Jak1 knock-down protected BMMs from the IFN-β-mediated inhibition of osteoclastogenesis. (A) BMMs were first infected with viruses harboring empty vector (pSuper) or Jak1 siRNA construct (pSuper-Jak1siRNA). After 24 hours, cells were stimulated with RANKL (100 ng/mL) to induce OC differentiation in the presence or absence of IFN-β. (B) At 1 day after Jak1 siRNA viral infection, total-cell lysates were examined for Jak1 expression by Western blotting. (C) At the end of culture, cells were stained for TRAP activity. MR represents M-CSF plus RANKL. IFN-β was used at 10 U/mL. Results are representative of at least 3 experiments with similar results. (D) OC numbers in experiments using varying concentrations of IFN-β were counted. Data are means (± SD) from 3 random fields in representative experiment. Asterisks represent statistical difference between the values obtained from cells cultured in the presence or absence of IFN-β with M-CSF and RANKL (*P < .05; **P < .01). Daggers represent significant difference between pSuper- and pSuper-Jak1siRNA–infected cells at the same IFN-β concentration (†P < .05; ‡P < .01).