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Biomedical subjects

T Wong

Publications and source records attributed to T Wong.

At least 91 records · Page 5Linked to original sources
PubMed1997

Intrachain disulfide bond in the core hinge region of human IgG4.

IgG is a tetrameric protein composed of two copies each of the light and heavy chains. The four-chain structure is maintained by strong noncovalent interactions between the amino-terminal half of pairs of heavy-light chains and between the carboxyl-terminal regions of the two heavy chains. In addition, interchain disulfide bonds link each heavy-light chain and also link the paired heavy chains. An engineered human IgG4 specific for human tumor necrosis factor-alpha (CDP571) is similar to human myeloma IgG4 in that it is secreted as both disulfide bonded tetramers (approximately 75% of the total amount of IgG) and as tetramers composed of nondisulfide bonded half-IgG4 (heavy chain disulfide bonded to light chain) molecules. However, when CDP571 was genetically engineered with a proline at residue 229 of the core hinge region rather than serine, CDP571 (S229P), or with an IgG1 rather than IgG4 hinge region, CDP571(gamma 1), only trace amounts of nondisulfide bonded half-IgG tetramers were observed. Trypsin digest reversephase HPLC peptide mapping studies of CDP571 and CDP571(gamma 1) with on-line electrospray ionization mass spectroscopy supplemented with Edman sequencing identified the chemical factor preventing inter-heavy chain disulfide bond formation between half-IgG molecules: the two cysteines in the IgG4 and IgG1 core hinge region (CPSCP and CPPCP, respectively) are capable of forming an intrachain disulfide bond. Conformational modeling studies on cyclic disulfide bonded CPSCP and CPPCP peptides yielded energy ranges for the low-energy conformations of 31-33 kcal/mol and 40-42 kcal/mol, respectively. In addition, higher torsion and angle bending energies were observed for the CPPCP peptide due to backbone constraints caused by the extra proline. These modeling results suggest a reason why a larger fraction of intrachain bonds are observed in IgG4 rather than IgG1 molecules: the serine in the core hinge region of IgG4 allows more hinge region flexibility than the proline of IgG1 and thus may permit formation of a stable intrachain disulfide bond more readily.

Alkylation↗
PubMed1997

One clinical visit for a multiple implant restoration master cast fabrication.

The making of a one-piece, long-span, implant-supported prosthesis with conventional procedures frequently has difficulties associated with the accuracy of fit. This article presents a clinical and laboratory procedure for making an accurate implant working cast that facilitates fabrication of the casting on the master cast. The procedure demonstrates the process of sectioning and rejoining of the resin between the transfer copings and then pouring the impression by first joining the analogs alone with impression plaster, sectioning it, and rejoining it again to stabilize the analogs, and finally, using dental stone to pour the impression. Clinical, radiographic, and laboratory (optical microscope) measurements for one clinical implant restoration confirm the accuracy of fit of this one prosthesis made with this procedure. Its advantage is that it can allow fabrication of the final casting on the cast, thereby eliminating the clinical time necessary to obtain repetitive solder indexes, and thus minimizing inconvenience to the patient.

Calcium Sulfate↗
PubMed1996

Repeat HLA-B and -DR loci mismatching at second liver transplantation improves patient survival.

The role of HLA matching in liver transplantation remains uncertain, and the effect of HLA mismatches on the outcome of second transplants has not been studied. In renal transplantation, if HLA mismatches are repeated in the second graft there is a greatly increased risk of immunological graft failure. In the present study, 78 patients who had received second liver transplants were studied. HLA typing was performed using standard complement-dependent microcytotoxicity for class I (A and B) antigens, and a combination of restriction fragment length polymorphism and serology for HLA-DR. Patient survival at follow-up for those with a repeat B locus mismatch was improved (79% compared with 43%, P < 0.02), and a similar effect was noted for repeat DR mismatches (67% vs. 47%, P = 0.06). In the subgroup of patients who received a second transplant for graft rejection, 90% of patients with a repeat B mismatch were alive at follow-up compared with 46% without B mismatches (P = 0.02). This improvement in patient survival was evident during the first 2 months after the second transplant. In this study, repeat HLA-B and -DR mismatching improves survival after second transplantation.

Adolescent↗
PubMed1996

Optimally functional fluorescein isothiocyanate-labelled fibrinogen for quantitative studies of binding to activated platelets and platelet aggregation.

Dynamic and quantitative studies of the binding of fibrinogen (Fg) to its receptor, GPIIb-IIIa, on activated platelets, leading to platelet aggregation, are best studied with fluorescently-labelled Fg by flow cytometry. Due to conflicting reports on the functionality of FITC-labelled Fg, we have developed a reproducible and 'mild' labelling of fibrinogen with FITC-celite at pH 7.4-8.5 for direct and dynamic studies of specific Fg binding to activated platelets evaluated for native platelet-rich plasma, for washed platelets, and for activated, fixed platelets. We have demonstrated the equivalence of FITC-labelled and unlabelled Fg for binding to activated GPIIb-IIIa receptors, and in the rate and extent of mediating platelet aggregation. We found that FITC-Fg labelled at pH > or = 9 had reduced to absent specific binding to activated platelets, whether using soluble FITC or FITC-celite. The FITC-labelled Fg must be diluted 3-fold with unlabelled Fg when evaluating maximal Fg binding to activated platelets in order to prevent autoquenching of the FITC-Fg which leads to underestimation of Fg levels. The dissociation constant (KD) of Fg on stable preparations of activated, fixed platelets, determined with FITC-Fg binding to platelets by flow cytometry, was in the range reported for 125I-labelled Fg, 70-255 nm with Bmax = 10000-25000 Fg per platelet (n = 20). The FITC-Fg was used to monitor Fg binding to activated platelets directly by plasma, as well as to evaluate platelet subpopulations which maximally bind Fg according to the concentration of ADP used as activator. It is expected that this 'mildly' labelled FITC-Fg will stimulate further studies of platelet activation directly in native anticoagulated blood/plasma, for both basic and clinical research.

Blood Platelets↗
PubMed1996

Modulation of lysyl oxidase by dietary copper in rats.

Lysyl oxidase levels were estimated in rat tissues using an enzyme-linked immunosorption assay (ELISA) and a functional assay standardized against known amounts of purified lysyl oxidase. High concentrations of lysyl oxidase (> or = 150 micrograms/g of tissue or packed cells) were detected in connective tissues, such as tendon and skin. Values for aorta, kidney, lung and liver ranged from 30 to 150 micrograms/g of tissue; values for skeletal muscle and diaphragm were < 30 micrograms/g tissue. Purified rat skin lysyl oxidase catalyzed the release of 50-100 Bq of tritium per micrograms enzyme in assays that used 3H-elastin-rich substrates. In dense connective tissues, good agreement was obtained for the values from ELISA and those derived from measurements of functional activity in aorta, lung, skin and tendon (r2 > 0.9). When egg white-based experimental diets containing 2 or 10 micrograms/g added copper were fed to weanling rats, values for skin lysyl oxidase functional activity in the group fed 2 micrograms/g added copper were one-third to one-half the values for skin lysyl oxidase functional activity in rats fed 10 micrograms/g copper. This reduction in lysyl oxidase activity, however, had minimal effect on indices of collagen maturation in rat skin, e.g., collagen solubility in neutral salt and dilute acid or the levels of acid stable cross-links. Moreover, copper deficiency did not influence the steady-state levels of lysyl oxidase specific mRNA in rat skin or the apparent amounts of lysyl oxidase in rat skin as determined by ELISA. These observations underscore that the concentration of lysyl oxidase is relatively high in dense corrective tissues, and although decreasing dietary copper influences functional activity, there is little apparent effect on the production of lysyl oxidase protein.

Administration, Oral↗
PubMed1996

International comparison of baccalaureate nursing degrees: collaboration in qualitative analysis.

This paper describes a study which investigated the perceived similarities and differences of a selection of baccalaureate nursing degrees from different continents. An international research team was formed, and by using a modified version of the Delphi process and nominal group techniques the group undertook a qualitative analysis of curriculum documents. The major areas analysis were: aims, content, methods and assessment. Under these headings the group produced a list of key issues supported by a number of indicative statements by collating the independent analyses undertaken by each of the team members. Examples of findings are that critical thinking and personal development are most obvious in aims but that the progression of curricula may not achieve this, there are differences in 'western' and 'asian' orientations to the concept of personal autonomy. Sciences are valued more than arts or humanities. The lecture method as well as practice placement dominate the teaching methods. Transcultural nursing is not significant except where there are two therapeutic ideologies in existence. Assessment methods are largely summative. The findings have application in the development of credit transfer and international exchange schemes. The conclusions highlight areas of special considerations when designing such schemes.

China↗
PubMed1996

Platelets from bleeding Simmental cattle have a long delay in both ADP-activated expression of GpIIB-IIIA receptors and fibrinogen-dependent platelet aggregation.

We have previously reported that platelets from bleeding Simmental cattle do not aggregate in vitro in response to ADP, collagen and calcium ionophore A23187, though calcium mobilization and myosin light chain phosphorylation do occur. The aggregation abnormality, measured by aggregometry, was ascribed to abnormal cytoskeletal expression, with the maximal numbers of activated GpIIb-IIIa receptors per platelet no different from that seen in normal bovine platelets activated with ADP. We have therefore sought to compare the kinetics of micro-aggregation with the rate of expression of GpIIb-IIIa receptors required for mediating fibrinogen (Fg)-dependent platelet aggregation, to provide a more direct molecular explanation for the aggregation abnormality. We compared aggregation kinetics of ADP-activated platelets using both aggregometry and particle counting to monitor micro-aggregation. Fibrinogen receptor expression was monitored with FITC-labelled human Fg and with the reporting antibody for activated GpIIb-IIIa, FITC-PAC1, using flow cytometry. The affected platelets show a marked delay in onset of microaggregation for ADP-activated platelets stirred with human Fg, paralleded by an unusual delay in activated GpIIb-IIIa receptor expression (DARE) for otherwise competent Fg binding. The on-rates for Fg binding to platelets maximally pre-activated with PMA are identical for normal and affected platelets, whether comparing the binding of human or bovine Fg. The unique DARE syndrome explains the observed delay in aggregation of platelets from affected Simmental cattle and predicts the bleeding problems due to delayed binding of adhesive proteins.

Adenosine Diphosphate↗
PubMed1995

Improving long-term prognosis for survivors of mechanical ventilation in patients with AIDS with PCP and acute respiratory failure. Five-year follow-up of intensive care unit discharges.

BACKGROUND: Before 1987, the hospital survival of patients with acquired immunodeficiency syndrome, Pneumocystis carinii pneumonia, and acute respiratory failure receiving mechanical ventilation was less than 15%. Hospital survival has improved since then, but concerns have been raised that the post-hospital discharge survival of these patients remains extremely poor. This study evaluated the long-term survival of patients discharged alive after an acute episode of acute respiratory failure caused by P carinii pneumonia. METHODS: A prospective cohort study was conducted for the 5-year period from May 1987 through May 1992 in an urban teaching hospital. Forty-seven patients discharged from the hospital after receiving mechanical ventilation and/or continuous positive airway pressure for acquired immunodeficiency syndrome, P carinii pneumonia, and acute respiratory failure were followed up from their initial intensive care unit admission until death or termination of the study to measure the long-term survival and cumulative probability of survival of the study cohort. Actuarial life-table analysis was performed, and long-term cumulative probability of survival was calculated on the basis of the life-table analysis. Median survival was estimated by means of the product-limit method. RESULTS: During the 5-year follow-up of the 47 subjects, 31 patients died, 12 were unavailable for follow-up, and four were still alive at the end of the cutoff. The cumulative survival rate at 1 year was 80% (95% confidence interval, 92% to 68%); at 2 years, 49% (95% confidence interval, 65% to 34%); at 3 years, 18% (95% confidence interval, 32% to 4%); and at 4 years, 6% (95% confidence interval, 17% to 0%). Median survival time for all subjects was 602 days (1.65 years), and the longest survival time for a single patient was 1774 days (4.86 years). CONCLUSIONS: Post-hospital discharge survival of patients with acquired immunodeficiency syndrome, P carinii pneumonia, and acute respiratory failure has improved dramatically in the past decade. Patients can undergo intubation and mechanical ventilation with the hope of reasonable long-term survival.

AIDS-Related Opportunistic Infections↗
PubMed1995

p32, a platelet autoantigen recognized by an SLE-derived autoantibody that inhibits platelet aggregation.

We have previously described an SLE-derived human hybridoma autoantibody, 9604, which binds to activated but not to resting platelets, inhibits platelet aggregation, and immunoprecipitates a surface-labelled poly-peptide of 32,000 molecular weight (MW) (p32). In the present study, using a murine monoclonal anti-p32 antibody (8E8), we show that p32 is responsible for the binding of 9604 to activated platelets. First, 8E8 bound to the surface of activated but not resting platelets, as detected by flow cytometry, showing saturation with 1900 antibody molecules bound/platelet and a Kd of 72 nM. Second, complete inhibition of the binding of 9604 to ADP-activated platelets by 8E8 and inhibition of the reactivity of 8E8 with p32 by 9604 demonstrated that 8E8 and 9604 recognize the same 32,000 MW platelet polypeptide. Isolation of platelet proteins, using an 8E8-affinity column, showed high MW bands corresponding to multimers of p32 under non-reducing conditions, and isolated p32 tended to self-associate even under reducing conditions. High performance liquid chromatography (HPLC) demonstrated that the native p32-containing protein has an approximate MW of 450,000. A comparison of the functional properties of murine monoclonal 8E8 and human monoclonal 9604 revealed that both antibodies are cytotoxic to platelets in 51Cr-release assays. In contrast, 8E8, unlike 9604, did not affect platelet aggregation, suggesting that different epitopes may be recognized by the two antibodies. These findings demonstrate that p32 is a subunit of an activation marker that is expressed on the surface of activated platelets and recognized by an SLE-derived anti-platelet autoantibody. Our data also indicate that murine monoclonal antibodies produced against platelet autoantigens may not mimic the functional activities of spontaneously occurring autoantibodies, probably due to the recognition of different epitopes.

Animals↗
PubMed1995

Postsynaptic cAMP pathway gates early LTP in hippocampal CA1 region.

The role of the cAMP pathway in LTP was studied in the CA1 region of hippocampus. Widely spaced trains of high frequency stimulation generated cAMP postsynaptically via NMDA receptors and calmodulin, consistent with the Ca2+/calmodulin-mediated stimulation of postsynaptic adenylyl cyclase. The early phase of LTP produced by the same pattern of high frequency stimulation was dependent on postsynaptic cAMP. However, synaptic transmission was not increased by postsynaptic application of cAMP. Early LTP became cAMP-independent when protein phosphatase inhibitors were injected postsynaptically. These observations indicate that in early LTP the cAMP signaling pathway, instead of transmitting signals for the generation of LTP, gates LTP through postsynaptic protein phosphatases.

Animals↗
PubMed1995

The effect of high-dose medium- and long- term progestogen exposure on endometrial vessels.

A total of 19 paraffin-embedded endometrial tissue blocks were obtained from high-dose progestogen-exposed patients. A labelled streptavidin-biotin-alkaline phosphatase method was used with antibodies against von Willebrand factor (vWF) and CD34. The density of CD34 and vWF positive (CD34+ and vWF+) vessels in progestogen-exposed endometria (103 +/- 9.6/mm2 and 106 +/- 8.7/mm2) was significantly lower than in endometria from women with normal cycles (169 +/- 9.3/mm2 and 136 +/- 8.0/mm2) (P < 0.05). In women with normal menstrual cycles the concentration of CD34+ vessels was significantly higher than the number of vWF+ vessels (P = 0.0001). By comparison, the concentration of CD34+ vessels was similar to the concentration of vWF+ vessels in progestogen-exposed endometria. The ratios of vascular density as determined by vWF+ and CD34+ staining the control and progestogen groups were 0.81 and 1.05 respectively (P = 0.0001). Dilated venules were seen in the progestogen group. This study has demonstrated firstly that CD34 antibody detected the endothelial cells in a higher proportion of small endometrial vessels than vWF, and secondly that high-dose progestogen exposure significantly decreased the density of microvessels and increased the number of dilated venules in endometrium.

Antigens, CD↗
PubMed1995

An isoleucyl-tRNA synthetase gene from Campylobacter jejuni.

A complete isoleucyl-tRNA synthetase gene (ileS) of Campylobacter jejuni was isolated from a C. jejuni TGH9011 genomic DNA library constructed in pBluescript. The complete coding sequence, flanking regions and transcription start point were determined. The deduced isoleucyl-tRNA synthetase (IleRS) had 917 amino acids with a molecular mass of 105,399 Da, which was consistent with the observed size of 105 kDa in Escherichia coli maxicells. The ileS gene was mapped onto the physical map of the C. jejuni genome. Alignment of the C. jejuni IleRS sequence with six other bacterial IleRS sequences and two lower eukaryotic IleRS sequences identified seven conserved motifs, including the two signature sequences, HIGH and KMSKS, of class I aminoacyl-tRNA synthetases.

Amino Acid Sequence↗