Noncytolytic Clearance of Sindbis Virus Infection from Neurons by Gamma Interferon Is Dependent on Jak/Stat Signaling

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Abstract
The alphavirus Sindbis virus (SINV) causes encephalomyelitis in mice by infecting neurons of the brain and spinal cord. The outcome is age dependent. Young animals develop fatal disease, while older animals recover from infection. Recovery requires noncytolytic clearance of SINV from neurons, and gamma interferon (IFN-γ) is an important contributor to clearance in vivo. IFN-γ-dependent clearance has been studied using immortalized CSM14.1 rat neuronal cells that can be differentiated in vitro. Previous studies have shown that differentiated, but not undifferentiated, cells develop prolonged SINV replication and respond to IFN-γ treatment with noncytolytic clearance of virus preceded by suppression of genomic viral RNA synthesis and reactivation of cellular protein synthesis. To determine the signaling mechanisms responsible for clearance, the responses of SINV-infected differentiated neurons to IFN-γ were examined. IFN-γ treatment of SINV-infected differentiated CSM14.1 cells, AP-7 olfactory neuronal cells, and primary dorsal root ganglia neurons triggered prolonged Stat-1 Tyr701 phosphorylation, Stat-1 Ser727 phosphorylation, and transient Stat-5 phosphorylation. Inhibition of Jak kinase activity with Jak inhibitor I completely reversed the neuroprotective and antiviral activities of IFN-γ in differentiated cells. We conclude that activation of the Jak/Stat pathway is the primary mechanism for IFN-γ-mediated clearance of SINV infection from mature neurons.

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