Chromosome radiosensitivity in human G2 lymphocytes and cell-cycle progression

Purpose : To investigate the possibility that the differential G2- phase radiosensitivity of human peripheral blood lymphocytes, found in normal individuals using the 'G2-phase chromosome radiosensitivity assay', could be attributed to heterogeneity in cellular progression to mitosis rather than di fferences in radiosensitivity. Materials and methods : Human peripheral blood lymphocytes, from four different donors, were exposed to 50cGy X-rays and sampled at different times. The progression of cells into mitosis was monitored by 5-bromo 2-deoxyuridine (BrdUrd) incorporation. Results : The heterogeneous G2-phase chromosome radiosensitivity among different donors was abolished when homogeneous G2-phase cell populations were scored; they contained similar frequencies of cells in early or late G2-phase. Conclusions : The heterogeneous G2-phase chromosome radiosensitivity, usually found in different normal donors, is caused by the analysis of different cell populations rather than reflecting intrinsic differences in radiosensitivity.