Effects of Glutamine on Lymphocyte Proliferation,Cytokine Production and Activation-Induced Cell Death

Autor: Wei-Kuo Chang, 張維國
Rok vydání: 2000
Druh dokumentu: 學位論文 ; thesis
Popis: 88
Glutamine is the most abundant amino acid in the body. Glutamine can be produced in sufficient quantities under stable conditions, but becomes a limiting substrate during metabolic stresses, which are associated with increased susceptibility to infection and impairment of the immune response. Low levels of glutamine have been shown to compromise lymphocyte proliferation, production of interleukin-2 (IL-2) and interferon-g (IFN-g), surface activation markers (CD25, CD45RO, CD71). Although glutamine is known to be important for lymphocyte functions, the mechanism by which glutamine modulates lymphocyte functions is not known. In our study, we investigated the mechanisms of glutamine in lymphocyte proliferation, the Th1/Th2 cytokine responses, and activation-induced cell death. On the first part of experiments, we found that glutamine supplementation significantly enhanced phytohaemagglutinin (PHA) stimulated lymphocyte proliferation and propagation of the cell cycle from G1 to S and G2/M phases. Glutamine could also enhance both the intracellular reactive oxygen species (ROS) and glutathione (GSH) levels in PHA-stimulated lymphocytes. Inadequate of glutamine caused a poor lymphocyte proliferation in association with decrease of intracellular GSH levels. Addition of exogenous GSH significantly enhanced lymphocyte proliferation; whereas blockade of GSH synthesis enhanced ROS production and suppressed lymphocyte proliferation. These results suggest that the modulation of PHA-stimulated lymphocyte proliferation by glutamine is closely related to the maintenance of appropriate intracellular redox status. On the second part of our experiment, we evaluated the role of glutamine in Th1/Th2 cytokine responses. Peripheral blood mononuclear cells were stimulated with PHA, live attenuated bacillus Calmette-Guerin (BCG), or measles virus in the presence of different glutamine concentrations. We found that glutamine at an optimal concentration (0.6 mM) significantly enhanced PHA-stimulated lymphocyte proliferation as well as Th1 [Interferon-g (IFN-g) and interleukin-2 (IL-2)] and Th2 cytokine (IL-4 and IL-10) production. In the absence of glutamine, BCG and measles virus elicited minimal lymphocyte proliferation, whereas BCG enhanced Th1 cytokine response and measles virus promoted Th2 cytokine response. Interestingly, addition of glutamine promoted the BCG-elicited a Th1 cytokine response (IFN-g), but suppressed the measles-induced Th2 cytokine response (IL-10). These results suggest that appropriate glutamine levels may influence host responses to different antigens and microorganisms. Furthermore, predominate the Th1, but not Th2, cytokine responses require the presence of optimal concentration of glutamine. On the third part of our experiment, we demonstrated that glutamine can influence the activation-induced cell death. We used the combination of PMA, a potent protein kinase C (PKC) activator, and ionomycin, a calcium-dependent pathway activator which mimics the T cell receptor-mediated signaling pathway in human T cell leukemia cell line. Activation of T cells with these agents will rapidly induce CD95L expression, then triggers cell death in CD95-positive cells. In this study, we employed this model to elucidate the role of glutamine in the AICD responses of human T cells. We demonstrated several lines of evidences to support these concepts: (1) glutamine significantly enhanced IL-2 production, cell proliferation and cell viability in PMA + ionomycin-induced Jurkat T cells; (2) glutamine decreased percentage of apoptotic cells and cell damage in PMA + ionomycin-induced Jurkat T cell; (3) glutamine down-regulated the CD95 and CD95L expression, but up-regulated the CD45RO and Bcl-2 expression in PMA + ionomycin-induced Jurkat T cell. Furthermore, glutamine attenuated caspase-3 and caspase-8 activity in PMA + ionomycin induced Jurkat T cells. Taken together, these observations implicate that glutamine behaves as a survival nutrient which plays a crucial role in rescue activated T cells form apoptosis by up-regulating the expression of Bcl-2 and inhibiting the CD95-mediated AICD. All of these results suggest that glutamine not only crucial in the modulation of lymphocyte proliferation, Th1 and Th2 responses, but also activation-induced cell death. Given the importance of lymphocyte responses by glutamine, it appears that glutamine may be crucial for immune response against microbes, especially for eradication intracellular organism, and recovery from catabolic stress.
Databáze: Networked Digital Library of Theses & Dissertations
Externí odkaz: