An Anergic Cytotoxic T Lymphocyte Clone Exhibits Granule Exocytosis-Mediated Cytotoxicity

T cell receptor (TCR) occupancy in the absence of a costimulatory signal transforms T helper (Th) cells or cytotoxic T lymphocytes (CTL) into a state of anergy. The anergic T cells are unable to produce cytokines; nevertheless, they maintain their killing activity. We investigated the mechanisms through which anergic CTL causes lysis of target cells. Treatment of a CTL clone with phorbol myristate acetate and calcium ionophore A23187 (P/A) transformed these cells to anergic cells. While the anergic CTL clones failed to secrete TNF-α in the culture supernatant, they were still able to kill antigen-specific target cells via a granule exocytosis-mediated pathway. This was evident by the synthesis of perforin mRNA and release of N-α-benzyloxycarbonyl-l-lysine thiobenzyl ester esterase by these cells. The anergic CTL clone also showed a low degree of Fas-mediated lysis of normal target cells. In addition, we generated anergic bulk CTL by treatment with P/A and observed that the anergic bulk CTL failed to produce TNF upon antigen stimulation, but retained target killing activity via a granule exocytosis mechanism. Our results suggest that the killing mechanisms of anergic CTL are mediated to a large extent by a granule exocytosis-mediated pathway.