Research On Molecular Mechanism Of Blautia Coccoides Priming Host Innate Immunity Against Enteric Virus Mediated By Type ? Interferon Through Acetic Acid

Mammalian intestines are colonized by enormous number of commensal bacteria and designated as‘host second genome'and the‘biggest secretory organ'.During the million years of co-evolution with the harboring host,the commensal intestinal microbial communities have established a co-dependent and mutually restrained ecosystem that is of vital importance to host healthy status,which is now termed as‘Holoboints'.Intestinal microbiome work with host cells to maintain intestinal homeostasis and regulate host physiological functions and immune responses directly or indirectly via producing bioactive metabolites.Cumulative evidences suggest that intestinal microbes can prime host cells into an immune activated baseline to antagonize pathogenic microorganisms,especially viruses through the secretory factors and metabolites.However,the molecular mechanisms that microbiota metabolites regulate host mononuclear phagocytes-mediated type I interferon(IFN-I)antiviral innate immune responses are not fully elucidated.In order to confirm whether intestinal microbiome can activate IFN-I mediated host anti-enteric virus innate immunity,we first gavaged groups of C57BL/6J mice with the cocktail of four broad-spectrum antibiotics to establish microbiota-deficient model and subsequently infect commensal depleted mice and fecal microbiota transplanted controls with Encephalomyocarditis virus(EMCV),the results demonstrate that microbiota can indeed influence the neuropathogenesis post EMCV infection.Further studies revealed that microbiota can regulate the antiviral immune responses of natural killer cells and mononuclear phagocytes in the systemic immune system including peripheral blood mononuclear cells and the spleen.Intestinal microbes can also modulate the expression of systemic and cerebral IFN-I and interferon stimulated genes(ISGs).Additionally,we demonstrated that commensal bacteria can influence host anti-enteric virus innate immunity through mononuclear phagocytes and IFN-I signaling pathways mediated by IRF3 and IFNAR using Irf3^-/-?Ifnar^-/-and macrophage depleted mice.To further identify specific intestinal commensal bacteria that possesses modulatory functions on innate immunity,we performed 16S r RNA sequencing of fecal samples collected from conventional and microbiota depleted mice post infection.It was indicated that the alteration of bacterial composition on the genus of Blautia,Akkermanisa,lachnoclostridium and lactobacillus were closely correlated with the IFN-I level in the brain tissues of infected mice.Subsequently,we colonized the Abx-mice with Blautia coccoides and clarified that this specific bacterium can induce IFN-I expression in mononuclear phagocytes to protect animals from EMCV infection.Given the fact that Blautia is one of the fundamental commensal bacteria that produces short-chain fatty acids(SCFAs)in the colon,and the most abundant metabolite it generates is acetate.Thus,we tested whether acetate,propionate or butyrate can induce IFN-I to antagonize EMCV infection.The data indicate that mice gavaged with acetate or propionate for 3 weeks can significantly reduce the mortality of EMCV inoculation whereas butyrate oral gavage failed to provide protective effect.In addition,bone marrow-derived macrophages(BMDMs)treated with acetate exhibited remarkably upregulated IFN-I and ISGs transcripts following EMCV infection and RAW264.7 cells pretreated with acetate or propionate can greatly prohibit EMCV replication.Collectively,these data indicated that acetate and propionate can inhibit EMCV infection in mononuclear phagocytes and this effect directly correlate with the expression of IFN-I.Taken together,we utilized an enteric virus,EMCV to inoculate PBS-treated or antibiotic cocktail-administrated mice(Abx)orally or intraperitoneally to examine the impact of microbiota depletion on virulence and viral replication in vivo.Microbiota depletion exacerbated the mortality,neuropathogenesis,viremia and viral burden in brain following EMCV infection.Furthermore,Abx-treated mice exhibited severely diminished macrophage activation and impaired type I IFN production and ISG expression in PBMC,spleen or brain.With the help of fecal bacterial 16S r RNA sequencing of PBS and Abx mice,we identified a single commensal bacterium B.coccoides that can restore macrophage-and IFNAR-dependent type I IFN responses to restrict systemic enteric virus infection.These findings may provide insight into the development of novel therapeutics in preventing enteric virus infection or possibly,alleviates the clinical diseases by activating host systemic innate immune responses via respective probiotic treatment using B.coccoides.