Enhanced mitogen-induced proliferation of rat splenocytes by low-dose whole-body X-irradiation.

To elucidate the stimulative effect on the immune system, we studied the effect of acute low-dose whole-body X-irradiation on the mitogen-induced proliferative responses of rat splenocytes and thymocytes. Concanavalin A (Con A)-induced mitogen response of rat splenocytes 4 hours after 5 cGy irradiation was significantly higher (by 80%, p < 0.02) than that in sham-irradiated controls; whereas that of rat thymocytes did not show change after irradiation of 1-10 cGy. In the rats X-irradiated with doses greater than 25 cGy, Con A-induced mitogen responses of splenocytes and thymocytes were reduced. In a way similar to the Con A-induced mitogen response of splenocytes, the mitogen response of splenocytes induced by phytohemagglutinin (PHA) or lipopolysaccharide (LPS) was significantly increased by X-irradiation with 5 cGy (by 50%, p < 0.02). The enhancement of mitogen response of splenocytes was observed within a few hours after irradiation, being a temporary effect. After 5 cGy irradiation the level of leukotriene B4 (LTB4) in the supernatant fraction of the splenocyte suspension showed a significant increase (by 40%, p < 0.05).