Radioautographic Studies of the Effect of Irradiation on the Long-Lived Lymphocyte of the Rat

The long-lived small lymphocytes of the rat thoracic duct lymph, mesenteric lymph nodes, and spleen are very radiosensitive. Approximately 90% are destroyed by 300 r of total-body gamma irradiation. The majority of small cells surviving this amount of irradiation show a postirradiation enlargement which is most pronounced at 10 to 11 days. The enlargement includes an increase in nuclear diameter and an extensive increase in cytoplasm. Evidence is presented to show that some of these enlarged small lymphocytes undergo division. Labeled small lymphocytes transfused into irradiated recipients show a similar enlargement. This suggests that the hypertrophy and subsequent division of small lymphocytes is a secondary effect of irradiation and is probably mediated through the irradiated animal. (auth)