NKR-P1A STIMULATION OF ARACHIDONATE-GENERATING ENZYMES IN RAT NK CELLS IS ASSOCIATED WITH GRANULE RELEASE AND CYTOTOXIC ACTIVITY

NKR-P1A protein has been implicated in the triggering of NK-mediated n atural killing contributing to target cell recognition by NK cells, Th e aim of the present work was to assess whether NKR-P1A receptor trigg ering also induced arachidonic acid (AA) generation and to determine t he possible role of this event on granule release and cytotoxicity, We demonstrated that activation of fresh peripheral blood rat NK cells b y cross-linking with the anti-NKR-P1A 3.2.3 mAb induced calcium-depend ent AA release, which is due to the activation of cytosolic phospholip ase A(2) (cPLA(2)), secretory phospholipase A(2) (sPLA(2)), and diacyl glycerol/monoacylglycerol lipase, We also documented the presence of a type II sPLA, activity in the supernatant fluids from NKR-P1A-activat ed rat NK cells, suggesting that AA and lysophospholipids could be mob ilized from the outside of the cell, The involvement of AA-generating enzymes in NKR-P1A-induced cytotoxic functions was also investigated, Treatment of effector cells with arachidonyl trifluoromethylketone, a cPLA(2) inhibitor; p-bromophenacylbromide, a sPLA(2) inhibitor; or RHC 80267, a diacylglycerol lipase inhibitor, led to a partial inhibition of the redirected lysis against P815 target cells as well the granule content release induced by NKR-P1A cross-linking, A complete abolishme nt of these events was observed when the cells were simultaneously inc ubated with all three inhibitors, Taken together, our results support a crucial role for the arachidonate-generating enzymes in the inductio n of lytic activity of NK cells directly or by leading to generation o f additional mediators that can play a role in the context of NK cell activation and cytotoxic functions.