Chun Hung Ma

The Chinese University of Hong Kong, Hong Kong, Hong Kong

Are you Chun Hung Ma?

Claim your profile

Publications (6)25.55 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We described a 5-min colorimetric test for paratyphoid A fever, which detects anti-Salmonella O2 antibodies by inhibiting the binding between 2 types of reagent particles. This test (TUBEX-PA) is based on that (TUBEX-TF) used for typhoid fever, which detects anti-O9 antibodies. TUBEX-PA showed a sensitivity of 81.0% (47/58 culture-confirmed patients) to 93.3% (14/15) and was 98.1% (52/53) specific for healthy subjects. However, TUBEX-PA also detected 50% (7/14) to 81.8% (9/11) of typhoid patients, and conversely, TUBEX-TF detected 46.7% (7/15) to 73.3% (11/15) of paratyphoid A cases. This cross-detection could be abrogated in both tests by adding a blocker (heterologous antigen) to remove the antibodies responsible, which presumably bind to a common antigen (O12) located close to O2 and O9. The presence of anti-O12 antibodies in typhoid (9/12 or 75.0% sensitive) and paratyphoid A (22/33 or 66.7%) patients was demonstrated directly using a prototypic TUBEX test designed specifically to detect these antibodies. Thus, using TUBEX-PA and TUBEX-TF together can increase the diagnostic accuracy of detecting both typhoid and paratyphoid A fever, while the further use of differential tests allows possible immediate discrimination between these diseases.
    Diagnostic Microbiology and Infectious Disease 09/2008; 62(2):142-50. · 2.26 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: It is puzzling how autoreactive B cells that escape self-tolerance mechanisms manage to produce Abs that target vital cellular processes without succumbing themselves to the potentially deleterious effects of these proteins. We report that censorship indeed exists at this level: when the Ab synthesis in the cell is up-regulated in IL-6-enriched environments (e.g., adjuvant-primed mouse peritoneum), the cell dies of the increased intracellular binding between the Ab and the cellular autoantigen. In the case in which telomerase is the autoantigen, mouse hybridoma cells synthesizing such an autoantibody, which appeared to grow well in culture, could not grow in syngeneic BALB/c mice to form ascites, but grew nevertheless in athymic siblings. Culture experiments demonstrated that peritoneal cell-derived IL-6 (and accessory factors) affected the growth and functions of the hybridoma cells, including the induction of mitochondria-based apoptosis. Electron microscopy revealed an abundance of Abs in the nuclear chromatin of IL-6-stimulated cells, presumably piggy-backed there by telomerase from the cytosol. This nuclear presence was confirmed by light microscopy analysis of isolated nuclei. In two other cases, hybridoma cells synthesizing an autoantibody to GTP or osteopontin also showed similar growth inhibition in vivo. In all cases, Ab function was crucial to the demise of the cells. Thus, autoreactive cells, which synthesize autoantibodies to certain intracellular Ags, live delicately between life and death depending on the cytokine microenvironment. Paradoxically, IL-6, which is normally growth-potentiating for B cells, is proapoptotic for these cells. The findings reveal potential strategies and targets for immunotherapy.
    The Journal of Immunology 08/2008; 181(3):2246-57. · 5.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Bacterially-produced antibody fragments, such as single-chain Fv (scFv) which comprises the variable regions of the light (VL) and heavy (VH) chains joined together by a short flexible linker, are useful as diagnostic and therapeutic agents. We previously constructed a scFv fragment from a hybridoma antibody (Mab2) but it unexpectedly lacked the unique carrier specificity of the native antibody. Thus, it bound indiscriminately to various phosphorylcholine (PC)-associated antigens, whereas the hybridoma antibody recognized the PC epitope only in the context of the immunizing antigen. Here, we investigated whether the problem was linker-related by changing the linker composition or by deleting it, but these attempts proved futile. Instead, we have constructed a recombinant Fab fragment of the antibody in bacteria that was carrier-specific. This suggests that constant regions are required for the carrier specificity, which presumably helps to mould the fine structure of the antibody combining site or in stabilizing such a structure. Consistent with this global effect is the finding that replacing specific residues in VH with germ-line residues, namely, VH49 glycine and VH30 threonine, both thought previously to be important for the carrier specificity, had no effect on the carrier specificity of the recombinant Fab.
    Journal of Immunological Methods 05/2007; 321(1-2):152-63. · 2.23 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The recent outbreak of severe acute respiratory syndrome (SARS) provided an opportunity to study the antibody response of infected individuals to the causative virus, SARS coronavirus. We examined serum samples obtained from 46 patients with SARS, 40 patients with non-SARS pneumonia, and 38 healthy individuals, by use of Western blotting (WB), enzyme-linked immunoassay (ELISA), and immunofluorescence assay, using both native and bacterially produced antigens of the virus. We found a highly restricted, immunoglobulin G-dominated antibody response in patients with SARS, directed most frequently (89% by ELISA) and predominantly at the nucleocapsid. Almost all of the subjects without SARS had no antinucleocapsid antibodies. The spike protein was the next most frequently targeted, but only 63% of the patients (by ELISA) responded. Other targets of the response identified by use of WB included antigens of 80 and 60 kDa. Several nonstructural proteins cloned were not antigenic, and the culture-derived nucleocapsid appeared to be specifically degraded.
    The Journal of Infectious Diseases 08/2004; 190(2):379-86. · 5.85 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: To investigate why the serum of a pediatric patient with systemic lupus erythematosus was persistently (>30 months) and strongly positive for antibodies to double-stranded DNA (dsDNA) as revealed by enzyme-linked immunosorbent assay (ELISA), but yielded negative results on the antinuclear antibody test (HEp-2 immunofluorescence [IF]). The patient's antibodies were isolated on dsDNA and single-stranded DNA (ssDNA) supports, which were then examined by dsDNA ELISA and HEp-2 IF. Tests included the use of various inhibitors to determine the fine specificity of the antibodies. Other tests performed included immunoblotting, immunoprecipitation, Crithidia luciliae IF, and neutrophil IF. The antibodies isolated from the dsDNA and ssDNA supports were similar, in that they were of the IgG type, bound well in the dsDNA ELISA, and recognized a normally hidden nucleolar RNA antigen in HEp-2 cells. With both the dsDNA ELISA and nucleolar antigens, inhibition studies revealed that the epitope recognized was guanosine 5'-triphosphate (GTP). Binding of the antibodies was better to GTP than to guanosine 5'-monophosphate or cytidylyl (3'-5') guanosine, and, in turn, was better than to guanosine, while N7-methylated GTP was unreactive. The antibodies did not bind to dsDNA present in solution or in HEp-2 or Crithidia cells, but bound transfer RNA well and recognized a cytoplasmic RNA antigen in neutrophils. A new problem in dsDNA ELISA is revealed in the occurrence of a hitherto-unknown and unusual buckling of the insolubilized DNA molecule, which, absent in dsDNA found in solution or in whole cells, presumably creates gaps of single-strandedness in the molecule. A new antibody specific for GTP is described in this patient, which may be clinically important.
    Arthritis & Rheumatology 06/2004; 50(5):1533-8. · 7.48 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Transforming growth factor-beta-1 (TGF-Beta(1)) has been implicated in bone mineral density (BMD) determination. We investigated the relationship between the TGF polymorphism, BMD, and vertebral fractures in 588 Chinese men and women. No association between TGF polymorphism and BMD was observed in postmenopausal women (aged 55-59 years), elderly men (aged 70-79 years), or elderly women (aged 70-79 years) at the hip, spine, or total body ( P > 0.05 by two-way ANOVA). In all study groups, there was no effect of an interaction between TGF polymorphism and calcium intake on BMD ( P > 0.05 for the interaction effects by two-way ANOVA). No statistical significant association was observed between TGF polymorphism and vertebral fracture in elderly men or women ( P > 0.05 by the chi-square test), even though men of the TT and TC genotypes seem to have more vertebral fractures. Contrary to previous studies that found an association between BMD and TGF polymorphism in the Japanese, we found no association between TGF polymorphism and BMD of elderly Chinese men or women. This finding could result from different sampling methods between the previous and current studies and environmental factors and ethnic differences between the two populations.
    Journal of Bone and Mineral Metabolism 01/2004; 22(2):148-52. · 2.22 Impact Factor