Murine Ifit3 restricts West Nile virus infection and pathogenesis

Abstract The host interferon (IFN) response is the first line of defense for mammalian cells against invading pathogens. Among the most upregulated IFN-stimulated genes are members of the IFN-induced protein with tetratricopeptide repeats (IFIT) family of proteins. IFITs play a critical role in the host antiviral response by distinguishing between ‘self’ and ‘non-self’ RNA. Recent findings demonstrate that human IFIT3 binding to IFIT1 alters the viral RNA binding specificity of IFIT1. Uniquely, mice encode two copies of the Ifit3 gene, Ifit3a and Ifit3b, that differ by only five amino acids. To determine the function of mouse Ifit3 and to gain further understanding of the role of IFIT3 in antiviral immunity, we used CRISPR/Cas9 gene editing to generate Ifit3a/b DKO mice. Our results demonstrate that Ifit3 is important for survival of infection with West Nile virus (WNV, strain NY99). Whereas approximately 65% of WT C5BL/6J mice survive infection with WNV-NY99, Ifit3a/b DKO mice were more susceptible with only 20% of animals surviving infection. Virological analysis of lymphoid and CNS tissues revealed that Ifit3a/b DKO mice have increased viral loads in the brain, spinal cord, and liver compared to WT animals, and gene expression analysis of WT animals corroborated that Ifit3a and Ifit3b are highly induced in these tissues during infection. Detailed immunological analysis of Ifit3a/b DKO animals did not show a loss in the ability to generate WNV-specific antibodies, but did reveal a significant decrease in the number of CD8+ T cells in the spleen and a delayed CD8+ T cell response in the spinal cord. Altogether, our data suggest that Ifit3 restricts WNV infection and pathogenesis in distinct anatomic locations, most notably in specific regions of the CNS.