Release and retention of labelled DNA in the thymus and spleen of irradiated mice.

The process of release and retention of labelled DNA in thymus and spleen of normal and irradiated (60Co) mice has been studied after administration of 3H-thymidine. The results indicate that the dividing fraction of lymphoid cells is more resistant to radiation than the fraction of nondividing lymphocytes. The time courses of the specific activities of DNA in thymus and spleen were different especially after irradiation with lethal doses. It is suggested that the process of depletion in the lymphoid series is probably similar for both thymus and spleen but, the different cellular composition of these organs led to apparently unrelated results.