The effect of tacrolimus on the formation of TRAP(+) multinucleated cells. (A) TRAP staining assay showed that 60 ng/ml of RANKL and 50 ng/ml of M-CSF induced differentiation of PBMCs into TRAP (+) multinucleated cells, implicating osteoclasts (a). However, addition of tacrolimus gradually decreased the number of TRAP (+) multinucleated osteoclasts in a tacrolimus dose-dependent manner (b to d) (magnitude × 200). (B) Tacrolimus significantly suppressed number of TRAP(+) cells at 0.5 Mm and 1.0 Mm doses (*P <0.05 and †P <0.01). M-CSF, macrophage colony-stimulating factor; RANKL, receptor activator of NF-κB ligand; TRAP, tartrate-resistant acid phosphatase.