AUTOLOGOUS KILLING BY A POPULATION OF INTERMEDIATE T-CELL RECEPTOR-CELLS AND ITS NK1.1(-) SUBSETS, USING FAS LIGAND FAS MOLECULES() AND NK1.1()

Self-reactive clones, estimated by anti-V beta monoclonal antibodies ( mAb) in conjunction with the Mis system, are confined to a population of intermediate (int) T-cell receptor (TCR) (or CD3) cells (i.e. TCRin t cells), but are not found among TCRhigh cells. The next questions to be answered are whether autologous killing is confined to TCRint cell s and how such killing is mediated. In this study, Cr-51-labelled thym ocytes of syngeneic or allogeneic origin were used as target cells (4- hr assay). When liver and splenic mononuclear cells (MNC) obtained fro m B6 mice were used as effector cells, prominent autologous killing wa s seen in liver MNC, but not splenic MNC. Such killing was not seen wh en thymocytes from B6-lpr/lpr mice (i.e. Fas(-)) were used as target c ells, nor when liver MNC from MRL-gld/gld mice (i.e. Fas ligand(-)) we re used as effector cells (target thymocytes of MRL-+/+ mice). Cell se paration experiments using a cell sorter revealed that autologous kill ing was mediated for the most part by CD3(int) cells, while allogeneic killing was mediated entirely by natural killer (NK) cells, TCRint ce lls and TCRhigh cells. Among CD3(int) cells, the NK1.1(+) subset (i.e. NK1.1(+) T cells) manifested a higher level of autologous killing tha n did the NK1.1(-) subset. Consistent with the results of a functional assay, it was found by reverse-transcription-polymerase chain reactio n (RT-PCR) assay that CD3(int) cells among liver MNC showed the expres sion of Fas ligand mRNA, while thymocytes expressed Fas mRNA. When cla ss I major histocompatibility complex (MHC)- thymocytes (from beta(2)- microglobulin-deficient mice) were used as target cells, NK cells, but not CD3(int) cells, showed potent cytotoxicity. These results suggest that autologous killing is a major function of TCRint cells with self -reactivity, and that such killing is mediated by means of Fas ligand/ Fas molecules.