Thymocyte proliferation and apoptosis induced by ionizing radiation.

Proliferation and apoptosis of rat and mouse thymocytes caused by ionizing radiation were studied. The percentage of proliferating cells was determined by the method of colchicine metaphases and the apoptosis was estimated as DNA fragmentation. In vitro irradiation with 0.05-0.2 Gy was found to stimulate thymocyte proliferation, the maximum was observed at 0.05 Gy for mouse thymocytes and at 0.1 Gy for rat thymocytes. These doses caused a slight decrease in DNA fragmentation, as compared to control. By raising the radiation dose, proliferation was reduced and DNA fragmentation was increased. The results obtained indicate that low radiation doses stimulate cell proliferation while higher doses trigger apoptosis of thymocytes.