DISTINCT T-CELL-RECEPTOR SIGNALING REQUIREMENTS FOR PERFORIN-MEDIATEDOR FASL-MEDIATED CYTOTOXICITY

A diverse array of signals are generated in a cytotoxic T lymphocyte ( CTL) after the T cell receptor (TCR) engages the class I major histoco mpatibility complex (MHC) peptide complex. These signals result in a m ultitude of CTL effector functions, including cellular cytotoxicity, c ell surface receptor expression, and cytokine secretion. We have exami ned signaling through the TCR in a wild type CD8(+), MHC-restricted, a ntigen-specific CTL clone, 14-7, and its interleukin 2-dependent varia nt clone 14-7FD. We report here that 14-7FD is unable to kill via the perforin mechanism of killing, yet is still able to kill via the Fas l igand/Fas mechanism and secrete interferon-gamma in an antigen-specifi c manner. 14-7FD has cytolytic granules that contain perforin and seri ne esterases, which are secreted after phorbol ester and Ca2+ ionophor e treatment. Lastly, to investigate which TCR signaling requirements w ere operational in 14-7FD, we examined TCR-triggered intracellular Ca2 + mobilization in the two clones. After TCR engagement, 14-7FD failed to mobilize intracellular Ca2+, which may be the cause for its inabili ty to trigger the perforin/granule exocytosis mechanism of killing. Th ese results indicate that the signal transduction events that trigger perforin killing and the signaling requirements to induce Fast express ion are distinct. We hypothesize that these two distinct TCR signal tr ansduction requirements allow for separate activation of these two mec hanisms of killing relating to their role in eradication of infected c ells or regulation of immune responses.