Japanese encephalitis virus infection modulates the expression of suppressors of cytokine signaling (SOCS) in macrophages: implications for the hosts' innate immune response

Abstract

Viruses have evolved various mechanisms to subvert the host's immune system and one of them is preventing the infected cells from sending out chemotactic signals to activate the adaptive immune response. Japanese encephalitis virus (JEV) is a neuropathologic flavivirus that is responsible for significant number of child mortalities in various parts of South-East Asia. In this study we show that JEV modulates suppressors of cytokine signaling (SOCS)1 and 3 expression in macrophages to bring about changes in the JAK-STAT signaling cascade, so as to inhibit proinflammatory cyto/chemokine release. Using real time PCR, immunoblotting and immunofluorescent staining, we show that the expression of type 1 interferons and intracellular expression of viral genes are also affected over time. Also, following the initial activation of SOCS1 and 3, there is production of interferon-inducible anti-viral proteins in the cells which may be responsible for inhibiting viral replication. However, even at later time points, viral genes were still detected from the macrophages, albeit at lesser quantities, than earlier time points, indicative of intracellular persistence of the virus in a latent form. On knocking down SOCS1 and SOCS3 we found a significant decrease in viral gene expression at an early time point, indicating the dysregulation of the signaling cascade leading to increased production of interferon-inducible anti-viral proteins. Taken together, our study provides an insight into the role of JEV infection in modulating the JAK-STAT pathway with the help of SOCS leading to the generation of an antiviral innate immune response.

Keywords: 2′-5′-oligoadenylate synthetase-like; ABCE1; ATP-binding cassette, sub-family E protein; Flavivirus; IFIT1; IFNα; IFNβ; IRF; JAK; JEV; Japanese encephalitis virus; NFκB; OASL; PKR; PMΦ; SMΦ; SOCS; STAT; Suppressors of cytokine signaling; Type-1 interferons; interferon alpha; interferon beta; interferon regulatory transcription factor; interferon-induced protein with tetratricopeptide repeats 1; janus kinase; nuclear factor kappa B; peritoneal macrophage; protein kinase R; qRT-PCR; quantitative real time polymerase chain reaction; signal transducers and activators of transcription; splenic macrophage; suppressors of cytokine signaling.