Membrane signal transduction in T cells in aging humans

The interaction of the T cell receptor complex with the ligand is associated with early molecular events involved in the process of signal transduction. These events include, changes in membrane potentials, intracellular free calcium [(Ca++)i], and the activation and translocation of protein kinase C (PKC). The aim of this study was to elucidate the abnormalities in membrane signal transduction pathway as the basis of T cell-mediated immune deficiency associated with aging. Peripheral blood mononuclear cells from aging humans and sex-matched young subjects were stimulated with anti-CD3 monoclonal antibody, WT31 monoclonal antibody (defines epitopes for alpha/beta T cell receptor genes), and phytohemagglutinin (PHA), and examined for the changes in plasma membrane potentials, changes in (Ca++)i, and the activation of PKC. The membrane potentials were measured with DiOC5 dye using FACS. Intracellular free calcium was measured with quin-2 dye and spectrofluorimeter, and the membrane and cytosolic PKC were measured by an enzyme assay. The resting membrane potentials in aging T cells were decreased (plasma membrane depolarized) when compared to T cells from young subjects. In T cells from aging humans, there was a lack of a change in the membrane potentials or membrane potentials were increased (plasma membrane hyperpolarized) following activation with anti-CD3 and WT31 monoclonal antibodies, whereas in young T cells membrane potentials were decreased (depolarized). The basal [Ca++]i levels in aging T cells were less than that in young T cells, and a much smaller rise in [Ca++]i was observed following activation with PHA and anti-CD3 monoclonal antibody in aging T cells than in the young T cells. In aging cells there was less translocation of PKC from cytosol to the membrane following activation with anti-CD3 and WT31. This study demonstrates that the abnormal membrane signal transduction pathway plays a role in T cell dysfunctions associated with human aging.