Biomedical subjects

P C Calder

Publications and source records attributed to P C Calder.

147 records · Page 9Linked to original sources

PubMedDate not supplied

Glutamine requirement of proliferating T lymphocytes.

Glutamine is required for lymphocyte proliferation but the site of glutamine action is not yet known. In this study, the effect of glutamine on key events that occur during lymphocyte activation [interleukin-2 (IL-2) production, IL-2 use, IL-2 receptor expression, transferrin receptor expression] was investigated. Rat or mouse spleen lymphocytes were cultured in the presence of the T-cell mitogen concanavalin A (Con A) and various concentrations of glutamine. There was a trend (not significant) for the ratio of CD4+:CD8+ spleen lymphocytes to increase (from 1.9 to 2.6) as the concentration of glutamine in culture medium increased from 0 to 2 mmol/L. As the concentration of glutamine increased, there was an increase in the proportion of cells expressing the IL-2 receptor (from 30 to 45%) and the transferrin receptor (from 34% to 55%). As the concentration of glutamine increased there was a 2.7-fold increase in the concentration of IL-2 in the culture medium. The IL-2 concentration was decreased when an IL-2 receptor-blocking antibody was included in the culture medium; the IL-2 concentrations measured were taken to indicate the initial Con A-stimulated production of IL-2. In these conditions, the IL-2 concentration in the medium increased 39-fold as the glutamine concentration increased. The use of IL-2 by an IL-2-dependent cell line was dependent on the glutamine concentration in the culture medium. Thus, all four components of lymphocyte activation investigated (IL-2 production, IL-2 use, IL-2 receptor expression, transferrin receptor expression) were dependent on the concentration of glutamine present in the culture medium. Thus, glutamine might provide an early signal in the lymphocyte activation process.

Animals↗

PubMedDate not supplied

The proposed role of glutamine in some cells of the immune system and speculative consequences for the whole animal.

The activity of glutaminase is high in lymphoid organs, lymphocytes and macrophages and increases in the popliteal lymph node in response to an immunological challenge. Consistent with this high activity, glutamine is utilised at a high rate by resting lymphocytes and macrophages in culture. Mitogenic stimulation of lymphocytes increases both glutaminase activity and the rate of glutamine utilisation. The major products of glutamine utilisation by lymphocytes and macrophages in culture are glutamate, aspartate, lactate and ammonia; < 25% of the glutamine used is completely oxidised. It is suggested that the high rate of glutamine utilisation by cells of the immune system serves to maintain a high intracellular concentration of intermediates of biosynthetic pathways such that optimal rates of DNA, RNA and protein synthesis can be maintained. In the absence of glutamine, lymphocytes do not proliferate in vitro; proliferation increases greatly as the glutamine concentration increases. The synthesis of interleukin-2 by lymphocytes and of interleukin-1 by macrophages is glutamine-dependent. Macrophage-mediated phagocytosis is influenced by glutamine availability. Glutamine is synthesized in skeletal muscle. Skeletal muscle and plasma glutamine levels are lowered by sepsis, injury, burns, surgery and endurance exercise and in the overtrained athlete. These observations indicate that a significant depletion of the skeletal muscle glutamine pool is characteristic of trauma and it has been suggested that the lowered plasma glutamine concentration contributes, at least in part, to the immunosuppression which accompanies such situations. Beneficial effects of the provision of glutamine or its precursors have been reported in patients following surgery, radiation treatment or bone marrow transplantation or suffering from injury, sepsis or burns.

Animals↗

PubMedDate not supplied

Dietary glutamine enhances cytokine production by murine macrophages.

To examine the effects of dietary glutamine on cytokine production by macrophages, mice were fed for 2 wk on a control diet that included 200.0 g casein/kg providing 19.6 g glutamine/kg or a glutamine-enriched diet that provided 54.8 g glutamine/kg partly at the expense of casein. There were no differences in weight gain between animals fed the two diets. The plasma concentrations of a number of amino acids differed according to the diet fed; this variation largely reflected the variation in the levels of the different amino acids in the diets. Plasma glutamine concentration was not significantly affected by dietary glutamine level. The production of three cytokines, tumor necrosis factor-alpha, interleukin-1 beta, and interleukin-6, was greater for lipopolysaccharide-stimulated macrophages from mice fed the glutamine-enriched diet. Thus, increasing the amount of glutamine in the murine diet enhances the ability of macrophages to respond to stimulation, at least in terms of cytokine production. These observations suggest that increasing the availability of glutamine orally could promote immune responses involving macrophage-derived cytokines.

Amino Acids↗