Radiation-induced apoptosis in the scid mouse spleen after low dose-rate irradiation

Purpose: To elucidate the process of radioadaptation, the role of DNA-PK activity was examined using the scid mouse defective in DNA-PKcs. Materials and methods: The induction of apoptosis in the spleens of the C.B-17 Icr scid mouse and the parental mouse was studied after chronic irradiation with gamma-rays at 1.5 Gy (0.001 Gy min(-1) 1 for 25 h) followed by challenge irradiation with X-rays at 3.0 Gy (1.0 Gy min(-1) for 3 min). Results : When the wild-type mouse was previously exposed to chronic irradiation (1.5 Gy) at a low dose-rate (0.001 Gy min(-1)), apoptosis induced by acute irradiation (3.0 Gy, 1.0 Gy min(-1)) was significantly suppressed, especially in the splenic white pulp. There was no change by acute irradiation after chronic irradiation in the scid mouse, although an effect was detected in the spleen after acute irradiation alone. Conclusions : These data suggest that DNA-PK activity might play a major role in the radioadaptive response following preirradiation at a low dose-rate.