Project summary Many liver pathogens, like hepatitis C virus (HCV), have established mechanisms to subvert the host immune response and to establish persistent infection. Dissecting these mechanisms and gaining insight into factors that contribute to viral clearance versus chronicity in the liver is notoriously difficult. Access to human liver tissue is limited. The only immunocompetent animal model of HCV infection, the chimpanzee, is no longer readily available for research. However, we have recently succeeded in establishing the first immune- competent mouse model of an HCV-related virus, Norway rat hepacivirus (NrHV). Our preliminary characterization of this model revealed significant virological and immunological similarities with HCV infection in humans. This advance now opens the opportunity to interrogate hepatic antiviral immunity, host-virus interactions, viral adaptation, immune evasion strategies and pathogenesis of a hepatotropic virus at an unprecedented level. In this proposal we plan to comprehensively analyze innate and adaptive intrahepatic immune responses during hepacivirus infection in vivo and to define determinants of viral clearance. The natural host of NrHV is the rat. In immune-competent mice NrHV is cleared after several weeks of infection. Thus we plan to adapt this virus to the mouse, select for viral variants that can establish chronicity and systematically analyze mechanisms of host-adaptation and immune evasion. Through NrHV infection of the genetically diverse Collaborative Cross mouse colony at UNC, we will map the host genetic determinants of clearance and persistence. We anticipate that combined approaches of viral adaptation to the murine host and a host genetic screen will meet an important unmet need in establishing a robust model of virus-associated liver disease. Taken together, our proposed research will use a diverse and multidisciplinary approach to shed new light on hepatotropic virus infection in vivo. These insights should provide new strategies for vaccine development or treatment of virus-associated liver disease.