The accumulation of non-replicative, non-functional, senescent T cells with age is avoided in calorically restricted mice by an enhancement of T cell apoptosis.

Peripheral blood lymphocytes of elderly humans show an increased percentage of T cells with characteristics of replicative senescence. Similarly, the overall decrease in T cell proliferation in aged mice reflects a progressively increasing proportion of non-functional cells rather than a uniform decline in function by all cells. The improved immune function of calorically restricted (CR) animals is, paradoxically, accompanied by a relative lymphopenia. To test whether the reduction in lymphocyte number in the CR mice might reflect more efficient elimination of T cells, we measured apoptosis in young, old and CR old mice. T cell apoptosis induced by irradiation, Staurosporine, anti-CD3, and heat shock was reduced by 62, 42, 32, and 30%, respectively, in old compared with young mice. Caloric restriction normalized apoptosis in T cells from aged mice. Enhanced elimination of non-functional T cells in CR mice may be, at least in part, responsible for their improved immune functional status relative to non-CR mice of the same age.