The novel Lambda-interferons IL-28A and IL-29 inhibit HCV replication in vitro and hepatic IL-28 mRNA expression is increased in HCV and CMV infection in vivo

Introduction: IL-28A and IL-29 belong to a novel group of interferons named interferon (IFN)-lambdas. Recently, we demonstrated antiviral properties for these cytokines in intestinal epithelial cells (Am J Physiol Gastrointest Liver Physiol 2005; 289:G960–8). Aims/Methods: The aim of this study was to analyze receptor expression, signal transduction and antiviral functions, particularly against hepatitis C virus (HCV) infection, mediated by IL-28A and IL-29 in hepatic cells. The mRNA expression of IL-10R2 and IL-28R1, the receptor subunits required for IL-28A and IL-29 signaling, was determined by RT-PCR in hepatic cell lines. Lambda-interferon induced signal transduction was analyzed by Western blotting using phospho-specific antibodies against STAT proteins. The activation of the antiviral proteins was analyzed by luciferase assays and Northern Blot analysis. The effect of IL-28A and IL-29 on replication of HCV was analyzed in Huh-7 cells stably expressing HCV replicons and firefly genes using luciferase assays. The IL-28A mRNA expression in HCV infected human liver biopsy samples (n=10) and control liver biopsy samples (n=19) was measured by quantitative PCR. To analyze regulation of IL-28 mRNA expression in viral infection in vivo, C57BL/6 mice were infected i.v. with one million pfu murine cytomegaly virus (MCMV) of the Smith strain for 45 hours. Murine IL-28 mRNA expression in liver tissue was measured by RT-PCR. Results: Both receptor subunits necessary for IFN-lambda signaling (IL-10R2 and IL-28R1) are expressed in the hepatic cell lines HepG2, Hep3B and Huh-7. The IL-28R receptor complex is functional resulting in increased phosphorylation of STAT-1 and STAT-3 proteins following IL-28A and IL-29 stimulation. Moreover, both cytokines activate the transcription of the antiviral proteins MxA and 2',5'-OAS. 100 ng/ml of IL-28A and IL-29 decreased HCV replication in Huh-7 cells to 1.76±0.08% and 1.38±0.20%, respectively (control 100%, IFN-alpha 10 U: 0.31±0.14%). IL-28A mRNA expression was significantly higher in liver biopsy samples of HCV patients than in samples of patients with non-viral hepatitis (36.7-fold increase; p<0.05). Similarly, murine IL-28 mRNA expression was increased 3-fold in liver tissue from MCMV infected mice compared to uninfected control mice (p=0.003). Conclusion: Hepatic IL-28 mRNA expression is elevated in human HCV and murine CMV infection and IFN-lambda mediated signaling inhibits HCV replication in vitro. These results suggest that IFN-lambda could play a role in the antiviral immune defense against HCV and may have a therapeutic potential.