AN ANERGIC CYTOTOXIC T-LYMPHOCYTE CLONE EXHIBITS GRANULE EXOCYTOSIS-MEDIATED CYTOTOXICITY

T cell receptor (TCR) occupancy in the absence of a costimulatory sign al transforms T helper (Th) cells or cytotoxic T lymphocytes (CTL) int o a state of anergy. The anergic T cells are unable to produce cytokin es; nevertheless, they maintain their killing activity. We investigate d the mechanisms through which anergic CTL causes lysis of target cell s. Treatment of a CTL clone with phorbol myristate acetate and calcium ionophore A23187 (P/A) transformed these cells to anergic cells. Whil e the anergic CTL clones failed to secrete TNF-alpha in the culture su pernatant, they were still able to kill antigen-specific target cells via a granule exocytosis-mediated pathway. This was evident by the syn thesis of perforin mRNA and release of N-alpha-benzyloxycarbonyl-L-lys ine thiobenzyl ester esterase by these cells. The anergic CTL clone al so showed a low degree of Fas-mediated lysis of normal target cells. I n addition, we generated anergic bulk CTL by treatment with PIA and ob served that the anergic bulk CTL failed to produce TNF upon antigen st imulation, but retained target killing activity via a granule exocytos is mechanism. Our results suggest that the killing mechanisms of anerg ic CTL are mediated to a large extent by a granule exocytosis-mediated pathway. (C) 1998 Academic Press.