An augmentation of Fas (CD95/APO-1) antigen induced by radiation: Flow cytometry analysis of lymphoma and leukemia cell lines

An augmentation of Fas antigen induced by radiation was examined using flow cytometry. Six cell lines established from lymphomas or leukemias (HD-70, FLAM-76, CML-C-1, CML-C-2, DL-40 and DL-95) were used in this study. Each c ell line was distributed to two dishes. The cells in one dish were irradiat ed at 10 Gy with cobalt-60 gamma-rays. The control cells were not irradiate d. At 6 h, 24 h, and 48 h after treatment, irradiated and non-irradiated ce lls of each cell line were stained with fluorescein isocyanate (FITC)-conju gated anti-human Fas antibody, and analyzed with flow cytometry. Mean fluor escence intensity (MFI) values of irradiated or non-irradiated cells were e xamined. MFI rates (MFI value of irradiated cells/MFI value of non-irradiat ed cells) of each cell line were calculated at each investigated time point , and an augmentation of the Fas antigen expression with radiation was eval uated. FLAM-76 did not express Fas antigen at any time. An augmented expres sion of Fas antigen due to irradiation was observed in the other five cell lines. These findings strongly suggest that radiation can augment Fas antig en expression in certain tumor cells. Further studies using Fas ligand or s pecific anti-Fas antibody are needed.