Simian varicella virus inhibits the interferon gamma signalling pathway

The alphaherpesvirus simian varicella virus (SVV) causes varicella and zoster in nonhuman primates. Herpesviruses evolved elaborate mechanisms to escape host immunity, but the immune evasion strategies employed by SVV remain ill-defined. We analysed whether SVV impairs the cellular response to key antiviral cytokine interferon-γ (IFNγ). SVV infection inhibited the expression of IFNγ-induced genes like C-X-C motif chemokine 10 and interferon regulatory factor 1. Phosphorylation and nuclear translocation of the signal transducer and activator of transcription 1 (STAT1) was blocked in SVV-infected cells, which did not involve cellular and viral phosphatases. SVV infection did not downregulate IFNγ receptor α and β chain expression on the cell surface. Instead, STAT1, Janus tyrosine kinases 1 (JAK1) and JAK2 protein levels were significantly decreased in SVV-infected cells. Collectively, these results demonstrate that SVV targets three proteins in the IFNγ signal transduction pathway to escape the antiviral effects of IFNγ.