EGFR抑制剂C225对人前列腺癌细胞的放射增敏作用

目的 探讨表皮生长因子抑制剂C225对人前列腺癌细胞株(DU145) 放射敏感性的影响。方法 实验组用表皮生长因子抑制剂C225(100 nmol/L)处理后,⁶⁰Co γ射线(吸收剂量率1.953 Gy/min)对体外培养的DU145细胞进行0、2、4、6 和8 Gy 照射,用MTT法、集落形成法检测细胞增殖和细胞存活率;用单击多靶模型拟合剂量存活曲线;用流式细胞仪检测细胞周期和凋亡。结果 C225对照射后DU145细胞增殖有明显抑制作用。C225组的放射生物学参数值(D₀、D_q、N、SF₂)较对照组低。C225组和对照组的RBE 比值为1.39。C225组处于S期的细胞比例降低,出现明显的G₀/G₁期阻滞。C225组细胞的早期凋亡率在照射剂量达4 Gy后明显高于对照组(t=-14.55,P＜0.05)。结论 表皮生长因子抑制剂C225通过抑制细胞增殖、G₀/G₁ 期阻滞和诱导凋亡来增加人前列腺癌细胞放射敏感性。     

P53在电离辐射诱导的细胞周期解耦联中的作用

目的 探讨p53基因在电离辐射(IR)诱导的MCF-7细胞周期解耦联中的作用。 方法 构建RNAi表达载体,经磷酸钙共沉淀法转染293T细胞形成病毒包装颗粒,感染MCF-7后采用Western blot检测P53蛋白的表达,建立p53基因沉默模型。将p53野生型(+ +)和沉默模型(- -)经电离辐射处理后,采用流式细胞术分别测定细胞周期并分析细胞多倍体的变化。结果 与p53^{+ +}组比较,p53^{- -}模型组G₀ G₁期细胞百分数减少,S期、G₂期增加(P<0.01),倍体分析表明二倍体数减少,四倍体、八倍体均增加(P<0.01)。在p53^{+ +}和p53^{- -}细胞中,与假照射组比较,4 Gy照射后G₀ G₁期、S期细胞百分数减少,而G₂期增多(P<0.01);倍体分析表明,照射后二倍体数减少,四倍体、八倍体均增加(P<0.01)。与p53^{+ +}+IR组比较,p53^{- -}+IR 组发生G₀ G₁期、S期细胞百分数减少,G₂+M期增多(P<0.01),二倍体数减少,四倍体增多(P<0.01),八倍体无明显差别。结论 电离辐射可以诱导细胞发生G₂期阻滞和细胞周期解耦联;P53在电离辐射诱导的MCF-7细胞G₂期阻滞中发挥作用,而在细胞周期解耦联中可能不发挥作用。     

肺癌A549放射抗拒细胞亚系的建立及抗拒机制的研究

目的 建立肺癌细胞系A549的放射抗拒模型并探讨放射抗拒的机制。方法 应用两种方案对非小细胞肺癌A549细胞系进行X射线照射:一组照射5次,每次剂量600 cGy;另一组照射15次,每次剂量200 cGy。照射完成后对存活细胞单克隆化分别命名为A549-S1和A549-S2,采用克隆形成实验测定两种细胞亚系及亲本A549细胞的放射敏感性,流式细胞术检测细胞周期特征,RT-PCR和Western blot分别测定3种细胞Notch1的表达。结果 与亲本A549细胞相比,A549-S1细胞显示出明显放射抗性,D₀、D_q及N值增大,细胞存活曲线肩区增宽,在SF₂水平上,放射抗性是A549的1.38倍,细胞的S期比例较A549细胞明显增高, G₀/G₁期比例下降(P<0.05),Notch1的表达较A549细胞明显增强。而A549-S2的放射敏感性与亲本细胞相比稍增强,D₀、D_q及N值均减小,细胞存活曲线肩区变窄,在SF₂水平上,放射抗性是A549细胞的0.84倍,细胞S期、G₀/G₁期比例较A549细胞减少,而G₂/M期比例明显增加(P<0.05),Notch1表达与亲本A549细胞相比无明显变化。结论 A549细胞亚系放射抗拒的形成与不同照射方案有一定关系,得出的放射抗拒细胞亚系显示出与亲本不同的细胞周期特征,而细胞特征的变化可能与Notch1的表达增强有关。     

125I粒子组织间永久种植致大鼠坐骨神经早期损伤的病理学观察

目的 探讨¹²⁵I粒子持续性低剂量率照射下肿瘤细胞的凋亡和周期改变。方法 采用CL187人结肠癌细胞系体外培养,分为空白对照组、⁶⁰Co单次高剂量率照射组、¹²⁵I低剂量率照射组。单次高剂量率组以2 Gy/min给予细胞1、2、4、6、8和10 Gy的照射,低剂量率组以2.77cGy/h的初始剂量率给予相同剂量照射,照射后24 h根据肿瘤细胞死亡率和14 d克隆形成率评价不同照射方式对肿瘤细胞的杀伤效果。同时,用放射性¹²⁵I粒子以2.77 cGy/h的剂量率,给予细胞2、5和10 Gy的照射,应用流式细胞术测量其凋亡和细胞周期的变化。结果 低剂量率组照射后细胞死亡率在1 Gy时低于⁶⁰Co单次高剂量率组,随着剂量的上升,2 Gy后,超过单次高剂量率组,但整体上¹²⁵I粒子照射后细胞死亡率高于⁶⁰Co组(P=0.011)。¹²⁵I持续性低剂量率照射组的克隆增殖率明显低于⁶⁰Co单次高剂量率组(P=0.0021)。低剂量率照射下,2 Gy时仅能引起G₂/M期阻滞和凋亡,5 Gy时达到峰值,10 Gy时细胞周期阻滞和凋亡的比率依然很高,但相对于5 Gy有所下降;同时G₂/M期阻滞和凋亡变化呈现出相同的趋势。结论 在相同剂量条件下,¹²⁵I粒子持续照射低剂量率照射比⁶⁰Co单次高剂量照射对CL187肿瘤细胞具有更强的杀伤效应;G₂/M期阻滞引起的凋亡是低剂量率照射杀伤肿瘤细胞的主要机制。     

咖啡酸苯一酯对人宫颈癌HeLa细胞的放射增敏作用

目的 探讨咖啡酸苯一酯(CAPE)对人宫颈癌HeLa细胞的放射增敏作用。方法 将宫颈癌HeLa细胞经不同浓度的CAPE作用24 h,四甲基偶氮唑盐比色法(MTT)法检测细胞抑制效应与CAPE浓度的关系。将HeLa细胞设对照组和药物组,两组均经⁶⁰Coγ射线照射0、2、4、6和8 Gy,计数细胞克隆;另将HeLa细胞设对照组、CAPE组、单纯照射组、照射+CAPE组,流式细胞检测技术分析CAPE对细胞周期的影响。结果 CAPE对HeLa细胞的抑制率呈剂量依赖性增加(F=126.49~3654.88,P<0.01);细胞经⁶⁰Coγ射线照射后,HeLa细胞克隆存活率随着照射剂量的增加而降低(F=174.42~9422.81,P<0.01);相同剂量下,药物组的HeLa细胞克隆存活率低于对照组(F=120.14~251.91,P<0.01);药物组和对照组HeLa细胞的平均致死剂量(D₀)为1.45和1.82 Gy、准阈剂量(D_q)为1.89和3.21 Gy, 药物组较小,放射增敏比(SER)为1.26>1;与对照组相比, CAPE组及单纯照射组G₂/M期的细胞比例升高(P<0.01),而在照射+CAPE组则降低(P<0.01)。结论CAPE通过对人宫颈癌HeLa细胞G₂/M期的阻滞及可能抑制细胞亚致死性损伤修复能力,发挥放射增敏作用。     

60Co γ射线对盐诱导激酶2的诱导表达作用

目的 探讨电离辐射对盐诱导激酶2（SIK2）蛋白和mRNA的诱导表达作用及细胞周期相关性。方法 HepG2细胞用⁶⁰Co γ射线照射,蛋白质印迹法和实时定量PCR法分别检测细胞的SIK2蛋白和mRNA的表达,胸腺嘧啶双阻滞法同步化细胞,流式细胞术测定细胞周期的变化。结果 HepG2细胞2 Gy照射后4、6、10 h,SIK2蛋白表达显著增加 （t=3.00、3.98、4.17,P<0.05）;10 Gy大剂量照射后,SIK2蛋白表达增加的趋势与2 Gy一致,但增加的幅度较前者低。2和10 Gy照射后SIK2基因 mRNA均在10 h出现了增加（t=4.54、2.74,P<0.05）。照后10 h出现了细胞G₂/M阻滞高峰。利用同步化细胞分析表明,细胞周期不同时相中SIK2 mRNA的表达无明显差别。结论 2和10 Gy照射均能诱导SIK2蛋白表达增加,2 Gy的作用更加明显。细胞照射后10 h,SIK2 mRNA的表达水平增加,但与辐射诱发细胞G₂/M期阻滞引起不同时相细胞的分布变化无关。     

腺病毒介导的人视网膜母细胞瘤94基因对人食管癌细胞辐射增敏作用的研究

目的 探讨重组腺病毒人视网膜母细胞瘤94基因(Ad-Rb94)对γ射线杀伤人食管癌 EC109细胞的增敏作用。方法 将Ad-Rb94体外转染后的EC109细胞,按数字随机表法,分为空白对照组、Ad-LacZ对照组、Ad-Rb94组、照射组和Ad-Rb94联合照射组,观察EC109的细胞的抑制率、细胞周期和Rb蛋白的表达。结果 Ad-Rb94组、照射组和Ad-Rb94联合照射组对EC109细胞生长均具有抑制作用,Ad-Rb94联合照射组的抑制效应最强,明显高于Ad-Rb94组和照射组(F=23.31,P<0.05)。Ad-Rb94联合照射组EC109细胞出现明显的G₂期阻滞,G₂期细胞所占比例达50%。Ad-Rb94联合照射组表达Rb蛋白的细胞明显增加,阳性率达71%,较Ad-Rb94组和照射组差异有统计学意义(χ²=8.31和6.73,P<0.05)。结论 Rb94基因联合照射能明显提高对人食管癌细胞的辐射增敏性。     

血管内皮抑素联合照射对肺癌H-520细胞周期及信号传导通路的影响

目的 探讨血管内皮抑素对肺鳞癌细胞系H-520细胞放射增敏作用的机制。 方法 重组人血管内皮抑素联合⁶⁰Co γ线作用于H-520细胞后,集落形成实验检测重组人血管内皮抑素对H-520细胞的放射增敏作用;流式细胞术检测细胞周期变化及磷酸化p38-MAPK蛋白的表达水平;RT-PCR检测周期相关基因cyclin D1、cdk2、cdk4及凋亡相关基因survivin的表达情况;Western-blotting检测磷酸化Akt蛋白表达情况。结果 血管内皮抑素可以增加细胞对⁶⁰Co γ射线的放射敏感性,联合组D₀、D_q、N、D₁₀、 SF₂较照射组低,放射增敏比为1.45;200 μg/ml血管内皮抑素处理后H-520细胞发生G₀/G₁期阻滞,周期相关基因cyclin D1、cdk2、cdk4及凋亡相关基因survivin表达下降;血管内皮抑素联合照射后磷酸化p38-MAPK蛋白及磷酸化Akt蛋白表达下降。结论 血管内皮抑素可能通过抑制H-520细胞增殖,诱导细胞发生G₀/G₁期阻滞,促进细胞凋亡及阻断p38-MAPK和PI3K/Akt信号通路传导,发挥放射增敏作用。     

Effect of subsequent acute-dose irradiation on cell survival in vitro following low dose-rate exposures

Purpose : Following acute irradiation, excess radiosensitivity is generally seen at doses <1 Gy, a phenomenon termed 'low-dose hyper-radiosensitivity' (HRS). A very strong, HRS-like inverse dose-rate effect has also been described following continuous low dose-rate (LDR) irradiation at <30 cGy h -1. We report on the sequential irradiation of a cell line by such LDR exposures followed by low acute doses, where either treatment individually would elicit a hypersensitive response. The aim was to determine if a prior LDR exposure would remove the HRS normally seen in response to very small acute radiation doses. Materials and methods : T98G human glioma cells were given single continuous LDR exposures of 5-60 cGy h -1 using a 60 Co γ-source. At intervals of 0 or 4 h following LDR irradiation, cells were further irradiated with a range of acute doses using 240-kVp X-rays. The response to the combined treatment was assessed using high-precision clonogenic cell survival assays, and the amount of HRS at acute doses <1 Gy was determined. Results : LDR at ≥60 cGy h -1 to total doses up to 5 Gy in asynchronously growing cells did not remove HRS in the subsequent acute-dose survival curve. In confluent cultures, subsequent acute-dose HRS was not present after an LDR dose of 5 Gy at either 60 or 30 cGy h -1, but returned if a 4-h interval was left between LDR and acute-dose irradiation. In confluent cultures, acute-dose HRS remained for LDR treatments at 5 or 10 cGy h -1 or if the total dose was 2 Gy. Taking all cultures and dose-rates together, the 'degree' of acute-dose HRS, as measured by α s, was significantly greater in cells irradiated at LDR to a total dose of 2 than of 5Gy. Conclusions : Initial LDR exposure can affect a subsequent HRS response. HRS is reduced after LDR exposures at greater dose intensity, but can recover again within 4 h of completion of LDR exposure. This suggests that processes determining increased resistance to small acute doses (removal of HRS) might be governed by the level of repairable DNA lesions.     

Effect of subsequent acute-dose irradiation on cell survival in vitro following low dose-rate exposures

PURPOSE: Following acute irradiation, excess radiosensitivity is generally seen at doses <1 Gy, a phenomenon termed "low-dose hyper-radiosensitivity" (HRS). A very strong, HRS-like inverse dose-rate effect has also been described following continuous low dose-rate (LDR) irradiation at <30 cGy h(-1). We report on the sequential irradiation of a cell line by such LDR exposures followed by low acute doses, where either treatment individually would elicit a hypersensitive response. The aim was to determine if a prior LDR exposure would remove the HRS normally seen in response to very small acute radiation doses. MATERIALS AND METHODS: T98G human glioma cells were given single continuous LDR exposures of 5-60 cGy h(-1) using a (60)Co gamma-source. At intervals of 0 or 4 h following LDR irradiation, cells were further irradiated with a range of acute doses using 240-kVp X-rays. The response to the combined treatment was assessed using high-precision clonogenic cell survival assays, and the amount of HRS at acute doses <1 Gy was determined. RESULTS: LDR at > or = 60 cGy h(-1) to total doses up to 5 Gy in asynchronously growing cells did not remove HRS in the subsequent acute-dose survival curve. In confluent cultures, subsequent acute-dose HRS was not present after an LDR dose of 5 Gy at either 60 or 30 cGy h(-1), but returned if a 4-h interval was left between LDR and acute-dose irradiation. In confluent cultures, acute-dose HRS remained for LDR treatments at 5 or 10 cGy h(-1) or if the total dose was 2 Gy. Taking all cultures and dose-rates together, the "degree" of acute-dose HRS, as measured by alpha(s), was significantly greater in cells irradiated at LDR to a total dose of 2 than of 5Gy. CONCLUSIONS: Initial LDR exposure can affect a subsequent HRS response. HRS is reduced after LDR exposures at greater dose intensity, but can recover again within 4 h of completion of LDR exposure. This suggests that processes determining increased resistance to small acute doses (removal of HRS) might be governed by the level of repairable DNA lesions.     

Low dose radiation induced immunomodulation: effect on macrophages and CD8+ T cells

PURPOSE: The aim of the present investigation was to study the effect of fractionated whole body low dose ionizing radiation (LDR) on the functional responses of T lymphocytes, their subpopulations and macrophages. MATERIALS AND METHODS: C57BL/6 mice were exposed to 4 cGy from a (60)Co source, at 0.31 cGy/min, at 24 h intervals for 5 days (total dose 20 cGy). Phagocytic activity was measured by flow cytometry using Bioparticles and nitric oxide generation was estimated by spectrophotometry. Proliferation of lymphocytes in response to concanavalin A (con A) and alloantigens was measured by (3)H thymidine incorporation. Expression of cell surface markers was assessed by flow cytometric analysis of antibody labeled cells. Target cell killing by cytotoxic T cells (CTL) generated against allogenic cells was assessed by flow cytometry using PKH26 labeled target cells. Cytokines were estimated by enzyme linked immunosorbent assay. RESULTS: Exposure to LDR enhanced nitric oxide secretion and phagocytosis. The expression of early activation antigen, CD69, was enhanced in CD8(+) T lymphocytes concomitant with enhanced proliferation in response to con A. In addition, mixed lymphocyte reaction (MLR) and CTL response were augmented and secretion of interferon gamma (IFN-gamma) was suppressed following LDR exposure. CONCLUSIONS: LDR exposure enhanced the function of macrophages and responses of CD8(+) T cells in C57BL/6 mice.     

Low dose radiation induced immunomodulation: Effect on macrophages and CD8+ T cells

Purpose: The aim of the present investigation was to study the effect of fractionated whole body low dose ionizing radiation (LDR) on the functional responses of T lymphocytes, their subpopulations and macrophages.

Materials and methods: C57BL/6 mice were exposed to 4 cGy from a ⁶⁰Co source, at 0.31 cGy/min, at 24 h intervals for 5 days (total dose 20 cGy). Phagocytic activity was measured by flow cytometry using Bioparticles® and nitric oxide generation was estimated by spectrophotometry. Proliferation of lymphocytes in response to concanavalin A (con A) and alloantigens was measured by ³H thymidine incorporation. Expression of cell surface markers was assessed by flow cytometric analysis of antibody labeled cells. Target cell killing by cytotoxic T cells (CTL) generated against allogenic cells was assessed by flow cytometry using PKH26 labeled target cells. Cytokines were estimated by enzyme linked immunosorbent assay.

Results: Exposure to LDR enhanced nitric oxide secretion and phagocytosis. The expression of early activation antigen, CD69, was enhanced in CD8⁺ T lymphocytes concomitant with enhanced proliferation in response to con A. In addition, mixed lymphocyte reaction (MLR) and CTL response were augmented and secretion of interferon gamma (IFN-γ) was suppressed following LDR exposure.

Conclusions: LDR exposure enhanced the function of macrophages and responses of CD8⁺ T cells in C57BL/6 mice.     

电离辐射对小鼠脾细胞中调节性T细胞及其相关分子表达的影响

目的 观察不同剂量X射线照射后不同时间小鼠脾细胞中调节性T细胞和叉头状转录因子(Foxp3)的表达变化,探讨X射线对调节性T细胞以及相关因子Foxp3的影响。方法 112只雄性ICR小鼠,随机平均分为低剂量(0.075 Gy)组和高剂量(2 Gy)组,用X射线深部治疗机分别进行0.075和2 Gy全身照射,于照射后0、4、8、16、24、48和72 h处死,取脾脏,分别应用流式细胞术和RT-PCR法检测调节性T细胞和Foxp3的表达水平。结果 0.075和2 GyX射线全身照射后,小鼠脾细胞CD4+CD25+Treg 细胞百分比均在照射后8 h达高峰,随后一直保持较高水平,高于照射前水平(2 Gy,在8、16、48、72h时,t=4.65、4.28、3.71、2.88,P<0.05; 0.075 Gy,在8、16、24、72h时,t=8.73、10.55、4.21、4.65,P<0.05)。Foxp3在mRNA水平,0.075 Gy照射后变化不明显,而2 Gy照射后于24 h形成峰值。Foxp3在蛋白质水平,0.075 Gy照射后并未有显著变化;而2 Gy照射后于16 h形成峰值,随后略有下降,但仍保持较高水平。结论 调节性T细胞及相关分子Foxp3的不同变化可能成为高、低剂量X射线诱导不同免疫效应的原因之一。     

Possible role of elevation of glutathione in the acquisition of enhanced proliferation of mouse splenocytes exposed to small-dose γ-rays

Purpose : To examine the relation between the induction of an increased glutathione level and the elevated proliferative response of mouse splenocytes by a small dose of γ-rays. Materials and methods : Male ICR strain mice, 7 weeks of age, were divided into irradiated and non-irradiated control groups. Irradiation was done with γ-rays from a 137 Cs source at a dose of 50cGy (1.11Gy/min). Glutathione content in the splenocytes was measured using a modified spectrophotometric technique. Concanavalin A (Con A)-induced proliferative response of the splenocytes after whole-body γ-ray irradiation was estimated from the 3 H-thymidine incorporation into the cells. Results : The glutathione level in mouse splenocytes increased 2h after whole-body γ-ray irradiation at 50 cGy, peaked at 4h and thereafter decreased almost to the zero-time level by 12-h postirradiation. A significant enhancement of Con A-induced proliferation was observed in the splenocytes obtained from the wholebody-irradiated animals between 2h and 6h post-irradiation. Glutathione exogenously added to splenocytes obtained from normal mice enhanced the Con A-induced proliferation of splenocytes in a dose-dependent manner. This enhancement was completely blocked by buthionine sulfoximine, a specific inhibitor of the de novo pathway of glutathione synthesis. Conclusions : The induction of endogenous glutathione immediately after low-dose γ-ray irradiation is at least partially responsible for the enhancement of immune function, and may throw light on the mechanisms of carcinostatic effects induced by low dose ionizing radiation.     

Influence of dose-rate, post-irradiation incubation time and growth factors on interphase cell death by apoptosis and clonogenic survival of human peripheral lymphocytes.

PURPOSE: To investigate the effects of dose-rate, post-irradiation incubation time and growth factors on radiation-induced interphase cell death by apoptosis and reproductive cell death in human peripheral lymphocytes. MATERIALS AND METHODS: Lymphocytes in G0-phase were exposed in vitro to 1-3Gy 137Cs gamma-radiation at a high- (HDR, 45Gy/h) or a low dose-rate (LDR, 0.024Gy/h). HDR exposures were performed either on day 1 (HDR1) simultaneously with the start of the 3 Gy LDR exposure, or on day 6 (HDR6) when the LDR exposures ended. Apoptosis was studied at different times after irradiation by measuring (1) cellular membrane integrity, (2) morphological changes and (3) cell size reduction. Clonogenic survival was analysed for cells plated directly after irradiation (LDR, HDR6, HDR1 day 1) or after 5 days post-irradiation incubation (HDR1 day 6). RESULTS: A significant decrease in reproductive cell death was observed after 3 Gy LDR exposure as compared with the HDR1 exposure for cells plated day 6. For the lower doses applied, the dose-rate effect could not be statistically verified. A decrease in apoptosis for all three doses applied (i.e. 1, 2 and 3Gy) was observed when the LDR exposures were compared with the HDRI analysed day 6, although not of statistical significance. Radiation-induced apoptosis was efficiently counteracted by growth factors up to 24-48 h after 3 Gy HDR exposure. The prevention of radiation-induced cell death by growth factors was dependent on dose and post-irradiation time in G0. When the growth factors were added after a prolonged post-irradiation incubation in G0 (HDR 1 cells plated day 6), a significant increase in reproductive cell death was found (3 Gy) as compared with HDR protocols where the growth factors were added directly after irradiation (HDR 1 plated day 1 and HDR6). CONCLUSIONS: A dose-rate effect on radiation-induced apoptosis was indicated but not statistically verified. A significant dose-rate effect on reproductive cell death was observed. This dose-rate effect was, however, inverted when growth factors were added directly after the HDR irradiations.     

辐射对EL-4、J774A.1细胞CD2、CD48表达的影响

目的　通过时程及量效研究观察不同剂量X射线照射对EL 4和J774A 1细胞株中表面分子CD2、CD4 8的影响。方法　采用荧光免疫流式细胞术检测蛋白表达的变化。结果　 (1)EL 4细胞CD2分子表达结果显示 ,0 0 75GyX射线照射后CD2合成在照射后 4h即开始升高 ,至 8～ 16h达峰值 (P <0 0 5～ 0 0 1) ,2Gy照射后则从照射后 4h开始下降 ,至 8h达最低点 (P <0 0 1) ,一直持续较低至 4 8h恢复 ;8h量效结果显示 ,在低剂量区 0 0 5 0 ,0 0 75Gy使CD2表达上调 ,而高剂量范围中 1,2Gy使CD2表达下调。 (2 )J774A 1细胞CD4 8分子表达结果显示 ,0 0 75GyX射线照射后CD4 8合成在照射后 2h即开始升高 ,至 4h达峰值 (P <0 0 5 ) ,随后急剧下降 ,8h恢复至假照射水平 ,16～4 8h下降明显低于假照射水平 (P <0 0 5 ) ,2Gy照射后则从照射后 2h开始下降 ,至 8h达最低点(P <0 0 1) ,随后有所恢复 ,但直至 4 8h仍未能恢复至假照射水平。 4h量效结果显示 ,在低剂量区0 0 5 0 ,0 0 75 ,0 10 0Gy使CD4 8表达上调 ,而高剂量范围中 1～ 6Gy均使CD4 8表达下调 (P <0 0 5～0 0 1)。结论　X射线照射可引起CD2、CD4 8不同的辐射效应 ,两者的相互作用体现出低剂量辐射具有不同于高剂量辐射的兴奋效应。     

Compromising Effect of Low Dose-rate Total Body Irradiation on Allogeneic Bone Marrow Engraftment

The protraction of total body irradiation (TBI) to a continuous low dose-rate has been investigated for its effect on donor marrow engraftment in murine bone marrow transplant (BMT) models of varying histocompatibility. Three different BMT combinations were used: syngeneic [B6-Gpi-1^a → B6-Gpi-1^b], H-2 compatible allogeneic [BALB.B (H-2^b) → B6 (H-2^b)] and H-2 mismatched allogeneic [BALB/c (H-2^d) → B6 (H-2^b)]. TBI was delivered over a range of doses at either a high (HDR, 40 cGy/min) or low (LDR, 2 cGy/min) dose rate followed by infusion of 10⁷ bone marrow cells from syngeneic or allogeneic donors. The level of donor (Gpi-1^a) engraftment was determined from blood Gpi-typing at different times after TBI and BMT. Radiation dose–response relationships corresponding to long-term haemopoietic engraftment at 20 weeks showed a dose-sparing effect of LDR that became more prominent with increasing genetic disparity between donor and host. For fully allogeneic (H-2 incompatible) BMT, a dose as high as 16 Gy LDR was still not sufficient for achieving chimerism in all recipients. In many cases allogeneic BMT gave transient blood chimerism enabling the recipient to survive the acute effects of high dose TBI with full long-term repopulation from surviving stem cells of the host. Radiation cell survival curves were obtained for the frequency of alloreactive precursors of proliferating T-lymphocytes (pPTL) remaining in the spleen at 1 day after TBI. A radiation dose-sparing effect of LDR was also found for pPTL depletion. These data suggest that radiation damage repair during LDR irradiation in an immunocyte target cell population is mainly responsible for enhanced graft rejection thus rendering protracted TBI less effective for application in clinical allogeneic BMT.     

Influence of dose-rate,post-irradiation incubation time and growth factors on interphase cell death by apoptosis and clonogenic survival of human peripheral lymphocytes

Purpose: To investigate the effects of dose-rate, post-irradiation incubation time and growth factors on radiation-induced interphase cell death by apoptosis and reproductive cell death in human peripheral lymphocytes. Materials and methods : Lymphocytes in G0-phase were exposed in vitro to 1-3Gy 137Cs gamma-radiation at a high- (HDR, 45Gy/h) or a low dose-rate (LDR, 0.024Gy/h). HDR exposures were performed either on day 1 (HDR1) simultaneously with the start of the 3Gy LDR exposure, or on day 6 (HDR6) when the LDR exposures ended. Apoptosis was studied at different times after irradiation by measuring (1) cellular membrane integrity, (2) morphological changes and (3) cell size reduction. Clonogenic survival was analysed for cells plated directly after irradiation (LDR, HDR6, HDR1 day 1) or after 5 days post-irradiation incubation (HDR1 day 6). Results: A significant decrease in reproductive cell death was observed after 3Gy LDR exposure as compared with the HDR1 exposure for cells plated day 6. For the lower doses applied, the dose-rate effect could not be statistically verified. A decrease in apoptosis for all three doses applied (i.e. 1, 2 and 3Gy) was observed when the LDR exposures were compared with the HDR1 analysed day 6, although not of statistical significance. Radiation-induced apoptosis was e fficiently counteracted by growth factors up to 24-48h after 3Gy HDR exposure. The prevention of radiation-induced cell death by growth factors was dependent on dose and post-irradiation time in G0. When the growth factors were added after a prolonged post-irradiation incubation in G0 (HDR1 cells plated day 6), a significant increase in reproductive cell death was found (3Gy) as compared with HDR protocols where the growth factors were added directly after irradiation (HDR1 plated day 1 and HDR6). Conclusions: A dose-rate effect on radiation-induced apoptosis was indicated but not statistically verified. A significant dose-rate effect on reproductive cell death was observed. This dose-rate effect was, however, inverted when growth factors were added directly after the HDR irradiations.