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Biomedical subjects

J Ng

Publications and source records attributed to J Ng.

At least 145 records · Page 8Linked to original sources
PubMed1984

Effect of 5'-methylthioadenosine, 3-deazaadenosine, and related compounds on human natural killer cell activity. Relation to cyclic AMP and methylation potential.

The effect of 5'-methylthioadenosine (MTA) on human natural killer (NK) cell activity was examined and compared with the effect of 3-deazaadenosine (c3-ado) and periodate-oxidized adenosine (ado-ox). MTA inhibited NK cell activity in concentrations above 30 microM, but in concentrations below 10 microM a slight enhancing effect was often observed. C3-ado and ado-ox were 10 and 3 times more potent, respectively, as inhibitory agents and did not increase NK cell activity in low concentrations. The inhibitory effect of c3-ado was unaffected by preincubation of the cells but was enhanced by the addition of L-homocysteine. In concentrations that caused inhibition of NK cell activity all three agents caused a fall in the methylation index (AdoMet/AdoHcy) but no or an inconsistent effect on the level of cyclic AMP. An increase in the level of AdoHcy was observed already after 1 h of incubation but was more pronounced after 4 h of preincubation with the adenosine derivatives. The inhibition of cytotoxicity was mainly on their initiation of lysis, with a smaller effect on target cell binding. Antibody-dependent cellular cytotoxicity and lectin-dependent cellular cytotoxicity appeared to be less sensitive to inhibition by c3-ado. Our results show that several adenosine analogues inhibit NK-cell-mediated cytotoxicity in parallel with a decreased methylation index. The results suggest that a methylation step is critical in lymphocyte-mediated cytotoxicity and that NK cell activity is more sensitive to inhibition of this step than antibody- or lectin-dependent cytoxicity.

Adenosine↗
PubMed1981

Effect of hypo- and hypertonic saline and raffinose on cell content of Na, Cl and K in respiring rat kidney cortex at 37 degree.

Changes in cell Na, K and Cl content (per kg dry weight) and concentration (per kg intracellular water) were measured in respiring rat renal cortical slices incubated for 60 min at 37 degree in hypo- and hypertonic saline with and without the addition of a non-electrolyte (raffinose). Both hypertonic saline and raffinose increased cellular concentration of Na, Cl and K, the former by producing minimal cell shrinkage and major entry of Na and Cl into the cell, the latter entirely by cell shrinkage leading also to a loss of Na content but not of K. In hypotonic saline both content and concentration of Na and Cl did not change significantly, whereas that for K dropped markedly. Addition of ouabain (1 mmol/1) produced a significant gain of cell Na and loss of K on a one to one basis but did not alter the effect of raffinose. It is concluded that sustained changes in cell ion concentrations and content in response to pericellular osmolality are produced and that these are directed towards equilibrating cellular activity of water to that of the surrounding medium.

Animals↗
PubMed1981

Hypo- and hyperosmolal saline and raffinose on kidney cortical cell volume at 37 degrees C.

Cell water content was measured in respiring rat renal cortical slices incubated in hypo- and hyperosmolal saline with and without raffinose and ouabain for 60 min at 37 degrees C. At 60 min, hyposmolal saline (228 mosmol/kg H2O) caused a 16% swelling of cells, whereas addition of 73 mM raffinose (299 mosmol/kg H2O) caused a 33% shrinkage. Physiological saline plus raffinose (364 mosmol/kg H2O) caused a 28% cell shrinkage, whereas addition of saline (385 mosmol/kg H2O) produced only a 10% decrease in cell volume. The effects of raffinose were reversible. At physiological Na concentrations, osmole for osmole raffinose was 4 times as effective in shrinking cells as saline, but only 2 times as effective at Na of 112 mM. Osmotic effectiveness of saline changed, that of raffinose did not. Ouabain caused no changes in cell volume and did not prevent the effect of raffinose. In conclusion, there is no volume regulation to nonelectrolyte solutes and only partial volume regulation to saline, and this is due to differential osmotic effects of these solutes, that of saline decreasing from low to high Na.

Animals↗
PubMed1981

Analysis of the biosynthesis of HLA-DR glycoproteins in human malignant melanoma cell lines.

Human malignant melanoma cell line SK-MEL-37 expresses HLA-DR antigens having a characteristic 2-chain structure, with heavy chains (alpha) of approximately 32,000 daltons and light chains (beta) of approximately 28,000 daltons. Nonequilibrium pH-gradient electrophoresis (NEPHGE) on HLA-DR immunoprecipitated by rabbit anti-HLA-DR sera from [35S]-methionine-labeled, pulse-chased cells showed 2 closely spaced heavy-chain components (1, 2) and 4 light-chain spots (3-6). From nonchased samples, numerous more-basic components running in the heavy chain region were also precipitated. In particular, a very basic, 30,000 dalton component (pl approximately 8.5) was prominent (component 7); this spot probably corresponds to the invariant (Ii) peptide previously demonstrated in lymphoid cell HLA-DR precipitates (9) and the M-1 peptide of Shackelford and Strominger (10). None of these components (alpha, beta, or component 7) was precipitated from extracts of HLA-DR-negative melanoma cells. Pulse-chase experiments and the use of different labeled sugar precursors showed that component 7 is a partially glycosylated intracellular precursor, possibly of the HLA-DR alpha-chain. None of the immunoprecipitates, even from cells pulse-labeled for only 15 min, contained a peptide migrating in the 55,000 to 60,000 m.w. region. It was concluded that melanoma HLA-DR is not synthesized via a polyprotein precursor. In contrast to these results, obtained with rabbit anti-HLA-DR sera, a mouse monoclonal anti-HLA-DR was found to precipitate only biosynthetically completed alpha (1, 2) and beta (3-6) chains.

Alkaline Phosphatase↗
PubMed1976

Toxicity and mutagenicity of 2,4,-6-trinitrotoluene and its microbial metabolites.

TNT (2,4,6-trinitrotoluene) of explosive grade is highly toxic to marine forms that included fresh water unicellular green algae (Selenastrum capricornutum), tidepool copepods (Tigriopus californicus), and oyster larvae (Crassostrea gigas), and mutagenic to Salmonella typhimurium. On the basis of mutagenic assays carried out with a set of histidine-requiring strains of the bacterium, TNT was detected as a frameshift mutagen that significantly accelerates the reversion rate of a frameshift tester, TA-98. In contrast, the major microbial metabolites of TNT appeared to be nontoxic and nonmutagenic.

Animals↗
PubMed1975

Fractionation and characterization of surface antigens from group A Neisseria meningitidis.

Group A meningococcal surface components were first subjected to fractionation with a mixture of chloroform-methanol. Sodium dodecyl sulfate-acrylamide gel electrophoresis of the aqueous phase containing 30 to 40% of the original material revealed only two polypeptide components and a slowly migrating carbohydrate component. The soluble fraction of the interphase was found to contain most of the bacterial surface proteins and the chloroform-methanol phase essentially all of the lipid components. The components of the aqueous phase were further fractionated by use of the hydrophobic affinity column, 4-phenylbutylamino-Sepharose and gradient elution with NaCl to yield fractions I and II. Fraction II was further separated into a minor and a major component (IIb) with Sepharose G-200. Fraction I contained the group A polysaccharide in ionic linkages with a minor polypeptide component (6%). It elicited bactericidal antibodies in rabbits and protected mice against homologous challenge, whereas the polysaccharide alone was non-immunogenic in these animals. Fraction IIb was a polysaccharide-polypeptide complex with unknown linkages; it induced a low concentration of rabbit antibodies that were bactericidal to group A and C meningococci. Mice vaccinated with fraction IIb were most resistant to homologous challenge and the resistance was also extended to challenges with group B and C cells. Fractions I and IIb appeared to be useful alternatives to the currently employed group-specific polysaccharide vaccines for the protection against drug-resistant meningococci. A simplified procedure for the preparation of group-specific polysaccharide was presented.

Amino Acids↗
PubMed1968

A new serological group (E) of Neisseria meningitidis.

A new serological group of encapsulated Neisseria meningitidis, tentatively classified as group E, produced halo precipitates with homologous antiserum. Group-specific complement-fixing antibodies were produced in rabbits by inoculation with lysed cells. The group E isolates are immunologically related to group C, as shown by precipitation and quantitative agglutination. Antisera to group E strains did not protect mice challenged with groups A, B, or C organisms. Until now, a comparison of group E strains with the X, Y, and Z strains of Slaterus has not been conducted.

Agglutination Tests↗