T-Cell Stimulation through the T-Cell Receptor/CD3 Complex Regulates CD2 Lateral Mobility by a Calcium/Calmodulin-Dependent Mechanism

Abstract

T lymphocyte activation through the T cell receptor (TCR)/CD3 complex alters the avidity of the cell surface adhesion receptor CD2 for its ligand CD58. Based on the observations that activation-associated increases in intracellular [Ca 2+] ([Ca 2+] i) strengthen interactions between T cells and antigen-presenting cells, and that the lateral mobility of cell surface adhesion receptors is an important regulator of cellular adhesion strength, we postulated that [Ca 2+] i controls CD2 lateral mobility at the T cell surface. Human Jurkat T leukemia cells were stimulated by antibody-mediated cross-linking of the TCR/CD3 complex. CD2 was labeled with a fluorescently conjugated monoclonal antibody. Quantitative fluorescence microscopy techniques were used to measure [Ca 2+] i and CD2 lateral mobility. Cross-linking of the TCR/CD3 complex caused an immediate increase in [Ca 2+] i and, 10–20 min later, a decrease in the fractional mobility of CD2 from the control value of 68 ± 1% to 45 ± 2% (mean ± SEM). One to two hours after cell stimulation the fractional mobility spontaneously returned to the control level. Under these and other treatment conditions, the fraction of cells with significantly elevated [Ca 2+] i was highly correlated with the fraction of cells manifesting significantly reduced CD2 mobility. Pretreatment of cells with a calmodulin inhibitor or a calmodulin-dependent kinase inhibitor prevented Ca 2+-mediated CD2 immobilization, and pretreatment of cells with a calcineurin phosphatase inhibitor prevented the spontaneous reversal of CD2 immobilization. These data suggest that T cell activation through the TCR/CD3 complex controls CD2 lateral mobility by a Ca 2+/calmodulin-dependent mechanism, and that this mechanism may involve regulated phosphorylation and dephosphorylation of CD2 or a closely associated protein.