The Acquisition of a Memory Phenotype by Murine CD4⁺ T Cells Is Accompanied by a Loss in Their Capacity to Increase Intracellular Calcium

Abstract

During the process of aging, the fraction of CD4⁺ T Cells with a naive phenotype, that is, Pgp-1^- CD45RB^HighMEL-14⁺, decreases in favor of CD4⁺ T memory cells. Total CD4⁺ T cells from aged mice displayed a diminished calcium response to anti-CD3 and even ionomycin as compared to the cells from young mice, and this was related to the changed composition of the CD4⁺ T-cell population. Regardless the age of the donor mice, naive CD4⁺ T cells effectively increased intracellular calcium, whereas memory CD4⁺ T cells were impaired in this regard. In addition, a heterogeneity in the differentiation stage of the naive CD4⁺ T cells was shown by the observation that calcium mobilization in naive CD4⁺ T cells from young mice was more profound than that in their aged counterparts. These data thus indicate that during the acquisition of a memory phenotype, murine CD4⁺ T cells lose the capacity to increase intracellular calcium, which in turn may be responsible for the decreased level of IL-2 production by these cells.