Glutathione or GSH is a tripeptide comprised of the amino acids glutamic acid, cysteine, and glycine that the human body produces intracellularly. It is known to have a significant role in DNA and protein synthesis, amino acid transport, and metabolism of numerous compounds. GSH serves as the major antioxidant present in all cells of the body which reverses oxidative damage caused by endogenous free radicals. Because various lymphocytic functions are extremely sensitive to the presence of reactive oxygen species, even a slight reduction in normal GSH concentration can impair lymphocyte functioning. Evidence suggests that GSH can increase the functional capability of lymphocytes such as natural killer cells, cytotoxic T cells, and Helper T cells, as well as, offer protection against microbial, viral, and parasitic infections. Thus, glutathione may have a significant role in modulating the immune system. In addition, GSH levels are typically below optimal levels in sick individuals, those with significant inflammation, and especially older adults whose demand for GSH’s antioxidant activity is increased. Consistent with these statements, it has been well established that T cell-mediated immune response is diminished in aged individuals. Therefore, the immune functioning of individuals with suboptimal GSH levels, especially older adults, may be enhanced through GSH supplementation. An in vitro lymphoblast cell culture model will be used to study the effects of glutathione on immune function. A human peripheral blood T lymphocyte cell line, Loucy, will be used for this project. The experimental culture will be supplemented with glutathione in increasing concentrations and compared with a control culture lacking supplementation. Cell proliferation and lymphoblast activation will be measured at regular intervals. Proliferation will be measured using the vital dye Trypan Blue (which distinguished live and dead cells) and counting by hemacytometer. Lymphoblast activation will be measured by the presence of specific cell surface receptors indicating activation. These cell surface receptors can be quantified by flow cytometry using fluorescent antibodies specific for these receptors. The antibodies will bind receptors present on the cell surface and their fluorescence quantified by the flow cytometer, thus, antibody fluorescence will correspond with cell surface marker presence which will indicate the level of lymphoblast activation. Given that GSH is integral for lymphoblast activation and subsequent T-cell mediated immune response, supplementing Loucy cells with glutathione should increase lymphoblast activation, which will be indicated by greater cell proliferation and surface receptor activation. This outcome should support the hypothesis that GSH supplementation in individuals lacking optimal GSH, will improve immune system functioning.