Double-stranded RNA (dsRNA) and its mimic, polyinosinic acid:polycytidylic acid [poly(I):poly(C)], are recognized by toll-like receptor 3 (TLR3) that induces the production of IFN-β in many cell types. In the present study, we investigated the effects of poly(I):poly(C) on mouse osteoblastic MC3T3-E1 (E1) cells. Poly(I):poly(C) markedly increased IFN-β mRNA level in a dose-dependent manner. The increase in the IFN-β mRNA level was apparent as early as 1 h after adding poly(I):poly(C) to the culture and peaked at 12 h. Stimulation with poly(I):poly(C) enhanced the expression of CXCL10 mRNA and TLR3 in E1 cells. Moreover, poly(I):poly(C) induced tyrosine phosphorylation of the transcription factor STAT1 in E1 cells. An anti-IFN-β neutralizing antibody partially inhibited poly(I):poly(C)-induced CXCL10 mRNA, TLR3 mRNA and STAT1 phosphorylation. These results indicate that osteoblasts secrete IFN-β in response to viral infection and that endogenous IFN-β induces both CXCL10 and TLR3 production via an IFN-α/β receptor-STAT1 pathway. It is suggested that osteoblasts are involved in host defense as well as bone metabolism.

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