HIV pseudotypes bearing native hepatitis C virus (HCV) glycoproteins (strain H and Con1) are infectious for the human hepatoma cell lines Huh-7 and PLC͞PR5. Infectivity depends on coexpression of both E1 and E2 glycoproteins, is pH-dependent, and can be neutralized by mAbs mapping to amino acids 412-447 within E2. Cell-surface expression of one or all of the candidate receptor molecules (CD81, low-density lipoprotein receptor, scavenger receptor class B type 1, and dendritic cell-specific intercellular adhesion molecule 3 grabbing nonintegrin) failed to confer permissivity to HIV-HCV pseudotype infection. However, HIV-HCV pseudotype infectivity was inhibited by a recombinant soluble form of CD81 and a mAb specific for CD81, suggesting that CD81 may be a component of a receptor complex. Hepatitis C virus (HCV) is an enveloped, positive-stranded RNA virus classified in the family Flaviviridae. Infection is often associated with chronic disease, sometimes resulting in cirrhosis and hepatocellular carcinoma. The principal site of replication is thought to be the liver, although several laboratories have suggested that HCV may infect a wider range of cell types including monocytes͞macrophages and B cells (1, 2).HCV encodes two putative envelope glycoproteins (gps), E1 and E2, which are believed to be type I integral transmembrane proteins. In vitro expression studies have shown that both gps associate to form heterodimers, which accumulate in the endoplasmic reticulum (ER), the proposed site for HCV assembly and budding (reviewed in ref.3). The lack of in vitro systems for HCV propagation has hampered biological and physiochemical studies on the virion and its mechanism(s) of cell entry, and the cellular receptors remain unknown. HCV purified from plasma has been reported to exist in association with plasma lipoproteins, suggesting that the virus may use the low-density lipoprotein receptor (LDLR) to gain entry into cells (4-6).The selective association of a virus with a target cell is usually determined by an interaction between the viral gps and specific cell-surface receptor(s) and is an essential step in the initiation of infection. Such interaction(s) often define the host range and cellular or tissue tropism of a virus and have a role in determining virus pathogenicity. In the absence of native HCV particles, truncated version(s) of the E2 gp (7, 8), E1E2 gp-liposomes (9), and virus-like particles expressed in insect cell systems (10, 11) have been used as mimics to study virus-cell interactions. Truncated soluble versions of E2 have been reported to bind specifically to human cells and were used to identify interactions with CD81 (7, 8), scavenger receptor class B type 1 (SR-B1) (12), and dendritic cell-specific intercellular adhesion molecule 3 grabbing nonintegrin (DC-SIGN) (13,14). One limitation with these studies is that they measure only HCV gp-cell attachment and not virus-mediated cell fusion. To overcome the lack of a conventional cell culture system for the propagation of infectious HCV particles, ps...

Little is known about the role of Abs in determining the outcome of hepatitis C virus (HCV) infection. By using infectious retroviral pseudotypes bearing HCV glycoproteins, we measured neutralizing Ab (nAb) responses during acute and chronic HCV infection. In seven acutely infected health care workers, only two developed a nAb response that failed to associate with viral clearance. In contrast, the majority of chronically infected patients had nAbs. To determine the kinetics of strain-specific and crossreactive nAb emergence, we studied patient H, the source of the prototype genotype 1a H77 HCV strain. An early weak nAb response, specific for the autologous virus, was detected at seroconversion. However, neutralization of heterologous viruses was detected only between 33 and 111 weeks of infection. We also examined the development of nAbs in 10 chimpanzees infected with H77 clonal virus. No nAb responses were detected in three animals that cleared virus, whereas strain-specific nAbs were detected in six of the seven chronically infected animals after Ϸ50 weeks of infection. The delayed appearance of high titer crossreactive nAbs in chronically infected patients suggests that selective mechanism(s) may operate to prevent the appearance of these Abs during acute infection. The long-term persistence of these nAbs in chronically infected patients may regulate viral replication.