DNA supercoiled domains and radiosensitivity of subpopulations of human peripheral blood lymphocytes

Enriched human B- and T-lymphocyte subpopulations were isolated by means of a Percoll step gradient centrifugation procedure. 60Co gamma-irradiation dose-response curves for these subpopulations were obtained by applying a modified nucleoid sedimentation technique, which was also employed for the determination of the superhelical content by means of ethidium bromide intercalation. Although a similarity in the average superhelical density of B- and T1-lymphocytes was shown, B-lymphocytes exhibited a more pronounced reduction in sedimentation ratio, suggesting a higher radiosusceptibility than the T1-lymphocytes. By applying the single hit kinetics of the target theory to the dose-response curves, an estimation of the supercoil domain sizes was made: B- cells, 5.5 X 10(9), 1.78 X 10(9) and 7.78 X 10(8) D; T-cells, 4.55 X 10(9), 1.75 X 10(9) and 7.67 X 10(8) D. The differences in radiosensitivity of lymphocyte subpopulations can not, therefore, be entirely ascribed to differences in DNA superstructure.