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T J Liang

Publications and source records attributed to T J Liang.

At least 19 recordsLinked to original sources
PubMed2003

Spatial distribution of high-energy electron emission from water plasmas produced by femtosecond laser pulses.

High energy electrons emitted by water plasmas produced by a single or a multiple laser pulse are investigated. The multipulse mode greatly enhances the generation and the temperature of hot electrons. Directional emission of high energy electrons over 25 keV is observed in two symmetric directions with respect to the laser axis and at 46 degrees from the directions of the laser electric field. Two-dimensional particle-in-cell simulations reproduce well the experimental results and indicate that the acceleration mechanism of the high energy electrons is due mainly to the resonance absorption at the edge of the spherical droplets formed by the leading pulse.

Journal Article↗
PubMed2002

Sequential analysis of hepatitis B virus core promoter and precore regions in cancer survivor patients with chronic hepatitis B before, during and after interferon treatment.

We analysed the hepatitis B virus (HBV) core-promoter (CP) and precore (PC) regions before, during and after interferon treatment in young Caucasian cancer survivors who had acquired HBV infection during chemotherapy for malignancies. Fourteen patients with chronic hepatitis B [hepatitis B e antigen (HBeAg) /HBV-DNA positive] received alpha-2a interferon (IFN), 5 MU/m2 t.i.w. for 12 months. HBV CP and PC region sequences were analysed following polymerase chain reaction (PCR) amplification. Sera from responders were studied at: T(0) (before starting IFN), T(1) [at alanine aminotransferase (ALT) peak preceding HBeAg seroconversion], T(2) (at ALT normalization), T(3) (at end of IFN) and T(4) (at one year after IFN) and in nonresponders at time points T(0), T(3) and T(4). Amplified HBV-DNA was cloned and sequenced automatically. Six of 14 patients (43%) responded to IFN treatment. Five of the six (83%) responders displayed the double CP mutation A1762T/G1764A always in association with a T1753C change. None of the nonresponders showed these mutations at any time point. The G1896A change creating the PC stop codon mutation was never detected in any of the patients. In our cancer survivors, IFN-induced HBeAg/anti-HBe seroconversion appeared to correlate with CP mutations and was not influenced by previous chemotherapy. These mutations in addition to low HBV DNA levels and elevated ALT can be considered favourable factors of response to IFN-induced anti-HBe seroconversion.

Adolescent↗
PubMed2001

Effects of laser polarization on jet emission of fast electrons in femtosecond-laser plasmas.

Effects of laser polarization on fast electron emission are studied from an aluminum target irradiated by ultrashort laser pulses at 2 x 10(16) W/cm(2). Jet emission of outgoing fast electrons collimated in the polarization direction is observed for s-polarized laser irradiation, whereas for p-polarized irradiation highly directional emission of outgoing fast electrons is found in the direction close to the normal of the target. The behavior of ingoing fast electrons into the target for s- and p-polarized irradiation is also investigated by observing x-ray bremsstrahlung radiation at the backside of the target.

Journal Article↗
PubMed2001

Monoclonal antibodies with broad specificity for hepatitis C virus hypervariable region 1 variants can recognize viral particles.

The hypervariable region 1 (HVR1) of the E2 protein of hepatitis C virus (HCV) is a highly heterogeneous sequence that is promiscuously recognized by human sera via binding to amino acid residues with conserved physicochemical properties. We generated a panel of mAbs from mice immunized with HVR1 surrogate peptides (mimotopes) affinity-selected with sera from HCV-infected patients from a phage display library. A high number of specific clones was obtained after immunization with a pool of nine mimotopes, and the resulting mAbs were shown to recognize several 16- and 27-mer peptides derived from natural HVR1 sequences isolated from patients with acute and chronic HCV infection, suggesting that HVR1 mimotopes were efficient antigenic and immunogenic mimics of naturally occurring HCV variants. Moreover, most mAbs were shown to bind HVR1 in the context of a complete soluble form of the E2 glycoprotein, indicating recognition of correctly folded HVR1. In addition, a highly promiscuous mAb was able to specifically capture bona fide viral particles (circulating HCV RNA) as well as rHCV-like particles assembled in insect cells expressing structural viral polypeptides derived from an HCV 1a isolate. These findings demonstrate that it is possible to induce a broadly cross-reactive clonal Ab response to multiple HCV variants. In consideration of the potentially important role of HVR1 in virus binding to cellular receptor(s), such a mechanism could be exploited for induction of neutralizing Abs specific for a large repertoire of viral variants.

Antibodies, Monoclonal↗
PubMed2001

Hot electrons in the interaction of femtosecond laser pulses with foil targets at a moderate laser intensity.

Characteristics of hot electrons produced in the interaction of femtosecond laser pulses with foil targets were investigated at a moderate laser intensity. Both outgoing and ingoing hot electrons from the femtosecond laser plasma were studied. A collimated jet of outgoing hot electrons was observed in the target normal direction. An ingoing energetic hot-electron beam was found in the laser propagation direction, while the low-energy ingoing electrons spread into wider cone angle due to the collisional effects in the plasma and target material. These observations were supported by three-dimensional Monte Carlo simulations. The hot-electron temperature obtained from electron spectra and absorption experiments implies that resonance absorption is partially responsible for the generation of hot electrons.

Journal Article↗
PubMed2001

Additive activation of hepatic NF-kappaB by ethanol and hepatitis B protein X (HBX) or HCV core protein: involvement of TNF-alpha receptor 1-independent and -dependent mechanisms.

Alcohol consumption and viral hepatitis infection synergistically accelerate liver injury, but the underlying mechanism is not fully understood. Here we have examined the effects of ethanol on hepatitis B protein X (HBX)- or hepatitis C core protein (HCV core protein)-mediated activation of NF-kappaB, a critical signal in hepatic injury, regeneration, and tumor transformation. Acute ethanol or acetaldehyde exposure potentiates HBX or HCV core protein activation of NF-kappaB in primary mouse hepatocytes. Such potentiation can be abolished by blocking ethanol metabolism or overexpression of dominant negative NF-kappaB-inducing kinase (NIK), IkappaB kinase (IKK), or IkappaB. Moreover, pertussis toxin attenuates NF-kappaB activation induced by acetaldehyde but not by HBX or HCV core protein, whereas HBX or HCV core protein-mediated activation of NF-kappaB is abolished completely in tumor necrosis factor a receptor 1 (TNFR1) (-/-) hepatocytes. Finally, chronic ethanol consumption induces hepatic CYP2E1 protein expression and potentiates HBX or HCV core protein activation of NF-kappaB in the liver. These findings suggest that ethanol activates hepatic NF-kappaB via its metabolism and that HBX or HCV core protein activates hepatic NF-kappaB via TNFR1. With the essential role of TNFR1 in alcoholic liver injury, targeting TNFR1 by hepatitis viral proteins could contribute to cooperative effects of alcohol consumption and viral hepatitis on liver disease.

Acetaldehyde↗
PubMed2001

Experimental study of a subpicosecond pulse laser interacting with metallic and dielectric targets.

We have studied laser absorption, hot electron emission, and the energy spectrum of hot electrons produced during the interaction of a 150 fs, 5 mJ, 800 nm p-polarized laser pulse at 8x10(15) W/cm(2) with metallic and dielectric target materials. Because dielectric targets are much less conductive, the charge separation potential in dielectric targets is higher than that of metallic targets. This leads to a smaller laser absorption, fewer emitted electrons, and a lower hot electron temperature in dielectric than in metallic targets.

Journal Article↗
PubMed2001

Conditional liver-specific expression of simian virus 40 T antigen leads to regulatable development of hepatic neoplasm in transgenic mice.

Adaptive epigenetic changes and toxicity often accompany constitutive expression of a transgene or knockout of an endogenous gene in mice. These considerations potentially limit the usefulness of transgenic technology in studying the in vivo functions of a gene. Using conditional gene expression technology, it is possible to override such restrictions to achieve temporal and tissue-specific manipulation of gene expression in vivo. Based on the tetracycline regulatory system, we established a binary transgenic model in which the conditional expression of two transgenes, SV40 T antigen (TAg) and lacZ, can be tightly regulated in the liver by administration of tetracycline. The mouse albumin or mouse major urinary protein promoter was used to achieve liver-specific expression of the tetracycline-responsive transcriptional activator (tTA) in one set of transgenic mice. These mice were crossed with transgenic mice carrying either TAg or lacZ under the control of the tTA-regulated promoter. Analyses of mice transgenic for both tTA and TAg (or lacZ) revealed that the liver-specific expression of the transgenes could be suppressed to undetectable levels and regulated in a reversible fashion by tetracycline administration and withdrawal. Mice with tTA and TAg transgenes developed hepatocellular adenomas and hyperplasia that could be prevented by continuous tetracycline administration. Our report demonstrates the value of this binary transgenic model in studying the physiological functions of any potential genes of interest in a liver-specific manner.

Adenoma↗
PubMed2001

Molecular anatomy and pathophysiologic implications of drug resistance in hepatitis B virus infection.

Synthesis of the hepatitis B virus (HBV) DNA genome occurs within the viral nucleocapsid in a mechanistically ordered fashion. The nucleocapsid contains small pores that permit influx of nucleotide triphosphates and metabolites of nucleoside analogues such as lamivudine for DNA synthesis. Lamivudine is a potent inhibitor of HBV and human immunodeficiency virus (HIV) reverse transcriptases, but substitutions of isoleucine or valine for methionine within the tyrosine-methionine-aspartate-aspartate (YMDD) motif are associated with virologic and clinical resistance to lamivudine therapy. Under lamivudine selection pressure, the high viral production rate and the low fidelity viral polymerase contribute to frequent development of the YMDD mutants. However, the pattern and dynamics of emergence of the mutant viruses over the wild-type virus are determined by multiple factors including replication efficiency, host immune response, and availability of replication space. Structural modeling of HIV reverse transcriptase has permitted key insights into the molecular basis of lamivudine resistance of HBV based on evolutionary relatedness of HIV and HBV. The side groups of isoleucine and valine of the YMDD mutants sterically prevent lamivudine from appropriately configuring into the nucleotide binding site of the reverse transcriptase. Aminotransferase flares are associated with lamivudine therapy and may signify clinical resistance with emergence of YMDD mutants. They may also herald the recovery phase with seroconversion and viral clearance. Reconstitution of the endogenous anti-HBV immune response may be equally important in the control of viral replication by lamivudine and other nucleoside analogues.

Drug Resistance, Microbial↗
PubMed2001

Emergence of a distinct pattern of viral mutations in chimpanzees infected with a homogeneous inoculum of hepatitis C virus.

BACKGROUND & AIMS: Prospective, long-term study of viral evolution and immunologic responses in chimpanzees infected with a homogeneous hepatitis C virus (HCV) population is crucial in understanding the pathogenesis of HCV-host interactions. METHODS: A molecular clone was constructed of HCV genotype 1b and RNA transcribed from this clone inoculated intrahepatically into chimpanzee X0142. Serum was taken from X0142 at week 2 and inoculated intravenously into a second chimpanzee (X0234). Detailed virologic, serologic, and immunologic analyses of these 2 chimpanzees were performed. RESULTS: Both chimpanzees developed persistent viremia, with titers of 10(3) to 10(5) genomes/mL, for 80 weeks (X0142) and 55 weeks (X0234) of follow-up. A late antibody response against the nonstructural proteins and a weak, transient T-helper proliferative response were detected in both animals. In X0142, 25 mutations emerged in the virus population by week 78 and 15 in X0234 by week 35. A relatively large proportion of mutations affecting protein sequences appeared in the NS5A gene (33% in X0142 and X0234 combined), and 5 mutations were common to both chimpanzees. CONCLUSIONS: In this long-term study of the molecular evolution of HCV genotype 1b from a cloned source, the appearance of a distinct pattern of mutations is suggestive of an adaptive response of HCV in vivo. In addition, a limited virus-specific immunity may contribute to HCV persistence.

Alanine Transaminase↗
PubMed2001

Hepatitis C virus-like particles induce virus-specific humoral and cellular immune responses in mice.

We have recently described the production of hepatitis C virus-like particles (HCV-LPs) in insect cells that resemble the putative virions. Here we evaluate the humoral and cellular immunogenicity of the virus-like particles with or without viral p7 protein, a small viral polypeptide that resides between the structural and nonstructural regions of the HCV polyprotein and whose function has not been defined. Immunized BALB/c mice developed high titers of anti-E2 antibodies and virus-specific cellular immune responses including cytotoxic T lymphocytes and T helper responses with gamma interferon production. The virus-like particles without p7 generated a higher cellular immune response with a more T(H)1 profile than the particles with p7. Immunization of heat-denatured particles resulted in substantially lower humoral and cellular responses, suggesting that the immunogenicity is strongly dependent on particle formation. Administration of CpG oligonucleotide or cationic lipid 3beta-[N-(N',N'-dimethylaminoethane)carbamoyl]cholesterol (DC-Chol), two potent adjuvants, did not significantly enhance the immunogenicity of HCV-LPs. Our results indicate that HCV-LPs can induce humoral and cellular immune responses and offer a promising approach to vaccine development.

Adjuvants, Immunologic↗
PubMed2001

Genetic immunization of wild-type and hepatitis C virus transgenic mice reveals a hierarchy of cellular immune response and tolerance induction against hepatitis C virus structural proteins.

To study the effect of genetic immunization on transgenic expression of hepatitis C virus (HCV) proteins, we evaluated the immunological response of HCV transgenic mice to HCV expression plasmids. FVB/n transgenic mice expressing HCV structural proteins (core, E1, and E2) and wild-type (WT) FVB/n mice were immunized intramuscularly with plasmids expressing core (pHCVcore) or core/E1/E2 (pHCVSt). After immunization, HCV-specific humoral and cellular immune response was studied. Both WT and transgenic mice immunized with either HCV construct produced antibodies and exhibited T-cell proliferative responses against core or envelope. In WT mice immunized with pHCVSt, cytotoxic T-lymphocyte (CTL) activities were detected against E2 but not against core or E1, whereas strong CTL activities against core could be detected in WT mice immunized with pHCVcore. In pHCVSt-immunized, transgenic mice, CTL activities against the core or envelope were completely absent, but core-specific CTL activities could be detected in pHCVcore-immunized transgenic mice. A similar pattern of immune responses was also observed in other mouse strains, including a transgenic line expressing human HLA-A2.1 molecules (AAD mice). Despite the presence of a peripheral cellular immunity against HCV, no liver pathology or lymphocytic infiltrate was observed in these transgenic mice. Our study suggests a hierarchy of CTL response against the HCV structural proteins (E2 > core > E1) in vivo when the proteins are expressed as a polyprotein. The HCV transgenic mice can be induced by DNA immunization to generate anti-HCV antibodies and anticore CTLs. However, they are tolerant at the CTL level against the E2 protein despite DNA immunization.

Adoptive Transfer↗
PubMed2001

X-deficient woodchuck hepatitis virus mutants behave like attenuated viruses and induce protective immunity in vivo.

The X protein (HBX) of the hepatitis B virus (HBV) has been shown to be important for the establishment of HBV infection in vivo. Our previous studies suggested that interaction of HBX with the proteasome complex may underlie the pleiotropic functions of HBX. In this study, we generated a series of woodchuck hepatitis virus (WHV) X mutants, including mutants of the domain interacting with the proteasome, and studied their infectivity in woodchucks. Many of the mutants were defective in transactivation but none of them were completely replication defective in vitro. In vivo, all the wild-type and some X mutant-transfected animals demonstrated evidence of infection with anti-WHc and/or anti-WHs seroconversion. Most of the wild-type- and X mutant-transfected animals had transient viremia. Some animals were later challenged with infectious WHV. Animals inoculated with X mutants, including those with no serologic evidence of infection, were protected from the challenge, suggesting previous infection with resulting protective immunity. Our study demonstrates that the previously described functional domains of HBX are biologically important and the X-defective mutants, possibly as attenuated viruses, are not completely replication defective in vivo.

Animals↗
PubMed2000

Structural and functional characterization of interaction between hepatitis B virus X protein and the proteasome complex.

Hepatitis B virus (HBV) has a unique fourth open reading frame coding for a 16.5-kDa protein known as hepatitis B virus X protein (HBX). The importance of HBX in the life cycle of HBV has been well established, but the underlying molecular function of HBX remains controversial. We previously identified a proteasome subunit PSMA7 that interacts specifically with HBX in the Saccharomyces cerevisiae two-hybrid system. Here we demonstrate that PSMC1, an ATPase-like subunit of the 19 S proteasome component, also interacts with HBX and PSMA7. Analysis of the interacting domains among PSMA7, PSMC1, and HBX by deletion and site-directed mutagenesis suggested a mutually competitive structural relationship among these polypeptides. The competitive nature of these interactions is further demonstrated using a modified yeast two-hybrid dissociator system. The crucial HBX sequences involved in interaction with PSMA7 and PSMC1 are important for its function as a transcriptional coactivator. HBX, while functioning as a coactivator of AP-1 and acidic activator VP-16 in mammalian cells, had no effect on the transactivation function of their functional orthologs GCN4 and Gal4 in yeast. Overexpression of PSMC1 seemed to suppress the expression of various reporters in mammalian cells; this effect, however, was overcome by coexpression of HBX. In addition, HBX expression inhibited the cellular turnover of c-Jun and ubiquitin-Arg-beta-galactosidase, two well known substrates of the ubiquitin-proteasome pathway. Thus, interaction of HBX with the proteasome complex in metazoan cells may underlie the functional basis of proteasome as a cellular target of HBX.

Adenosine Triphosphatases↗
PubMed2000

Pathogenesis, natural history, treatment, and prevention of hepatitis C.

Approximately 4 million persons in the United States and probably more than 100 million persons worldwide are infected with hepatitis C virus. The virus has the unique ability to cause persistent infection in susceptible hosts after parenteral or percutaneous transmission, and its underlying mechanisms are not well understood. The immunologic correlates of protection and viral clearance and the pathogenesis of liver injury are yet to be defined, but recent studies suggest the importance of cell-mediated immune responses. Although 70% to 80% of infected persons become chronic carriers, most have relatively mild disease with slow progression. However, chronic and progressive hepatitis C carries significant morbidity and mortality and is a major cause of cirrhosis, end-stage liver disease, and liver cancer. Development of an effective hepatitis C virus vaccine is not imminent, but recent advances in technology and basic knowledge of molecular virology and immunology have engendered novel approaches to the fundamental problems encountered in vaccine development. Current therapy for hepatitis C, although effective in some patients, is problematic and still evolving. Advances in modern biology and immunology promise new therapies for this important disease.

Antibody Formation↗
PubMed2000

Infusion of alpha-galactosidase A reduces tissue globotriaosylceramide storage in patients with Fabry disease.

Fabry disease is a lysosomal storage disorder caused by a deficiency of the lysosomal enzyme alpha-galactosidase A (alpha-gal A). This enzymatic defect results in the accumulation of the glycosphingolipid globotriaosylceramide (Gb(3); also referred to as ceramidetrihexoside) throughout the body. To investigate the effects of purified alpha-gal A, 10 patients with Fabry disease received a single i.v. infusion of one of five escalating dose levels of the enzyme. The objectives of this study were: (i) to evaluate the safety of administered alpha-gal A, (ii) to assess the pharmacokinetics of i.v.-administered alpha-gal A in plasma and liver, and (iii) to determine the effect of this replacement enzyme on hepatic, urine sediment and plasma concentrations of Gb(3). alpha-Gal A infusions were well tolerated in all patients. Immunohistochemical staining of liver tissue approximately 2 days after enzyme infusion identified alpha-gal A in several cell types, including sinusoidal endothelial cells, Kupffer cells, and hepatocytes, suggesting diffuse uptake via the mannose 6-phosphate receptor. The tissue half-life in the liver was greater than 24 hr. After the single dose of alpha-gal A, nine of the 10 patients had significantly reduced Gb(3) levels both in the liver and shed renal tubular epithelial cells in the urine sediment. These data demonstrate that single infusions of alpha-gal A prepared from transfected human fibroblasts are both safe and biochemically active in patients with Fabry disease. The degree of substrate reduction seen in the study is potentially clinically significant in view of the fact that Gb(3) burden in Fabry patients increases gradually over decades. Taken together, these results suggest that enzyme replacement is likely to be an effective therapy for patients with this metabolic disorder.

Adult↗
PubMed2000

Development of a plant-derived subunit vaccine candidate against hepatitis C virus.

Hepatitis C virus (HCV) is a major cause of acute and chronic hepatitis with over 180 million cases worldwide. Vaccine development for HCV has been difficult. Presently, the virus cannot be grown in tissue culture and there is no vaccine or effective therapy against this virus. In this research, we describe the development of an experimental plant-derived subunit vaccine against HCV. A tobamoviral vector was engineered to encode a consensus sequence of hypervariable region 1 (HVR1), a potential neutralizing epitope of HCV, genetically fused to the C-terminal of the B subunit of cholera toxin (CTB). This epitope was selected from among the amino acid sequences of HVR1 "mimotopes" previously derived by phage display technology. The nucleotide sequence encoding this epitope was designed utilizing optimal plant codons. This mimotope is capable of inducing cross-neutralizing antibodies against different variants of the virus. Plants infected with recombinant tobacco mosaic virus (TMV) engineered to express the HVR1/CTB chimeric protein, contained intact TMV particles and produced the HVR1 consensus peptide fused to the functionally active, pentameric B subunit of cholera toxin. Plant-derived HVR1/CTB reacted with HVR1-specific monoclonal antibodies and immune sera from individuals infected with virus from four of the major genotypes of HCV. Intranasal immunization of mice with a crude plant extract containing the recombinant HVR1/CTB protein elicited both anti-CTB serum antibody and anti-HVR1 serum antibody which specifically bound to HCV virus-like particles. Using plant-virus transient expression to produce this unique chimeric antigen will facilitate the development and production of an experimental HCV vaccine. A plant-derived recombinant HCV vaccine can potentially reduce expenses normally associated with production and delivery of conventional vaccines.

Administration, Intranasal↗