Innate Immune Mechanisms Controlling Flavivirus Neurovirulence

Summary West Nile virus is a pathogen of global concern. Since its introduction to the US in 1999, it has caused thousands of deaths and tens of thousands of hospitalizations. West Nile virus is transmitted to humans by the bite of infected mosquitos; the virus mediates a febrile illness and can progress to invasive infection of the central nervous system causing severe encephalopathy. WNV neuroinvasive disease also causes cognitive and motor sequelae that can last for months or years after the virus is cleared. In order to successfully treat these symptoms, gaining a clearer understanding of the immune response to WNV and the factors that determine the initiation and severity of neuroinvasive disease is critical. There is incomplete understanding of what virus and host determinants control or mediate WNV neuroinvasion, how the immune response to WNV within the CNS is initiated and regulated, and how the acute response to WNV influences long-term inflammatory sequelae of WNV encephalitis. The goal of the proposed studies is to address these knowledge gaps by gaining a molecular understanding of WNV neuroinvasion, CNS immunity, and inflammatory sequelae. We will do this by deploying newly-developed unique mouse models, recombinant forms of WNV, and an array of single-cell and spatial transcriptomic and epigenomic methods. First, we will define the cells that initiate the immune response to WNV in the periphery, and the targets of the cytokines produced by this response that control WNV neuroinvasion. Second, we will define the signaling circuits by which WNV initiates and propagates inflammatory responses within the CNS. Third and finally, we will use a recombinant WNV strain expressing Cre recombinase to mark CNS cells that survive WNV infection and assess their contribution to persistent inflammatory sequelae that persist after WNV clearance. New understanding gained from the proposed studies will significantly advance our understanding of the determinants and consequences of WNV neuroinvasive disease, and will inform ongoing efforts to mitigate and ameliorate these consequences in human patients.