Glutamine and the immune system

Glutamine is utilised at a high rate by cells of the immune system in cultu re and is required to support optimal lymphocyte proliferation and producti on of cytokines by lymphocytes and macrophages. Macrophage-mediated phagocy tosis is influenced by glutamine availability. Hydrolysable glutamine dipep tides can substitute for glutamine to support in vitro lymphocyte and macro phage functions. In man plasma and skeletal muscle glutamine levels are low ered by sepsis, injury, burns, surgery and endurance exercise and in the ov ertrained athlete. The lowered plasma glutamine concentrations are most lik ely the result of demand for glutamine (by the liver, kidney, gut and immun e system) exceeding the supply (from the diet and from muscle). It has been suggested that the lowered plasma glutamine concentration contributes, at least in part, to the immunosuppression which accompanies such situations. Animal studies have shown that inclusion of glutamine in the diet increases survival to a bacterial challenge. Glutamine or its precursors has been pr ovided, usually by the parenteral route, to patients following surgery, rad iation treatment or bone marrow transplantation or suffering from injury. I n most cases the intention was not to stimulate the immune system but rathe r to maintain nitrogen balance, muscle mass and/or gut integrity. Neverthel ess, the maintenance of plasma glutamine concentrations in such a group of patients very much at risk of immunosuppression has the added benefit of ma intaining immune function. Indeed, the provision of glutamine to patients f ollowing bone marrow transplantation resulted in a lower level of infection and a shorter stay in hospital than for patients receiving glutamine-free parenteral nutrition.