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T Jake Liang

Publications and source records attributed to T Jake Liang.

44 records · Page 3Linked to original sources
PubMed2003

The clearance of hepatitis C virus infection in chimpanzees may not necessarily correlate with the appearance of acquired immunity.

Clearance of hepatitis C virus (HCV) infection in humans and chimpanzees is thought to be associated with the induction of strong T-cell responses. We studied four chimpanzees infected with HCV derived from an infectious full-length HCV genotype 1b cDNA. Two of the chimpanzees cleared the infection to undetectable levels for more than 12 months of follow-up; the other two became persistently infected. Detailed analyses of HCV-specific immune responses were performed during the courses of infection in these chimpanzees. Only weak and transient T helper responses were detected during the acute phase in all four chimpanzees. A comparison of the frequency of gamma interferon (IFN-gamma)-producing CD4(+) and CD8(+) T cells in peripheral blood by ELISpot assay did not reveal any correlation between viral clearance and T-cell responses. In addition, analyses of IFN-gamma, IFN-alpha, and interleukin-4 mRNA levels in liver biopsies, presumably indicative of intrahepatic T-cell responses, revealed no distinct pattern in these chimpanzees with respect to infection outcome. The present study suggests that the outcome of HCV infection in chimpanzees is not necessarily attributable to HCV sequence variation and that chimpanzees may recover from HCV infection by mechanisms other than the induction of readily detectable HCV-specific T-cell responses.

Amino Acid Sequence↗
PubMed2002

Impaired effector function of hepatitis C virus-specific CD8+ T cells in chronic hepatitis C virus infection.

The cellular immune response contributes to clearance of hepatitis C virus (HCV) and persists for decades after recovery from infection. The immunological basis for the inefficiency of the cellular immune response in chronically infected persons is not known. Here, we used four HLA-A2 tetramers, specific for two HCV core and two HCV NS3 epitopes, to investigate at the single-cell level effector function and phenotype of HCV-specific CD8+ T cells in 20 chronically infected and 12 long-term recovered patients. Overall, HCV-specific, tetramer+ T cells were more frequently found in PBMCs of chronically infected patients than in those of recovered patients. However, when compared with HCV-tetramer+ T cells of recovered patients, they displayed an impaired proliferative capacity. As a result of the impaired proliferative capacity, HCV-specific T cell lines derived from chronically infected patients displayed less peptide-specific cytotoxicity than those from recovered patients. In addition, proliferation and ex vivo IFN-gamma production of HCV-tetramer+ cells, but not influenza-virus-specific T cells, were defective in chronically infected patients and could not be restored by in vitro stimulation with peptide and IL-2. At least three distinct phenotypes of HCV-specific CD8+ T cells were identified and associated with certain functional characteristics. In addition, impairment of proliferative, cytokine, and cytotoxic effector functions of tetramer+ T cells in viremic patients was associated with weak ex vivo HCV-specific CD4+ T cell responses. Thus, the defective functions of HCV-specific CD8+ T cells might contribute to viral persistence in chronically infected patients, and knowledge on their reversibility may facilitate the development of immunotherapeutic vaccines.

Adult↗
PubMed2002

Structural features of envelope proteins on hepatitis C virus-like particles as determined by anti-envelope monoclonal antibodies and CD81 binding.

The envelope glycoprotein E2 of hepatitis C virus (HCV) is a major component of the viral envelope. Knowledge of its topologic features and antigenic determinants in virions is crucial in understanding the viral binding sites to cellular receptor(s) and the induction of neutralizing antibodies. The lack of a robust cell culture system for virus propagation has hampered the characterization of E2 presented on the virion. Here we report the structural features of hepatitis C virus-like particles (HCV-LPs) of the 1a and 1b genotypes as determined by various mouse and human monoclonal anti-envelope antibodies. Our results show that the E2 protein of HCV-LPs reacts with human monoclonal antibodies recognizing conformational determinants. Monoclonal antibodies (mAbs) specific for the hypervariable region 1 (HVR-1) sequence reacted strongly with HCV-LPs, suggesting that the HVR-1 is exposed on the viral surface. Several mAbs recognized both HCV-LPs with equally high affinity, indicating that the corresponding epitopes [amino acids (aa) 192-217 of E1 and aa 412-423, aa 522-531, and aa 640-653 of E2] are conserved in both genotypes and exposed on the surface of the HCV-LP. The E2 and E1/E2 dimers of 1a bound strongly to the recombinant large extracellular loop (LEL) of CD81 (CD81-LEL) of human and African green monkey, while the HCV-LP of 1a bound weakly to human CD81-LEL. E1/E2 dimers and the HCV-LPs of 1b did not bind CD81-LEL, consistent with the notion that CD81 recognition by E2 is strain-specific and does not correlate with permissiveness of infection. A model of the topology and exposed antigenic determinants of the envelope proteins of HCV is proposed.

Animals↗
PubMed2002

Neutropenia during combination therapy of interferon alfa and ribavirin for chronic hepatitis C.

Interferon therapy of hepatitis C causes a decrease in neutrophil counts, and neutropenia is a common reason for dose adjustment or early discontinuation. However, it is unclear whether neutropenia caused by interferon is associated with an increased rate of infection. In this study, we assessed factors associated and clinical consequences of neutropenia before and during interferon therapy of chronic hepatitis C. A total of 119 patients with chronic hepatitis C treated with the combination of interferon alfa and ribavirin were analyzed. In these studies, neutropenia was not used as an exclusion or dose modification criterion. In multivariate analysis, only black race was associated with baseline neutropenia. During treatment, neutrophil counts decreased by an average of 34%. Among 3 blacks with baseline neutropenia without cirrhosis or splenomegaly, there was little or no decrease in neutrophil counts (despite typical decreases in platelet and lymphocyte counts). Documented or suspected bacterial infections developed in 22 patients (18%), but in no patient with neutropenia. United States population estimates suggest that 76,000 blacks with hepatitis C have neutrophil counts below 1,500 cells/microL and might be denied therapy if this exclusion criterion was generally applied. In conclusion, neutropenia is frequent during treatment of hepatitis C with interferon and ribavirin, but it is not usually associated with infection. Constitutional neutropenia, which is common among blacks, should not exclude patients from therapy with interferon as these patients usually have minimal further decreases in neutrophil counts on therapy and are not excessively prone to bacterial infections.

Adult↗
PubMed2002

Molecular and immunological significance of chimpanzee major histocompatibility complex haplotypes for hepatitis C virus immune response and vaccination studies.

The chimpanzee is a critical animal model for studying cellular immune responses to infectious pathogens such as hepatitis B and C viruses, human immunodeficiency virus, and malaria. Several candidate vaccines and immunotherapies for these infections aim at the induction or enhancement of cellular immune responses against viral epitopes presented by common human major histocompatibility complex (MHC) alleles. To identify and characterize chimpanzee MHC class I molecules that are functionally related to human alleles, we sequenced 18 different Pan troglodytes (Patr) alleles of 14 chimpanzees, 2 of them previously unknown and 3 with only partially reported sequences. Comparative analysis of Patr binding pockets and binding assays with biotinylated peptides demonstrated a molecular homology between the binding grooves of individual Patr alleles and the common human alleles HLA-A1, -A2, -A3, and -B7. Using cytotoxic T cells isolated from the blood of hepatitis C virus (HCV)-infected chimpanzees, we then mapped the Patr restriction of these HCV peptides and demonstrated functional homology between the Patr-HLA orthologues in cytotoxicity and gamma interferon (IFN-gamma) release assays. Based on these results, 21 HCV epitopes were selected to characterize the chimpanzees' cellular immune response to HCV. In each case, IFN-gamma-producing T cells were detectable in the blood after but not prior to HCV infection and were specifically targeted against those HCV peptides predicted by Patr-HLA homology. This study demonstrates a close functional homology between individual Patr and HLA alleles and shows that HCV infection generates HCV peptides that are recognized by both chimpanzees and humans with Patr and HLA orthologues. These results are relevant for the design and evaluation of vaccines in chimpanzees that can now be selected according to the most frequent human MHC haplotypes.

Alleles↗
PubMed2002

Interaction of hepatitis C virus-like particles and cells: a model system for studying viral binding and entry.

Hepatitis C virus-like particles (HCV-LPs) containing the structural proteins of HCV H77 strain (1a genotype) was used as a model for HCV virion to study virus-cell interaction. HCV-LPs showed a buoyant density of 1.17 to 1.22 g/cm(3) in a sucrose gradient and formed double-shelled particles 35 to 49 nm in diameter. Flow cytometry analysis by an indirect method (detection with anti-E2 antibody) and a direct method (use of dye-labeled HCV-LPs) showed that HCV-LPs binds to several human hepatic (primary hepatocytes, HepG2, HuH7, and NKNT-3) and T-cell (Molt-4) lines. HCV-LPs binding to cells occurred in a dose- and calcium-dependent manner and was not mediated by CD81. Scatchard plot analysis suggests the presence of two binding sites for HCV-LPs with high (K(d) approximately 1 microg/ml) and low (K(d) approximately 50 to 60 microg/ml) affinities of binding. Anti-E1 and -E2 antibodies inhibited HCV-LPs binding to cells. While preincubation of HCV-LPs with very-low-density lipoprotein (VLDL), low-density lipoprotein (LDL), or high-density lipoprotein (HDL) blocked its binding to cells, preincubation of cells with VLDL, LDL, HDL, or anti-LDL-R antibody did not. Confocal microscopy analysis showed that, after binding to cells, dye-labeled HCV-LPs were internalized into the cytoplasm. This process could be inhibited with anti-E1 or anti-E2 antibodies, suggesting that E1 and E2 proteins mediate HCV-LPs binding and, subsequently, their entry into cells. Altogether, our results indicate that HCV-LPs can be used to further characterize the mechanisms involved in the early steps of HCV infection.

Antigens, CD↗