The efficiency of VSV replication in the brain, excluding the OB, was examined by quantifying infectious VSV as well as viral RNA. Early after infection, at 2 d.p.i., virus titers in brains were low (,10 4 to 10 5 pfu/g) and roughly equivalent in wt and Ifit2 2/2 mice ( Figure 4A , p.0.25). Similarly, viral RNA levels at the same Figure 3 . Ifit2 does not inhibit VSV entry and replication in olfactory bulbs. A, schematic entry route of VSV into the central nervous system of wt mice after intranasal infection, and VSV spread within brain, as reported in the literature. OB, olfactory bulbs; CX, cortex; MB, midbrain; CB, cerebellum; BS, brain stem; SC, spinal cord. B, VSV P protein in OB of VSV-infected wt, Ifit2 2/2 and IFNAR 2/2 mice at 2 d.p.i., detected by immunohistofluorescence. C, VSV RNA levels in OB of uninfected or VSV-infected wt, Ifit2 2/2 and IFNAR 2/2 mice at 1, 2 or 6 d.p.i., plotted as mean+SD on log scale; ND, none detected. D, infectious VSV titers in wt and Ifit2 2/2 OB at 2 and 6 d.p.i.; plotted as pfu/g with mean on log scale; dashed line depicts threshold of detection. In C and D, n = 4-8 mice per infected group accumulated from three independent experiments; in B, n = 2 mice from two independent experiments. All infections were 4610 2 pfu of VSV administered intranasally. Asterisks indicate statistical significance: ** p = 0.006, * p,0.05; n.s.: not significant. doi:10.1371/journal.ppat.1002712.g003 time were low and comparable between wt and Ifit2 2/2 ( Figure 4B , p.0.25). However, at the same time, levels of VSV RNA (380-fold, p,0.05) were much higher in the brains of IFNAR 2/2 mice ( Figure 4B , right panel). Later in the course of infection (6 d.p.i.), brains of wt mice accumulated only ,5-fold more infectious VSV, with occasional clearance of the virus. In contrast, we detected markedly higher VSV titers in the brains of Ifit2 2/2 mice (,350-fold higher compared to wt mice, p = 0.0009), reaching ,10 8 pfu/g ( Figure 4A ); the high virus load likely caused the pronounced lethality. Differences in viral RNA levels in brains of wt and Ifit2 2/2 mice at 6 d.p.i. correlated well with levels of infectious VSV ( Figure 4B ). To determine whether Ifit2 selectively restricts replication of VSV in particular regions of the brain, we measured viral RNA levels in cortex, midbrain, cerebellum and brain stem at 6 d.p.i. In wt mice, VSV RNA was present prominently in the cortex, midbrain and brainstem, but not in the cerebellum ( Figure 4C ), which is consistent with published results [24] . However, in Ifit2 2/2 mice, viral RNA was 200-fold or more (p,0.05) abundant in all regions of the brain examined, including the cerebellum. The increase of VSV replication in Ifit2 2/2 brains was not due to a broadened cell tropism of the virus; immunostaining for viral P protein showed exclusive localization to neurons and not other cell types, such as astrocytes ( Figure 4D ). From the above observations, we conclude that after intranasal infection by VSV, Ifit2 protects mice from neuropathogenesis by suppressing replication or spread of the virus in brain neurons.