Host Factors Controlling Neuroinvasive Flavivirus Pathogenesis

ABSTRACT Flaviviruses such as Powassan virus (POWV), West Nile virus (WNV), and Japanese encephalitis virus (JEV) are transmitted by ticks and mosquitoes. The outcomes of flavivirus infection are heterogeneous, with only a subset progressing to neuroinvasive disease (e.g. encephalitis, meningitis, or paralysis). We hypothesize that host genetic variation, particularly in antiviral response genes, contributes to differential disease outcome following flavivirus infection. The Collaborative Cross (CC) panel of recombinant inbred mice provides an ideal system to discover novel mechanisms of immune-mediated control of flavivirus pathogenesis because these mice exhibit an expanded range of immune phenotypes on reproducible genetic backgrounds. We infected 17 CC lines with POWV and identified multiple highly susceptible lines, including CC071 and CC015, and a single resistant line, CC045. Most phenotypes were concordant among POWV, WNV, and JEV, but some lines exhibited virus-specific resistance, implying that there are both virus-specific and pan-flavivirus mechanisms that control resistance to neuroinvasive flaviviruses. We propose to use the CC to determine the viral and immunologic features of POWV pathogenesis and to identify host genes that contribute to POWV resistance. Aim 1: Define viral and immunologic features of POWV pathogenesis in CC mice. We found that CC045 mice exhibited equivalent viremia but lower brain viral loads compared to CC071 mice, suggesting that POWV resistance may result from reduced neuroinvasion. We will assess brain viral loads and infiltrating leukocytes in susceptible and resistant CC lines following POWV infection. We will assess blood-brain barrier permeability at baseline and in response to viral infection and inflammatory stimuli. We will generate primary cells from susceptible and resistant CC lines and measure replication of POWV and other flaviviruses. Aim 2: Map quantitative trait loci and evaluate antiviral activity of host factors associated with POWV resistance. To identify polymorphic host genes that determine the outcome of POWV infection, we generated two F2 crosses of susceptible and resistant lines (CC071 x CC045 and CC015 x CC045) and evaluated lethality in ~300 F2 mice per cross following POWV infection, as well as CNS viral loads in ~120 F2 mice. We will map QTL associated with POWV resistance in both crosses and investigate candidate genes under significant QTL. Aim 3: Distinguish pan-flavivirus and virus-specific restriction factors in CC mice. We will infect additional CC lines with JEV to identify lines that are differentially resistant to JEV compared to POWV or WNV. We will evaluate brain viral loads and infiltrating leukocytes following JEV infection. We will generate F2 progeny of susceptible and resistant lines and map QTL associated with JEV resistance. The proposed studies will provide insight into the pathogenic mechanisms of POWV and reveal polymorphic host immune mechanisms that impact susceptibility to flavivirus neuroinvasive disease. This work will provide the foundation for future investigations of novel immune factors that control flavivirus pathogenesis.