Cellular Mechanism for Impaired Hepatitis C Virus Clearance by Interferon Associated with IFNL3 Gene Polymorphisms Relates to Intrahepatic Interferon-λ Expression

The single nucleotide polymorphism located within the IFNL3 (also known as IL28B) promoter is one of the host factors associated with hepatitis C virus (HCV) clearance by interferon (IFN)-alpha therapy; however the mechanism remains unknown. We investigated how IL28B gene polymorphism influences HCV clearance with infected primary human hepatocytes, liver biopsies, and hepatoma cell lines. Our study confirms that the rs12979860-T/T genotype has a strong correlation with ss469415590-Delta G/Delta G single nucleotide polymorphism that produces IFN-lambda 4 protein. We found that IFN-alpha and IFN-lambda 1 antiviral activity against HCV was impaired in IL28B T/T infected hepatocytes compared with C/C genotype. Western blot analysis showed that IL28B TT genotype hepatocytes expressed higher levels of IFN-lambda proteins (IL28B, IL-29), preactivated IFN-stimulated gene (ISG) expression, and impaired Stat phosphory when stimulated with either IFN-alpha or IFN-lambda 1. Furthermore, we showed that silencing IFN-lambda 1 in T/T cell line reduced basal ISG expression and improved antiviral activity. Likewise, overexpression of IFN-lambda (1 to 4) in C/C cells induced basal ISG expression and prevented IFN-alpha antiviral activity. We showed that IFN-lambda 4, produced at low level only in T/T cells induced expression of IL28B and IL-29 and prevented IFN-alpha antiviral activity in HCV cell culture. Our results suggest that IFN-lambda 4 protein expression associated with the IL28B-T/T variant preactivates the Janus kinase-Stat signaling, leading to impaired HCV clearance by both IFN-alpha and IFN-lambda.