BIOLOGICAL DOSIMETRY - THE POTENTIAL USE OF RADIATION-INDUCED APOPTOSIS IN HUMAN T-LYMPHOCYTES

An assay for biological dosimetry based on the induction of apoptosis in human T-lymphocytes is described. Radiation-induced apoptosis was a ssessed by flow cytometric identification of cells displaying apoptosi s-associated DNA condensation. CD4 and CD8 T-lymphocytes were analysed . They were recognized on the basis of their cell-surface antigens. Fo ur parameters were measured for both cell types: cell size, granularit y, antigen immunofluorescence and DNA content. Apoptosis was quantifie d as the fraction of CD4-, or CD8-positive cells with a characteristic reduction of cell size and DNA content. At doses below 1 Gy, levels o f radiation-induced apoptosis increased for up to 5 days after irradia tion. Optimal dose discrimination was observed 4 days after irradiatio n, at which time the dose-response curves were linear, with a slope of 8% +/- 0.5% per 0.1 Gy. In controlled, dose-response experiments the lowest dose level at which the radiation-induced apoptosis frequency w as still significantly above control was 0.05 Gy. After 5 days post-ir radiation incubation, intra-and interdonor variations were measured an d found to be similar; thus, apoptotic levels depend more on the dose than on the donor. The results demonstrate the potential of this assay as a biological dosimeter.