不同传能线密度射线0~1Gy照射诱发染色体畸变的量-效关系研究

目的 建立0~1Gy范围内⁶⁰Coγ射线、 ²⁵²Cf 中子、单能中子及 ¹²C 重离子诱发染色体畸变剂量-效应曲线,用于评价职业受照或低剂量辐射损伤。方法 采用不同照射装置1Gy以内照射离体人外周血,于培养开始加秋水仙素,培养48h收获,制备染色体标本,Metafer中期细胞自动寻找系统,人机交互计数染色体畸变,最优拟合数据得到相应模型。结果 在低剂量范围内,以双着丝粒体+环(dic+r)为终点,⁶⁰Coγ射线为线性模型, ²⁵²Cf 中子、单能中子及 ¹²C 重离子为线性平方模型;以无着丝粒断片(ace)为终点,⁶⁰Coγ射线和 ¹²C 重离子为线性平方模型, ²⁵²Cf 中子和单能中子为线性模型;以总畸变为终点,4种射线均为线性平方模型。结论 高传能线密度(LET)射线损伤效应高于低LET射线,4种射线损伤效应依次为 ²⁵²Cf 混合中子 >单能中子> ¹²C 重离子> ⁶⁰Co γ射线。在低剂量范围内dic+r指标适用于高LET照射的剂量估算。     

不同剂量率γ射线照射诱发淋巴细胞早熟凝集染色体环产额的研究

目的 比较不同剂量率γ射线照射诱发的淋巴细胞早熟凝集染色体环(PCC-R)的产额,建立不同剂量率的人外周血早熟凝集染色体环与辐射剂量之间的剂量效应曲线。方法 取健康成年人外周血,分别用吸收剂量率为0.5和1.0Gy/min的 ⁶⁰Co γ 射线照射,吸收剂量为 0、 1、 2、 5、 10、 15、 20和25Gy。培养48h,终止培养前1h加入冈田酸(okadaic acid)诱导早熟凝集染色体,观察人外周血淋巴细胞PCC-R产额与照射剂量的关系。结果 在20 Gy剂量范围内,人外周血淋巴细胞PCC-R产额随着剂量的增加而增加。在25 Gy剂量范围内,在相同剂量情况下,吸收剂量率为1.0 Gy/min的PCC-R产额都要高于0.5 Gy/min的产额,且在20和25 Gy剂量点的差异有统计学意义。结论 PCC-R作为大剂量受照情况下的生物剂量指示剂,基于不同剂量率建立的剂量效应关系曲线所估算剂量的结果会有所不同。     

60Coγ射线超大剂量照射离体人外周血染色体畸变的剂量-效应研究

目的 探讨超大剂量γ射线离体照射后人外周血淋巴细胞染色体畸变的量效关系,建立双+环(dic+r)大剂量-效应曲线。方法 外周静脉血样采自3名健康男性,经 ⁶⁰Co γ线(0~50 Gy,剂量率2.35Gy/min)照射。采用即刻加秋水仙素的微量全血法,分别培养52、72及96h。计数有丝分裂指数(MI)、双着丝粒体(dic)和环(r)畸变数,拟合dic+r剂量-效应曲线,对2例受大剂量照射的事故患者进行剂量估算。结果 MI随照射剂量的增加而逐渐减少。每细胞dic+r频率随照射剂量增加而增加直到23Gy(5Gy之后增加幅度较前变小),＞23Gy后趋于饱和。对所获数据进行回归分析,拟合dic+r大剂量-效应曲线(5~23Gy):每细胞dic+r频率y=-1.608(±0.300)+0.830 (±0.051)D-0.013(±0.002) D² (R²=0.998)。用拟合曲线对2例受照患者剂量的估算结果与用物理方法和电子自旋共振(ESR)法估算的剂量及临床表现基本一致。结论 本研究建立的dic+r大剂量-效应曲线, 可估计的上限剂量达23Gy,有可能提高常规染色体畸变分析用作生物剂量计的实用价值。     

60Co γ射线诱发小鼠外周血网织红细胞微核率的研究

目的 通过观察不同剂量⁶⁰Co γ射线照射后小鼠外周血网织红细胞微核率的变化,为使外周血网织红细胞微核成为探索快速高通量的生物剂量计提供科学依据。方法 ⁶⁰Co γ射线照射ICR小鼠,按不同照射剂量分为0、0.5、1、2、4和8 Gy组,眼球取血,流式细胞术(FCM)检测和显微镜观察小鼠外周血网织红细胞微核率的变化。结果 流式细胞术检测网织红细胞微核率随剂量增加逐渐增加,2 Gy达峰值,之后随剂量的增加而减少;显微镜观察的网织红细胞微核率变化趋势与流式细胞术检测结果基本一致。照射剂量在0~2 Gy剂量范围内,小鼠的外周血网织红细胞微核率的剂量-效应关系满足直线模型(R²=0.9063),并且2 Gy照射组与0 Gy组相比差异有统计学意义(t=-2.856,P<0.05)。结论 流式细胞术检测外周血网织红细胞微核率,在一定剂量范围内可成为早期快速、高通量的辐射损伤生物剂量计。     

包钢选矿厂含钍粉尘作业工人外周血淋巴细胞适应性反应的研究

目的 探索低剂量天然放射性钍是否诱导出职业人员的外周血淋巴细胞适应性反应。方法 选择包钢选矿厂含钍粉尘作业工人(暴露组)和对照人员各20例,采集外周静脉血,分析染色体畸变。同时,对采集的外周血用⁶⁰Coγ射线离体照射2.0Gy,分析非稳定性染色体畸变或用单细胞凝胶电泳分析DNA链断裂水平。结果 照射前两组的双着丝粒畸变暴露组较高,照射2.0Gy⁶⁰Coγ射线后观察到的双着丝粒畸变暴露组低于对照组,但两组间差异无统计学意义(U=0.0026、0.0084,P>0.05),三着丝粒畸变在两组间差异具有统计学意义(U=3.1622, 0.001<P<0.002);两组间的"彗星"尾长差异有统计学意义(t=25,P<0.001)。结论 低剂量天然放射性钍诱导出职业人员的外周血淋巴细胞染色体畸变和DNA损伤的适应性反应。     

60Coγ射线照射对人血小板功能的影响

以不同剂量的⁶⁰Coγ射线照射富含血小板血浆后,检测其代谢及释放产物的变化⁶⁰Coγ射线照射剂量达5Gy时,血小板表面活化标记蛋白GMP-140分子的表达显着增多,且随剂量的增加而增高,血浆内血小板TxB₂的产生及释放当剂量为2.5Gy时就呈显着升高,γ射线剂量大于5Gy时,血浆内vWF的浓度显着升高；结果提示；⁶⁰Coγ射线照射剂量达5 Gy后,可激活体外的血小板,导致后者代谢旺盛。内容物释放增多。     

60Coγ射线诱导人外周血淋巴细胞核质桥的剂量-效应关系研究

目的 确定核质桥判定标准,建立 ⁶⁰Co γ 射线诱导正常人外周血淋巴细胞中核质桥（NPB）的剂量-效应曲线。 方法 用 ⁶⁰Co γ 射线照射3名健康男性离体外周血,照射剂量分别为0、1、2、3、4、5和6 Gy,剂量率为1 Gy/min,采用胞质分裂阻滞微核（CBMN）法进行细胞培养、收获、制片、染色。在光学显微镜下分析双核细胞中NPB及微核（MN）。 结果 在0~6 Gy ⁶⁰Co γ 射线照射后,人外周血双核淋巴细胞中的NPB符合泊松分布,且NPB频率随吸收剂量增加而增加（H=19.51,P<0.01）,拟合回归方程为线性平方模式y=（1.39×10^-3）x² + （4.94×10^-3）x （R²=0.981,P < 0.01）。 结论 成功建立 0~6 Gy ⁶⁰Co γ 射线诱导正常人外周血淋巴细胞中NPB的剂量-效应曲线。     

不同结构类型双着丝粒体建立的剂量-效应曲线估算剂量可行性研究

目的 探讨基于不同结构类型双着丝粒体（dicentrics,dic）建立的剂量-效应曲线估算生物剂量的可行性。方法 采集两名健康人外周血样品,用0、0.5、1、2、3、4、5和6 Gy ⁶⁰Co γ射线（剂量率为0.27 Gy/min）离体照射人外周血,常规培养、收获和制备染色体标本,镜下分析并记录不同结构类型dic;应用CABAS软件建立dic剂量-效应曲线;并对两验证样本进行剂量估算。结果 不同结构类型dic率均随受照剂量的增加而升高（R²=0.886~0.943,P<0.01）,各剂量点经典型和单端型dic构成比之和约占所有类型dic的92%以上,而近距型dic和双端型dic分别在各照射剂量点的构成比均<4%。不同结构类型dic剂量-效应曲线的R²值均达到0.998;应用4条曲线估算的受照射剂量差异无统计学意义（P>0.05）。经典型dic剂量-效应曲线估算较高剂量时（3.9 Gy）,相对偏差均≤13.08%。结论 基于不同结构类型dic建立的剂量-效应曲线具有估算生物剂量的可行性。     

不同剂量60Co γ 射线部分照射人离体血对染色体畸变形成的影响

目的 分析不同剂量60Co γ射线部分照射人离体血对淋巴细胞染色体畸变形成的影响.方法 用0～8 Gy(剂量率为0.35 Gy/min)60Coγ射线在37 ℃条件下照射3份离体健康人外周血标本,以0.5∶1的比例与同一供血者的未受照血混合,120 min后进行培养、制片,显微镜下分析染色体畸变(双着丝粒+着丝粒环)的变化,借此进行剂量估算.结果 各组的双着丝粒体+着丝粒环和总畸变,以及断片和单体断裂均随着剂量的增加而增加.用双着丝粒+着丝粒环进行的剂量估算,0.5～2 Gy组大于照射剂量的1/3,4～8 Gy组均接近照射剂量的1/3.结论 染色体畸变可以作为估算非均匀照射的生物学指标之一.

Abstract：

Objective To investigate the effects of 60Co γ-ray partial radiation on chromosome aberration in human peripheral blood in vitro.Methods The samples of heparinized peripheral whole blood from 3 healthy persons were exposed to 60Co γ-rays at the doses between 0 and 8 Gy with the dose rate of 0.35 Gy/min at the temperature of 37 ℃ ,and then mixed with the unirradiated blood samples of the Microscopy was used to observe the chromosome aberration double ( centromere + centromere) and the biological dose was estimated thereby.ResultsThe amounts of double centromere + centromere were increased along with the dose of irradiation in all groups.The estimated biological dose was higher than the 1/3 of the irradiation dose when the dose was between 0.5 to 2 Gy,and was close to the 1/3 of the irradiation dose when the dose was between 4 to 8 Gy.Conclusion Chromosome aberration can be used as a biomarker in estimation of uneven irradiation.     

60Coγ射线诱导EJ细胞DNA损伤及γH2AX 表达的研究

目的 探讨不同剂量⁶⁰Coγ射线对EJ细胞DNA损伤的情况,不同剂量⁶⁰Coγ 射线照射EJ细胞后诱导磷酸化组蛋白H2AX焦点形成,以及与γH2AX表达量的关系。方法 单细胞凝胶电泳检测DNA链断裂损伤情况。免疫荧光法检测不同剂量γ 射线照射后立即、以及2 Gy γ 射线照射后不同时间的EJ细胞中γH2AX焦点的数量。流式细胞分析法检测不同剂量γ 射线照射后EJ细胞中γH2AX 蛋白表达量的变化。结果 单细胞凝胶电泳结果显示,γ射线照射后DNA损伤情况明显加重,随照射剂量的增加,细胞尾矩不断加大,0 Gy组尾矩为0.24,4 Gy照射组尾矩为5.26;免疫荧光结果显示,随着照射剂量的增加,γH2AX焦点数目及大小均明显增加,照射的剂量范围从0.1~4 Gy均可检测,且照射剂量和焦点形成数目之间存在剂量-效应关系,0.1 Gy照射组每个细胞中的焦点数平均达12.37个,4 Gy照射组每个细胞中的焦点数平均达46个;2 Gy γ 射线照射后24 h仍可检测到γH2AX焦点,随时间延长焦点数目减少、强度减弱,具有时间依赖性。流式细胞检测结果表明,γ 射线照射后γH2AX 蛋白表达量明显增加,呈现明显量效关系,0.1和4 Gy照射组γH2AX阳性细胞表达率分别为7.4%和29.2%。结论 免疫荧光法检测照射后γH2AX焦点数目比其他实验方法更能敏感、直观的反映DNA损伤及修复情况,有望成为检测辐射损伤的理想生物指标。     

Complex chromosome aberrations in peripheral blood lymphocytes as a potential biomarker of exposure to high-LET alpha-particles

PURPOSE: To determine the induction and transmission, to second and third division cells, of complex chromosome aberrations in peripheral blood lymphocytes after exposure to high-LET alpha-particles in vitro. MATERIALS AND METHODS: Separated peripheral blood lymphocytes collected from four healthy donors were irradiated in vitro with either high-LET alpha-particles (121 keV/microm; 0.5 Gy) or low-LET X-rays (250kV constant potential; 3 Gy). Cells were harvested in first, second and third division post-irradiation and chromosome aberrations observed at each cell division were analysed by combining the techniques of FISH and DAPI/Hoechst 33258 harlequin staining. Whole chromosome probes were used for chromosomes 1, 2 and 5, together with a pan-centromeric probe and the resulting chromosome 'painting' patterns were classified according to the Savage and Simpson (S & S) scheme (Savage and Simpson 1994a, Savage and Tucker 1996). RESULTS: A greater proportion of complex chromosome aberrations was observed, defined as involving three or more breaks in two or more chromosomes, relative to total exchanges, after exposure to 0.5 Gy alpha-particles (mean 1 track/cell) than after the high reference dose of 3 Gy X-rays (49-56% and 20-22%, respectively). Qualitatively, alpha-particles induced chromosome aberrations of far greater complexity than those observed after X-rays. This was reflected by both the rapid reduction in the percentage of damaged cells between first and second division indicative of cell death, and the spectrum of aberration types observed in second and third division cells post-irradiation. Regardless of this complexity, 15% of the complexes induced by alpha-particles at first division were potentially transmissible and by third division, transmissible-type complexes, specifically insertions, represented the predominant complex type (65%). CONCLUSION: Transmissible-type complexes were observed, specifically insertions, in both second and third division cells after exposure to high-LET alpha-particles (0.5 Gy) in vitro. The authors predict these cells to be stable and to be capable of persisting through many cell generations. Considering that the induction of complex chromosome aberrations by low-LET radiation is strongly dependent on dose, so that they are expected to be undetectable at environmental exposures, insertions are much more likely to be a characteristic feature of high-LET radiation at all doses. From this the usefulness of insertions as biomarkers of past exposure to environmentally relevant doses of high-LET alpha-particles is supported.     

离体人血受照后染色体培养中若干问题的探讨

探讨了人离体血经X线照射后，染色体培养过程中松胞素B（Cyt-B)及培养时间对分裂指数（MI）的影响。结果表明：（1）0-15Gy照射，培养体系中加入Gyt-B，MI均有所增加；10Gy以上影响较在，25Gy不再有影响。（2）6-25Gy，延长培养时间MI明显增加，在6-10G 间仅靠延长时间即可获足够分析用的分裂像。（3）加Cyt-B的同时延长培养时间，其MI高于单纯加Gyt-B或延长时间者，特别是15Gy，昭后只有加Gyt-B同时延长培养时间才能使MI增多至可供分析，以上结果提示：（1）辐射事故中当以染色体畸变估算大于6Gy受昭者的剂量时，必须延长培养时间，有条件者加Cyt-B方可增加培养成功的机会，提供足够的分裂像。（2）改变培养条件，加Cyt-B并延长培养时间有可能制定出剂量上限高于5Gy的剂量效应刻度曲线，从而进一步提高其作为生物剂量计的临床应用价值。     

mBAND analysis of chromosome aberrations in lymphocytes exposed in vitro to alpha-particles and gamma-rays

PURPOSE: To investigate the profiles of chromosome damage induced in vitro by exposure to alpha-particles and gamma-rays. MATERIALS AND METHODS: Human peripheral blood lymphocytes were exposed to three dose regimes: alpha-particle doses of 0.2 and 0.5 Gy and a gamma-ray dose of 1.5 Gy. After culturing for 47 hours, chromosome aberrations involving the number 5 chromosomes were identified using a multi-coloured banding (mBAND) technique. RESULTS: Analysis of the frequencies of chromosome 5 breaks within aberrant cells and within aberrant number 5 chromosomes demonstrated that alpha-particle irradiation is more likely to result in multiple breaks in a chromosome than gamma-irradiation. Additionally, overdispersion was observed for all doses for the distribution of breaks amongst all cells analysed and breaks amongst total number 5 chromosomes, with this being greatest for the 0.2 Gy alpha-particle dose. The ratio of interchanges to intrachanges (F ratio) was 1.4 and 2.4 for 0.2 and 0.5 Gy alpha-particles respectively and 5.5 for 1.5 Gy gamma-rays. Evaluation of simple versus complex exchanges indicated ratios of 1.9 and 2.7 for 0.2 and 0.5 Gy alpha-particles respectively and 10.6 for 1.5 Gy gamma-rays. The majority of the intrachanges involving chromosomes 5 induced by alpha-particle radiation were associated with more complex exchanges. CONCLUSIONS: This study has confirmed that exchanges induced by exposure to high linear energy transfer (LET) alpha-particle radiation comprise a greater proportion of intrachanges than those induced by exposure to low LET gamma-rays. However, since the majority of these are associated with complex rearrangements and likely to be non-transmissible, this limits their applicability as a marker of past in vivo exposure.     

mBAND analysis of chromosome aberrations in lymphocytes exposed in vitro to α-particles and γ-rays

Purpose:?To investigate the profiles of chromosome damage induced in vitro by exposure to α-particles and γ-rays.

Materials and methods:?Human peripheral blood lymphocytes were exposed to three dose regimes: α-particle doses of 0.2 and 0.5 Gy and a γ-ray dose of 1.5 Gy. After culturing for 47 hours, chromosome aberrations involving the number 5 chromosomes were identified using a multi-coloured banding (mBAND) technique.

Results:?Analysis of the frequencies of chromosome 5 breaks within aberrant cells and within aberrant number 5 chromosomes demonstrated that α-particle irradiation is more likely to result in multiple breaks in a chromosome than γ-irradiation. Additionally, overdispersion was observed for all doses for the distribution of breaks amongst all cells analysed and breaks amongst total number 5 chromosomes, with this being greatest for the 0.2 Gy α-particle dose. The ratio of interchanges to intrachanges (F ratio) was 1.4 and 2.4 for 0.2 and 0.5 Gy α-particles respectively and 5.5 for 1.5 Gy γ-rays. Evaluation of simple versus complex exchanges indicated ratios of 1.9 and 2.7 for 0.2 and 0.5 Gy α-particles respectively and 10.6 for 1.5 Gy γ-rays. The majority of the intrachanges involving chromosomes 5 induced by α-particle radiation were associated with more complex exchanges.

Conclusions:?This study has confirmed that exchanges induced by exposure to high linear energy transfer (LET) α-particle radiation comprise a greater proportion of intrachanges than those induced by exposure to low LET γ-rays. However, since the majority of these are associated with complex rearrangements and likely to be non-transmissible, this limits their applicability as a marker of past in vivo exposure.     

Dose- and time-response relationships for lethal mutations and chromosomal instability induced by ionizing radiation in an immortalized human keratinocyte cell line

PURPOSE: To investigate the relationship between two well-established delayed effects of ionizing radiation, experiments were conducted to determine the induction and expression of lethal mutations (delayed reproductive death) and chromosomal instability with respect to dose and time in a human immortalized keratinocyte cell line. METHODS: HPV-G cells were gamma- or alpha-irradiated and maintained in culture for up to 72 population doublings. At intervals, measurements were made of cloning efficiency and the cells examined for apoptosis and cytogenetic aberrations. RESULTS: The descendants of cells surviving 1 or 3 Gy gamma-irradiation, but not 0.5 Gy gamma-irradiation, exhibited a reduced colony-forming efficiency. The reduction persisted at a constant rate of 15-20% clonogenic cell loss per population doubling for up to 72 population doublings. Apoptosis was demonstrated in all colonies in the 1 and 3 Gy groups at 30 and 72 population doublings post-irradiation but not in the 0.5 Gy group. A significant persistent reduction in colony-forming ability (approximately 80%) was demonstrated in the progeny of cells irradiated with 0.5 Gy alpha-particles. After 30 population doublings, the proportion of chromosomally aberrant cells was significantly greater than control values for all doses of both high- and low-LET radiations. The major cytogenetic aberrations (chromatid breaks, chromosome fragments and minutes) were consistent with the transmission of chromosomal instability. The expression of instability declined between 30 and 72 population doublings in the 0.5 Gy and 3 Gy gamma-irradiation groups, but persisted up to 72 population doublings in the 1 Gy group. The expression of chromosomal instability was greater in the descendants of alpha-irradiated cells and showed little evidence of reduction with time. CONCLUSIONS: Unstable aberrations characteristic of radiation-induced chromosomal instability may commonly result in apoptosis and account for a component of the delayed reproductive death/lethal mutation phenotype in HPV-G cells. However, the absence of lethal mutations in the descendants of 0.5 Gy gamma-irradiated cells indicates a low-LET threshold effect for this particular endpoint. Overall, and particularly at low doses, there is no direct correlation between the two endpoints, indicating the absence of a simple relationship between these manifestations of radiation-induced genomic instability.     

CB微核法在忻州事故生物剂量估算中的应用

本文作者报道了在忻州放射事故中３４例受检者ＣＢ法微核的检测结果。同时，用本实验室建立的ＣＢ微核剂量效应曲线对上述受检者进行生物剂量估算，并与染色体畸变分析估算的剂量进行比较，结果两种方法估算的剂量基本一致。表明ＣＢ微核法是估算事故受照者所受剂量的一种较为理想的方法。     

Reduction of survival and induction of chromosome aberrations in tobacco irradiated by carbon ions with different linear energy transfers

Purpose : To determine the relationship between linear energy transfer (LET) and the relative biological effectiveness (RBE) for survival reduction and chromosome aberration induction in plants. Materials and methods : Tobacco seeds were exposed to carbon ions having LET ranging from 92 to 260 keV μ m -1. Survival rate was determined at 7 weeks after sowing. Chromosome aberrations were observed when the root length reached about 0.5mm (immediately after radicle emergence), 3 and 10 mm. Results : The RBE for both endpoints increased with increasing LET and showed the highest value at 230 keV μ m -1. The highest RBE was 65.0 for survival reduction and 52.5 for chromosome aberration induction. The types and yield ratio of chromosome aberrations such as fragments and bridges were not affected by radiation type at 0.5mm root length. As the roots elongated from 0.5 to 10 mm, the frequency of aberrant cells gradually decreased. The number of cells with fragments decreased faster than the number of cells with bridges. The decrement of chromosome aberrations appeared to be slower in roots irradiated by carbon ions than in roots irradiated by γ -rays. Conclusions : The results show a close relationship between survival reduction and chromosome aberration induction in plants. The types and yield ratio of initial chromosome aberrations did not differ among γ -rays and carbon ions with different LET.     

Reduction of survival and induction of chromosome aberrations in tobacco irradiated by carbon ions with different linear energy transfers

PURPOSE: To determine the relationship between linear energy transfer (LET) and the relative biological effectiveness (RBE) for survival reduction and chromosome aberration induction in plants. MATERIALS AND METHODS: Tobacco seeds were exposed to carbon ions having LET ranging from 92 to 260 keV microm(-1). Survival ratc was determined at 7 weeks after sowing. Chromosome aberrations were observed when the root length reached about 0.5 mm (immediately after radicle emergence), 3 and 10 mm. RESULTS: The RBE for both endpoints increased with increasing LET and showed the highest value at 230 keV um(-1). The highest RBE was 65.0 for survival reduction and 52.5 for chromosome aberration induction. The types and yield ratio of chromosome aberrations such as fragments and bridges were not affected by radiation type at 0.5mm root length. As the roots elongated from 0.5 to 10 mm, the frequency of aberrant cells gradually decreased. The number of cells with fragments decreased faster than the number of cells with bridges. The decrement of chromosome aberrations appeared to be slower in roots irradiated by carbon ions than in roots irradiated by gamma-rays. CONCLUSIONS: The results show a close relationship between survival reduction and chromosome aberration induction in plants. The types and yield ratio of initial chromosome aberrations did not differ among gamma-rays and carbon ions with different LET.     

Chromosome aberrations in mixed cultures of in vitro irradiated and unirradiated human lymphocytes

Human whole blood samples were exposed to different doses (1, 2, 4, 6 or 10 Gy) of gamma-radiation and mixed with different volumes of non-irradiated blood before culturing to simulate partial body irradiations. Chromosome aberrations were analysed and the frequency of dicentrics was found to be lower than expected, particularly when irradiated blood was mixed with large volumes of non-irradiated blood and after exposure to high radiation doses. For the mixtures of irradiated and unirradiated blood the deviation from the Poisson distribution depends on the respective proportions and on the doses. The results can be correlated to in vivo aberration frequencies in case of therapeutical treatments, but the yields of aberrations are generally underestimated in vitro.