Acute effects of whole-body proton irradiation on the immune system of themouse

The acute effects of proton whole-body irradiation on the distribution and function of leukocyte populations in the spleen and blood were examined and compared to the effects of photons derived from a Co-60 gamma-ray source. Adult female C57BL/6 mice were exposed to a single dose (3 Gy at 0.4 Gy/min ) of protons at spread-out Bragg peak (SOBP), protons at the distal entry ( E) region, or gamma rays and killed humanely at six different times thereaf ter. Specific differences were noted in the results, thereby suggesting tha t the kinetics of the response may be variable. However, the lack of signif icant differences in most assays at most times suggests that the RBE for bo th entry and peak regions of the Bragg curve was essentially 1.0 under the conditions of this study. The greatest immunodepression was observed at 4 d ays postexposure. Flow cytometry and mitogenic stimulation analyses of the spleen and peripheral blood demonstrated that lymphocyte populations differ in radiosensitivity, with B (CD19(+)) cells being most sensitive, T (CD3()) cells being moderately sensitive, and natural killer (NK1.1(+)) cells be ing most resistant. B lymphocytes showed the most rapid recovery. Compariso n of the T-lymphocyte subsets showed that CD4(+) T helper/inducer cells wer e more radiosensitive than the CD8(+) T cytotoxic/suppressor cells. These f indings should have an impact on future studies designed to maximize protec tion of normal tissue during and after proton-radiation exposure. (C) 2000 by Radiation Research Society.