Coronaviruses and Arteriviruses

This chapter summarizes the interactions of coronaviruses and arteriviruses with the innate immune response, including the type I interferon (IFN) system; and the strategies employed by these viruses to evade or inhibit the antiviral IFN response. Coronaviruses and arteriviruses are a group of enveloped animal RNA viruses that are united in the order Nidovirales. Very little is known about the inhibition of the type I IFN pathway by arteriviruses, while significant advances have been made, primarily using MHV and SARS-CoV, toward understanding how coronaviruses evade type I IFN induction and the type I IFN signaling pathway. Devaraj et al. showed that the papain-like protease (PLpro) domain of the SARS-CoV replicase protein, nsp3, one of the gene 1 proteins, is an IFN antagonist. In this report, using a plasmid-based expression system, the authors showed that PLpro interacts with IRF3 and inhibits its phosphorylation and nuclear translocation, thereby affecting the downstream activation of the type I IFN gene. Some studies have shown that coronaviruses employ posttranscriptional strategies to suppression general host gene expression in infected cells. The availability of transgenic and other valuable natural mouse models for MHV, SARS-CoV, and HCoV-229E enables researchers to investigate the role of nonstructural and accessory proteins in virulence and pathogenesis. Using such systems, the potential identification of some common, evolutionarily conserved molecular mechanisms of immune evasion among different groups of coronaviruses is an exciting possibility in the future.