Hepatitis C virus (HCV) can initiate infection by cell-free particle and cell-cell contact-dependent transmission. In this study we use a novel infectious coculture system to examine these alternative modes of infection. Cell-to-cell transmission is relatively resistant to anti-HCV glycoprotein monoclonal antibodies and polyclonal immunoglobulin isolated from infected individuals, providing an effective strategy for escaping host humoral immune responses. Chimeric viruses expressing the structural proteins representing the seven major HCV genotypes demonstrate neutralizing antibody-resistant cell-to-cell transmission. HCV entry is a multistep process involving numerous receptors. In this study we demonstrate that, in contrast to earlier reports, CD81 and the tight-junction components claudin-1 and occludin are all essential for both cell-free and cell-to-cell viral transmission. However, scavenger receptor BI (SR-BI) has a more prominent role in cell-to-cell transmission of the virus, with SR-BI-specific antibodies and small-molecule inhibitors showing preferential inhibition of this infection route. These observations highlight the importance of targeting host cell receptors, in particular SR-BI, to control viral infection and spread in the liver. Hepatitis C virus (HCV) establishes chronic infection in 3%of the world's population, resulting in a progressive liver disease that is one of the leading indications for liver transplantation. HCV has evolved several immune evasion strategies in order to persist within the infected host (15,20,40), including genetic escape from humoral immune responses (25,46). However, functional constraints may restrict antigenic change in some regions of the virally encoded E1E2 envelope glycoproteins, such as the CD81 receptor binding site (9,11,33). The observation that glycoprotein-specific antibodies from chronically infected subjects neutralize the infectivity of laboratory prototype HCV strains yet demonstrate a limited ability to control HCV replication in vivo (40) suggest that additional means of evading antibody responses may exist.How virus particles disseminate within an immune-competent host has been a relatively neglected area of study; however, it is becoming increasingly clear that viruses employ multiple strategies to infect new target cells. Diffusion through the pericellular environment or the vascular circulation introduces a rate-limiting step in virus entry and exposes particles to the humoral immune system. Consequently, a number of viruses have evolved direct cell-to-cell modes of transmission that maximize particle delivery, often in a neutralizing antibody (nAb)-resistant manner (reviewed in reference 30).We (44) and others (48) previously reported that HCV strain JFH-1 could be transmitted via cell-free and cell-to-cell routes in vitro. We extend these observations and show that disruption of HCV particle assembly or physical separation of target and producer cells ablates transmission, demonstrating that intact virions are transferred via cell-cell conta...

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Chronic hepatitis C virus (HCV) infection is a major cause of liver disease worldwide.Restriction of HCV infection to human hepatocytes suggests that liver-specific host factors play a role in the viral life cycle. Using a yeast-two-hybrid system, we identified apolipoprotein E (apoE) as a liver-derived host factor specifically interacting with HCV nonstructural protein 5A (NS5A) but not with other viral proteins. The relevance of apoE-NS5A interaction for viral infection was confirmed by co-immunoprecipitation and co-localization studies of apoE and NS5A in an infectious HCV cell culture model system. Silencing apoE expression resulted in marked inhibition of infectious particle production without affecting viral entry and replication. Analysis of particle production in liver-derived cells with silenced apoE expression showed impairment of infectious particle assembly and release. The functional relevance of the apoE-NS5A interaction for production of viral particles was supported by loss or decrease of apoE-NS5A binding in assembly-defective viral mutants. H epatitis C virus (HCV) is a major cause of liver disease, including liver cirrhosis and hepatocellular carcinoma. 1 Current treatment by interferon-alpha and ribavirin is limited by resistance, toxicity, and high costs. 1,2 Novel treatment approaches are therefore urgently needed. HCV is an enveloped single-stranded RNA virus of positive polarity that is a member of the genus Hepacivirus within the family Flaviviridae. 3,4 The HCV RNA genome encodes a unique polyprotein of approximately 3000 amino acids and is flanked at its 5Ј and 3Ј ends by two highly conserved untranslated regions involved in the transla- Conclusion: These results suggest that recruitment of apoE by NS5A is important for viral assembly and release of infectious viral particles. These findings have important implications