Search

To further assess the role of CD48 in the interaction of human gamma/delta T cells with their specific target, we generated two series of alloreactive clones, L and K. These clones express a V1-D-J1-C delta chain associated to V3-J2-C2 (L) or V2-J2-C2 (K) gamma chain. Functionally they were CTLs able to lyse the sensitizing B-cell line E418. The cytotoxicity of the L and K clones toward E418 was inhibited by anti-CD48 mAb. That of the L clones was also inhibited by anti-HLA class I mAbs. Variation in L and K lysis profile was observed against a panel of CD48+ targets, further strengthening the argument that they display distinct specificities and suggesting that they do not recognize CD48. Heterogeneity in TCR gene segment usage, MHC-dependent recognition of E418 by the L clones, and resistance of some CD48+ targets strongly suggest that CD48 itself does not interact with L and K TCR. Transfection of CHO cells with CD48 induced killing by the K clones. This killing was inhibited by anti-CD48 mAbs. Taking into account the recent reports on CD48 as an accessory molecule, our results suggest that by binding to CD2 (and/or an unknown ligand), CD48 may serve to strengthen E/T interaction and may contribute to the activation of a minor subset of gamma/delta T cells.

The expression of Fas Ligand (FasL) on human TCRalpha/beta and TCRgamma/delta CD4 − /CD8 − MHC class II-alloreactive clones and Fas/FasL-mediated cytotoxicity were investigated. These clones mediated a HLA-DR2-restricted cytotoxicity toward E418 B cell line (Fas + ). Northern blot analysis demonstrated that all the clones expressed Fast mRNA upon stimulation with E418 specific target. FasL surface expression was detected by immunofluorescence analysis using Fas-Fc soluble protein as well as anti-FasL polyclonal antibodies. Cytotoxicity experiments performed in the presence of anti-Fas, anti-FasL and Fas-Fc molecule indicated that these reagents were unable to inhibit T cell clone mediated lysis toward E418. In addition, when emetine, known to inhibit the induction of Fas-mediated killing, was added during the cytolysis effector phase, no inhibition was observed. These data strongly suggest that Fas/FasL pathway is not involved in this particular T-cell clone-mediated lysis. This cytotoxicity is extracellular Ca 2+ -dependent and is abolished in the presence of EGTA suggesting that it is mainly perforin/granzymebased.