Collaborative cross mice as a new model for diverse human outcomes of St. Louis encephalitis virus disease

PROJECT ABSTRACT St. Louis encephalitis virus (SLEV) is a re-emerging mosquito-borne flavivirus that causes a spectrum of manifestations in people ranging from febrile illness to encephalitis and death. Clinical disease caused by SLEV is indistinguishable from related West Nile virus (WNV). Although critical for understanding disease and evaluating countermeasures, current SLEV mouse models are limited in several ways. Prior studies used inbred or immunodeficient mice restricting assessment of the role of innate immunity, intracranial inoculation that artificially bypasses neuroinvasion, and virus strains that were serially passaged in mouse brains which artificially selects for neurovirulence. Compared to inbred or immunodeficient mice, recombinant mice better represent of human genetic diversity which can translate to similar disease to humans. Recombinant Collaborative Cross (CC) mice that were generated from a panel of 8 recombinant inbred strains represent the myriad of outcomes in people infected with the flaviviruses Zika, Powassan, and WNV. WNV-infected CC mice develop a spectrum of outcomes including asymptomatic, symptomatic with central nervous system (CNS) disease, and asymptomatic with CNS disease, where the innate immune response is the major mediator of protection from CNS disease. To circumvent limitations of existing SLEV mouse models, the goal of this project is to develop immunocompetent recombinant CC mouse models of SLEV. We hypothesize that CC mice model human SLEV including to produce clinical disease, viral tropism, and kinetics that parallel the spectrum of human SLEV outcomes, and that protection from CNS disease associates with robust innate immune responses manifest as higher expression or levels of interferon stimulated genes including the antiviral sensor RIG-I and effector cytokines including interferons (IFN)-α/β/γ. These hypotheses will be tested in two project Aims. Aim 1: Define SLEV clinical disease and viral tropism and kinetics in CC mice. We will use CC strains that manifest variable WNV outcomes and inoculate animals via the footpad with a SLEV mosquito- transmitted doses. We will assess clinical disease, infection kinetics and tropism, and viral genomic changes that associate with neuroinvasion. Aim 2: Link elevated innate immune responses to control of SLEV CNS disease in CC mice. We will measure innate responses via gene expression analyses and levels of signaling and secreted effector proteins and correlate these changes with clinical disease, virus levels in blood and target tissues, and histopathologic lesions in the brain. Augmented disease in CC mice treated with IFN- receptor blocking antibody will support IFN signaling as the mediator of protection. This project will develop new human-relevant mouse models of SLEV which can be further used to study the spectrum of pathogenesis, define virus-host interactions and host genetic determinants of susceptibility and severity, test interventions like therapeutics and candidate vaccines, and rapidly adapt to model disease for other new or re-emerging encephalitic flaviviruses.