Copyright /999 by The Gerontological Society ofAmerica TheAge-Dependent Cytokine Production by Murine CD8+ T Cells as Determined by Four-Color Flow Cytometry Analysis

Flow cytometry has been used to simultaneously examine intracellular cytokineproduction and expression ofCD44and CD45RB by murine CDa+ T cellsderivedfrom young (2-3 months) or aged (18-22 months) mice. Cytokineproductionby aged CDa+ T cellsdiffersfrom thot by CDa+ T cellsderivedfrom young animals in thata significantlyhigherpercentageof the aged can be triggered to produce interleukin (IL)-4, interferon (IFN)--y, and tumor necrosis factor ct (TNFct). Conversely, a greater fraction ofyoung CD8+ T cells produce IL-2. Aged mice not only have a high er percentage of CDa+/CD44hi T cells,but also a largerfraction ofthese cellsare IFN-'Y+ and IL-~, while a lowerfraction are IL-2+ than is observed in young CD8+/CD44hi T cells. In terms ofrelativecontribution to total cytokine synthesis, a greaterfraction of CDa+ T cellsproduceIFN--yand IL-4 than in CM T cells,whereasCM T cellsare the majorproducersofIL-2. THE effect of aging on T-cell function has been a focusof several investigations (1-5). Although the details of the aging process have not yet been fully elucidated, advancing age is often characterized by cellular and humoral immune dys-function, which leads to a higher incidence of cancer, autoim-mune disorders, and infections (6-9). Because cytokines fre-quently serve as key immune mediators to facilitate the interactions between T cells and other cellular components i