Hepatitis C virus (HCV) infection is the most common blood borne infection in the U.S. with estimates of 4 million HCV-infected individuals in the U.S. and 170 million worldwide1. The majority (70%–80%) of HCV infections persist and about 30% of individuals with persistent infection develop chronic liver disease, including cirrhosis and hepatocellular carcinoma2. Epidemiological, viral, and host factors have been associated with the differences in HCV clearance or persistence and studies have demonstrated that a strong host immune response against HCV favors viral clearance3,4. Thus, variation in genes involved in the immune response may contribute to the ability to clear the virus. In a recent genome-wide association study, a single nucleotide polymorphism (rs12979860) 3kb upstream of the IL28B gene, which encodes the type III interferon IFN-λ3, was shown to associate strongly with more than a 2-fold difference in response to HCV drug treatment5. To determine the potential effect of rs12979860 variation on outcome to HCV infection in a natural history setting, we genotyped this variant in HCV cohorts comprised of individuals who spontaneously cleared the virus (N = 388) or had persistent infection (N = 620). We show that the C/C genotype strongly enhances resolution of HCV infection amongst individuals of both European and African ancestry (European: OR = 0.38, p = 10−7; African: OR = 0.32, p = 10−4; combined: OR = 0.33, p <10−12). To date, this is the strongest and most significant genetic effect associated with natural clearance of HCV, and these results implicate a primary role for IL28B in resolution of HCV infection.

Natural killer (NK) cells provide a central defense against viral infection by using inhibitory and activation receptors for major histocompatibility complex class I molecules as a means of controlling their activity. We show that genes encoding the inhibitory NK cell receptor KIR2DL3 and its human leukocyte antigen C group 1 (HLA-C1) ligand directly influence resolution of hepatitis C virus (HCV) infection. This effect was observed in Caucasians and African Americans with expected low infectious doses of HCV but not in those with high-dose exposure, in whom the innate immune response is likely overwhelmed. The data strongly suggest that inhibitory NK cell interactions are important in determining antiviral immunity and that diminished inhibitory responses confer protection against HCV.