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Biomedical subjects

D Wong

Publications and source records attributed to D Wong.

At least 145 records · Page 8Linked to original sources
PubMed1997

Transience and settlement: Singapore's foreign labor policy.

"Foreigners constitute 15 percent of the population and over 20 percent of the labor force in Singapore.... This large foreign labor force is managed by a comprehensive and highly selective foreign labor policy, which is described in this paper. The strict enforcement of a guestworker policy of transience on the one hand, and the liberal encouragement of settlement on the other, are the twin pillars of this policy. Seen originally as a dispensable appendage to a labor-scarce economy, foreign labor has now become integral to the economic and increasingly, population policy of the country, as evidenced by the recent announcement of a national policy to ¿attract foreign talent'."

Asia↗
PubMed1996

Prevention of hepatitis C virus infection in chimpanzees by hyperimmune serum against the hypervariable region 1 of the envelope 2 protein.

The identification of the neutralization domains of hepatitis C virus (HCV) is essential for the development of an effective vaccine. Here, we show that the hypervariable region 1 (HVR1) of the envelope 2 (E2) protein is a critical neutralization domain of HCV. Neutralization of HCV in vitro was attempted with a rabbit hyperimmune serum raised against a homologous synthetic peptide derived from the HVR1 of the E2 protein, and the residual infectivity was evaluated by inoculation of HCV-seronegative chimpanzees. The source of HCV was plasma obtained from a patient (H) during the acute phase of posttransfusion non-A, non-B hepatitis, which had been titered for infectivity in chimpanzees. The anti-HVR1 antiserum induced protection against homologous HCV infection in chimpanzees, but not against the emergence of neutralization escape mutants that were found to be already present in the complex viral quasispecies of the inoculum. The finding that HVR1 can elicit protective immunity opens new perspectives for the development of effective preventive strategies. However, the identification of the most variable region of HCV as a critical neutralization domain poses a major challenge for the development of a broadly reactive vaccine against HCV.

Amino Acid Sequence↗
PubMed1996

Genetic analysis of macromolecular transport across the nuclear envelope.

Numerous factors that promote movement of macromolecules in and out of the nucleus have now been identified. These include both soluble cytoplasmic and nucleoplasmic proteins and proteins of the nuclear pore complex (NPC). Genetic analyses of the nuclear transport process in the model organism, the budding yeast Saccharomyces cerevisiae, have revealed remarkable conservation of all of these factors. In addition, important clues as to how these factors promote the unique bidirectional movement across the NPC have emerged from studies of yeast. We summarize the characterization and genetic interactions of the soluble transport factors and present data to illustrate how genetic experiments can be used to further define the import and export pathways.

Biological Transport, Active↗
PubMed1996

Platelet/endothelial cell adhesion molecule-1 (PECAM-1) expression by human brain microvessel endothelial cells in primary culture.

PECAM-1 expression was investigated in primary cultures of human brain microvessel endothelial cells (HBMEC). HBMEC constitutively express PECAM-1 along their apical cell surface, advancing processes and on the basal surface at points of contact with the extracellular matrix. Surface expression is not altered by cytokine or lipopolysaccharide treatment. This distribution may mediate cell-cell contract and migration during angiogenesis and HBMEC-leukocyte interactions in CNS inflammation.

Antigens, Surface↗
PubMed1996

Striatal dopamine D2 receptor quantification and superior temporal gyrus: volume determination in 14 chronic schizophrenic subjects.

Chronic schizophrenic (n = 14) and normal subjects (n = 15) were studied with resonance imaging (MRI) and positron emission tomography (PET). Two PET scans were carried out to estimate caudate dopamine D2 receptor densities. MRI was used to measure the volume of the superior temporal gyrus. Average striatal D2 receptor density (Bmax) was significantly higher in the schizophrenic group than in the normal group. Average left superior temporal gyral volume was significantly smaller in the schizophrenic group than in the normal group, and the same tendency was found for the right superior temporal gyrus. Thus, the main finding of this combined analysis of functional and structural neuroimaging techniques was an inverse relationship between reduced superior temporal gyral volume and elevated striatal D2 receptor Bmax values. These preliminary findings require confirmation in larger groups of patients and control subjects.

Adult↗
PubMed1996

Managing HIV. Part 5: Treating secondary outcomes. 5.1 HIV and skin disease.

The skin is the largest and most visible organ of the body, and a perception of good health depends on its appearance as well as its function. As about 90% of HIV-infected patients develop cutaneous signs and symptoms, diagnosis and management are vital in recognising progression of HIV infection.

Acyclovir↗
PubMed1996

Do the Framingham Safety Surveys improve injury prevention counseling during pediatric health supervision visits?

BACKGROUND: Previous studies suggest that injury prevention counseling by pediatricians is effective but accomplished infrequently. The Framingham Safety Surveys (FSS) are brief questionnaires designed to facilitate physician education of parents regarding injury prevention. OBJECTIVE: To determine whether the FSS improve pediatricians' injury prevention counseling. DESIGN: Nonrandomized comparison of a 4-week baseline period and subsequent intervention periods. SETTINGS: Private practice; university hospital clinic. PATIENTS: Patients coming for health supervision visits. INTERVENTION: Provision to the physician of one of the FSS, completed by the parent just before the health supervision visit. OUTCOME MEASURES: (1) After each visit parents completed a checklist of safety issues discussed by the pediatrician. Injury prevention was compared for the two periods by means of three criteria: number of issues discussed (quantity), identification and discussion of specific high-risk behaviors (efficiency), and recognition of high-risk families (targeting). (2) Each physician's assessment of the value of the FSS was obtained by questionnaire. RESULTS: A total of 144 parents (50 from the private practice, 94 from the clinic) completed checklists during the baseline period, and 168 (38 from the private practice, 130 from the clinic) during the intervention period. Use of the FSS produced no detectable improvement in any of the three measures. Seventy-seven percent of the physicians indicated that the FSS were helpful in educating families about safety, 38% thought that the FSS helped identify high-risk families, and 54% said they would use it again. CONCLUSIONS: Although most physicians believed the FSS were useful, introduction of the surveys as employed in this study did not improve injury prevention counseling.

Adolescent↗
PubMed1996

Non-vascular vitreoretinopathy: the cells and the cellular basis of contraction.

BACKGROUND: We consider epiretinal membrane in terms of the two repair processes of gliosis and fibrosis and look at the cellular basis of contraction. METHODS: Pathological material removed at surgery was examined by a range of morphological procedures. Cultures of fibroblasts, retinal pigment epithelium cells and retinal glia were subjected to bioassays which relate to behavioural activities in scar formation. RESULTS AND CONCLUSIONS: Our findings highlight the importance of activities such as migration and adhesion in the formation of epiretinal membranes, and also show that these activities are central to our understanding of contraction.

Animals↗
PubMed1996

'En bloc' dissection of epimacular membranes using aspiration delamination.

'En bloc' dissection is a technique in which epiretinal membranes (ERM) are separated from the retina as a single lamina with a 20-gauge blunt flute needle. We used this technique to remove epimacular membranes of various aetiologies in a consecutive series of 25 eyes, with a minimum follow-up of 5 months (mean 10.4 months). Small residual epicentres of ERM away from the fovea remained in 7 (29.1%) eyes only; 3 were inside and 4 outside the temporal vascular arcades. Postoperatively 64% (16/25) of patients achieved a final visual acuity of 6/12 or better and 76% (19/25) achieved a final visual acuity of 6/18 or better. Progressive lens opacities were the most important postoperative complication in phakic eyes that significantly affected the visual results. This technique successfully removed epimacular membranes over a wide area, without the need to find a starting edge or the use of sharp instruments near the retina. Diaphanous ERMs with ill-defined borders and tenaciously adherent membranes could be removed with minimal trauma to the underlying retina. Histopathological and immunohistochemical examination of 10 ERMs demonstrated the absence of internal limiting lamina in 6 (60%).

Adolescent↗
PubMed1996

Regualtion by cytokines and lipopolysaccharide of E-selectin expression by human brain microvessel endothelial cells in primary culture.

E-selectin is an adhesion molecule expressed on endothelial cells after treatment with inflammatory agents in vitro and in inflammatory diseases in vivo. Interactions between leukocytes and endothelial cells are mediated partly through this adhesion molecule. In this study, the kinetic expression of E-selectin by human cerebral endothelium was studied under standard conditions and following treatment of primary cultures with bacterial lipopolysaccharide (LPS), tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), and interferon-gamma (IFN-gamma). Surface expression of E-selectin was detected by immunocytochemistry, ELISA and immunoelectron microscopy. Untreated human cerebral endothelial cells constitutively expressed low levels of E-selectin. Treatment with LPS, TNF-alpha and IL-beta increased the mean level of E-selectin expression per cell and the percentage of cells expressing E-selectin, in a time and concentration-dependent manner. E-selectin expression was maximal by 4 h post-stimulation and returned unstimulated levels by 48 h. LPS and TNF-alpha were most effective followed by IL-1beta, while the IFN-gamma had no effect on E-selectin expression. Immunoelectron microscopy demonstrated that E-selectin was preferentially expressed on the apical surface of unstimulated and TNF-alpha treated cells. Cytokine stimulation induced a several-fold increase of E-selectin expression on the apical and to a lesser extent on the basal cell surface. Modulation of E-selectin expression on cerebral endothelium by inflammatory cytokines suggests a potentially important role of this adhesion molecule in the recruitment of leukocytes in central nervous (CNS) inflammation.

Adult↗
PubMed1996

Autoradiographic method for isolation of diverse microbial species with unique catabolic traits.

A novel autoradiographic method for isolation of bacteria with unique catabolic traits was developed to overcome many of the limitations of traditional selective enrichment techniques. The method consists of five steps. (i) An environmental sample is directly plated (without enrichment) on a microporous filter atop a solid medium that allows cultivation of diverse kinds of microorganisms. (ii) Once colonies form, two replicas of the filter are prepared and the colonies are regrown. (iii) The replica filters are starved 24 to 72 h to deplete intracellular carbon reserves and then (iv) placed on Na(inf2)(sup35)SO(inf4)-containing solid media with and without a test compound. (v) Following an incubation period, the replica filters are exposed to film in order to identify colonies that incorporate more (sup35)S into cell biomass in the presence of the test compound than in its absence, providing presumptive evidence for metabolism of the compound. The colonies identified in this manner can be recovered from the master filter. To demonstrate this technique, bacteria capable of degrading benzoate were isolated from a single soil slurry by traditional enrichment as well as by autoradiography. From the enrichment culture, a single isolate able to degrade benzoate was obtained. In contrast, 18 distinct strains were obtained by purifying 19 putative benzoate-degrading colonies identified by autoradiography. Each of the 18 strains was able to completely transform the substrate, as determined by high-performance liquid chromatography analyses. The doubling times of a subset of the isolates grown in benzoate medium ranged from 1.4 to 17.1 h, whereas the doubling time of the isolate obtained by enrichment was 2.0 h. These data demonstrate that the method described here can be used to obtain a collection of diverse organisms able to metabolize a specific compound.

Journal Article↗
PubMed1996

Foreign domestic workers in Singapore.

"This paper discusses the regulatory and economic context of Filipina migration into domestic waged labor in Singapore. It places this migration in the history of female rural-urban migration as well as the history of domestic labor in Singapore. Finally, it raises the question as to why domestic waged labor has persisted in the global capitalist economy."

Asia↗
PubMed1995

Arabidopsis mutants deficient in T-DNA integration.

Arabidopsis thaliana mutants originally isolated as hypersensitive to irradiation were screened for the ability to be transformed by Agrobacterium transferred DNA (T-DNA). One of four UV-hypersensitive mutants and one of two gamma-hypersensitive mutants tested showed a significant reduction in the frequency of stable transformants compared with radioresistant controls. In a transient assay for T-DNA transfer independent of genomic integration, both mutant lines took up and expressed T-DNA as efficiently as parental lines. These lines are therefore deficient specifically in stable T-DNA integration and thus provide direct evidence for the role of a plant function in that process. As radiation hypersensitivity suggests a deficiency in repair of DNA damage, that plant function may be one that is also involved in DNA repair, possibly, from other evidence, in repair of double-strand DNA breaks.

Agrobacterium tumefaciens↗
PubMed1995

Chronic parenterally administered nicotine and stress- or ethanol-induced gastric mucosal damage in rats.

Mini-osmotic pumps containing solutions of either 0.9% NaCl (infused at the rate of 0.5 microliter/h) or nicotine (infused in doses of 0.224, 1.03 or 1.88 mg/kg per day) were implanted s.c. into rats 12 days before experimentation. The alkaloid increased solid food consumption, but fluid intake and average weight gain were similar among the animals given saline or nicotine. Chronic nicotine treatment dose dependently intensified cold (4 degrees C)-restraint stress-induced ulceration and increased mast cell degranulation. Oral administration of 40% ethanol to nicotine-treated animals also produced greater mucosal damage; mast cell degranulation by ethanol was significantly worsened after alkaloid treatment. These findings show that the stress ulcer-intensifying action of the alkaloid is mainly through a systemic mechanism. In the case of ethanol-evoked mucosal damage, in addition to a topical effect, stimulation of the stomach wall ganglia is likely to participate in the exaggerated post-vagal ulcerogenic responses as seen in stress.

Animals↗
PubMed1995

Expression of vascular cell adhesion molecule-1 (VCAM-1) by human brain microvessel endothelial cells in primary culture.

Vascular cell adhesion molecule-1 (VCAM-1) is an endothelial cell membrane glycoprotein that has been implicated in leukocyte/endothelial cell interactions in inflammation. In this study, we report the expression of VCAM-1 in primary cultures of human brain microvessel endothelial cells (HBMEC) under standard conditions and following bacterial lipopolysaccharide (LPS), tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1 beta), or interferon-gamma (IFN-gamma) treatment. Surface expression was detected and quantitated by light and immunogold electron microscopy and ELISA. Unstimulated cerebral endothelial cells (EC) constitutively expressed low levels of VCAM-1. LPS, TNF-alpha, or IL-1 beta increased the overall intensity of surface staining and the percentage of cells expressing VCAM-1 in a time- and concentration-dependent manner. LPS had the most potent effect, followed by TNF-alpha and then IL-1 beta. IFN-gamma did not upregulate VCAM-1. The level of VCAM-1 expression increased by 12-24 hr and returned to unstimulated levels by 48 hr. Immunoelectron microscopy demonstrated that VCAM-1 was preferentially localized on the apical as compared to the basal surface in both unstimulated and cytokine-treated cells. In addition, the intensity of immunostaining was significantly greater in stimulated versus unstimulated EC. The polarization and significant upregulation of VCAM-1 after cytokine treatment suggest a possible role of this adhesion molecule in inflammatory and autoimmune processes within the central nervous system.

Brain↗
PubMed1995

Activity of the yeast FLP recombinase in Arabidopsis.

The coding sequence for FLP recombinase, originally from the 2 mu plasmid of Saccharomyces cerevisiae, was introduced into Arabidopsis behind the cauliflower mosaic virus 35S promoter. FLP activity was monitored by the glucuronidase activity resulting from inversion of an antisense-oriented GUS reporter gene flanked by a pair of FRT target sites in inverted repeat. FLP-dependent Gus activity was observed in both transient assays and transgenic plants. The FLP system will be useful for a variety of in planta genetic manipulations.

Arabidopsis↗