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Biomedical subjects

Z Xiang

Publications and source records attributed to Z Xiang.

At least 19 recordsLinked to original sources
PubMed1996

Novel vaccine approaches.

Recent advances in immunology, molecular biology, and peptide biochemistry have allowed the construction of subunit vaccines based on viral or bacterial recombinants, peptides or plasmid vectors. Although none of these approaches is currently being used for mass vaccination (with the exception or vaccinia-rabies G protein recombinant virus for wildlife immunization); several of them are undergoing clinical trials. None of these different vaccine constructs is likely to be totally effective in either the prevention of infectious diseases or immunotherapy of cancer. Recombinant viral vaccines such as those based on vaccinia or adenovirus as a rule induce potent immune responses. Vaccinia viruses have the added advantage of being heat stable and immunogenic after oral application, making them good candidates for wildlife immunization. Recombinants based on replication-defective adenoviruses are safer compared with vaccinia virus recombinants and, as far as our data indicate, have superior efficacy. In addition, they induce excellent immunity upon application to mucosal membranes, suggesting their usefulness as vaccines for infectious agents that enter through the airways or the genital tract. Peptides are of limited benefit in infectious disease prevention but might provide custom-made vaccines for cancer therapy. Genetic vaccines that were first described less than 5 years ago have already progressed to phase I clinical trials in healthy human adults. Provided that their safety can be confirmed, they might be suited to induce immunity to numerous agents.

Humans↗
PubMed1995

Upregulation of class I major histocompatibility complex antigens by interferon gamma is necessary for T-cell-mediated elimination of recombinant adenovirus-infected hepatocytes in vivo.

Recombinant adenoviruses are attractive vehicles for liver-directed gene therapy because of the high efficiency with which they transfer genes to hepatocytes in vivo. First generation recombinant adenoviruses deleted of E1 sequences also express recombinant and early and late viral genes, which lead to development of destructive cellular immune responses. Previous studies indicated that class I major histocompatibility complex (MHC)-restricted cytotoxic T lymphocytes (CTLs) play a major role in eliminating virus-infected cells. The present studies utilize mouse models to evaluate the role of T-helper cells in the primary response to adenovirus-mediated gene transfer to the liver. In vivo ablation of CD4+ cells or interferon gamma (IFN-gamma) was sufficient to prevent the elimination of adenovirus-transduced hepatocytes, despite the induction of a measurable CTL response. Mobilization of an effective TH1 response as measured by in vitro proliferation assays was associated with substantial upregulation of MHC class I expression, an effect that was prevented in IFN-gamma-deficient animals. These results suggest that elimination of virus-infected hepatocytes in a primary exposure to recombinant adenovirus requires both induction of antigen-specific CTLs as well as sensitization of the target cell by TH1-mediated activation of MHC class I expression.

Adenoviruses, Human↗
PubMed1995

Atrophic nonunion can be predicted with dual energy x-ray absorptiometry in a canine ostectomy model.

This study demonstrated that dual energy x-ray absorptiometry can be used to distinguish between normal union and atrophic nonunion, with high sensitivity and high negative predictive value, by 8 weeks after surgery in a canine model. Eighteen adult mixed-breed dogs were divided into two equal groups: normal union and atrophic nonunion. In the normal union group, a 5 mm mid-diaphyseal transverse ostectomy was performed in the right tibia, and the bone was stabilized with a unilateral external fixator. In the atrophic nonunion group, a 5 mm mid-diaphyseal ostectomy was performed; the distal 1.5 cm of the bone ends, including the periosteum, were frozen twice to -20 degrees C using liquid nitrogen and thawed slowly twice; and the bone was stabilized with a unilateral external fixator. The members of the research team were blinded to the group assignments until after all dogs were killed and all data were acquired. Radiography and dual energy x-ray absorptiometry of both tibiae were performed at weeks 1, 2, 3, 4, 6, 8, 10, 12, 14, and 16 after surgery. All dogs were killed at 16 weeks, and the torsional stiffness and maximum torque of both tibiae of five dogs in each group were determined. Mechanically, the tibiae in the normal union group had significantly higher maximum torque (43-fold higher) and torsional stiffness (86-fold higher) than the tibiae in the atrophic nonunion group. The sensitivity and negative predictive value of dual energy x-ray absorptiometry for predicting nonunion were 100% by 8 weeks after surgery. The specificity and positive predictive value reached 78 and 82%, respectively, by 16 weeks. Radiographic scores were significantly higher for the union group than for the nonunion group beginning at 2 weeks after surgery. The earliest time after surgery that radiography classified an ostectomy as a nonunion was significantly later (4.6 +/- 1.2 weeks) than for dual energy x-ray absorptiometry (2.6 +/- 1.4 weeks). Before these results can be extrapolated to human applications, further animal studies must be performed to evaluate clinically or experimentally induced fractures, or both, rather than the well defined ostectomies that were performed in this study.

Absorptiometry, Photon↗
PubMed1995

Manipulation of the immune response to a plasmid-encoded viral antigen by coinoculation with plasmids expressing cytokines.

Inoculation of plasmid vectors encoding a viral protein into muscle tissue was shown to result in expression of the transantigen and, consequently, an antiviral immune response. Here, we show that coinoculation of a plasmid expressing the glycoprotein of rabies virus with plasmids encoding mouse cytokines modulated the immune response to the viral protein. Coinoculation with a vector expressing mouse granulocyte-macrophage colony-stimulating factor (GM-CSF) enhanced the B and T helper cell activity to rabies virus, while coinoculation with a plasmid expressing interferon-gamma (IFN gamma) resulted in a decrease of the immune response to the viral antigen.

Animals↗
PubMed1995

Analysis of expression of CagA and VacA virulence factors in 43 strains of Helicobacter pylori reveals that clinical isolates can be divided into two major types and that CagA is not necessary for expression of the vacuolating cytotoxin.

Colonization of the mucosa of the stomach and the duodenum by Helicobacter pylori is the major cause of acute and chronic gastroduodenal pathologies in humans. Duodenal ulcer formation strongly correlates with the expression of an antigen (CagA) that is usually coeexpressed with the vacuolating cytotoxin (VacA), a protein that causes ulceration in the stomach of mice. However, the relationship between these two virulence factors is unknown. To define whether CagA and VacA are coexpressed in all clinical isolates and their relationships, we collected 43 clinical isolates of H. pylori and studied their genetic and phenotypic properties. Based on this analysis, most of the strains could be classified into two major types. Type I bacteria had the gene coding for CagA and expressed the CagA protein and the vacuolating cytotoxin. Type II bacteria did not have the gene coding for CagA and did not express either the CagA protein or the vacuolating cytotoxin. Type I and type II bacteria represented 56 and 16%, respectively, of the 43 clinical isolates, while the remaining 28% had an intermediate phenotype, expressing CagA independently of VacA or vice versa. This finding shows that although it is present in most cytotoxic strains, CagA is not necessary for the expression of the vacuolating cytotoxin.

Antigens, Bacterial↗
PubMed1995

Helicobacter pylori-specific CD4+ T-cell clones from peripheral blood and gastric biopsies.

Colonization of human gastric mucosa with cytotoxic strains of the bacterium Helicobacter pylori is associated with peptic ulcer and with chronic gastritis. Since little is known about the T-cell response to H. pylori, we investigated the CD4+ T-cell response both in peripheral blood mononuclear cells (PBMCs) and at the site of infection. First, we compared the bulk PBMC proliferative response to the bacterium in individuals with and without symptoms of gastroduodenal disease. We found that the PBMCs from virtually all individuals proliferate in response to heat-inactivated bacteria. Second, we cloned H. pylori-specific CD4+ T lymphocytes from the PBMCs of three patients and from both the gastric mucosa and PBMCs of a fourth patient. We have found that CD4+ T-cell clones specific for H. pylori from peripheral blood samples and gastric mucosae of infected patients are major histocompatibility complex class II restricted and discriminate between several cytotoxic and noncytotoxic bacterial strains. Moreover, they are polyclonal in terms of T-cell receptor usage and major histocompatibility complex restriction. Our results demonstrate that the T-cell response to the whole bacterium in PBMCs does not correlate with antibody response, infection, or disease. However, H. pylori-specific CD4+ T cells are detectable, at the clonal level, in both the periphery and gastric mucosa of infected patients. Localization of these cells at the site of disease suggests they are effectors of the immune response to the bacteria.

Adult↗
PubMed1995

Helicobacter pylori induced interleukin-8 expression in gastric epithelial cells is associated with CagA positive phenotype.

AIMS: To use a range of natural phenotypically variant strains of Helicobacter pylori with disparate CagA and VacA (vacuolating cytotoxin) expression to determine which bacterial factors are more closely associated with epithelial interleukin-8 (IL-8) induction. METHODS: Gastric epithelial cells (AGS and KATO-3) were co-cultured with five H pylori strains which were variously shown to express the cagA gene/CagA protein, VacA and/or to exhibit biological cytotoxicity. Secreted IL-8 was assayed by enzyme leaked immunosorbent assay (ELISA) and IL-8 messenger RNA (mRNA) was assayed using a reverse transcription polymerase chain reaction based technique (RT-PCR). RESULTS: Strains expressing CagA, including a variant strain (D931) which is non-cytotoxic and does not express the VacA protein, were found to upregulate epithelial IL-8 secretion and gene expression. In contrast, strains with no CagA expression, even in the presence of VacA and/or biological cytotoxicity, (G104, BA142), failed to induce IL-8 protein or mRNA above control values. CONCLUSIONS: These results strongly support a role for H pylori CagA or coexpressed factors other than the cytotoxin in upregulation of gastric epithelial IL-8. Increased epithelial IL-8 secretion and concomitant neutrophil chemotaxis and activation in addition to direct cytotoxicity may be an important factor in tissue damage and ulceration.

Animals↗
PubMed1995

Induction of interleukin-8 secretion from gastric epithelial cells by a cagA negative isogenic mutant of Helicobacter pylori.

The ability of Helicobacter pylori strains to induce interleukin-8 (IL-8) gene expression and protein secretion from gastric epithelial cell lines in vitro is variable. This cellular response is associated with bacterial expression of the CagA protein present in type I H pylori strains. To determine the role of CagA in this host cell response, an isogenic cagA negative mutant, N6.XA3, was constructed. The cagA negative isogenic mutant and the wild-type parental cagA positive strain, N6, were cocultured with AGS, ST-42 and KATO-3 gastric epithelial cell lines and secreted interleukin-8 assayed by enzyme linked immunosorbent assay. In all three cell lines there was no significant difference in the IL-8 secretion induced by the cagA negative isogenic mutant, N6.XA3, and the wild-type parent strain, N6. These studies show that CagA is not the inducer of IL-8 secretion from gastric epithelial cells. As all wild-type CagA positive strains studied to date induce IL-8, the bacterial factor(s) inducing this inflammatory response is closely associated with the expression of CagA.

Antigens, Bacterial↗
PubMed1995

Bromodeoxyuridine immunohistochemistry of epon-embedded undecalcified bone in a canine fracture healing model.

We evaluated bromodeoxyuridine (BrdU) immunohistochemistry of paraffin-, methyl methacrylate (MMA)-, and epon-araldite (epon)-embedded canine bone specimens to establish an optimal technique for studying cell kinetics of fracture healing in a canine tibial gap model. Dogs were sacrificed 4 months after tibial ostectomy and 1 hr after i.v. injection of BrdU (100 mg/kg). BrdU immunohistochemical staining with a peroxidase-labeled streptavidin-biotin (LAB-SA) method was performed on thin sections of tibia fixed in 70% ethanol and embedded in paraffin, MMA, or epon. Thin section of small intestines fixed in 70% ethanol and 10% neutral buffered formalin and embedded in paraffin, MMA, or epon were BrdU-stained and served as a model for proliferating tissue. Good and consistent BrdU immunostaining without detachment of bone sections was obtained for epon-embedded undecalcified bone sections. BrdU-positive cells were easily identifiable, in contrast to negligible background staining. BrdU-labeled osteoprogenitor cells and osteoblasts were observed around and on the surface of woven bone in external and internal callus of the ostectomy gap. Nuclei of osteocytes were not labeled. In contrast to the epon-embedded specimens, BrdU immunostaining of paraffin-embedded decalcified and MMA-embedded undecalcified bone specimens was unsatisfactory. The results of this study suggest that BrdU immunohistochemistry of ethanol-fixed, epon-embedded, undecalcified canine bone sections is a technique suitable for study of fracture healing with the described methodology.

Animals↗
PubMed1994

Gene structure of the Helicobacter pylori cytotoxin and evidence of its key role in gastric disease.

The gram negative, microaerophilic bacterium Helicobacter pylori colonizes the human gastric mucosa and establishes a chronic infection that is tightly associated with atrophic gastritis, peptic ulcer, and gastric carcinoma. Cloning of the H. pylori cytotoxin gene shows that the protein is synthesized as a 140-kD precursor that is processed to a 94-kD fully active toxin. Oral administration to mice of the purified 94-kD protein caused ulceration and gastric lesions that bear some similarities to the pathology observed in humans. The cloning of the cytotoxin gene and the development of a mouse model of human gastric disease will provide the basis for the understanding of H. pylori pathogenesis and the development of therapeutics and vaccines.

Amino Acid Sequence↗
PubMed1994

Identification of a higher molecular weight protein that shows apparent cross-reactivity with anti-p21ras monoclonal antibodies on western blots.

We have characterized the immune cross-reactivity of several commercially available monoclonal antibodies prepared against the p21ras proteins and used in Western blotting experiments against human tissue homogenates. Under optimal conditions, only two bands were observed on Western blots. One of these comigrated with control p21ras protein. A second protein of apparent mobility corresponding to approximately 54 kDa was also observed with all four monoclonal antibodies tested. Protein sequencing by automated Edman degradation indicates that the 54 kDa species corresponds to human immunoglobulin heavy chain. Under suboptimal conditions, another high molecular weight species of apparent mobility 65 kDa was also observed to cross-react with some of the monoclonal antibodies tested. This 65 kDa species was identified by protein sequencing as human serum albumin. Coomassie blue staining of SDS-polyacrylamide gels indicates that serum albumin is a major contaminant of many surgically obtained human tissue samples, while p21ras and immunoglobulin heavy chain are present at much lower concentrations. These results may be of significance when using monoclonal antibodies to determine p21ras levels of whole tissue homogenates by dot-blot, slot-blot or microplate assays.

Amino Acid Sequence↗
PubMed1994

Quantal mechanism of long-term potentiation in hippocampal mossy-fiber synapses.

1. The quantal mechanism underlying the expression of long-term potentiation (LTP) was studied in the mossy-fiber (mf) synapses of the rat hippocampus. Whole-cell recordings were used to measure the excitatory postsynaptic currents (EPSCs) before and after LTP induction in brain slices maintained at 31 +/- 1 degrees C. 2. Evoked EPSCs were recorded from 473 CA3 pyramidal neurons. The mf synapses were stimulated using paired pulses (40-ms interpulse interval) repeated every 2-10 s. At least 400 pairs of mf responses were obtained before and during the expression of LTP, which was produced by high-frequency (100 Hz) mf stimulation. Sufficiently stationary data were obtained from five neurons that exhibited LTP and that also satisfied strict criteria and procedures that are necessary for eliciting and identifying unitary mf responses. 3. Three independent lines of evidence implicated a presynaptic component to the mechanism underlying mf LTP. The first was based on a graphical version of the classical method of variance. The graphical variance (GV) method was evaluated by clamping the cell at two different holding potentials during paired-pulse facilitation (PPF). The results indicated that the GV method can distinguish changes in mean quantal content m and mean quantal size q in rat mf synapses. The same analysis, when applied to PPF before and after LTP induction, indicated that both result from an increase in m. 4. The second line of evidence was based on the classical method of failures. Consistent with the inference that mf LTP is due to an increase in m, there was a statistically significant reduction in the number of quantal release failures.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Molecular characterization of the 128-kDa immunodominant antigen of Helicobacter pylori associated with cytotoxicity and duodenal ulcer.

Helicobacter pylori has been associated with gastritis, peptic ulcer, and gastric adenocarcinoma. We report the nucleotide sequence and expression of an immunodominant antigen of H. pylori and the immune response to the antigen during disease. The antigen, named CagA (cytotoxin-associated gene A), is a hydrophilic, surface-exposed protein of 128 kDa produced by most clinical isolates. The size of the cagA gene and its protein varies in different strains by a mechanism that involves duplication of regions within the gene. Clinical isolates that do not produce the antigen do not have the gene and are unable to produce an active vacuolating cytotoxin. An ELISA to detect the immune response against a recombinant fragment of this protein detects 75.3% of patients with gastroduodenal diseases and 100% of patients with duodenal ulcer (P < 0.0005), suggesting that only bacteria harboring this protein are associated with disease.

Amino Acid Sequence↗
PubMed1993

Hippocampal circuitry complicates analysis of long-term potentiation in mossy fiber synapses.

Much of the current interest in the hippocampus concerns a rapid and persistent form of synaptic plasticity, called long-term potentiation (LTP), that is a candidate substrate for some of the mnemonic functions of this structure. There are at least two kinds of LTP in the hippocampus. One form is found at the synapse between the mossy fibers of the granule cells and the pyramidal neurons of the CA3 region. Attempts to examine the mechanism underlying this form of LTP have yielded contradictory conclusions. The authors show how the complex circuitry of the dentate gyrus and adjacent hippocampus may have caused the contradictions. To overcome problems introduced by the circuitry, a specific set of procedures and criteria for evoking and identifying mossy fiber responses is proposed. Use of these or similar procedures and criteria will improve the design and interpretation of experiments on mossy fiber LTP and allow more informative comparisons among species and brain regions and across laboratories.

Animals↗
PubMed1993

Detection in an enzyme immunoassay of an immune response to a recombinant fragment of the 128 kilodalton protein (CagA) of Helicobacter pylori.

The possibility of using a recombinant fragment of the CagA (128 kDa protein) for the diagnosis of Helicobacter pylori infection was evaluated. Following cloning of the gene coding for the CagA, a recombinant fragment of it was expressed in Escherichia coli, purified and used in Western blot and an EIA to screen sera from 82 patients with gastroduodenal disease who underwent endoscopic examination. In Western blot, good correlation was found between the serological data obtained with the recombinant antigen and those obtained using non-purified extracts of Helicobacter pylori. The EIA using the antigen showed a sensitivity of 96.2% and a specificity of 96.6% compared with Western blot. These data indicate that the recombinant protein is a reliable antigen for detection of infections with Helicobacter pylori strains that are associated with disease. The EIA assay described may be used in follow-up of the progression of the illness and the results of therapy.

Adult↗
PubMed1992

Citrate as an aluminum chelator and positive effector of the sodium efflux in single barnacle muscle fibers.

The injection of citrate produces considerably greater stimulation of the Na efflux in ouabain-poisoned fibers (from the barnacle Balanus nubilus) than in unpoisoned fibers. When injected in excess together with Al into unpoisoned fibers it is without effect. Its injection is also without effect on the decline in the Na efflux elicited by injecting Al beforehand. Citrate injection into ouabain-poisoned fibers following peak stimulation by injecting Al produces a further rise which is a function of the Al concentration. Al injection after peak stimulation of the ouabain-insensitive Na efflux by citrate is usually without significant effect. Injection of aspartate into poisoned fibers causes a small rise in the remaining Na efflux and fails to prevent the response to Al injection from occurring. Taken together, these observations are in keeping with the view that citrate is not only a powerful chelator of Al but also a powerful activator of reverse Na+/Ca2+ exchange in ouabain-poisoned fibers, presumably because of its ability to raise myoplasmic pMg.

Aluminum↗
PubMed1992

Effects of amygdala lesions on reflex facilitation and conditioned response acquisition during nictitating membrane response conditioning in rabbit.

The present study demonstrated that large lesions of the amygdala disrupt the maintenance of reflex facilitation of the unconditioned nictitating membrane (NM) response and slow the acquisition of conditioned NM responses in rabbit. Before behavioral training, the central nucleus of the amygdala and adjacent areas were lesioned electrolytically. In the 1st experiment, the lesioned animals exhibited no reflex facilitation of the unconditioned NM response at conditioned stimulus (CS)-unconditioned stimulus (US) intervals of 125-8,000 ms. In the 2nd and 3rd experiments in which one CS-US interval (500 ms) was used, the lesions disrupted the maintenance of reflex facilitation but did not alter the facilitation exhibited in the 1st block of training. The lesions retarded the acquisition of conditioned NM responses when the 1000-Hz tone CS intensity was 65 dB but not when the intensity was 85 dB.

Acoustic Stimulation↗