小鼠DNA双链断裂修复缺陷细胞的γ射线剂量率效应

γ-ray dose rate effect in DNA double-strand break repair deficient murine cells

目的 探讨γ射线照射后小鼠DNA双链断裂修复缺陷细胞 (SCID)的剂量率效应和潜在致死性损伤的修复。方法 采用低剂量率和高剂量率以及间隔 2 4h的 2次γ射线照射正常细胞(CB .17+/ +)和SCID细胞 ,通过成克隆分析法观察被照射细胞的存活分数。结果 应用间隔 2 4h的2次γ射线照射CB .17+/ +细胞时 ,其存活分数明显高于相同剂量的单次照射 ,而SCID细胞二者无明显差异。在高剂量率单次和 2次γ射线照射时 ,SCID细胞均比CB .17+/ +细胞更敏感。在低剂量率γ射线照射时 ,SCID细胞亦显示比CB .17+/ +细胞更敏感。低剂量率γ射线照射CB .17+/ +细胞和SCID细胞后 ,二者的存活分数均明显高于高剂量率照射。结论 SCID细胞不具有DNA双链断裂的修复能力。SCID细胞和CB .17+/ +细胞均具有剂量率效应。

Objective To analyze the dose rate effect and potentially lethal damage repair in DNA double strand break repair deficient murine cells (SCID) irradiated by γ ray. Methods The wild type(CB.17+/+) and SCID cells were exposed to γ ray at high and low dose rates. The high dose rate exposure was fractionated into two equal doses at 24?h intervals. The survival rates of irradiated cells were calculated by clony forming analysis. Results When γ ray was given to wild type(CB.17+/+) cells in two fractions at 24?h intervals, the survival rate was significantly higher than that when the same total dose was given singly. In contrast, there was no difference in the survival rates between the single and fractionated exposure in SCID cells. SCID cells were more sensitive than CB.17+/+ cells to both low and high dose rates γ ray exposure for cell killing. The survival rate by low dose rate exposure was significantly higher than that by high dose rate exposure, not only in CB.17+/+ cells but also in SCID cells. Conclusions SCID cells are deficient in repairing γ ray induced double strand breaks. There is dose rate effect in both SCID and CB.17+/+ cells.