CYTOTOXICITY OF FAS LIGAND AGAINST LYMPHOMA-CELLS WITH RADIATION-INDUCED FAS ANTIGEN

Fas antigen, also termed APO-1 or CD95, is a transmembrane protein and a member of the tumor necrosis factor receptor/nerve growth factor re ceptor superfamily which mediates apoptosis upon oligomerization. The Fas/Fas ligand system is considered to be a key regulator of apoptosis . Recently, we have demonstrated that Fas antigen expression is induce d by low-dose irradiation of some types of lymphomas, and we also demo nstrated that irradiation-induced Fas antigen expression increased wit h the passage of time until peaking at 48 h after irradiation in CML-C 1, CML-C2, DL-40, and DL-95 cell lines. In this study, we also examine d the potential cytotoxicity of Fas ligand peptide against several typ es of lymphoma/leukemia cell lines that showed induction of Fas antige n expression under irradiation. Flow cytometry analysis was performed at 6, 24 and 48 h after irradiation. Samples (1x10(6) cells/ml) from i rradiated and non-irradiated cells of each cell line were incubated wi th or without 5 mu g/ml of Fas ligand peptide for 2 h at 37 degrees C in a humidified atmosphere of 5% carbon dioxide (CO2) in air. The kill ing effect of Fas ligand against cell lines of CML-C1, DL-40, and DL-9 5 were clearly identified as the percentage of cells with Fas antigen expression induced by irradiation. Concerning HD-70 cell line, for whi ch soluble Fas antigen has been identified, the killing effects were c learly observed in samples pre-treated with PBS washings. To our knowl edge, this is the first report describing a possible application of th e Fas/Fas ligand system in treatment of certain types of malignancies in which Fas antigen is inducible by irradiation.