[Augmentation in mitogen-induced proliferation of rat splenocytes by low dose whole body X-irradiation].

The hypothesis of radiation hormesis has been proposed. To elucidate the hormetic effect on the immune system, we studied the effect of low dose whole body irradiation on the in vitro mitogen-induced proliferation of rat thymocytes and splenocytes. The rats were irradiated with low doses (0.01-2 Gy) of X-ray and the cells were cultivated in the presence of various mitogens. The cell proliferation was evaluated by the incorporation of 3H-thymidine into the cells. Concanavalin A (Con A)-induced proliferation of splenocytes prepared at 4 hr after irradiation was augmented with 0.05 Gy, whereas that of thymocytes was not affected. Irradiation of rats with 0.05 Gy also induced the enhanced proliferation of splenocytes stimulated by phytohemagglutinin or lipopolysaccharide, though their responses were lower than that by Con A. This augmentation in mitogen-induced proliferation of splenocytes was observed within a few hours after irradiation, being a temporary effect. These results suggest that very low dose whole body irradiation possibly induce a hormesis-like effect on the immune splenocytes.