Regulation of Antiviral Responses in Plasmacytoid Dendritic Cells to Chikungunya Virus by the Gut Microbiota

Project Summary Chikungunya virus (CHIKV) is a re-emerging mosquito-transmitted alphavirus in the Togaviridae family that causes severe acute and chronic polyarthritis and affects millions of people globally. Despite the morbidity associated with CHIKV infection and the large population at risk, no approved vaccines or therapeutics are

available to prevent or treat CHIKV infection. Moreover, the acquired factors that dictate the severity of symptoms or progression from acute to chronic disease are poorly understood. Mouse models of CHIKV pathogenesis have highlighted a critical role of type I interferon (IFN) signaling in limiting viral dissemination and preventing fatal

CHIKV infection. Recently, several studies have implicated the gut microbiota in priming systemic IFN responses or modulating viral pathogenesis at sites distant from the gastrointestinal tract. Despite the growing evidence that the gut microbiota shapes antiviral responses at extra-intestinal sites, its role in influencing host immunity to

alphavirus infections has not been explored. The proposed project builds upon extensive preliminary data suggesting that the gut microbiota modulates systemic innate antiviral responses to limit CHIKV dissemination. Subcutaneous CHIKV infection of either oral antibiotic (Abx)-treated or germ-free (GF) mice results in increased viral burden in the blood and in

tissues distant from the inoculation site. This enhanced viral dissemination is due to increased viral replication in monocytes of the blood or spleen. Furthermore, upon CHIKV infection, microbiota-depleted mice demonstrate a blunted systemic type I IFN response that normally is promoted by circulating plasmacytoid dendritic cells

(pDCs). Re-colonization of either Abx-treated or GF mice with fecal microbiota transfers derived from untreated Abx-naïve controls restores type I IFN responses and decreases viral burden in the blood. Notably, the introduction of a single bacterial species (e.g., Clostridium) or its derived metabolite, the secondary bile acid

(BA), deoxycholic acid, into Abx-treated or GF mice also can restrict viral dissemination in the blood. I hypothesize that specific BA-transforming bacterial species instruct type I IFN responses in pDCs. In the absence of these microbial factors, pDCs cannot respond rapidly enough to produce IFNs and restrict

monocytes in circulation from CHIKV infection, leading to enhanced viral dissemination. Aim 1 of this proposal focuses on characterizing immune pathways by which the gut microbiota instructs pDC function in response to CHIKV infection. Aim 2 focuses on identifying the molecular components, specifically BAs, generated by

specific Clostridium species that restrict CHIKV infection of monocytes and dissemination. Together, these results will enhance our understanding of how the gut microbiota shapes the innate immune response to limit infection and pathogenesis of alphaviruses, and potentially other viruses with a tropism for monocytes.