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Biomedical subjects

S C Cheung

Publications and source records attributed to S C Cheung.

29 records · Page 2Linked to original sources
PubMed1991

Expression of defective virus and cytokine genes in murine AIDS.

A syndrome characterized by severe immunodeficiency and lymphoproliferation develops in susceptible strains of mice infected with a mixture of murine leukemia viruses (MuLVs) designated LP-BM5 MuLV. The etiologic agent in this mixture has been shown to be a replication-defective virus (BM5d) with a 4.8-kb genome that required replication-competent helper viruses, primarily ecotropic (BM5e), for cell-to-cell spread in the host. In the present study, we studied the expression of BM5d and BM5e in tissues of infected mice at various times after inoculation in relation to the expression of cytokine genes that may contribute to the pathogenesis of this disorder. Northern (RNA) analysis of total RNA showed that BM5d was expressed at significant levels in lymphoid tissues within 1 week of infection and that the levels of expression increased with time after inoculation. By 16 weeks postinfection, BM5d was expressed in all tissues examined. Expression of BM5e was relatively more restricted to lymphoid tissues and was detected at lower levels than expression of BM5d at early times after infection, but this virus was expressed in all tissues by 16 weeks. Infection with the virus mixture was associated with constitutive expression of tumor necrosis factor in all tissues examined and of interleukin-1 (IL-1) in lymphoid tissues within 1 week of infection, and at later times with widespread expression of these cytokines and gamma interferon. Also, the levels of interferon regulatory factor 1 mRNA were significantly increased in all infected tissues during the infection. In contrast, expression of IL-3, IL-4, IL-5, and IL-6 was not detectable by Northern analysis of the respective mRNAs in any infected tissue at early or late times postinfection.

Animals↗
PubMed1989

Inhibition of interferon-alpha/beta induction in L-929 cells by benzene and benzene metabolites.

Murine L-929 cells were treated with benzene or a series of benzene metabolites, washed and then interferon-alpha/beta was induced with polyriboinosinic-polyribocytidylic acid. Exposure of the cells to benzene or phenol, a monocyclic metabolite of benzene, did not affect interferon-alpha/beta induction. However, exposure of the cells to p-benzoquinone, hydroquinone or catechol, dihydroxy- and diketo-metabolites of benzene, resulted in a severe inhibition of interferon-alpha/beta production. There was no significant loss of viability of the cell cultures. Additional studies with p-benzoquinone indicated that inhibition of interferon-alpha/beta was reversible and could be abrogated by addition of reduced glutathione to the cell cultures.

Animals↗
PubMed1989

Analysis of monoamines in the cerebrospinal fluid of Chinese patients with neurological diseases.

Levels of dopamine (DA), 3-methoxy-4-hydroxy-phenylacetic acid (HVA), 5-hydroxy-indoleacetic acid (HIAA), 5-hydroxytryptamine (HT), 5-hydroxytryptophan (HTP), and 3, 4-dihydroxyphenylalanine (DOPA) in cerebrospinal fluids (CSF) of twenty-four Chinese with or without neurological diseases were determined simultaneously. The level of HIAA in the CSF of myelopathy-spondylosis patients and the level of DA in CSF of the myelopathy-tumor patients were higher than that of the control. No difference in levels of monoamines and their metabolites was observed between the control and patients with dementia.

Adolescent↗
PubMed1988

Inhibition of interferon gamma production by benzene and benzene metabolites.

We exposed spleen cells from female Swiss/Webster mice to benzene and benzene metabolites to determine the effects of such exposure on interferon gamma induction by concanavalin A. Exposing the cells to benzene or phenol did not affect interferon gamma production, but exposing them to p-benzoquinone, catechol, or hydroquinone significantly inhibited interferon gamma production. Cell viability, as determined by trypan blue viability staining, was not influenced by the chemical treatment. When interferon gamma production was inhibited, the inhibition was dose dependent. The time of optimum production of interferon gamma after exposure to concanavalin A was not affected by treatment of the cells with p-benzoquinone. These data indicate the importance of dihydroxy and diketo metabolites as immunotoxic derivatives of benzene.

Animals↗
PubMed1979

Changes in diffraction patterns with length in single muscle fibres at rest.

The addition of a simple X--Y sampling circuit to a closed circuit television system (CCTV) permits measurements of a narrow profile of the laser diffraction patterns from single frog muscle fibres at rest. Results confirm that maximum intensity occurs at 2.95-3.00 micron, but a positive linear relationship between the dispersions of sarcomeres and sarcomere lengths from 2.7--3.8 micron is obtained in four isolated single fibres.

Animals↗
PubMed1976

Antibiotic sensitivity of the yeast and mycelial phases of Histoplasma capsulatum.

Cycloheximide and chloramphenicol in combination have a greater effect on yeast cells of Histoplasma capsulatum than on the mycelial phase of this fungus. In contrast, clotrimazole was found to be more effective against mycelia. Miconazole produced a pronounced effect against both phases wheras tolnaftate was only slightly active. Sulfadiazine and griseofulvin were completely inactive against both phases. The differential sensitivities of the 2 phases of H. capsulatum to various antibiotics can be useful in studying the transition of the dimorphic fungus from 1 phase to the other.

Anti-Bacterial Agents↗
PubMed1975

Stability of amphotericin B in fungal culture media.

We have found that amphotericin B is unstable in two commonly employed fungal culture media. This instability leads to inaccuracies in determining the actual level of susceptibility of slow-growing strains that require prolonged incubation for growth. To help compensate for this problem, we have described two rapid methods of susceptibility testing.

Amphotericin B↗
PubMed1975

Response of yeast and mycelial phases of Histoplasma capsulatum to amphotericin B and actinomycin D.

The dimorphic fungus Histoplasma capsulatum exists in two phases: a unicellular yeast form at 37 C and a mycelium at 25 C. We have found that these two phases have selective drug susceptibilities. The mycelial form of H. capsulatum was much more susceptible to the polyene antibiotic amphotericin B than the yeast form; in contrast, the yeast form was more susceptible to the antibiotic actinomycin D. The changes in susceptibility occurred early in the transition between the two phases and permitted the transitions to be blocked by sublethal concentrations of the appropriate drugs.

Amphotericin B↗