Abstract
CD4(+) T cells can be divided into three subsets: naive (Tn), central memory (Tcm), and effector memory (Tem) lymphocytes. These subpopulations differ in phenotype, migratory capacity, pattern of secreted cytokines, and activation threshold. T-cell activation is associated with changes in membrane potential, which provide an electrical driving force for calcium entry into the cytosol. These phenomena were shown to precede lymphocyte proliferation, cytokine synthesis, migration, and apoptosis. Hence the aim of the study was the analysis of these early activation events in the subsets of CD4(+) T cells. We measured the membrane potential and intracellular calcium concentration ([Ca(2+)](i)) in CD4(+) Tn, Tcm, and Tem cells as well as the dependency of these parameters in CD4(+) T cells on their cell-to-cell contacts with other leukocyte subsets. The data indicate that membrane potential of CD4(+) T cells is a subset specific feature maintained by direct contact with monocytes. In addition, monocytes were found to control Ca(2+) influx in CD4(+) T cells.