Host: The Japan Radiation Research Society
Co-host: City of Kitakyushu, University of Occupational and Environmental Health, Japan
We previously reported that a lifespan was shortened in B6C3F1 mice which continuously irradiated with gamma-ray at low-dose rate (20 mGy/22h/day) up to accumulated dose of 8 Gy for about 400 days, suggested the life shortening due to early neoplastic death. One of the possible mechanisms for such early neoplastic death may be changes of the immune system associated with growth inhibition or elimination of tumor cells. We investigated the proportion of helper T (Th1 and Th2) cells and the proliferative responses of T cells in the spleen of three strains (C57BL/6, C3H/HeN and B6C3F1) of mice. After irradiation with gamma-rays at high-dose rate (900 mGy/min), middle-dose rate (400 mGy/22h/day) or low-dose rate (20 mGy/22h/day) to achieve accumulated doses of 1-8 Gy, the splenic T cells were analyzed.
After high-dose rate gamma-irradiation, the increase in the proportion of helper T cells and the decrease in T cell proliferation were observed. After middle-dose rate gamma-irradiation, significant changes were not seen in the proportion of helper T cells, while the T cell proliferation was decreased. After low-dose rate gamma-irradiation, these responses differed between the strains. In C57BL/6 and C3H/HeN mice, any changes were not observed in T-cell responses at less than 8 Gy, while decrease in T cell proliferation and increase in the proportion of Th2 at 1 Gy and 2 Gy, respectively, were observed in B6C3F1 mice.
These results indicate that continuous low-dose rate irradiation results in changes of the immune system similarly to those upon high- or middle-dose rate irradiation, and that there is a clear strain difference in immune responses. Such changes of the immune system may lead to life shortening due to early neoplastic death observed in B6C3F1 mice continuously irradiated with low-dose rate gamma-rays. This study was performed under contract with the Aomori Prefectural Government, Japan.
