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Biomedical subjects

W K Chia

Publications and source records attributed to W K Chia.

14 recordsLinked to original sources
PubMed1996

Characterization of platelet-reactive antibodies in children with varicella-associated acute immune thrombocytopenic purpura (ITP).

Biochemical analyses were performed on blood samples obtained from two children (P1, P2) who presented with acute immune thrombocytopenic purpura (ITP) following a recent varicella zoster virus (VZV) infection. Patient sera had antibodies that were reactive with normal blood-group O platelets as measured by flow-cytometric assay. Western blot analysis of electrophoretically separated normal blood-group O platelets under reducing and non-reducing conditions demonstrated that these sera were reactive with platelet antigens of approximately 50 and approximately 110 kD, respectively. These 50/110 kD antigens were not reactive with seven sera from acute ITP patients whose illness was not preceded by VZV infection, with serum from a patient with a prior history of VZV and no thrombocytopenia, nor with normal healthy control sera. VZV antibodies (IgG and IgM), isolated from patient sera by affinity chromatography using immobilized purified VZV glycoproteins, were found to bind to gel-filtered autologous platelets and with normal blood-group O platelets, as analysed by flow cytometry. No binding was observed using antibodies similarly prepared from healthy volunteer sera. To investigate their ability to sensitize platelets to complement activation, affinity-purified VZV antibodies were incubated with platelets and then with purified complement components C1 and 125 I-labelled C4. Platelets reacted with VZV-specific antibodies from the two patients and showed increases of 2.3-2.4-fold of platelet-surface deposition of 125 I-C4b, compared to controls. These data provide evidence that virus-specific antibodies occurring in children with varicella-associated acute ITP cross-react with normal platelet antigens, and may contribute to platelet clearance.

Antibodies, Viral↗
PubMed1995

Programmed cell death induced by HIV type 1 antigen stimulation is associated with a decrease in cytotoxic T lymphocyte activity in advanced HIV type 1 infection.

The immune competence of peripheral blood mononuclear cells (PBMCs) from human immunodeficiency virus-seropositive (HIV+) patients was studied by assessing cytotoxic T lymphocyte (CTL) activity following recall HIV antigen stimulation. Target cells were HLA-A-matched EBV-transformed B cells expressing HIV-1 antigen. In the presence of recombinant IL-2 (rIL-2, 2 or 10 U/ml), about 50% of PBMCs from HIV+ asymptomatic patients responded to HIV-1 antigen stimulation in vitro with increased cytotoxic activity. In contrast, PBMCs from patients with overt AIDS, cultured in medium containing rIL-2 (2 U/ml) and HIV-1 antigen, showed no increase in cytotoxic activity; in the presence of rIL-2 (10 U/ml) and HIV-1 antigen, an inhibitory effect on CTL activity was observed. This inhibitory effect was associated with programmed cell death (apoptosis) of CD8+ lymphocytes and cells of both gamma/delta TcR-positive and -negative phenotypes. However, prior to the apoptosis, different TcR phenotypes of T lymphocyte reacted differently to HIV-1 antigen stimulation. The HIV-1 antigen initially appeared to cause gamma/delta TcR-positive T lymphocytes to proliferate and/or differentiate and later induced cell death. Whereas, prior to the apoptosis, no proliferation of gamma/delta TcR-negative T lymphocytes induced by HIV-1 antigen was observed.

Acquired Immunodeficiency Syndrome↗
PubMed1994

Lack of correlation between phenotype activation markers of CD8 lymphocytes and cytotoxic T lymphocyte (CTL) function in HIV-1 infection: evidence for rescue with rIL-2.

CTL activity against HIV-1 antigens expressed on HLA-A-matched EBV-transformed B target cells was detected in 33% (6/18) of freshly isolated PBMC (FPBMC) from patients in the early stages of HIV-1 infection (CDCII). No CTL activity was detected in FPMBC in patients with AIDS (CDCIV). However, the presence of CTL activity did not correlate with the expression of CTL activation markers. A dual-color flow cytometric examination revealed that the CD8+ lymphocytes bearing the memory (CD29) and activation (S6F1) surface molecules increased in number as the HIV-1 infection progressed. This functional and phenotypic discrepancy in memory CD8+ lymphocytes suggests that the memory CD8+ lymphocytes have lost cytotoxic function and become "paralyzed" as the HIV disease progresses. Incubation of PBMC of HIV(+) patients with rIL-2 reactivated predominantly HIV-specific CTL. However, rIL-2 stimulation also activated a "polyclonal or polyreactive" cytotoxic function. The reactivation of CTL function is rIL-2 dosage dependent and the amount of rIL-2 required for reactivation is associated with the severity of the disease. HIV antigen specific CTL in HIV(+) patients can be selectively expanded by HIV antigen stimulation in the presence of rIL-2. These results suggest that the in vivo IL-2 deficiency occurring in HIV-1 infection may be responsible in part for the "paralysis" of HIV specific CTL activity. Such activity can be rescued nonspecifically by exogenous rIL-2 stimulation and expanded specifically by HIV-1 antigen stimulation.

Antigens, Surface↗
PubMed1994

Alcoholism and rapid progression to AIDS after seroconversion.

Rapid progression of infection with human immunodeficiency virus type 1 (HIV-1) to AIDS after seroconversion is rare; it has been associated with coinfection by cytomegalovirus or human T lymphotrophic virus type I. We describe an alcoholic patient whose condition progressed to AIDS 3 months after HIV-1 seroconversion occurred. Culture of peripheral blood mononuclear cells yielded a syncytium-inducing variant of HIV-1. T lymphocytes showed no spontaneous cytotoxic activity against HIV-infected cells, nor could such activity be demonstrated following stimulation with HIV-1 antigen in the presence of recombinant interleukin-2. We hypothesize that our patient's accelerated course was due to alcohol abuse, which may have suppressed T cell function and stimulated HIV replication.

Acquired Immunodeficiency Syndrome↗
PubMed1990

Dimensional change of impressions on sterilization.

The volume of impressions, before and after disinfection in a gluteraldehyde solution for longer than ten hours (that is, sterilization), was measured indirectly from dies produced from the impressions. Three elastomeric impression materials were used in both acrylic resin and poly-vinyl-chloride 'trays' to form the impressions. One impression material appeared to be practically superior to the others with respect to variability of volume. The effect of tray material on change in volume (calculated as after disinfection minus before disinfection) was significant for one impression material; acrylic trays produced the greatest effect. The change in volume was significant for two impression materials; acrylic trays were associated with greater increase in volume. It was concluded that if impressions are to be sterilized, a tray material having minimal potential to absorb disinfectant should be used.

Dental Impression Materials↗
PubMed1990

Detection of enterovirus RNA in myocardial biopsies from patients with myocarditis and cardiomyopathy using gene amplification by polymerase chain reaction.

Recent molecular studies have suggested that viral myocarditis frequently underlies human congestive cardiomyopathy; however, only moderately sensitive and specific techniques were used. Polymerase chain reaction (PCR) gene amplification is a sensitive, specific technique ideally suited for the diagnosis of viral disease in small tissue samples where low copy numbers of the viral genome may be present. Using PCR and high stringency condition, we screened biopsies taken from 48 patients with clinically suspected myocarditis or dilated cardiomyopathy. Five patients demonstrated positive enteroviral signals by PCR; two of them had myocarditis by pathology, whereas the other three had changes consistent with cardiomyopathy. Four other patients had myocarditis diagnosed by pathology from 3 months to 1 year earlier but were now negative by both PCR and pathology. Both pathology and PCR were negative for active myocarditis in all other patients. Ventricular samples taken from left ventricular myectomy in four additional patients with hypertrophic cardiomyopathy, normal human ventricle samples, and uninfected monkey kidney cells were also negative by PCR. This study supports a link between viral infection and dilated cardiomyopathy in some patients. PCR gene amplification provides a new diagnostic approach to patients with suspected myocarditis.

Biopsy↗
PubMed1988

Development of urease conjugated enzyme-linked immunosorbent assays (ELISA) for the detection of IgM and IgG antibodies against Mycoplasma pneumoniae in human sera.

Urease conjugated enzyme linked immunosorbent assays (ELISA) were developed for the detection of human IgM and IgG antibodies against Mycoplasma pneumoniae. Results obtained by ELISA were compared with complement fixation test (CFT); which showed that of the 214 serum specimens tested, 80 were found to have antibody against M. pneumoniae. ELISA revealed that 70 of these specimens were IgG antibody, and 27 of them also contain IgM antibody. CFT failed to detect the presence of antibody against M. pneumoniae in five serum specimens tested. However, by using ELISA, three of them were found to have IgG and IgM antibodies. and the other two sera have IgG antibody only. Four out of the five specimens tested were the first serum specimens collected from patients with clinical and serological evidence of M. pneumoniae infection. In addition, 28 serum specimens, including 10 sera containing IgM rheumatoid factors and sera known to contain IgM antibody to other infectious organisms, were also tested for IgM antibody against M. pneumoniae by ELISA. None of these specimens showed a nonspecific reaction. ELISA had a sensitivity of 87.5% and a specificity of 96.3% when compared with CFT. Thus, ELISA developed in our laboratory is a specific test, and the results indicated that IgM ELISA might be used as a rapid diagnosis for M. pneumoniae infection.

Antibodies, Bacterial↗
PubMed1984

Serological evidence of infection with California serogroup viruses (family Bunyaviridae) in residents of Long Hua, suburb of Shanghai, People's Republic of China.

Sera from 126 residents of Long Hua, a suburb of Shanghai, in the People's Republic of China, were studied. Sera were tested for haemagglutination inhibiting antibodies to alphavirus (eastern equine encephalitis, western equine encephalitis), flavivirus (St. Louis encephalitis, Powassan, dengue) and California serogroup (snowshoe hare) antigens. Flavivirus antibodies were found in 14 (11.1%) and California serogroup antibodies in 5 (3.9%) individuals. Neutralizing antibodies with highest titres to snowshoe hare virus were demonstrated in 3 of the 5 California serogroup reactors. We believe this to be the first report of California serogroup virus antibodies in Chinese residents and the first evidence to suggest that California serogroup viruses may be circulating in the Orient.

Adolescent↗
PubMed1979

Quantitative determination of cytomegalovirus IgG antibody by enzyme-linked immunosorbent assay (ELISA).

Quantitative determination of cytomegalovirus (CMV) human IgG antibody by ELISA performed in polystyrene trays was carried out and compared with results obtained by the routine complement fixation (CF) test. The antibody titres of all the sera determined by ELISA were higher than those detected by the CF test. Of the 27 sera negative (less than 1:8) by the CF test, 22 of them were also negative (less than 1:50) by ELISA. The other five CF negative sera were found to have low levels of antibody by ELISA. ELISA is a sensitive and specific assay for CMV antibody. The CMV antigen adsorbed readily to the microtitre plates and the test was simple to perform. The results of ELISA could be obtained in 5 to 6h. A description of the test procedure is given including the method of CMV antigen attachment to the plates. The possibility of using paired sera at a single dilution in the ELISA test to detect seroconversion is discussed.

Antibodies, Viral↗
PubMed1975

Enzyme activity changes during cyclic AMP-induced stalk cell differentiation in P4, a variant of Dictyostelium discoideum.

The P4 variant of Dictyostelium discoideum is characterized by the production of fruiting structures in which the overall proportion of stalk to spore material is increased, relative to the wild type. The altered morphology of the mutant is due to increased sensitivity to cyclic AMP which promotes stalk cell differentiation. In the presence of 10-4 M-cyclic AMP the entire population of P4 amoebae forms clumps of stalk cells on the surface of the dialysis membrane support. Measurement of changes in activity of a range of developmentally-regulated enzymes during the development of P4 in the presence and absence of cyclic AMP has allowed us to identify three classes of enzyme: (i) Those, such as beta-glucosidase II, trehalose-6-phosphate synthetase and uridine diphosphogalactose-4-epimerase, which are required for the production of spores. (ii) Enzymes, primarily but perhaps not exclusively, required during stalk cell formation. Typical of these are N-acetylglucosaminidase and alkaline phosphatase. (iii) General enzymes, such as threonine dehydrase, alpha-mannosidase and uridine diphosphoglucose pyrophyosphorylase, which are present inboth pre-stalk and pre-spore cells and appear to be necessary for the development of both cell types.

Acetylglucosaminidase↗