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.
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 (greater than 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 beta-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 ([Ca2+]i) and calcium channel activity after stimulation with anti-CD3 mAb or PHA. [Ca2+]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 [Ca2+]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 Ca2+ stores. CD8+ cells from elderly donors, however, had a slightly, but significantly, greater [Ca2+]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 [Ca2+]i decline is predominantly 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.
Grossmann
A
A
University of Washington, Department of Pathology, Seattle 98195.
Ledbetter
J A
JA
Rabinovitch
P S
PS
D000328:Adult; D000368:Aged; D000375:Aging; D000911:Antibodies, Monoclonal / Q000502:physiology; D000945:Antigens, Differentiation, T-Lymphocyte / Q000276:immunology; D002455:Cell Division; D002469:Cell Separation; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000145:classification / Q000502:physiology; D008213:Lymphocyte Activation; D008934:Mitogens; D010641:Phenotype; D015398:Signal Transduction; D006377:T-Lymphocytes, Helper-Inducer / Q000276:immunology* / Q000502:physiology; D050378:T-Lymphocytes, Regulatory / Q000276:immunology* / Q000502:physiology
D000911:Antibodies, Monoclonal; D000945:Antigens, Differentiation, T-Lymphocyte; D008934:Mitogens