Human B and T lymphocytes differ in UV-induced repair capacity

Unstimulated human T lymphocytes are more readily killed by ultraviolet light (UV) than are B lymphocytes. The greater UV sensitivity of T cells can be explained by a less efficient process of excision repair; this was measured by following the restitution of DNA supercoiling in preparations of nucleoids obtained from purified and irradiated B and T lymphocytes after various periods of incubation. Differences in the sedimentation behaviour of irradiated B and T nucleoids in sucrose gradients are not attributable to differences in the degree of DNA supercoiling. The return to normal supercoiling for both B and T nucleoids is inhibited by hydroxyurea.