Wear particle-induced inflammatory osteolysis is the primary cause of aseptic loosening, which is the most common reason for total hip arthroplasty (THA) failure in the med- and long term. Recent studies have suggested an important role of gut microbiota (GM) in modulating the host metabolism and immune system, leading to alterations in bone mass. Probiotic bacteria administered in adequate amounts can alter the composition of GM and confer health benefits to the host. Given the inflammatory osteolysis that occurs in wear debris-induced prosthesis loosening, we examined whether the probiotic Lactobacillus casei could reduce osteolysis in a mouse calvarial resorption model. In this study, L. casei markedly protected mice from CoCrMo particles (CoPs)-induced osteolysis. Osteoclast gene markers and the number of osteoclasts were significantly decreased in L. casei -treated mice. Probiotic treatment decreased the M1-like macrophage phenotype indicated by downregulation of tumor necrosis factor α (TNF-α), interleukin (IL)-6 and inducible nitric oxide synthase (iNOS) and increased the M2-like macrophage phenotype indicated by upregulation of IL-4, IL-10 and arginase. Collectively, these results indicated that the L. casei treatment modulated the immune status and suppressed wear particle-induced osteolysis in vivo. Thus, probiotic treatment may represent a potential preventive and therapeutic approach to reduced wear debris-induced osteolysis.

Induction of type I IFNs during viral infection is crucial for host defense. IRF 3 and IRF7 play a critical role as key transcription factors in the activation of the IFN induction. Viruses have evolved a variety of strategies to evade innate immunity. Our previous studies have shown that the nonstructural protein (NSs) of the severe fever with thrombocytopenia syndrome virus (SFTSV) can suppress the IFN-β induction through its interaction with tank-binding kinase-1 and sequestering the inhibitor of nuclear factor kappa B kinase(IKK) complex into the inclusion bodies formed by NSs. In this study, we characterized the unique function of IRF7 in innate immunity and its role in inducing IFN-α in particular, regulated by NSs during the SFTSV infection in several cell types of human origin. Whereas IRF3 is constitutively expressed, IRF7 was significantly induced differentially in various cell types in response to SFTSV infection, promoted the induction of IFN-α2 and -α4, and further induced IFN-β, thus contributing to suppressing the viral replication. Our data indicate that NSs directly interacted with and sequestered IRF7 into the inclusion bodies, which is different from IRF3 indirectly interacting with NSs. Although interaction of NSs with IRF7 did not inhibit IRF7 phosphorylation, p-IRF7 was trapped in the inclusion bodies, resulting in a significant reduction of the IFN-α2 and -α4 induction and therefore enhanced viral replication. Interaction of the viral NSs with both IRF7 and IRF3 and subsequent sequestration of these transcription factors into viral inclusion bodies, a unique strategy used by this phlebovirus, may ensure effective evasion and suppression of host innate immunity.