Activation of endogenous type I IFN signaling contributes to persistent HCV infection.

HCV infection is a major world health problem, leading to both end-stage liver disease and primary liver cancer. Great efforts have been made in developing new therapies for HCV infection; however, combination therapy with pegylated IFN-α and ribavirin (pegIFN-RBV) remains the first choice of treatment for chronic HCV infection in most countries. The treatment response to pegIFN-RBV remains relatively low. Understanding the molecular mechanisms of persistent HCV infection and pegIFN-RBV resistance will suggest ways of improving the current standard of care and offers new antiviral therapies for both HCV and other viral infections. Recent data suggest that increased expression of hepatic IFN-stimulated genes (ISGs) before treatment is associated with treatment nonresponse in patients chronically infected with HCV. Although ISGs are generally antiviral in nature, in the case of HCV, the virus may exploit some of them to its benefit. This is not unique to HCV: Blockade of type I IFN signaling has been shown to control persistent LCMV infection. Thus, in certain viral infections, preactivation or overactivation of type I IFN signaling may contribute to viral persistence. In this review, we briefly summarize the findings from high-throughput gene expression profiling from patients chronically infected with HCV, then focus on a novel ubiquitin-like signaling pathway (ISG15/USP18) and its potential role in HCV persistence. Finally, the role of activation of endogenous type I IFN signaling in persistent HCV infection will be discussed in the context of recent studies indicating that blocking IFN signaling controls persistent LCMV infection.