Reduced proliferation in T lymphocytes in aged humans is predominantly in the CD8 + subset, and is unrelated to defects in transmembrane signaling which are predominantly in the CD4 + subset

Abstract

Peripheral blood lymphocytes (PBL) from elderly donors have a reduced proliferative response to phytohemagglutinin (PHA) and anti-CD3 monoclonal antibodies (mAb) compared to those from young donors. To examine whether this is due to intrinsic deficiencies in proliferative potential of T-cell subsets, we compared the growth of unsorted PBL vs sorted CD4 + or CD8 + CD11 − cells after anti-CD3 mAb or PHA stimulation. Unsorted PBL of elderly donors (>65 years) showed a significant decrease in proliferation compared to young donors (20–30 years) when stimulated with anti-CD3 mAb or PHA. Sorted CD4 + and CD8 + cells were grown in culture in the absence of accessory cells under optimized growth conditions (CD28 mAb, interleukin 2 and β-mercaptoethanol present). CD4 + cells from elderly donors showed no reduced growth after anti-CD3 mAb stimulation and only slightly decreased growth after stimulation with PHA. CD8 + CD11 − cells from elderly donors, however, showed a 20–30% reduction in the proportion of cells proliferating in response to the mitogens and up to 40% reduction in the rate of cell-cycle progression of the responding cells. We examined whether this reduced proliferation is related to decreased efficiency of signal transduction by comparing this to the mobilization of intracellular free calcium ([Ca 2+] i) and calcium channel activity after stimulation with anti-CD3 mAb or PHA. [Ca 2+] i was measured in CD4 and CD8 subsets of young and elderly donors using a flow cytometric assay with the dye indo-1. Compared to cells from young donors, CD4 + cells from elderly donors showed a [Ca 2+] i response which was up to 26% lower after stimulation with CD3 and 10% lower after stimulation with PHA. This appeared to be related to decreased calcium channel activity in elderly donors, rather than mobilization of intracellular Ca 2+ stores. CD8 + cells from elderly donors, however, had a slightly, but significantly, greater [Ca 2+] i response to CD3 mAb and PHA than did cells from young donors. Since the age-dependent defect in proliferation is mainly in CD8 + cells, but the [Ca 2+] i decline is predominately in the CD4 + subset, these results suggest that the reduced proliferation of T cells from older donors is not related to decreased efficiency of transmembrane signal transduction.