DNA Supercoiled Domains and Radiosensitivity of Subpopulations of Human Peripheral Blood Lymphocytes

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Abstract
Enriched human B- and T-lymphocyte subpopulations were isolated by means of a Percoll step gradient centrifugation procedure. 60Co γ-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 × 109, 1·78 × 109 and 7·78 × 108 D; T-cells, 4·55 × 109, 1·75 × 109 and 7·67 × 108 D. The differences in radiosensitivity of lymphocyte subpopulations can not, therefore, be entirely ascribed to differences in DNA superstructure.

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