Keywords: DNA-PK, adaptive response, low dose-rate, Bax, apoptosis, spleen, low radiation
Radiation-induced apoptosis in SCID mouse spleen after low dose or low dose-rate irradiation
Concerning human health, studies of radioadaptive responses are quite important in radiation biology, because the radiation response may strongly depend on previous radiation exposure. Therefore, we have studied the radiation-induced Bax and apoptosis in mouse spleen after whole-body irradiation with low dose or low dose-rate. By use of severe combined immunodeficiency (SCID) mouse defective DNA-PK activity, we examined the role of DNA-PK activity in radioadaptation induced by pre-irradiation with low dose or low dose-rate. Based on immunohistochemical analyses in the present study, we detected the dose- and time course-dependent induction of Bax and apoptosis after acute irradiation especially in splenic white pulp of both SCID and the parental mice. They were significantly suppressed in the parental mice 2 weeks after low-dose (0.45 Gy) irradiation or immediately after low dose-rate (0.001 Gy/min for 25 h, 1.5 Gy) irradiation, but not SCID mice under each condition. These data suggest that DNA-PKcs (expressed in the parental mice, not SCID mice) might play a major role on the suppression of the acute radiation-induced apoptosis in spleen by low dose or low dose-rate irradiation. We expect that the present findings will provide useful information for the clarification of radioadaptive response.