Role of nitric oxide in heat shock protein induced apoptosis of γδ cells

Abstract

Activation induced cell death (AICD) has been proposed to serve as a mechanism to limit T lymphocyte proliferation induced by antigenic stimulation. Heat shock proteins (hsp60 and hsp70) expressed on oral tumor cells serve as ligands for peripheral blood γδT lymphocytes. Tumor cell lysis by γδT lymphocytes is mediated via recognition of hsp expressed on tumor cells. In the present study, we report that upon stimulation with hsp, γδT lymphocytes isolated from oral cancer patients undergo AICD as confirmed by DNA ploidy, annexin V staining and confocal microscopy. In cocultures of γδT lymphocytes and tumor cells, addition of antihsp60 and antihsp70 MAb, but not anti-Fas MAb (ZB4), inhibited DNA fragmentation of γδT lymphocytes. Flow cytometric analysis revealed a down regulation of Fas expression on γδT lymphocytes upon incubation with hsp60 and hsp70. Increased expression of iNOS was observed in hsp-stimulated γδT lymphocytes. Addition of monomethyl L-arginine monoacetate, competitive inhibitor of NOS, inhibited nitric oxide (NO) production and apoptosis of γδT lymphocytes induced by hsp60 and hsp70. The NO-induced apoptosis of γδT lymphocytes involves activation of caspase-9 and loss of mitochondrial membrane potential. The present study explains a novel strategy adopted by tumor cells to evade immune recognition by γδT lymphocytes. © 2006 Wiley-Liss, Inc.