Diminished calcium influx in lectin-stimulated T cells from old mice.

T lymphocytes from aged donors function poorly, but the biochemical basis for the defect remains uncertain. We tested the hypothesis that T cells from old mice had a diminished ability to transmit extracellular signals into the cytoplasm, by measuring intracellular free calcium concentrations (Cai) in T cells stimulated by the polyclonal activator concanavalin A (Con A). Using the second-generation fluorochrome indo-1 as a reporter of Cai, we found that the Con A-induced elevation of Cai levels is reduced both in rate and extent in old T cells, as compared to T cells from young mice. Flow cytometric analysis showed that this age-sensitive change represents a decline, with age, in the number of T cells that can respond to Con A by increasing their Cai above resting baseline levels (100-120 nM). These results thus show that defects in activation are manifested by T cells from old donors within the first 5 minutes of the activation process, and suggest that aging may lead to alterations either in the surface molecules that receive extracellular signals, or in the sequence of coupled events by which these extracellular signals bring about alterations in the intracellular ionic milieu.