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Biomedical subjects

M H Ng

Publications and source records attributed to M H Ng.

At least 91 records · Page 5Linked to original sources
PubMed1991

Characterization and application of a murine monoclonal antibody that reacts specifically with the serogroup D1 Salmonella.

A murine hybridoma cell line that produces monoclonal antibody (mAb) against the serogroup D1 Salmonella lipopolysaccharide (LPS) antigen was established. The trisaccharide tyvelose alpha 1----3 mannose alpha 1----4 rhamnose was shown to be involved in the reactive epitope of the mAb since this mAb reacted strongly with strains of serogroup D1 Salmonella but not with Salmonella strains from the O serogroups of A, B, and D2, and sodium meta-periodate was found to destroy the reactivity of the serogroup D1 O-antigen with the mAb. As such this mAb was found to be a useful serotyping reagent for the identification of serogroup D1 Salmonella, and for the differentiation of strains of serogroups D1 and D2 Salmonella which have identical flagellar H antigens.

Animals↗
PubMed1991

Rotavirus infection of the oropharynx and respiratory tract in young children.

Oropharyngeal aspirates were obtained from 89 infants hospitalized with respiratory illnesses accompanied or not by diarrhea and 33 control patients without the diseases. Rotavirus was detected from 25 of these patients by immunocytology, isolation of the virus in cultures of MA104 cells, or both. None of the control patients gave a positive result. The infection involves squamous cells and globlet cells probably originating from the oropharynx, and ciliated columnar epithelial cells from the respiratory tract. The virus from 2 specimens was propagated by repeatedly passaging in the cultures and found to have characteristic morphology of rotavirus. The electrophoretic patterns of the viral RNA extracted from them are closely similar to those obtained with the rotavirus genome extracted from the stool of the same patients. Repeated stool specimens were also obtained, and sera were paired from some of these subjects. All but one of the patients who gave a positive virology for their aspirates also showed a significant rise in the titres of common group A rotavirus antibody, neutralizing antibody against one or more of serotypes of rotavirus, or both. Patients who excreted rotavirus in their stools were younger and had significantly lower titres of rotavirus antibodies in their acute sera, than those who shedded the virus in the oropharynx but did not excrete the virus in repeated stool specimens. The prevalence of rotavirus in the oropharyngeal aspirates from these patients surpassed that of adenovirus, respiratory syncytial virus, influenza virus, and herpes simplex virus combined.

Antibodies, Viral↗
PubMed1991

Trichinella spiralis: light microscope monoclonal antibody localization and immunochemical characterization of phosphorylcholine and other antigens in the muscle larva.

A panel of monoclonal antibodies was used to examine the structure of the muscle larva of Trichinella spiralis under the light microscope. Immunofluorescence and, in some cases, immunoperoxidase staining were used. All four antibodies reacted with the cuticle of the organism, although differences in the staining pattern were observed for some of these. Interestingly, all the antibodies also reacted with the stichosome. One of the antibodies (Ts2Ab) is specific for the hapten, phosphorylcholine. In a binding assay, this antibody also reacted with extracts of Trichuris suis, Ascaris suum, and Fasciolopsis buski, but not with extracts derived from Cysticercus cellulosae, Candida albicans, Salmonella typhi, or Escherichia coli. This crossreactivity was confirmed microscopically in which the cuticle, oviduct and eggs of T. suis, the cuticle, muscle cells, and eggs of A. suum, and the cuticle and vitelline glands of F. buski were seen to be clearly stained by the antibody. In addition, Ts2Ab also reacted with the cuticle and stichosome of the adult T. spiralis worm. In Western blot analysis, Ts2Ab recognized a 43-kDa antigen from T. spiralis muscle larvae extracts, while a previously studied antibody (7C2C5Ab) identified four major antigens (48.5, 47, 43, and 39 kDa) in this preparation. Similar results were obtained when the 24-hr excretory-secretory (ES) antigens of T. spiralis were immunoblotted with the antibodies, although the reactivity shown by Ts2Ab was relatively weak. With the 72-hr ES material, on the other hand, major antigens of lower mol wt (44, 28, and 25 kDa) were revealed by 7C2C5Ab, and no reactivity was seen with Ts2Ab. However, this antigen preparation reacted well with both antibodies in an enzyme-linked immunoassay. Taken together, the findings suggest that the 72-hr ES antigens probably result from extensive degradation of material originally secreted or excreted by the worm. Similar binding studies on the 24-hr ES preparation indicated that this source may be relatively rich in 7C2C5Ab-reactive epitopes and relatively poor in the antigen identified by Ts2Ab. Other studies performed demonstrated that the antigens recognized by these two antibodies were distinct and physically unassociated.

Animals↗
PubMed1991

Detection and prevalence of the "f" variant of Epstein-Barr virus in southern China.

The "f" variant of Epstein-Barr virus (EBV) may have an association with the development and/or maintenance of nasopharyngeal carcinoma (NPC) among Southern Chinese. This variant is detected at a higher frequency among individuals with elevated IgA antibody levels against EBV capsid antigen who have no detectable NPC and in NPC patients as compared to healthy individuals or patients who are in remission for NPC for over 3 years. Conversion or replacement of the f variant by the prototype BamHI F virus usually occurs by 3 to 4 years after radiotherapy. By 5 years post-therapy the majority of people in remission for NPC no longer harbor the f variant in their oropharynx. Eradication of this f variant, however, does not appear essential for maintenance of a disease-free state since several patients harboring this variant were in remission for NPC for up to 21 years. The virus strain detected directly in the nasopharynx is not always identical to that seen in the oropharynx. Dual infection was commonly observed in throat washings of NPC patients although the biopsy from tumors harbored unique strains of EBV.

Base Sequence↗
PubMed1991

An unusual case of hairy cell leukemia: death due to leukostasis and intracerebral hemorrhage.

Hairy cell leukemia (HCL) was diagnosed in a 71-year-old Chinese man. His clinical presentation and the characteristics of the hairy cells were typical of classic HCL. However, extreme leukocytosis (195 to 323 x 10(9) cells/L) in peripheral blood was in striking contrast. This leukocytosis, which was much more pronounced than any of the reported cases of HCL with leukocytosis, was associated with leukostasis in the cerebral vasculature and was causally related to a massive intracerebral hemorrhage and death. This mode of death in HCL has not been reported previously.

Aged↗
PubMed1991

Restriction fragment length polymorphism analysis of Vibrio cholerae strains associated with a cholera outbreak in Hong Kong.

We studied Vibrio cholerae El Tor isolates associated with an outbreak of cholera among Vietnamese refugees interned in Hong Kong. The restriction fragment length polymorphism of the enterotoxin gene was used as an epidemiological marker. All outbreak strains were indistinguishable. They were distinct from strains isolated in Hong Kong prior to the outbreak.

Cholera↗
PubMed1991

Characterization of murine monoclonal antibodies against serogroup B salmonellae and application as serotyping reagents.

Six murine hybridoma monoclonal antibodies reactive with lipopolysaccharide antigens of Salmonella typhimurium were obtained from a fusion of immune spleen cells from mice immunized with S. typhimurium and NS1 myeloma cells. Four antibodies appeared to be specific for serogroup B salmonellae, while the remaining two antibodies were found to be cross-reactive with Salmonella paratyphi A. The exquisite specificities of the Salmonella serogroup B monoclonal antibodies were demonstrated by their unique reactivities with different serotypes of group B salmonellae but with neither other O serogroups of salmonellae nor a wide spectrum of standard strains of other bacterial species. Serotyping of salmonella strains by the slide agglutination method with two of the serogroup B-specific monoclonal antibodies demonstrated their usefulness as serotyping reagents for the identification of serogroup B salmonellae in a routine diagnostic bacteriology laboratory.

Agglutination Tests↗
PubMed1991

Nasopharyngeal carcinoma and lymphoinfiltration.

Originally referred to as 'lymphoepithelioma', undifferentiated and poorly differentiated nasopharyngeal carcinoma (NPC) tissues showed intense lymphoinfiltration. In a study of cryosections from 15 NPC tissues, we found that infiltrating lymphoid elements were comprised predominantly of lymphocytes, but plasma cells, follicular dendritic cells, and eosinophils were also commonly seen. Subpopulations of lymphocytes having the same phenotypes tend to aggregate, forming clusters or secondary follicles in stromatous tissues. The tumor areas were mainly infiltrated by T cells. Tumor cells and/or apparently normal epithelium in the paratumorous areas frequently expressed CD21, CD23, CD40 and a B lymphocytes carcinoma cross-reacting antigen (BLCa), all of which are involved in B cell activation and proliferation. CD21 and BLCa were strongly expressed near the surface of both squamous and columnar epithelium by those epithelial cells which are at advanced stage of differentiation, while CD40 was expressed by epithelial cells at earlier stages of differentiation located at or near the basement membrane. CD23 was mainly expressed by columnar cells and basal cells underlying squamous epithelium, but not, or weakly so, by flattened squamous cells or reserve cells underlying columnar epithelium. The large majority of tumor cells expressed CD40 and BLCa. A substantial proportion of them also expressed CD23, but the tumor cells were not reactive for CD21. Despite eosinophilic infiltration, IL-6 was not detected in tumor tissues. IL-1 was, however, detected in abundance in the cytoplasm of follicular dendritic-like cells and in the intercellular spaces in tumor areas and surrounding stromatous tissues. The immunobiology of NPC is discussed in the light of these observations.

Antibodies, Monoclonal↗
PubMed1991

Bone marrow findings in lupus patients with pancytopenia.

The marrow findings of 23 lupus patients with pancytopenia were reported. The most common findings were dyserythropoiesis and hypoplasia, both occurring in 9/23 (39%) of the cases. Neither feature was definitely related to cytotoxic drug therapy since most cases were treated by steroids only. Three of the hypoplastic marrows also showed gelatinous transformation, a condition characterized by disruption of marrow architecture, fat atrophy, and deposition of hyaluronic acid. Another common finding was lymphocytosis which occurred in 5/23 (22%) of the cases, 2 of which also had associated plasmacytosis. Two cases were associated with hyperplastic marrow, indicating peripheral destruction of blood cells and compensatory marrow hyperplasia. Reports in the literature on bone marrows in systemic lupus erythematosus are conflicting, describing mainly hypoplasia, vasculitis, plasmacytosis, red cell aplasia, and myelofibrosis. In our series, we found hypoplasia and lymphocytosis/plasmacytosis; in addition we described findings previously unreported: gelatinous transformation, dyserythropoiesis, and marrow hyperplasia.

Bone Marrow↗
PubMed1990

Detection of subclinical nasopharyngeal carcinoma by fibreoptic endoscopy and multiple biopsy.

Of 6054 people who had high titres of antibodies against the viral capsid antigen of Epstein-Barr virus but no symptoms or signs of nasopharyngeal carcinoma as assessed by conventional methods, 130 were randomly recruited and examined by fibreoptic endoscopy and biopsy of several sites of the nasopharynx. 7 cases of nasopharyngeal carcinoma were detected. The tumours were largely confined to the pharyngeal recess, which suggests that it is the area of the nasopharynx most prone to the development of the tumour. Tumour was found in both recesses in 1 subject, who also had evidence of transition from severe epithelial dysplasia to carcinoma in a sample from the left roof, which suggests that the disease was multifocal in origin. This study showed that endoscopy and biopsy of several sites of the nasopharynx are more effective than the conventional approach in the detection of subclinical nasopharyngeal carcinoma among seropositive individuals at high risk of the disorder.

Adult↗
PubMed1990

Epstein-Barr virus genotypes associated with nasopharyngeal carcinoma in southern China.

We have used probes representing approximately two-thirds of the Epstein-Barr virus (EBV) genome to examine genetic polymorphism of wild-type EBV directly detected in 28 nasopharyngeal carcinoma (NPC) tissues from Southern China. In the hypervariable regions containing reiterated sequences, this analysis showed that while naturally occurring viruses are genetically diverse, only one genotype was detectable in each tumor specimen. Unique variants in NPC were detected in four regions of the EBV genome. Two of these appeared significant in their distribution. The type C variant resulting from loss of a BamHl site between the BamHl W1* and l1* regions was prevalent among isolates from Southern China, but not so common in the United States. An "f" variant having an extra BamHl site in the BamHl F region was almost exclusively detected in only Asian NPC biopsies.

Biopsy↗
PubMed1990

Distinct populations of rotaviruses circulating among neonates and older infants.

We obtained three stool specimens from each of 371 neonates. Two specimens were obtained between days 1 and 3 after birth, while they were in the hospital, and one specimen was obtained between days 6 and 14 after birth, after they had been discharged from the hospital. Seventy neonates excreted human rotavirus (HRV) while they were in the hospital, and the incidence rate for the cohort was 0.094 episodes per infant day. The incidence rate of community-acquired neonatal infections was markedly reduced to 0.022 episodes per infant day, with eight additional episodes of infection being detected after the infants were discharged from the hospital. Nevertheless, this was higher than the incidence of community-acquired HRV infection of 0.0037 episodes per infant day previously estimated by serology for the same cohort during the subsequent 2 years of infancy. None of the 78 episodes of neonatal HRV infection was accompanied by diarrhea. There were at least 44 distinct electropherotypes of HRV circulating among older infants in the community during the study period, and they comprised at least four different serotypes. Despite the genetic and antigenic diversity of the prevalent HRV isolates, only five electropherotypes with either serotype 2 or 4 specificity were isolated from the neonates, while serotype 1 and 3 viruses were not detected. Two of these electropherotypes, including one which was isolated from 57 of the 78 infants with episodes of infection, were isolated exclusively from the neonates. The other three electropherotypes were also isolated from the older infants; one was a major electropherotype and two were minor electropherotypes which were prevalent among the older infants. These results suggest that distinct populations of HRV cocirculate among neonates and older infants.

Age Factors↗
PubMed1989

A rapid method for detecting Trichinella spiralis larvae in pork using a monoclonal antibody-latex conjugate.

A simple, non-microscopic method was developed for the direct detection of Trichinella spiralis in pork. Samples of meat were treated with pepsin for 2 h to liberate the larvae, and sonicates were made from the deposit and used in an antigen detection system. In this system, latex particles, sensitized with a parasite-specific monoclonal antibody, were utilized in a slide or tube agglutination test. The efficiencies of these immunological methods were compared with that of trichinelloscopy in the examination of 102 pork specimens, 35 of which contained varying numbers of larvae after enzymatic digestion of 2 g of the meat. Trichinelloscopy detected 77.1% of these positive samples, but this was lower (55.5 and 41.7%) for those samples with a low larval burden (less than 50 or less than 10 larvae g-1 tissue, respectively). Better results (88.6, 76.5 and 60.0%) were obtained with the slide latex agglutination technique. The efficiency of detection was further improved (100%) using the more sensitive tube agglutination method. However, this was based on a small number (20) of samples examined and the limit of detection of this technique was subsequently found to be three larvae in total. No false-positives were seen with the latex agglutination methods from a total of 67 uninfected specimens examined.

Animals↗
PubMed1989

Reactivity of a new Pan-B monoclonal antibody (MA6) against human leukaemias.

The reactivity of a new Pan-B monoclonal antibody, MA6, against 69 cases of ALL, three plasmacytoma, 10 AML and five CML was evaluated. The antibody reacted positively against five of the 11 cases of U-ALL, 15 of the 26 C-ALL and all the cases of Pre B-ALL (one), B-ALL (one), B-CLL (12) and HCL (two). The MA6 did not react against the 16 cases of T-ALL, three plasmacytoma, 10 AML and five CML. The antibody has a broader spectrum of B-cell reactivity than CD9 and CD20 but is similar to the Pan-B antibody, CD19. MA6 appears to react against some of the very immature B cells and is therefore potentially useful, in conjunction with other antibodies such as CD9 and CD19, to confirm the B-lineage of some cases of U-ALL. The difference in the spectrum of reactivity against B-cell malignancies between MA6 and the other CDw40 antibody, G28-5, confirms their difference in antigenic specificity.

Antibodies, Monoclonal↗
PubMed1989

Nosocomial gastroenteritis in paediatric patients.

Between November 1982 and April 1985, 2228 children under the age of 5 years with acute gastroenteritis were admitted to the paediatric isolation ward of Queen Mary Hospital, Department of Paediatrics, University of Hong Kong. In 56.2% the causative agent was identified as rotavirus, Salmonella, Campylobacter, Shigella, Escherichia coli or a combination of these pathogens. Our isolation procedures included cohort nursing of all diarrhoeal patients in two separate rooms (each accommodating 6 patients), barrier gowns and stringent handwashing with chlorhexidine. A total of 163 cases (13.4% of all positive cases) were identified as nosocomial infections. Rotavirus was the responsible agent for nosocomial infection in 128 cases (20% of all rotavirus infection). There were 35 patients with bacterial nosocomial infection, (7% of all the bacterial positive cases). Nosocomial rotavirus gastroenteritis was 3.4 times more frequent than nosocomial gastroenteritis due to bacterial pathogens. We conclude that modification of our present isolation procedures is necessary in order to reduce rotavirus nosocomial infection.

Bacterial Infections↗
PubMed1989

Direct identification of serotypes of natural human rotavirus isolates by hybridization using cDNA probes derived from segment 9 of the rotavirus genome.

Under stringent hybridization conditions, cDNA of segment 9 of the rotavirus genome, which codes for the viral protein VP7, permitted differentiation of serotypes of culture-grown rotaviruses and natural isolates of human rotaviruses directly from clinical specimens. This was evident for the following reasons. (i) The cDNA of one serotype selectively hybridized with the RNA of the same serotype of culture-grown rotaviruses. (ii) Natural isolates of the virus thus identified as serotype 2 were also those which gave the short electrophoretic pattern characteristic of the genome of serotype 2, subgroup 1 viruses. Isolates having the long electrophoretic pattern characteristic of the genome of subgroup 2 viruses were identified as serotype 1, 3, or 4 by this method. (iii) For patients who had previously undergone serological analysis, the serotypes being excreted were the same serotypes against which there was the most marked serum neutralizing antibody response. Although the virus population was genetically diverse, the preponderance of the population prevalent in Guangzhou and Foshan in each of the three successive years between 1982 and 1985 comprised a single serotype. The dominant serotype changed from one year to another, but there was minimal cocirculation of different serotypes in this community. All virus isolates belonged to serotype 1,2,3, or 4, and there was no evidence to suggest that the other human rotavirus serotypes were prevalent in this community.

Antigens, Viral↗
PubMed1989

Molecular epidemiology of Vibrio cholerae in Hong Kong.

We studied restriction fragment length polymorphism of the enterotoxin genes of isolates of Vibrio cholerae El Tor, indistinguishable by bacteriophage typing, which were collected in Hong Kong since 1978. Using this approach, we could distinguish indigenous and exogenous strains obtained from different sources and epidemiological settings.

Autoradiography↗