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Biomedical subjects

C C Stewart

Publications and source records attributed to C C Stewart.

At least 127 records · Page 7Linked to original sources
PubMed1980

Effects of sample aging on total cholesterol values determined by the automated ferric chloride-sulfuric acid and Liebermann-Burchard procedures.

To investigate the comparability of three commonly used methods for determination of total cholesterol in plasma in several studies, we used fresh plasma samples as well as plasmas and reference sera that had been stored frozen at -15 degrees C for as long as several years. Duplicate determinations by the manual method of Abell et al. (J. Biol. Chem. 195: 357, 1952) were compared with estimates from one to five continuous-flow analyzers by the ferric chloride-sulfuric acid procedure and also with estimates from five to 13 continuous-flow analyzers by the Liebermann-Burchard procedure with calibrator, as part of the laboratory standardization activities of the Lipid Research Clinics. The agreement among all three procedures was generally within acceptable limits (within 5% of the manual method) when plasmas or sera were fresh or had been frozen for less than one month. Results by the manual method of Abell et al. agreed well with those by the automated Liebermann-Burchard method for samples that had been stored at -15 degrees C for as long as two years. However, the automated ferric chloride-sulfuric acid procedure often showed unacceptably high values (as compared with those from the manual method) for samples that had been stored frozen for a year or more. With the ferric chloride-sulfuric acid method, measured cholesterol concentration increased about 2.5% per year of storage for at least two years. We conclude that reference sera of plasmas that have been kept in long-term frozen storage (-15 degrees C) are not suitable for ongoing standardization of the automated ferric chloride-sulfuric acid assay for cholesterol.

Autoanalysis↗
PubMed1978

Cytocidal activity and proliferative ability of macrophages infiltrating the EMT6 tumor.

The EMT6 mouse tumor was selected for use in the study of cytocidal activity and proliferative ability of infiltrating macrophages because of its high plating efficiency when explanted to culture. The plating efficiency for cells directly plated in culture from the tumor was 28 +/- 9.3%, irrespective of the size of the tumor. Of the adherent cells derived from the tumor, the fraction that was macrophages increased from 27% at 7 days to 47% at 28 days after initial injection. Time-lapse cinemicrography was used to directly observe adherent cells derived from the tumor, and macrophages were found to be cytocidal. When grown in the presence of L-cell conditioned medium no macrophage colonies were found when cultures were established from untreated mice even though most tumor cell colonies contained macrophages. When mice were first treated with 0.8 mg BCNU prior to establishment of the cultures, in order to reduce the frequency of colony-forming tumor cells, approximately half the colonies found contained only macrophages. These results show that macrophages in this tumor are cytocidal and capable of proliferation.

Animals↗
PubMed1978

Proliferative capacity of mouse peritoneal macrophages in vitro.

Thioglycolate-stimulated mouse peritoneal macrophages cultured in the presence of macrophage growth factor (MGF) will continue to proliferate when they are removed from culture dishes with the local anesthetic lidocaine and subcultured. The number of times the cells can be subcultured and remain in a proliferative state is dependent on the number of previous cell divisions. One precursor cell (colony-forming cell) yields about 2.6 X 10(4) daughter cells. When MGF is removed from actively proliferating macrophages, they leave the cell cycle and enter a "resting" condition. When MGF is readded, cells reenter the cell cycle and proliferate with the same doubling time as if MGF had not been removed. Membrane 5'-nucleotidase activity was used as a probe to identify the state of macrophage activation. Proliferating macrophage populations had significantly higher enzyme levels than stimulated macrophages cultured without MGF. These enzymes levels were, however, lower than those found for resident (unstimulated) macrophages.

Animals↗
PubMed1978

Contact-mediated bone resorption by human monocytes in vitro.

Human circulating monocytes in tissue culture are capable of resorbing devitalized adult and fetal bone. An important component of this process is the adhesion of the cells to the mineralized substrate and the localized removal of matrix from beneath the attached cells. The process appears to involve both release of lysosomal enzymes onto the substrate and intracellular accumulation (transport) of resorbed matrix.

Animals↗
PubMed1978

Peritoneal exudate cells. V. Influence of age, sex, strain and species on the induction and the growth of macrophage colony forming cells.

We investigated the effects of age, sex and strain in the induction of peritoneal exudate colony-forming cells (PE-CFC) in mice. Sex and age (ranging from 3 weeks to 12 months) had no significant effect on the induction of PE-CFC. However, we found significant difference between strains in terms of the number of nucleated cells and the proportion of PE-CFC in exudate cells. When we investigated the mechanisms behind this strain difference, we found that it was due to neither the type of colony-stimulating factor employed in culture, nor the type of stimulants used to induce the exudate, nor the difference in the kinetics of appearance of PE-CFC in the peritoneal cavity. We also studied the induction of PE-CFC in rats and hamsters and the growth of these cells in vitro. Unlike mouse cells, PE-CFC from rats and hamsters could also use media conditioned by cells from other species as a source of colony-stimulating factor.

Age Factors↗
PubMed1978

Preliminary observations on the effect of glucan in combination with radiation and chemotherapy in four murine tumors.

The efficacy of glucan in combination with local radiation therapy was measured using three solid murine tumors of differing abilities to induce a host defense. Using the KHT fibrosarcoma which induces no measurable host defense, glucan did not improve tumor-free survival over radiation alone; the combination produced a marginal improvement in tumor-free survival in animals bearing the highly immunogenic EMT-6 tumor. The most marked improvement in tumor-free survival was found with the mildly immunogenic 6C3HED lymphosarcoma. The efficacy of glucan in combination with BCNU chemotherapy was measured using the disseminated AKR transplantable leukemia; the combination yielded a high level of cures compared to no survival for either agent alone. Using the AKR transplantable leukemia in an F1 model, the effect of amphotericin B (AmB) alone or in combination with BCNU was tested. AmB or BCNU alone had little or no curative effect when tested in (AKR X DBA)F1 mice, but 56% of mice were cured when combined therapy was employed. When tested in (AKR X C57BL)F1 or (AKR X A)F1 mice, a small fraction was cured with AmB alone while about 90% were cured with either BCNU alone or the combination.

Amphotericin B↗
PubMed1976

Effect of irradiation on immune responses.

The radioresistance of antibody-mediated immune response is lowest when radiation is given before antigen, and rises steadily with time after antigen stimulation to reach a maximum when serum antibody is at a maximum, suggesting that antibody-producing cells are highly resistant. Irradiation affects the antibody-mediated response by 1) lengthening the period between stimulation and production of detectabel levels of serum antibody, 2) decreasing the rate of increase in serum antibody levls, and 3) decreasing the maximum concentration of serum antibody. Irradiation affects the cell-mediated response by inhibiting immunization and delayed hypersensitivity reactions when administered before antigen. Because the cell-mediated response involves nonlymphoid cells whose precursors are also radiosensitive, irradiation following stimulation may also produce temporary suppression.

Animals↗
PubMed1975

Proliferation and colony-forming ability of peritoneal exudate cells in liquid culture.

Peritoneal exudate cells, obtained from mice injected with thioglycollate medium and cultured in medium containing L-cell-conditioned medium, will proliferate in an exponential fashion for 18 days with a doubling time of 68 h. After a 2 h pulse of tritiated thymidine, labeled adherent cells increased to a maximum of 22-34% during the 1st and 2nd wk of culture. Increasing the cell concentration from 2 times 10-3 to 2 times 10-5 cells/culture reduced exponential growth to 10 days and the doubling time was increased to 81.6 h. Under these culture conditions, peritoneal exudate cells were shown to form colonies on the surface of culture dishes when plated at low density. The cells within the colony were shown to be macrophages using yeast and antibody-coated sheep erythrocytes as a test for phagocytic function. The plating efficiolonies arose from a single precursor cell. The adherent cell population contains the colony-forming precursors. These precursors can be stimulated to form colonies for at least 2 wk by the addition of conditioned medium to cultures at various times after plating. While very few colony-forming cells could be demonstrated in the unstimulated peritoneal lavage, their numbers begin to increase in the exudate 4 h after injection of thioglycollate medium and reach a maximum by day 3 and then decrease. Isolated colonies may be useful in studying the function of macrophages.

Animals↗
PubMed1975

DNA-dependent RNA polymerase levels during the response of human peripheral lymphocytes to phytohemagglutinin.

The cellular levels of the various RNA polymerases have been monitored in resting human peripheral lymphocytes and in lymphocytes stimulated by phytohemagglutin. Activity was measured in the presence of exogenous templates following solubilization and chromatographic resolution of the different RNA polymerases. Resting lymphocytes contain Class I, II, and III RNA polymerases, although the respective levels of activity are very low compared to the levels in metabolically active cell types. During the PHA-induced transformation of resting lymphocytes, the Class I, II, and III enzyme levels rise dramatically. During four days exposure to PHA, the levels of RNA polymerases I and III (which synthesize, respectively, rRNA and the transfer and 5S RNAs) increase 17 fold, while the level of RNA polymerase II (which synthezies heterogeneous nuclear RNA) increase 8 fold. The possible relationship between enzyme levels and the regulation of gene expression is discussed.

Cells, Cultured↗