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Biomedical subjects

C W Evans

Publications and source records attributed to C W Evans.

36 records · Page 2Linked to original sources
PubMed1985

The effects of the B16 malignant melanoma on induced inflammatory responses in host mice: inhibition of macrophage exudation.

C57BL6 mice were injected with B16F1 or B16F10 cells and granulocyte- or macrophage-rich inflammatory responses were subsequently induced. Analysis of cell yields showed that the percentages of macrophages in the inflammatory exudates of tumour-bearing animals were significantly depressed. No significant changes were noted, however, in the levels of granulocytes in peritoneal exudates from tumour-bearing mice when compared to appropriate controls. In parallel studies, the levels of resident macrophages and granulocytes following lavage of non-stimulated peritoneal cavities of mice with and without tumours were monitored as were the levels of blood monocytes and leukocytes. No consistently significant changes were noted in the levels of blood leukocytes or monocytes in normal or tumour-bearing animals. Furthermore, no consistently significant changes were found in the percentages of granulocytes normally resident in the peritoneal cavities of mice with or without the B16 melanoma. It was found, however, that the percentages of resident macrophages in mice bearing the B16 malignant melanoma were significantly depressed relative to those found in normal animals.

Animals↗
PubMed1985

A study of the adhesive, locomotory and invasive behaviour of Walker 256 carcinosarcoma cells.

We have succeeded in selecting two variant strains of the Walker 256 carcinosarcoma which display markedly different adhesive properties. Both the high (W256A) and the low (W256S) adhesive variants respond chemotactically towards 10(-8) M f-met-leu-phe (FMLP) although there is a significant difference in their locomotory ability. Nevertheless, the fact that the essentially non-adherent W256S cells can migrate in vitro argues against any simple relationship between adhesion and locomotion. We suggest that traction is important in locomotion but that it need not arise only from direct adhesive interaction. We have also tested the invasive behaviour of the W256 variants using an in vitro model system in which disruption of a cellular barrier by the invasive cells can be recorded electrophysiologically. Although leucocytes can penetrate such a barrier they do so only under chemotactic stimulation, whereas W256 tumour cells of either variant strain will do so spontaneously. The tumour variants induce cell retraction within the barrier and this may lead ultimately to cell detachment and death. The holes which arise may then be colonized by tumour cells, and in this way the invasive process could be promoted. The molecular mechanisms by which tumour cells achieve destruction of the cellular barrier are not clear, but it is likely that a number of enzymes are involved.

Animals↗
PubMed1984

Cell adhesion and experimental metastasis: a study using the B16 malignant melanoma model system.

The adhesive properties of B16F1 and B16F10 cells have been studied following their rates of attachment to various substrates and by analysis of their rates of aggregation within the defined environment provided by a cone and plate viscometer. Contrary to previous reports, we found that the B16F10 cells (with significant lung-colonizing potential following tail vein injection) were less homotypically adhesive than B16F1 cells (which colonize lungs poorly). The adhesiveness of B16F10 cells approached that of B16F1 cells only under conditions (low shear, low cell number) where cell collisions were thought to be so few that quantitative differences in aggregation rate could not be determined. B16F1 cells also adhered more to lung cells than did B16F10 cells when assessed by aggregation rate. However, analysis of aggregate composition in which one cell type had been fluorescently labelled showed that B16F10 cells actually formed more mixed aggregates with lung cells than did B16F1 cells. There was no significant difference in the adhesiveness of B16F1 or B16F10 cells to liver cells as assessed by aggregation rate. Analysis of aggregate composition under these circumstances, however, showed that B16F10 cells formed fewer mixed aggregates with liver cells than did B16F1 cells. These results are consistent with the possibility that metastatic cells need to display poor homotypic adhesiveness in order to detach from the primary but enhanced heterotypic adhesiveness in order to colonize specific organs.

Animals↗
PubMed1983

Adaptation of the Boyden chamber to flow conditions: rheological effects on chemotaxis.

Although standard Boyden chambers assess chemotaxis under static fluid conditions they are routinely used as an experimental system to model the dynamic events associated with leukocyte extravasation in vivo. We have adapted the Boyden chamber system by incorporating it within the confines of a cone and plate viscometer which can then be employed to generate known shear conditions as the chemotactically responding cells migrate. Our results show that random locomotion of rat peritoneal exudate cells is stimulated under shear conditions within the range of 11.25-90/s relative to that under static conditions. Furthermore, chemotaxis to the synthetic tripeptide F-Met-Leu-Phe (FMLP) is also stimulated under shear conditions with the peak effect occurring near 22.5/s. This adaptation of the standard chamber system to allow the study of chemotaxis under flow conditions may provide further insight on the migratory properties of leukocytes in vivo.

Animals↗
PubMed1983

Cell adhesiveness and the cell cycle: correlation in synchronized Balb/c 3T3 cells.

The adhesiveness of Balb/c 3T3 cells partially synchronized either by drug treatment or by the mitotic cell shake-off procedure was assessed by following the aggregation kinetics of aliquots of the cells suspended under defined conditions within the confines of a cone and plate viscometer. M phase cells synchronized by either method were significantly more adherent than appropriate control cells. Cells arrested in S phase following drug treatment were found to be poorly adhesive whereas G1 phase cells prepared by allowing drug treated M phase cells to proceed through mitosis or by treating them with L-histidinol did not differ in their adhesiveness from appropriate control cells. The adhesiveness of control cell populations was found to vary with the extent of re-feeding indicating a possible metabolic dependency of cell adhesion. It is suggested that although M phase cells are poorly adherent to the substrate they are nevertheless considerably adherent in an aggregation system. There was no apparent correlation of the observed increase in intercellular adhesion with any particular stage of M phase (prophase, metaphase, anaphase, telophase). We propose that Balb/c 3T3 cells show an increase in cell-cell adhesiveness as they proceed into M phase and that this is maintained until after division is complete. Our suggestion that certain cell types may interact differently with each other and with the substrate in different stages of the cell cycle could have in vivo relevance in those processes such as tumour spread where considerable cell division is involved.

Animals↗
PubMed1983

Transepithelial chemotaxis of rat peritoneal exudate cells.

The migration of peritoneal exudate (PE) cells into plain Millipore filters mounted in Boyden chambers occurs under random, chemokinetic and chemotactic conditions. Significant migration of such cells in vivo, however, involves both transendothelial and transepithelial penetration and occurs predominantly under pathological conditions where chemotactic agents are presumed to be present in gradient form. When Madin-Darby canine kidney (MDCK) epithelial cells are grown as a confluent monolayer on the Millipore filter of a Boyden chamber, transepithelial migration is seen only under chemotactic conditions thus modelling in vivo behaviour more effectively. The MDCK cell line exists as 2 variant strains which model different regions of the mammalian nephron. Strain I MDCK cells share features of the distal and collecting tubules and have relatively high junctional resistance (greater than 1k omega cm2). Strain II MDCK cells model the proximal segment of the nephron and have relatively low junctional resistance (c. 70 omega cm2). We have found that PE cells penetrate the less resistant strain II MDCK monolayer at a faster rate (as assessed by leading front migration) than they penetrate the tighter strain I monolayer. We have also utilized the electrophysiological features of MDCK monolayers to monitor transepithelial penetration. Our electrophysiological data indicate that rat PE cells penetrate MDCK monolayers of either strain by a transjunctional route with consequent reversible dissolution of the junctional complex. This extracellular path of PE cell migration was confirmed by ultrastructural observations. The extent of junctional dissolution and the delay in re-establishment of monolayer integrity (as assessed by electrophysiological means) are related to the concentration of PE cells added to the MDCK monolayer. Brief treatment (10 min) of the MDCK monolayer with the cation chelating agent EDTA also disrupts monolayer integrity, although its re-establishment is significantly faster than when disruption occurs by PE cell transmigration. Our results show a clear parallel between PE cell migration across an MDCK monolayer and changes in its electrophysiological parameters and thus suggest that transepithelial chemotaxis may be directly assessed by electrophysiological means. The use of Boyden chambers modified by the incorporation of epithelial monolayers may prove useful in in vitro studies of inflammation and could be adapted for studies of other pathological processes, such as metastasis, where considerable cell invasion is involved.

Animals↗
PubMed1982

The adhesiveness of normal and SV40-transformed BALB/c 3T3 cells: effects of culture density and shear rate.

The adhesiveness of BALB/c 3T3 cells and their SV40 virally transformed counterparts as assessed by aggregation kinetics was found to vary as a function of cell culture density and aggregation conditions. In culture, SV3T3 cells were found to have a faster growth rate and a smaller cell volume than 3T3 cells. Although both cell-types displayed increasing adhesiveness with increasing culture density, the adhesiveness of SV3T3 cells was consistently lower than that of 3T3 cells of comparable culture density when the cells were aggregated under shear rate conditions less than or equal to 45/sec. When the shear rate was increased from 90 to 450/sec, however, the aggregation profile inverted, with the 3T3 cells becoming less adherent than the SV3T3 cells. The ability of the transformed SV3T3 to remain adherent under conditions of relatively high shear may facilitate extravasation during the process of tumour spread.

Animals↗
PubMed1982

Regulation of meiosis in the foetal mouse gonad.

In vitro culture of male and female gonads was found to have significant effects on gonadal structure and development. Culture resulted in a reduction of testicular cord diameter and a reduction in the number of Sertoli cells lining each cord in cross section. In the female, culture increased the percentage of pyknotic oocytes and fewer germ cells per unit of ovary volume reached diplotene. Mixed sex co-culture using different culture methods showed that day 14 p.c. testes inhibited meiosis in day 14 p.c. ovaries when the cultures were continued until the equivalent of day 21 p.c. Day 15 p.c. and mixed age co-cultures of mixed sex provided more equivocal data since meiosis was inhibited in some preparations but not in others. The possibility is suggested that prophase I may proceed irrevocably to diplotene after about day 15 p.c. and thus the inhibitory effects of foetal testes may be a function of female gonadal age. No evidence was found to support the hypothesis that mixed sex co-culture may stimulate meiosis precociously in foetal testes.

Animals↗
PubMed1981

Changes in lymphocyte adhesiveness during contact sensitization.

Lymphoid cells from the draining lymph nodes of mice 3 days after oxazolone application were found to be more adhesive to each other and to glass than cells from unsensitized nodes. Examination of the temporal sequence of changes during contact sensitization showed that during the first 4 days after oxazolone application there was an increase in both the cellularity of the draining node and in the intercellular adhesiveness of cells from the draining node, which persisted for at least 14 days. There was also an increase in the lymphoblast content; however, this was transient, peaking at Day 4 before returning almost to normal by Day 7. The intercellular adhesiveness of a lymphoblast-enriched subpopulation from the draining node was greater than the adhesiveness of a small lymphocyte subpopulation from the same node. However, the adhesiveness of both these subpopulations were greater than that of normal, unsensitized lymphoid cells. The implications of a change in cellular adhesiveness on the migratory properties in vivo of lymphocytes are discussed.

Animals↗
PubMed1980

Strategies for a statewide approach to improving geographic distribution of health professionals.

A combination of several educational strategies for improving the distribution of physicians and other health professionals is proposed as a coordinated state-level approach designed to achieve equitable access to health care in rural areas. The strategies in place in South Carolina are described to exemplify the concept and potential of such an approach. A unique characteristic is the suggestion that state health planners and sparsely populated rural communities accept as reality that health professionals, in general, and physicians, in particular, are unlikely to remain permanently in such communities and that communities institute procedures for a planned turnover that will assure continuity of the service rather than of the individual practitioner. Rural practice fellowship and rural practice scholarship components are proposed.

Area Health Education Centers↗
PubMed1978

A collision analysis of lymphoid cell aggregation.

We have obtained data on the frequency of aggregates of different size classes and on the maximum aggregate diameter of lymphoid cells subjected to aggregation in the laminar shear field of a Couette viscometer. Maximum aggregate diameter reached a plateau level during aggregation. This plateau is considered to be the result of a balance between the hydrodynamic shear forces tending to resist the formation of aggregates, and the adhesive forces of the aggregated cells tending to resist dissociation. Stepwise-increases in the shear rate produced aggregates of progressively smaller maximum diameter until the limiting (i.e. control equivalent) diameter was reached. Equations governing these stepwise changes in aggregate diameter were obtained by regression analysis, and an estimate of the force of dissociation (FD) was made from derived values of the critical shear rate. Thymocytes (FD=2.54 X 10(-6) N m-2/cell) were found to be more adhesive than lymphocytes (FD=2.05 X 10(-6) N m-2/cell), in agreement with current concepts. The observed data on aggregate frequency were seen to be of poor fit with a model of aggregation derived by collision analysis of the aggregation process. This led us to consider the possibility that all cells may not share the same probability of forming an adhesion. We thus derived further models of aggregation in which some fraction of the total cells was considered to have enhanced possibilities of a collision producing an adhesion. Of the models we considered, a 15% preferred fraction offered best agreement with the experimental observations. We therefore conclude that the populations of cells studied in this report are not 'homogenous' in that some cells are more adhesive than others. Alterations in the percentage of the preferred fraction of cells will lead to different aggregate-frequency indices. Such changes might be expected to occur during the initial stages of carcinoma development.

Animals↗