The role of Ca2+ and Mg2+ in the cytotoxic T lymphocyte reaction and in the secretion of N alpha-benzyloxycarbonyl-L-lysine thiobenzyl ester-serine esterase by human T cell clones

Human T cell clones contain enzymes that can cleave the substrate N-alpha-benzyloxycarbonyl-L-lysine thiobenzyl ester (BLT). All CTL clones tested in this study secreted BLT-serine esterase activity, whereas only one of three tested non-cytolytic T cell clones secreted this enzymatic activity upon Ag-specific activation. BLT-serine esterase secretion could also be induced by the Fc gamma+ target cell Daudi in the presence of mAb specific for the TCR/CD3 complex, CD2, or the T cell activation Ag Tp 103. In addition, anti-CD3 and a mitogenic combination of anti-CD2 mAb, induced secretion of BLT-serine esterase in the absence of target cells, whereas anti-Tp 103 failed to do so. The secreted BLT-serine esterase activity induced by the various ligands was inhibited by the serine esterase inhibitors PMSF and m-ABA, but not by N-alpha-p-tosyl-L-lysine chloromethyl ketone. Significant BLT-serine esterase activity was induced by target cells or soluble anti-CD3 in the absence of extracellular Ca2+ ions, provided that extracellular Mg2+ ions were present. The cytotoxic activities by the human CTL clones were completely blocked under these conditions. All ligands that induced BLT-serine esterase secretion in the absence of extracellular Ca2+, induced a transient rise of intracellular Ca2+. Soluble anti-CD3 mAb did not induce a transient rise in intracellular Ca2+ or secretion of BLT serine esterase in CTL preincubated for 2 h with 5 mM EGTA. These findings indicate that mobilization of intracellular Ca2+ in human CTL clones is required for induction of secretion of BLT-serine esterase.