An RNA virus, designated hepatitis G virus (HGV), was identified from the plasma of a patient with chronic hepatitis. Extension from an immunoreactive complementary DNA clone yielded the entire genome (9392 nucleotides) encoding a polyprotein of 2873 amino acids. The virus is closely related to GB virus C (GBV-C) and distantly related to hepatitis C virus, GBV-A, and GBV-B. HGV was associated with acute and chronic hepatitis. Persistent viremia was detected for up to 9 years in patients with hepatitis. The virus is transfusion-transmissible. It has a global distribution and is present within the volunteer blood donor population in the United States.

The majority of broadly neutralizing antibodies to hepatitis C virus (HCV) are against conformational epitopes on the E2 glycoprotein. Many of them recognize overlapping epitopes in a cluster, designated as antigenic domain B, that contains residues G530 and D535. To gain information on other regions that will be relevant for vaccine design, we employed yeast surface display of antibodies that bound to genotype 1a H77C E2 mutant proteins containing a substitution either at Y632A (to avoid selecting non-neutralizing antibodies) or D535A. A panel of nine human monoclonal antibodies (HMAbs) was isolated and designated as HC-84-related antibodies. Each HMAb neutralized cell culture infectious HCV (HCVcc) with genotypes 1–6 envelope proteins with varying profiles, and each inhibited E2 binding to the viral receptor CD81. Five of these antibodies neutralized representative genotypes 1–6 HCVcc. Epitope mapping identified a cluster of overlapping epitopes that included nine contact residues in two E2 regions encompassing aa418–446 and aa611–616. Effect on virus entry was measured using H77C HCV retroviral pseudoparticles, HCVpp, bearing an alanine substitution at each of the contact residues. Seven of ten mutant HCVpp showed over 90% reduction compared to wild-type HCVpp and two others showed approximately 80% reduction. Interestingly, four of these antibodies bound to a linear E2 synthetic peptide encompassing aa434–446. This region on E2 has been proposed to elicit non-neutralizing antibodies in humans that interfere with neutralizing antibodies directed at an adjacent E2 region from aa410–425. The isolation of four HC-84 HMAbs binding to the peptide, aa434–446, proves that some antibodies to this region are to highly conserved epitopes mediating broad virus neutralization. Indeed, when HCVcc were passaged in the presence of each of these antibodies, virus escape was not observed. Thus, the cluster of HC-84 epitopes, designated as antigenic domain D, is relevant for vaccine design for this highly diverse virus.

In 1967, it was reported that experimental inoculation of serum from a surgeon (G.B.) with acute hepatitis into tamarins resulted in hepatitis. In 1995, two new members of the family Flaviviridae, named GBV-A and GBV-B, were identified in tamarins that developed hepatitis following inoculation with the 11th GB passage. Neither virus infects humans, and a number of GBV-A variants were identified in wild New World monkeys that were captured. Subsequently, a related human virus was identified [named GBV-C or hepatitis G virus (HGV)], and recently a more distantly related virus (named GBV-D) was discovered in bats. Only GBV-B, a second species within the genus Hepacivirus (type species hepatitis C virus), has been shown to cause hepatitis; it causes acute hepatitis in experimentally infected tamarins. The other GB viruses have however not been assigned to a genus within the family Flaviviridae. Based on phylogenetic relationships, genome organization and pathogenic features of the GB viruses, we propose to classify GBV-A-like viruses, GBV-C and GBV-D as members of a fourth genus in the family Flaviviridae, named Pegivirus (pe, persistent; g, GB or G). We also propose renaming ‘GB’ viruses within the tentative genus Pegivirus to reflect their host origin.

The variability of the hepatitis C virus (HCV), which likely contributes to immune escape, is most pronounced in hypervariable region 1 (HVR1) of viral envelope protein 2. This domain is the target for neutralizing antibodies, and its deletion attenuates replication in vivo. Here we characterized the relevance of HVR1 for virus replication in vitro using cell culture-derived HCV. We show that HVR1 is dispensable for RNA replication. However, viruses lacking HVR1 (⌬HVR1) are less infectious, and separation by density gradients revealed that the population of ⌬HVR1 virions comprises fewer particles with low density. Strikingly, ⌬HVR1 particles with intermediate density (1.12 g/ml) are as infectious as wild-type virions, while those with low density (1.02 to 1.08 g/ml) are poorly infectious, despite quantities of RNA and core similar to those in wild-type particles. Moreover, ⌬HVR1 particles exhibited impaired fusion, a defect that was partially restored by an E1 mutation (I347L), which also rescues infectivity and which was selected during long-term culture. Finally, ⌬HVR1 particles were no longer neutralized by SR-B1-specific immunoglobulins but were more prone to neutralization and precipitation by soluble CD81, E2-specific monoclonal antibodies, and patient sera. These results suggest that HVR1 influences the biophysical properties of released viruses and that this domain is particularly important for infectivity of low-density particles. Moreover, they indicate that HVR1 obstructs the viral CD81 binding site and conserved neutralizing epitopes. These functions likely optimize virus replication, facilitate immune escape, and thus foster establishment and maintenance of a chronic infection.Hepatitis C virus (HCV) is a single-stranded positive-sense RNA virus of the family Flaviviridae that has infected an estimated 130 million people worldwide (1). Acute HCV infection is mostly asymptomatic; however, virus persistence can lead to severe liver disease, and within 20 years ca. 20% of chronically infected adults develop cirrhosis (46). In fact, morbidity associated with chronic HCV infection is the most common indication for orthotopic liver transplantation (7). The mechanisms that permit the virus to establish chronic infection in ca. 55 to 85% of cases (24) despite vigorous immune responses are incompletely understood.A number of studies have highlighted the pivotal role of strong, multispecific, and sustained T-cell responses for control of HCV infection (summarized in reference 53). Although resolution of acute HCV infection can occur in the absence of antibodies (47), mounting evidence indicates that neutralizing antibodies also contribute to protective immunity (summarized in reference 62). Nevertheless, HCV often successfully evades cellular and humoral immune pressure likely at least in part via the constant generation of variants created by an error-prone RNA replication machinery. In line with this notion, a high degree of HCV sequence evolution is associated with chronic disease, while a comparatively st...

The hepatitis C virus (HCV) genome codes for highly mannosylated envelope proteins, which are naturally retained in the endoplasmic reticulum. We found that the HCV envelope glycoprotein E2 binds the dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin (DC-SIGN) and the related liver endothelial cell lectin L-SIGN through high-mannose N-glycans. Hepatitis C virus (HCV)1 is the major causative agent of non-A, non-B hepatitis throughout the world with more than 170 million people infected (1). Contamination with infected blood by injecting drug users is the primary risk factor for acquiring HCV infection. The majority of infected patients are unable to clear the virus, and many develop chronic liver disease, cirrhosis, and hepatocellular carcinoma (2). Replication of the HCV genome could be demonstrated in vivo and in vitro in liver hepatocytes (3, 4) and hematopoietic cells including dendritic cells and B cells (5, 6). However, the molecular mechanism by which the virus targets to these sites of replication, notably in the liver, is not known.HCV is a small, enveloped, plus-strand RNA virus belonging to the family flaviviridae and genus hepacivirus. The HCV RNA genome is 9600 nucleotides in length and encodes a single polyprotein that is post-translationally cleaved into up to 10 polypeptides including three structural proteins (core, E1, and E2), located at the N terminus, and five nonstructural proteins (1,7,8). Shortly after translocation into the endoplasmic reticulum (ER), oligosaccharide transferase catalyzes addition of Glc3Man9GlcNAc2 complexes at up to 6 (E1) and 11 (E2) N-glycosylation sites (for review see Ref. 9). Glucose residues are removed by glucosidases I and II, and correctly folded proteins are released from ER chaperones calnexin and calreticulin (10 -13). The transmembrane domains of E1 and E2 are responsible for both heterodimerization (14) and retention of the glycoproteins in a high-mannose EndoH-sensitive glycoform in the ER (15)(16)(17). By analogy to other flaviviruses it is assumed that HCV capsids bud from the cytoplasm into the ER and that enveloped particles follow the secretion pathway through the Golgi. However, attempts to produce secreted HCV particles in vitro have not been successful so far (18 -20), and it is not known if E1 and E2 on mature infectious virions possess a high-mannose, complex, or mixed glycosylation.Several receptors have been proposed that could play a role in HCV entry into hepatocytes. The low density lipoprotein (LDL) receptor has been shown to mediate HCV internalization via binding to virus-associated LDL particles (21,22). A second putative HCV receptor, the tetraspanin CD81, has been identified as a high affinity binding receptor (1.8 nM) for soluble recombinant E2 from HCV genotype 1a (23, 24). CD81 and LDL receptor are expressed in most cell types and thus likely do not account for the hepatic tropism of the virus. Furthermore E2 binds to the hepatoblastoma cell line HepG2, which does not express CD81 (25). More recently tw...