Objective To investigate the long-term effects of high γ-ray dose on the mice immune system to stimulation of lipopolysaccharide(LPS).

Methods The mice were randomly divided into sham-irradiation group and irradiation group. Mice in sham-irradiation group received no irradiation, while mice in irradiation group received 6 Gy γ-ray irradiation. The mice were accepted intraperitoneal injection of LPS(20 mg/kg) in LPS treated group at 10 weeks after irradiation, while the mice in control group were accepted intraperitoneal injection of saline. The mice were sacrificed after 1 h and 24 h respectively. The white blood cells, CD4, CD8 and B220 cells in peripheral blood were detected. The index of spleen and thymus were calculated and the number of bone marrow nucleated cells per femur were counted.

Results Compared to the mice in sham-irradiation-control group, the ratio of CD4 cells in irradiation-control group increased(t=2.940, P < 0.05), while the CD8 and B220 cells decreased(t=6.485 and 4.351, both P < 0.01). Compared to the mice in sham-irradiation-LPS 1h group, the ratio of CD4(t=2.510, P < 0.05), CD8(t=2.862, P < 0.05) and B220(t=7.074, P < 0.01) cells in irradiation-LPS 1 h group significantly decreased. Compared to the mice in sham-irradiation-LPS 24 h group, the number of bone marrow nucleated cells in irradiation-LPS 24h group significantly increased(t=2.078, P < 0.05).

Conclusions The immune system of mice had not entirely recovered at 10 weeks after 6 Gy γ-ray irradiation. After the stimulation of LPS, the changes of thymus index and CD8, B220 cells numbers were less in the mice of irradiation group than the sham-irradiation group. The long-term effects of radiation on the mice immune system need to be further explored.