Target cell-induced inactivation of cytolytic lymphocytes. Role and regulation of CD45 and calyculin A-inhibited phosphatase in response to interleukin-2.

Cytolytic T lymphocyte (CTL) and natural killer cells (NK) lose their lytic potential after interaction with sensitive target cells that can be restored upon incubation with interleukin-2. In this study we observed that preincubation with Ser/Thr phosphatase inhibitor calyculin A inhibited both CTL and NK cell-mediated cytotoxicity (CMC) in a dose-dependent manner. In contrast, okadaic acid inhibited only CTL-CMC without significantly affecting NK-CMC. Incubation of CTL and NK cells with their sensitive TC inhibited both CTL-CMC by 74% and NK-CMC by > 80%. This loss in lytic activity was accompanied by a loss of 60% and > 80% in the cellular p-nitrophenyl phosphate phosphatase (pNPPase) activity in CTL and NK cells, respectively. When treated with 100 units/ml interleukin-2 for 16-18 h at 37 degrees C, inactivated CTL and NK cells recovered 70% and 100% of their lytic activity and approximately 60% and 100% of phosphatase activity, respectively. Analysis revealed that > 80% of the pNPPase activity was associated with membrane-bound CD45, and it is this phosphatase activity that was reversibly affected by target cell-induced inactivation/reactivation of CTL and NK cells. These results suggest that Ser/Thr phosphatases and CD45 play a key role in modulating the lytic activity of effector cells exposed to sensitive target cells.