Antigen-specific, but not natural killer, activity of T cell receptor-gamma delta cytotoxic T lymphocyte clones involves secretion of N alpha-benzyloxycarbonyl-L-lysine thiobenzyl ester serine esterase and influx of Ca2+ ions.

Analysis of Ag specificity of TRC-gamma delta+ T cells in humans has been hampered by the fact that cloned lines of these cells expanded in IL-2 generally display high NK-like cytotoxic activity. A TCR-gamma delta+ CTL clone, isolated in IL-4, strongly lysed a specific stimulator cell, the EBV-transformed cell line JY, but failed to lyse K562 and other target cells sensitive for NK cell activity. Subsequent culture of this clone (CD124) in IL-2 induced high cytotoxic activity against the NK sensitive target cells. K562 cells were unable to induce the secretion of N alpha-benzyloxycarbonyl-L-lysine thiobenzyl ester [(BLT)-serine esterase] or influx of Ca2+ ions in clone CD124 cultured in either IL-4 or IL-2. In contrast, JY cells induced high BLT-serine esterase secretion and an increase of cytosolic Ca2+ levels. By using a combination of a 51Cr-release assay and a BLT-serine esterase secretion assay, the reactivity of clone CD124 against a limited number of target cells was analyzed. CD124 which expresses HLA-A2 and -B7, recognized an Ag shared by JY (HLA-A2; B7; C blank; DR4,6) and one haplotype expressed by the cell line SPS (HLA-A1; B14; Cw6; DR4). The only specificity shared by SPS and JY was HLA-DR4. However, clone CD124 failed to lyse 5 other HLA-DR4+ target cells. The cytotoxic activity of clone CD124 was inhibited by the class I MHC specific mAb W6/32 and the anti-beta 2m mAb A88, but not, or only marginally, by the anti HLA-DQ mAb SPV-L3 or the anti-HLA-DR mAb 135. These data strongly suggest that clone CD124 recognizes a class I MHC Ag different from HLA-A, -B, or -C.