB ligand (RANKL)-mediated osteoclastogenesis. (a) RAW cells received the indicated cytokine treatments of IFN-γ (10 ng/ml) and/or RANKL (200 ng/ml). Cells were stained for the osteoclast marker tartrate-resistant acid phosphatase (TRAP) on day 5 and osteoclast numbers were counted; a 1× micrograph of a representative well is shown above its corresponding column. TRAP positivity and osteoclast formation are seen only in the absence of IFN-γ. (b)-(e) Micrographs (10×) of the same groups show that IFN-γ stimulates a stellate morphology and inhibits osteoclastogenesis. All panels represent continuous cytokine treatment, except for the IFN-γ washout group (e). OC, osteoclast.