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目的比较低水平电离辐射(LLIR)单次与分割照射的抗肿瘤效应。方法选用C57BL/6和ICR品系小鼠分别移植Lewis肺癌和S180肉瘤细胞，24 h后再分别接受7.5 cGy单次照射和分割照射(1.5 cGy×5 d)；然后观察20 d抑瘤率、脾NK细胞活性、T淋巴细胞表面CD4、CD8水平的变化以及荷瘤鼠的平均寿命。结果单次与分割照射对Lewis肺癌的抑瘤率分别为40.34%和51.19%，对S180肉瘤为34.26%和30.98%；脾NK细胞活性照后1～4 d升高；CD4、CD8水平及CD4/CD8比值均有不同程度增高；荷瘤鼠的生命延长率分别为8.45%和8.84%。结论本实验采用的低水平单次或分割照射对Lewis肺癌和S180肉瘤均有明显的抑瘤效果，能显著增强荷瘤机体的免疫机能以及延长荷瘤鼠的平均寿命。经比较，两种照射方式在肿瘤生长抑制和免疫刺激作用等方面差异无显著性(P＞0.05)。

Objective　To compare the anti-tumor effects of low level ionizing radiation with single or fractionated irradiation method. Methods　Lewis cells and S180 sarcoma were transplanted to C57BL/6 and ICR mice and were respectively irradiated with single dose(7.5 cGy) or fractionated dose(1.5 cGy×5 d) 24 h later. Then the tumor inhibitory rate, splenic NK cell activity, CD4 and CD8 levels on T lymphocyte surface, and the average longevity of tumor-bearing mice at 20 d were observed. Results　The tumor inhibitory rates of Lewis cancer with single or fractionated irradiation were 40.34% and 51.19% respectively, and that of S180 sarcome were 34.26% and 30.98%. Splenic NK cell activity was elevated in 1 to 4 days after irradiation. CD4 and CD8 levels and the ratio of CD4/CD8 all increased to some different extent after irradiation. And the life prolongation rates in S180 tumor-bearing mice were 8.45% and 8.84% respectively. Conclusions　Low dose and low dose rate radiation have obvious anti-tumor effects in mice with Lewis cancer and S180 sarcoma, and they enhance immunological function and prolong average longevity of the tumor-bearing mice. But there were no statistical difference(P＞0.05) in tumor growth inhibition and immunological function stimulation between the single and the fractionated irradiation.