Inhibition of IL-23-induced osteoclastogenesis by osteoprotegerin, anti-IL-17 antibody, and etanercept. Peripheral blood mononuclear cells (PBMC) were cultured during the first 3 days with macrophage-colony stimulating factor (M-CSF) and recombinant human (rh)IL-23 (1.0 ng/ml) (c). At the same time, osteoprotegerin (OPG, 250 ng/ml) (d), anti-IL-17 antibody (5 μg/ml) (e), or etanercept (0.01 μg/ml) (f) was added with rhIL-23 (1.0 ng/ml). Adherent cells were cultured with M-CSF alone during the last 7 days (days 4 to 10 (c–f)). As controls, PBMC were cultured with M-CSF alone during the first 3 days, after which adherent cells were cultured with M-CSF only (a) (negative control) or with soluble receptor activator of NF-κB ligand (sRANKL; 100 ng/ml) (b) (positive control). Osteoclasts were detected by immunohistological staining for vitronectin receptor αvβ3 (CD51/61). Original magnification ×100.