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Biomedical subjects

S Y Chan

Publications and source records attributed to S Y Chan.

At least 127 records · Page 7Linked to original sources
PubMed1995

Analysis of genomic sequences of 95 papillomavirus types: uniting typing, phylogeny, and taxonomy.

Our aim was to study the phylogenetic relationships of all known papillomaviruses (PVs) and the possibility of establishing a supratype taxonomic classification based on this information. Of the many detectably homologous segments present in PV genomes, a 291-bp segment of the L1 gene is notable because it is flanked by the MY09 and MY11 consensus primers and contains highly conserved amino acid residues which simplify sequence alignment. We determined the MY09-MY11 sequences of human PV type 20 (HPV-20), HPV-21, HPV-22, HPV-23, HPV-24, HPV-36, HPV-37, HPV-38, HPV-48, HPV-50, HPV-60, HPV-70, HPV-72, HPV-73, ovine (sheep) PV, bovine PV type 3 (BPV-3), BPV-5, and BPV-6 and created a database which now encompasses HPV-1 to HPV-70, HPV-72, HPV-73, seven yet untyped HPV genomes, and 15 animal PV types. Three additional animal PVs were analyzed on the basis of other sequence data. We constructed phylogenies based on partial L1 and E6 gene sequences and distinguished five major clades that we call supergroups. One of them unites 54 genital PV types, which can be further divided into eleven groups. The second supergroup has 24 types and unites most PVs that are typically found in epidermodysplasia verruciformis patients but also includes several types typical of other cutaneous lesions, like HPV-4. The third supergroup unites the six known ungulate fibropapillomaviruses, the fourth includes the cutaneous ungulate PVs BPV-3, BPV-4, and BPV-6, and the fifth includes HPV-1, HPV-41, HPV-63, the canine oral PV, and the cottontail rabbit PV. The chaffinch PV and two rodent PVs, Micromys minutus PV and Mastomys natalensis PV, are left ungrouped because of the relative isolation of each of their lineages. Within most supergroups, groups formed on the basis of cladistic principles unite phenotypically similar PV types. We discuss the basis of our classification, the concept of the PV type, speciation, PV-host evolution, and estimates of their rates of evolution.

Amino Acid Sequence↗
PubMed1995

Lymphoepithelial carcinoma of the salivary gland: in situ detection of Epstein-Barr virus.

AIM: To examine the role of Epstein-Barr virus (EBV) in lymphoepithelial carcinoma of the salivary gland in Hong Kong Chinese. METHODS: Ten cases of lymphoepithelial carcinoma of the salivary gland (eight parotid and two submandibular) were examined. In situ hybridisation was used to localise EBER RNA, immunohistochemical methods to detect expression of latent membrane protein 1 (LMP-1) in EBV positive tumours, and Southern blot analysis to examine the clonality of EBV in the two cases where frozen tissue was available. RESULTS: None of the cases had a history of Sjögren's syndrome or histological evidence of a benign lymphoepithelial lesion. The IgA antibody titre against EBV viral capsid antigen was elevated in four cases. All cases were EBV positive by in situ hybridisation, with a strong uniform positive signal in the epithelial cells, and all cases expressed LMP-1. Southern blot analysis revealed that the clonal episomal form of the virus was present. Two of the three female patients in this series also developed carcinoma of cervix. One of these carcinomas had histological features of a lymphoepithelioma-like carcinoma but was EBV negative. CONCLUSIONS: A consistent association between EBV and lymphoepithelial carcinoma of the salivary gland was found. The presence of the virus in a clonal episomal form, and the expression of LMP-1 viral oncoprotein is further evidence of the role of EBV in the oncogenesis of this tumour.

Adult↗
PubMed1994

Helper T lymphocyte unresponsiveness to cardiac allografts following transient depletion of CD4-positive cells. Implications for cellular and humoral responses.

Initial treatment of heterotopic cardiac transplant recipients with anti-CD4 mAb promotes long-term (> 60 days) allograft survival. We have used modified limiting dilution analysis to quantitate donor alloantigen-reactive helper T lymphocytes (HTL) and CTL in mice bearing long-term cardiac allografts. Despite repopulation of lymphoid tissues with CD4+ T cells, donor alloantigen-reactive IL-2 producing and IL-4-producing HTL were rare or not detectable in lymphoid tissues or in the graft. While donor-reactive precursor CTL were present in lymphoid tissues, modified limiting dilution analysis revealed that stimulated ("antigen-conditioned") CTL were not detectable, and few CTL were present in the graft. In addition, antibodies reactive with donor alloantigens were not detectable in the sera of mice bearing long-term cardiac allografts. To determine whether additional in vivo stimulation with donor alloantigens would elicit an immune response, sponge allografts were implanted into mice bearing long-term cardiac allografts. Previous reports from this laboratory have demonstrated that T cell infiltration of sponge allografts is dependent upon antigen-driven cytokine production. While third-party sponge allografts were readily infiltrated by third-party-reactive HTL and CTL, sponge allografts of the same strain as the cardiac allograft were not infiltrated by T cells. However, donor strain sponge allografts induced an IgM (but not IgG) alloantibody response. These data indicate that IgM alloantibody could be induced in the absence of a cellular response to the sponge allograft. Kinetic studies revealed that a transient IgM (but not IgG) response was induced by the initial cardiac transplantation in the absence of CD4+ cells. These IgM alloantibodies disappeared by day 21 despite the persistence of the allograft. These observations indicate that transient depletion of CD4+ T cells induces allograft-specific T cell tolerance, but does not eliminate the ability to mount an allograft-specific IgM response. To our knowledge, this is the first report of a transient humoral response to alloantigens that occurs in the absence of CD4+ T cells, and can be reinduced in "tolerant" animals that fail to mount a cellular immune response. Potential mechanisms involved in the development and maintenance of anti-CD4 mAb-induced tolerance are discussed.

Animals↗
PubMed1994

Previously undiagnosed lymphoma presenting as recurrent dacryocystitis.

Lymphoma occurring in the lacrimal sac is uncommon and usually occurs in patients with known systemic disease. We report the case of an 82-year-old woman who presented with recurrent right dacryocystitis and a mass in the left lower eyelid. The results of the biopsy of the eyelid and fine-needle aspiration of the swelling arising from the lacrimal fossa demonstrated low-grade B-cell non-Hodgkin's lymphoma. This unusual presentation and the histopathological features are described.

Aged↗
PubMed1994

Applications of electrospray mass spectrometry to erythropoietin N- and O-linked glycans.

The improved sensitivity and soft ionization characteristics of electrospray (ES) mass spectrometry (MS) has been applied to the glycan structures of recombinant erythropoietin (rEPO). The four glycopeptides (O-126, N-24, N-38, N-83) were mapped, isolated, deglycosylated, and the glycans profiled (without desialylation) by ES-MS as their methyl derivatives. The O-linked glycopeptide was also analyzed directly. In this fraction seven glycans were identified (two previously unreported) in addition to the unglycosylated peptide. The three N-linked fractions were divided with one fraction preceded by periodate oxidation and reduction to resolve isomeric structures, linkage, and branching patterns, and confirm the overall structural motif. All were methylated and profiled. Two biantennary, 8 triantennary, and 10 tetraantennary structures were identified with approximately 13% of each N-linked glycan possessing a single N-glycolylneuraminyl analog. The minimal energies of ionization, the absence of a matrix background, and enhanced sensitivity brings an improved technology for studying carbohydrate structural detail.

Carbohydrate Conformation↗
PubMed1994

Characterization of recombinant BHK-21 endogenous particles: R-type particles.

R-particles are morphologically unique, non-infectious, virus-like particles present in Syrian hamster cells, including recombinant BHK-21 cells. Hybridization and induction studies were employed to confirm and extend literature observations on the genetic relationship between R-particles and intracisternal A particles (IAPs). Dot blot hybridization techniques using IAP probes were developed to estimate the concentration of R-particles in culture fluids and in-process fractions in the purification of recombinant Factor VIII. From these studies it was determined that R-particles are removed to undetectable levels at an early step in the purification process. It was concluded from these data, the known lability and the lack of evident biological activity, that R-particles do not present a safety hazard for the production of Factor VIII.

Animals↗
PubMed1994

The Mastomys natalensis papillomavirus: nucleotide sequence, genome organization, and phylogenetic relationship of a rodent papillomavirus involved in tumorigenesis of cutaneous epithelia.

Mastomys natalensis is a rodent of African origin afflicted with a very high incidence of skin tumors (keratoacanthomas and squamous carcinomas), which are associated with a papillomavirus, M. natalensis papillomavirus (MnPV). We have determined the genomic sequence of MnPV, which has a size of 7687 bp. The genomic organization is similar to that of other papillomaviruses, with open reading frames E6, E7, E1, E2, and E4 in the early and L2 and L1 in the late region. Due to an unusually large hinge region, the transcriptional activator E2 has a size of 542 amino acids rather than 400 to 460 amino acids, as in other papillomaviruses. An open reading frame E5 coding for a small hydrophobic membrane protein is missing, as is the case for some cutaneous human papillomaviruses (HPV). This fact, together with the composition of cis-responsive elements in its long control region and phylogenetic evaluation of segments of its E6, E1, and L1 genes, indicates a relationship of MnPV to the cottontail rabbit papillomavirus and several HPV types found in lesions of cutaneous epithelia, in particular to those that are associated with epidermodysplasia verruciformis. MnPV may be a useful model system for tumorigenesis of cutaneous epithelia in humans.

Amino Acid Sequence↗
PubMed1994

Human papillomavirus type 2c is identical to human papillomavirus type 27.

Human papillomavirus type 27 (HPV-27) and HPV-2c are isolates of the same virus as judged by genomic sequence identity. In a 400-bp stretch of the long control region and the E6 and L1 genes no changes were found between HPV-27 and HPV-2c whereas 55 changes were found between HPV-27 and HPV-2a. This justifies the elevation of HPV-2c to type status and strongly suggests its identity with HPV-27. This reassessment makes HPV-27 one of the most abundant viruses associated with common warts.

Base Sequence↗
PubMed1994

The influence of antibody levels in dengue diagnosis by polymerase chain reaction.

The potential of RT-PCR to rapidly diagnose dengue infections from both acute and convalescent phase patients' sera was evaluated. The RNA extraction method involved binding of the viral RNA to silica particles in the presence of high concentration of guanidine thiocyanate. The protocol that was established was sensitive enough to detect 40 plaque forming units per 100 microliter of serum and results could be obtained within one day. Results from this study indicate that clinical samples should be collected in the early acute phase of illness when anti-dengue antibodies were undetectable or of low titres to ensure a more reliable diagnosis.

Aedes↗
PubMed1994

Second-line treatment with ifosfamide and carboplatin in patients with ovarian carcinoma relapsing after treatment with carboplatin.

20 patients with ovarian carcinoma whose disease had relapsed (1-42 months, median 4 months) after showing either response or stable disease to carboplatin, were treated with ifosfamide (5 g/m2 intravenously over 24 h, day 1) and carboplatin (200 mg/m2 intravenously day 2) as second-line treatment. The mean number of treatment cycles was 3.5 (range 1-6). The major toxicities were thrombocytopenia (WHO grade 3/4, 25%), neutropenia (WHO grade 3/4, 40%) and encephalopathy (WHO grade 3/4, 15%). Overall response rate was 15% [complete response, 0; partial response, 3 (15%); no change, 5 (25%) and progressive disease, 12 (60%)]. The median survival from the date of second-line treatment was 7 months. This combination offers no advantage over either agent used alone.

Adult↗
PubMed1994

Identification and assessment of known and novel human papillomaviruses by polymerase chain reaction amplification, restriction fragment length polymorphisms, nucleotide sequence, and phylogenetic algorithms.

The identification and taxonomy of papillomaviruses has become increasingly complex, as approximately 70 human papillomavirus (HPV) types have been described and novel HPV genomes continue to be identified. Methods and corresponding DNA sequence data bases were designed for the reliable identification of mucosal HPV genomes from clinical specimens. HPVs are identified by the amplification of a fragment of the L1 region by consensus primer polymerase chain reaction (PCR) and subsequent hybridization or restriction fragment length polymorphism analysis. L1 PCR fragments may be further characterized by nucleotide sequencing. Conservation of 30 (of 151) predicted amino acids identifies HPV genomic fragments, and nucleotide sequence alignments allow calculation of their phylogenetic relatedness. Sequence differences > 10% from any known HPV type suggest a novel HPV type. Phylogenetic relationships with known HPV types may permit predictions of biology. With these criteria, 10 PCR fragments were identified that would qualify as new genital HPV types after complete genomic isolation.

Amino Acid Sequence↗
PubMed1994

In situ detection of Epstein-Barr virus in gastric and colorectal adenocarcinomas.

The association of Epstein-Barr virus (EBV) with lymphoepithelioma-like carcinoma in the nasopharynx, which is common in Chinese from the southern region, is well established. Recently, EBV has also been found to be associated with lymphoepithelioma-like carcinomas (LELCs) and carcinomas with prominent lymphoid infiltrates in the stomach. We investigated for the presence of EBV in 74 cases of gastric adenocarcinoma and 36 cases of colorectal adenocarcinoma from Chinese patients by in situ hybridization (ISH) using an antisense EBER probe. In seven cases (9.5%) of gastric carcinoma, EBER was highly expressed in the adenocarcinoma cells and metastatic tumor cells in regional lymph nodes. In all these cases, the normal gastric epithelium was EBV negative. None of the colorectal carcinomas showed a positive signal. Isolated positive lymphoid cells were frequently found in both tumors. Of the seven positive cases, only one was LELC, and the others were conventional adenocarcinomas of the intestinal type. Five showed expression of the viral RNA in all tumor cells as well as the surrounding dysplastic epithelium. Interestingly, the sixth case showed distinct negative islands of dysplastic glands adjacent to strongly positive dysplastic glands and invasive carcinoma cells. This pattern of positivity, together with negative normal gastric epithelium and positive metastatic tumor, suggested that EBV infection occurred in the dysplastic phase and that an apparent growth advantage was conferred by the EBV infection.

Adenocarcinoma↗
PubMed1994

Detailed structural characterization of succinoglycan, the major exopolysaccharide of Rhizobium meliloti Rm1021.

The detailed structure of the symbiotically important exopolysaccharide succinoglycan from Rhizobium meliloti Rm1021 was determined by mass spectrometry with electrospray ionization and collision-induced dissociation of the octameric oligosaccharide repeating unit. Previously undetermined locations of the succinyl and acetyl modifications were determined, in respect to both residue locations within the octamer and the carbon positions within the pyranose ring. Glycosidic linkages determined previously by methylation analysis were also verified.

Carbohydrate Sequence↗
PubMed1994

Myocardial blood flow at rest and during pharmacological vasodilation in cardiac transplants during and after successful treatment of rejection.

BACKGROUND: The relative intracoronary flow reserve has been found to be reduced during acute transplant rejection, but the effects of rejection on absolute flows at rest and during hyperemia have not been established previously. This has now become possible through noninvasive quantification of myocardial blood flow with positron emission tomography. METHODS AND RESULTS: Myocardial blood flow (MBF) at rest and during dipyridamole-induced hyperemia was quantified in 10 transplant patients (group A) during an acute, biopsy-proven rejection episode and again after successful immunosuppressive treatment and in 6 transplant patients (group B) without prior rejection episode. In group A patients, MBF during rejection averaged 1.7 +/- 0.3 mL.min-1.g-1 at rest and 2.5 +/- 0.9 mL.min-1.g-1 during hyperemia; after recovery, MBF at rest had declined to 1.2 +/- 0.3 mL.-1.g-1 (P < .001) but had increased to 3.9 +/- 1.1 mL.-1.g-1 (P < .001) during hyperemia. Flows after recovery from rejection were similar to those in the group B patients (0.9 +/- 0.2 and 3.9 +/- 0.7 mL.min-1.g-1). Flow reserve in the group A patients was only 1.5 +/- 0.5 during rejection but improved to 3.4 +/- 0.9 at recovery (P < .001) and thus remained lower than in the control patients (4.5 +/- 0.7, P < .05). Minimal coronary resistance during dipyridamole vasodilation was elevated during rejection (40 +/- 11 mm Hg.mL-1.min-1.g-1); after recovery, it no longer differed from that in the group B patients (26 +/- 11 versus 22 +/- 4 mm Hg.mL-1.min-1.g-1). MBF during rejection was increased relative to cardiac work, as demonstrated by significantly higher ratios of blood flow to rate-pressure product than those at recovery and in the control patients. CONCLUSIONS: A decrease in hyperemic and an increase in resting myocardial blood flow, in excess to cardiac work, account for the previously reported reduction in coronary flow reserve. Because both alterations improve with antirejection treatment, they may reflect reversible alterations, presumably of endothelial function, local coagulation, and edema. The compromise in flow reserve and hyperemic flows may contribute to acute and chronic injury from rejection and thus provides a rationale for exercise restriction during rejection. The results further suggest a potential role for serial noninvasive flow measurements to guide immunosuppressive therapy.

Adult↗
PubMed1994

Detection and serotyping of dengue viruses by PCR: a simple, rapid method for the isolation of viral RNA from infected mosquito larvae.

Dengue viruses pose a considerable global public health problem with an estimated 100 million cases of illness every year. This illustrates the need for rapid and reliable diagnostic methods for proper patient management and disease control. Currently, laboratory diagnosis depends on serology or virus isolation, with both methods having certain drawbacks. Alternatively, reverse transcription and polymerase chain reaction (RT-PCR) offers the potential for the rapid, highly sensitive and specific detection of dengue viruses. Since we occasionally encounter the problem of insufficient amounts of patient serum for the direct detection of dengue viruses, a method was developed for the extraction of viral RNA after biological amplification in mosquito larvae. Using this method, 15 of 19 clinical samples tested were correctly identified using RT-PCR.

Animals↗
PubMed1994

Continuous spinal analgesia--initial experiences with differential sensory block and labour pain relief.

This report describes the use of microcatheters to provide continuous spinal analgesia for the relief of labour pain. Bupivacaine 0.025% was administered through a 28G spinal microcatheter resulting in a differential block which provided effective labour pain relief. Conduction by the smaller pain fibres from the uterus were blocked, while relatively sparing the larger A fibres. Motor power, sense of touch, and discrimination between blunt and sharp objects were therefore left relatively intact. Patients were thus spared the discomfort of motor paralysis and an intense sensory block. No patient had hypotension (blood pressure fall greater than 20%). However one patient suffered a severe post-dural puncture headache which required an epidural blood patch. Continuous intra-thecal spinal analgesia is a potential alternative to continuous epidural analgesia in the relief of labour pain.

Adult↗
PubMed1994

Assessment of excision margins following wide local excision for breast carcinoma using specimen scrape cytology and tumour bed biopsy.

Specimen scrape cytology (SSC) and tumour bed biopsy (TBB) were used to assess adequacy of wide local excision of breast cancer. Thirty-nine (49%) of 80 cases were SSC positive and 18 (23%) TBB positive. When the main specimen contained ductal carcinoma in situ (DCIS) 21 (66%) of 32 cases were SSC positive compared to 18 (38%) of 48 when DCIS was absent (chi 2 = 9.17, P < 0.01). TBB results were not affected by the presence of DCIS. These findings may reflect the multifocal nature of breast cancer and especially DCIS. It is postulated that positive specimen cytology could be a better indicator of inadequate local surgical treatment than involved tumour bed biopsies or positive margins judged by conventional histology.

Adenocarcinoma↗