Antigen receptor-triggered secretion of a trypsin-type esterase from cytotoxic T lymphocytes

Exocytosis of cytolysin-containing granules from cytotoxic T lymphocytes (CTL) was studied with the use of granule enzyme (BLT esterase) as a convenient biochemical marker. Using cloned CTL, we demonstrate here that BLT esterase secretion into the supernatant is specifically triggered by antigen-bearing target cells and that this secretion is inhibited by soluble monoclonal antibodies against the antigen-specific T cell receptor (TcR). Immobilized anti-receptor antibodies induced efficient enzyme secretion in the absence of target cells, thus implying a direct involvement of TcR complex in triggering exocytosis of granules. These results support the role of the granule exocytosis in CTL functions and provide a quantitative and direct assay of a rapid CTL functional response to antigenic stimulation.