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Jinhua Xiang

Publications and source records attributed to Jinhua Xiang.

13 recordsLinked to original sources
PubMed2006

Characterization of an immunodominant antigenic site on GB virus C glycoprotein E2 that is involved in cell binding.

GB virus type C (GBV-C) is a human flavivirus that may cause persistent infection, although most infected individuals clear viremia and develop antibodies to the envelope glycoprotein E2. To study GBV-C E2 antigenicity and cell binding, murine anti-E2 monoclonal antibodies (MAbs) were evaluated to topologically map immunogenic sites on GBV-C E2 and for the ability to detect or block recombinant E2 binding to various cell lines. Five competition groups of MAbs were identified. Groups I and II did not compete with each other. Group III competed with both groups I and II. Group IV did not compete with group I, II, or III. One MAb competed with all of the other MAbs, suggesting that the epitopes bound by these MAbs are intimately related. Individually, none of the MAbs competed extensively with polyclonal human convalescent antibody (PcAb); however, combinations of all five MAb groups completely blocked PcAb binding to E2, suggesting that the epitopes bound by these MAbs form a single, immunodominant antigenic site. Only group I and III MAbs detected purified recombinant E2 bound to cells in binding assays. In contrast, group II MAbs neutralized the binding of E2 to cells. Both PcAb and MAbs were conformation dependent, with the exception of one group II MAb (M6). M6 bound to a five-amino-acid sequence on E2 if the peptide included four C-terminal or eight N-terminal residues, suggesting that the GBV-C E2 protein contains a single immunodominant antigenic site which includes a complex epitope that is involved in specific cellular binding.

Amino Acid Sequence↗
PubMed2006

An 85-aa segment of the GB virus type C NS5A phosphoprotein inhibits HIV-1 replication in CD4+ Jurkat T cells.

GB virus type C (GBV-C) is an apparently nonpathogenic virus that replicates in T and B lymphocytes and is a common cause of persistent human infection. Among HIV-1-infected individuals, persistent coinfection with GBV-C is associated with prolonged survival, and infection of blood mononuclear cells or CD4+ T cells with GBV-C and HIV in vitro results in significantly reduced HIV-1 replication. To date, the viral protein(s) that lead to HIV inhibition have not been identified. The GBV-C nonstructural phosphoprotein (NS5A) is predicted to have pleotropic effects on cells, including interactions with the IFN-induced dsRNA-activated protein kinase (PKR). We studied GBV-C NS5A to determine whether it is involved in inhibition of HIV replication. GBV-C NS5A protein from an isolate that was cleared by IFN therapy did not inhibit PKR, whereas NS5A from an isolate that was not cleared by IFN-inhibited PKR function in a yeast genetic system. Both of these GBV-C NS5A proteins were expressed in a CD4+ T cell line (Jurkat), and both induced a potent, dose-dependent inhibition of HIV-1 replication, thus the effect was independent of PKR inhibition. NS5A induced the release of the chemokine SDF-1 and decreased surface expression of the HIV coreceptor CXCR4, potentially explaining the HIV inhibition. Deletion mapping of the NS5A protein found that an 85-aa region between amino acids 152 and 237 inhibits HIV-1 replication. Thus, GBV-C NS5A protein alters the cellular milieu necessary for HIV-1 replication and may provide a previously undescribed therapeutic approach for anti-HIV therapy.

CD4-Positive T-Lymphocytes↗
PubMed2005

South African GB virus C isolates: interactions between genotypes 1 and 5 isolates and HIV.

GB virus C (GBV-C) is a common, apparently nonpathogenic human flavivirus that has been associated in some studies with prolonged survival in human immunodeficiency virus (HIV)-positive persons. There are 5 distinct GBV-C genotypes localized to specific geographic regions, and genotype 2 has been previously shown to inhibit HIV replication in vitro in lymphocyte cultures. We identified GBV-C virus isolates representing genotypes 1, 2, and 5 in samples from South African blood donors. GBV-C genotype 1 and 5 isolates replicated in lymphocyte culture, inhibited X4 and R5 HIV-1 isolates, and induced RANTES and stromal-derived factor-1 chemokines in vitro. Thus, African GBV-C genotypes can inhibit HIV replication in vitro.

5' Untranslated Regions↗
PubMed2005

GB virus type C NS5A sequence polymorphisms: association with interferon susceptibility and inhibition of PKR-mediated eIF2alpha phosphorylation.

GB virus type C (GBV-C) causes persistent infection in humans, although the mechanism by which the virus avoids clearance by the host is unknown. To determine if amino acid polymorphisms in the GB virus type C (GBV-C) NS5A and E2 proteins alter response to interferon (IFN) therapy, we studied the sequence of GBVC NS5A and E2 obtained from people receiving IFN therapy. In addition, we expressed recombinant GBVC NS5A protein to determine if it interferes with RNA-activated protein kinase (PKR) function in vitro. GBVC NS5A amplified from a person whose virus was cleared by IFN therapy (IFN sensitive) demonstrated unique amino acid changes occurring in the region that aligns with the hepatitis C virus (HCV) IFN sensitivity-determining region (ISDR) compared with NS5A sequences from individuals who did not clear GBV-C (IFN resistant). There were no differences in the E2 sequences obtained from IFN-sensitive and IFN-resistant isolates. Using a yeast genetic system, IFN-resistant NS5A inhibited PKR-mediated phosphorylation of eukaryotic initiation factor 2alpha (eIF2alpha) in yeast, whereas IFN-sensitive NS5A did not inhibit PKR function. GBV-C NS5A amino acid polymorphisms appear to be involved in response to IFN therapy, and IFN-resistant GBV-C NS5A inhibited PKR-mediated eIF2alpha phosphorylation in a yeast genetic system, suggesting a mechanism by which GBV-C may evade clearance by naturally occurring host antiviral responses.

Amino Acid Sequence↗
PubMed2004

Inhibition of HIV-1 replication by GB virus C infection through increases in RANTES, MIP-1alpha, MIP-1beta, and SDF-1.

Background People coinfected with HIV and GB virus C (GBV-C) have lower mortality than HIV-positive individuals without GBV-C infection. HIV uses either of the chemokine receptors CCR5 and CXCR4 for entry into CD4-positive cells. Longer survival in HIV-positive individuals is associated with high serum concentrations of ligands for CCR5 (RANTES [regulated on activation, normal T-cell expressed and secreted] and macrophage inflammatory proteins [MIP] 1alpha and 1beta) and CXCR4 (stromal-derived factor [SDF-1]), and with decreased expression of CCR5 on lymphocytes. Methods Peripheral-blood mononuclear cells were coinfected with GBV-C and HIV, and HIV replication was monitored by measuring infectivity and HIV p24 antigen production. Chemokine secretion was measured by ELISA, chemokine-receptor expression by flow cytometry, and cellular chemokine mRNA expression by differential hybridisation. Findings GBV-C infection of peripheral-blood mononuclear cells resulted in decreased replication of both clinical and laboratory HIV strains that use either CCR5 or CXCR4 as their coreceptor. Inhibition was related to the dose and timing of the GBV-C infection. Expression of mRNA for RANTES, MIP-1alpha, MIP-1beta, and SDF-1 and secretion of the chemokines into culture supernatants were higher in GBV-C-infected cells than in mock-infected cells. The inhibitory effect of GBV-C on HIV replication was blocked by incubation with neutralising antibodies against the relevant chemokines, and surface expression of CCR5 was significantly lower in GBV-C-infected cells than in mock-infected cells. Interpretation GBV-C induces HIV-inhibitory chemokines and reduces expression of the HIV coreceptor CCR5 in vitro. This study provides insight into the epidemiological association between GBV-C infection and longer survival in HIV-infected individuals.

Cells, Cultured↗
PubMed2004

Persistent GB virus C infection and survival in HIV-infected men.

BACKGROUND: GB virus C (GBV-C), which is not known to be pathogenic in humans, replicates in lymphocytes, inhibits the replication of human immunodeficiency virus (HIV) in vitro, and has been associated with a decreased risk of death among HIV-positive persons in some, but not all, studies. Previous studies did not control for differences in the duration of HIV or GBV-C infection. METHODS: We evaluated 271 men who were participants in the Multicenter Acquired Immunodeficiency Syndrome Cohort Study for GBV-C viremia (by means of a reverse-transcriptase-polymerase-chain-reaction assay) or E2 antibody (by means of an enzyme-linked immunosorbent assay) 12 to 18 months after seroconversion to positivity for HIV (the early visit); a subgroup of 138 patients was also evaluated 5 to 6 years after HIV seroconversion (the late visit). RESULTS: GBV-C infection was detected in 85 percent of men with HIV seroconversion on the basis of the presence of E2 antibody (46 percent) or GBV-C RNA (39 percent). Only one man acquired GBV-C viremia between the early and the late visit, but 9 percent of men had clearance of GBV-C RNA between these visits. GBV-C status 12 to 18 months after HIV seroconversion was not significantly associated with survival; however, men without GBV-C RNA 5 to 6 years after HIV seroconversion were 2.78 times as likely to die as men with persistent GBV-C viremia (95 percent confidence interval, 1.34 to 5.76; P=0.006). The poorest prognosis was associated with the loss of GBV-C RNA (relative hazard for death as compared with men with persistent GBV-C RNA, 5.87; P=0.003). CONCLUSIONS: GBV-C viremia was significantly associated with prolonged survival among HIV-positive men 5 to 6 years after HIV seroconversion, but not at 12 to 18 months, and the loss of GBV-C RNA by 5 to 6 years after HIV seroconversion was associated with the poorest prognosis. Understanding the mechanisms of interaction between GBV-C and HIV may provide insight into the progression of HIV disease.

Adult↗
PubMed2004

Increased prooxidant production and enhanced susceptibility to glutathione depletion in HepG2 cells co-expressing HCV core protein and CYP2E1.

Hepatitis C virus (HCV) and HCV core protein are hypothesized to induce hepatic oxidative stress and exacerbate injury caused by other toxins such as ethanol that induce the cytochrome P450 enzyme, CYP2E1. In the current study, the effects of HCV core protein [sequence genotype 1b, (nt 342-915)] on parameters indicative of oxidative stress were evaluated in HepG2 cells stably over expressing CYP2E1 (E47), or vector controls (C34). Stable (>10 passages) expression of HCV core protein and CYP2E1 was confirmed in clonal cell lines at the level of mRNA and immunoreactive protein. Prooxidant production, as determined by cellular oxidation of dichlorodihydrofluorescin and dihydroethidium (HE), was increased by expression of HCV core protein in the presence or absence of CYP2E1. Depletion of glutathione (GSH) with buthionine sulfoximine (BSO) enhanced prooxidant production in both C34 and E47 cells. In addition, prooxidant production was greater in BSO-treated cells expressing HCV core protein, and this effect was further enhanced in cells expressing both HCV core and CYP2E1. The CYP2E1 inhibitor, 4-methylpyrazole, could suppress increased prooxidant production in E47 cells. Finally, cells co-expressing both CYP2E1 and HCV core protein showed significantly decreased viability following GSH depletion. These studies show simultaneous expression of HCV core protein and CYP2E1 increases parameters indicative of oxidative stress as well as sensitization to cell injury induced by GSH depletion. These results support the hypothesis that enhanced injury in hepatocytes over expressing both HCV core protein and CYP2E1 is mediated by increases in oxidative stress.

Buthionine Sulfoximine↗
PubMed2003

Clinical isolates of GB virus type C vary in their ability to persist and replicate in peripheral blood mononuclear cell cultures.

GB virus C/hepatitis G virus (GBV-C) replication in vitro is inefficient and inconsistent. In this study, clinical isolates of GBV-C were evaluated using peripheral blood mononuclear cell (PBMC) based culture methods. Isolates varied consistently in their ability to persistently replicate, and yield increased in cells grown without PHA/IL-2 stimulation. The deduced polyprotein sequence of an isolate that replicated well was determined (GenBank AY196904) and compared to 20 full-length GBV-C sequences. Fourteen of the 16 unique amino acid polymorphisms identified were in the coding regions for nonstructural proteins associated with interferon resistance and RNA replication. These data indicate that clinical GBV-C isolates vary in their ability to persist in culture, do not require PHA/IL-2 stimulation, and that sequence variability in key regulatory regions may affect growth in PBMC cultures. Since GBV-C appears to inhibit HIV replication in a coinfection model, these studies should facilitate determination of the mechanism of this interaction.

Amino Acid Sequence↗
PubMed2003

GB virus type C/hepatitis G virus: a non-pathogenic flavivirus associated with prolonged survival in HIV-infected individuals.

GB virus C (GBV-C) is a common virus that does not appear to cause disease. GBV-C persists in up to 50% of exposed individuals, and virus replication appears to be in lymphocytes including CD4+ T cells. GBV-C infection is common among HIV-positive people, and several studies have found that HIV-positive individuals co-infected with GBV-C survive for statistically significantly longer periods of time than people without GBV-C. In vitro studies suggest that GBV-C inhibits HIV replication and alters cytokine, chemokine and chemokine receptor expression. Thus, GBV-C may be a major factor influencing the natural history of HIV disease.

Animals↗
PubMed2002

Recombinant hepatitis C virus-like particles expressed by baculovirus: utility in cell-binding and antibody detection assays.

Hepatitis C virus (HCV) is difficult to study due to the lack of an efficient cell culture system or small animal model. As a result, HCV-cell interactions are not well-defined. In addition, several studies have identified a subset of patients in whom HCV RNA is present, but HCV antibody is not detected. We produced recombinant baculoviruses that expressed HCV structural proteins (core, E1 and E2, nt 342-2651) or control proteins. The HCV structural protein precursor was processed into immunoreactive proteins of appropriate size, and sucrose density sedimentation and electron microscopy of infected cell lysates demonstrated particle formation. To evaluate HCV antigenicity, particularly in patients who tested negative for HCV antibody in commercial HCV immunoassays but had persistent viremia, we evaluated the virus-like particles (VLPs) in solid-phase immunoassays. VLPs reacted with sera from HCV antibody positive subjects in these solid phase immunoassays, but not with control sera. Plasma samples from 19% (5/26) of HCV antibody negative subjects who were persistently HCV RNA positive also reacted with the HCV VLPs. When incubated with MOLT-4 cells at 4 degrees C, HCV VLPs demonstrated cell binding, and behaved similar to plasma-derived HCV preparations in a flow cytometry-based cell binding assay. These data suggest that recombinant HCV VLPs may allow identification of HCV antibody in patients, including some patients with persistent viremia and who are seronegative with current assays. In addition, HCV VLPs seem useful for evaluating HCV-cell interactions.

Animals↗
PubMed2002

Interactions Between GB Virus Type C and HIV.

GB virus C (GBV-C, also known as hepatitis G virus) commonly causes human infection. Genetically, it is closely related to hepatitis C virus, but GBV-C appears to grow primarily in lymphocytes, not hepatocytes. Although it causes persistent infection in about 25% to 50% of infected individuals, numerous studies have failed to connect GBV-C with any disease process. GBV-C is transmitted sexually, parenterally, and vertically, and due to these shared modes of transmission, coinfection is common among HIV-infected individuals. Of 10 studies done of HIV-GBV-C coinfection, eight found a beneficial effect of GBV-C viremia on HIV-related mortality or response to therapy. The mechanism by which GBV-C may improve survival of HIV-positive people is not known; however, in vitro studies suggest that GBV-C inhibits HIV replication, and preliminary data also point toward alterations in cytokine and/or chemokine expression by GBV-C-infected cells.

Journal Article↗