IFNAR signaling of neuroectodermal cells is essential for the survival of C57BL/6 mice infected with Theiler's murine encephalomyelitis virus

Theiler's murine encephalomyelitis virus (TMEV) is a single-stranded RNA virus that causes encephalitis followed by chronic demyelination in SJL mice and spontaneous seizures in C57BL/6 mice. Since earlier studies indicated a critical role of type I interferon (IFN-I) signaling in the control of viral replication in the central nervous system (CNS), mouse strain-specific differences in pathways induced by the IFN-I receptor (IFNAR) might determine the outcome of TMEV infection. Data of RNA-seq analysis and immunohistochemistry were used to compare the gene and protein expression of IFN-I signaling pathway members between mock- and TMEV-infected SJL and C57BL/6 mice at 4, 7 and 14 days post-infection (dpi). To address the impact of IFNAR signaling in selected brain-resident cell types, conditional knockout mice with an IFNAR deficiency in cells of the neuroectodermal lineage (NesCre IFNAR ), neurons (Syn1Cre IFNAR ), astrocytes (GFAPCre IFNAR ), and microglia (Sall1Cre IFNAR ) on a C57BL/6 background were tested. PCR and an immunoassay were used to quantify TMEV RNA and cytokine and chemokine expression in their brain at 4 dpi. RNA-seq analysis revealed upregulation of most ISGs in SJL and C57BL/6 mice, but Ifi202b mRNA transcripts were only increased in SJL and Trim12a only in C57BL/6 mice. Immunohistochemistry showed minor differences in ISG expression (ISG15, OAS, PKR) between both mouse strains. While all immunocompetent Cre-negative control mice and the majority of mice with IFNAR deficiency in neurons or microglia survived until 14 dpi, lack of IFNAR expression in all cells (IFNAR ), neuroectodermal cells, or astrocytes induced lethal disease in most of the analyzed mice, which was associated with unrestricted viral replication. NesCre IFNAR mice showed more Ifnb1, Tnfa, Il6, Il10, Il12b and Ifng mRNA transcripts than Cre IFNAR mice. IFNAR mice also demonstrated increased IFN-α, IFN-β, IL1-β, IL-6, and CXCL-1 protein levels, which highly correlated with viral load. Ifi202b and Trim12a expression levels likely contribute to mouse strain-specific susceptibility to TMEV-induced CNS lesions. Restriction of viral replication is strongly dependent on IFNAR signaling of neuroectodermal cells, which also controls the expression of key pro- and anti-inflammatory cytokines during viral brain infection.