Formation of human osteoclasts from PBMC induced by rhIL-23 (1.0 ng/ml) and M-CSF. As negative and positive controls, peripheral blood mononuclear cells (PBMC) were cultured with macrophage-colony stimulating factor (M-CSF) alone during the first 3 days; as a negative control, adherent cells were then cultured with only M-CSF (a), and as a positive control they were cultured with M-CSF plus soluble receptor activator of NF-κB ligand (sRANKL; 100 ng/ml) (b) for the last 7 days. Human osteoclasts induced from PBMC by recombinant human (rh)IL-23 (1.0 ng/ml) and M-CSF were detected by staining with tartrate-resistant acid phosphatase (TRAP) (c) and immunohistological staining by vitronectin receptor αvβ3 (CD51/61) (d). (e) Osteoclasts induced from PBMC by rhIL-23 (1.0 ng/ml) were also evaluated functionally by pit formation on Osteologic®. Original magnification ×100.