Induction of protective interferon-β responses in murine osteoblasts following infection.

Introduction: The refractory and recurrent nature of chronic staphylococcal osteomyelitis may be due, at least in part, to the ability of to invade and persist within bone-forming osteoblasts. However, osteoblasts are now recognized to respond to . infection and produce numerous immune mediators and bone regulatory factors that can shape the host response. Type I interferons (IFNs) are best known for their antiviral effects, but it is becoming apparent that they impact host susceptibility to a wide range of pathogens including . .

Methods: Here, we have assessed the local expression of IFN-β by specific capture ELISA in an established in vivo mouse model of staphylococcal osteomyelitis. RNA Tag-Seq analysis, specific capture ELISAs, and/or immunoblot analyses, were then used to assess the expression of type I IFNs and select IFN stimulated genes (ISGs) in . infected primary murine osteoblasts. The effect of IFN-β on intracellular . burden was assessed in vitro following recombinant cytokine treatment by serial colony counts of liberated bacteria.

Results: We report the presence of markedly elevated IFN-β levels in infected bone tissue in a mouse model of staphylococcal osteomyelitis. RNA Tag-Seq analysis of . infected osteoblasts showed enrichment of genes associated with type I IFN signaling and ISGs, and elevated expression of mRNA encoding IFN-β and ISG products. IFN-β production was confirmed with the demonstration that . induces its rapid and robust release by osteoblasts in a dose-dependent manner. Furthermore, we showed increased protein expression of the ISG products IFIT1 and IFIT3 by infected osteoblasts and demonstrate that this occurs secondary to the release of IFN-β by these cells. Finally, we have determined that exposure of . -infected osteoblasts to IFN-β markedly reduces the number of viable bacteria harbored by these cells.

Discussion: Together, these findings indicate an ability of osteoblasts to respond to bacteria by producing IFN-β that can act in an autocrine and/or paracrine manner to elicit ISG expression and mitigate . infection.