Jane Cole

UV-C sensitivity of unstimulated and stimulated human lymphocytes from normal and xeroderma pigmentosum donors in the comet assay : a potential diagnostic technique

We have studied incision-break formation in unstimulated and stimulated populations of human T-lymphocytes using the comet (single-cell microgel electrophoresis) assay. The frequency of strand breaks 1 h after UV-irradiation appears to be far greater in unstimulated than in stimulated lymphocytes from normal donors and the excess of strand breaks was observed for a far longer time after irradiation. This result corroborates the greater sensitivity of UV-C irradiation observed in a colony-forming assay but suggests that the defect may relate to a defect in strand rejoining rather than a defect in incision. Few strand breaks were seen in either unstimulated or stimulated lymphocytes of four xeroderma pigmentosum donors, suggesting that the method may offer a rapid diagnostic assay for XP.

Short-term tests for transplacentally active carcinogens: I. Micronucleus formation in fetal and maternal mouse erythroblasts

A cell-kinetic model for the application of the micronucleus test to polychromatic erythrocytes in mouse fetal liver, fetal blood, and maternal bone marrow after exposure to clastogenic agents is described. The time of expression and dose-response relationships obtained with gamma-radiation, methyl methanesulphonate, procarbazine, mitomycin C and benzo[a]pyrene are analysed in terms of this model. The numbers of target cells damaged per unit dose has been calculated and the dose equivalents obtained. Maternal and fetal cells show similar sensitivity to gamma-radiation, but fetal cells are markedly more sensitive to MMS and procarbazine. This probably due to differences in tissue distribution and metabolism. Maternal and fetal erythroid tissues can show linear and exponential dose-response relationships, which may not coincide (e.g. with MMS). It is concluded that risks from fetal exposure to genotoxic agents cannot be reliably predicted from in vivo tests restricted to adult animals. However, the micronucleus technique applied to fetal erythroid cells provides a rapid and reliable short-term test, appropriate to minimising risks of genome damage during prenatal development.

A further assessment of factors influencing measurements of thioguanine-resistant mutant frequency in circulating T-lymphocytes

We have used the T-Lymphocyte cloning technique as a method of monitoring the human population for somatic cell mutant frequency. We present a statistical analysis of the experimental factors which may influence the observed mutant frequency. We have obtained consistently high plating efficiencies of T-cells from the mononuclear cell fraction from donor blood samples (mean of 56%, based on 123 observations from 70 individuals). Nevertheless, an inverse correlation of mutant frequency with plating efficiency was observed, and some experimental factors (serum and interleukin-2 batch, and worker) may have a significant effect on the observed mutant frequency. We discuss the difficulties that these possible effects present in establishment of a reference database and design of long-term studies. No significant effect of donor sex on mutant frequency was observed, but age (1.3% increase per year for normal adults) and smoking (56% increase over normal non-smokers) both significantly increased the mutant frequency. We discuss the utility of the assay for the monitoring of populations for heritable DNA damage, and we compare the results to those obtained with lymphocytes using other endpoints, e.g. chromosome aberrations, micronuclei and sister-chromatid exchange.

Comparative Human Cellular Radiosensitivity: II. The Survival Following Gamma-irradiation of Unstimulated (G0) T-lymphocytes, T-lymphocyte Lines, Lymphoblastoid Cell Lines and Fibroblasts from Normal Donors, from Ataxia-telangiectasia Patients and from Ataxia-telangiectasia Heterozygotes

We have measured clonal survival following gamma-irradiation of unstimulated (G0) T-lymphocytes from 35 donors, of 11 T-lymphocyte cell lines, of six lymphoblastoid cell lines, and of nine primary fibroblast strains for which we have G0 T-lymphocyte material from the same donor. Amongst the G0 lymphocytes we have results from nine normal donors, from eight cord bloods, from seven ataxia-telangiectasia (A-T) patients and from nine A-T heterozygotes. Although there is some variation between samples, G0 T-lymphocytes from normal donors appear to be slightly more radioresistant than T-lymphocyte lines, with a more shouldered survival curve. From our limited sample, lymphoblastoid cell lines appear to be slightly more radiosensitive than T-lymphocytes. The overall radiosensitivity of primary fibroblasts appears to be broadly similar to that of G0 T-lymphocytes. In nine instances, five A-Ts and four A-T heterozygotes, both G0 T-lymphocytes and primary fibroblasts from the same donor were tested. In five cases there was closely similar radiosensitivity in the two cell types, but in four cases there was some discrepancy. Further work, especially with normal donors, will be required in order to establish how reliably radiosensitivity in other cell types can be predicted from that of G0 T-lymphocytes. In all cell types the hypersensitivity of A-T cells was confirmed. Furthermore, the marginally greater sensitivity of A-T heterozygotes, when compared as a group with normals, was confirmed with G0 T-lymphocytes. Our results also suggest a slightly increased radiosensitivity in G0 T-lymphocytes from some, but not all, cord blood samples.

An analysis of in vivo hprt mutant frequency in circulating T-lymphocytes in the normal human population: a comparison of four datasets☆

In this paper, we have compared mutant frequency data at the hprt locus in circulating T-lymphocytes from four large datasets obtained in the UK (Sussex), the USA (Vermont), France (Paris) and The Netherlands (Leiden). In total, data from > 500 non-exposed individuals ranging in age from newborns (cord blood samples) to > 80 years old have been included in the analysis. Based on raw data provided by the four laboratories, a model is presented for the analysis of mutant frequency estimations for population monitoring. For three of the laboratories, a considerable body of data was provided on replicate estimates of mutant frequency from single blood samples, as well as estimates from repeat blood samples obtained over a period of time from many of the individual subjects. This enabled us to analyse the sources of variation in the estimation of mutant frequency. Although some variation was apparent in the results from the four laboratories, overall the data were in general agreement. Thus, in all laboratories, cellular cloning efficiency of T-cells was generally high (> 30%), although in each laboratory considerable variation between experiments and subjects was seen. Mutant frequency per clonable T-cell was in general found to be inversely related to cloning efficiency. With the exception of a few outliers (which are to be expected), mutant frequencies at this locus were in the same range in each dataset; no effect of subject gender was found, but an overall clear age effect was apparent. When log mutant frequency was analysed vs log (age + 0.5) a consistent trend from birth to old age was seen. In contrast, the effect of the smoking habit did differ between the laboratories, there being an association of smoking with a significant increase in mutant frequency in the Sussex and Leiden datasets, but not in those from the Vermont or Paris datasets. Possible reasons for this are discussed. One of the objectives of population monitoring is an ability to detect the effect of accidental or environmental exposure to mutagens and carcinogens among exposed persons. The large body of data from non-exposed subjects we have analysed in this paper has enabled us to estimate the size of an effect that could be detected, and the number of individuals required to detect a significant effect, taking known sources of variation into account.(ABSTRACT TRUNCATED AT 400 WORDS)

Ethyl methanesulphonate mutagenesis with L5178Y mouse lymphoma cells: A comparison of ouabain, thioguanine and excess thymidine resistance

Complete inhibition of growth of sensitive L5178Y mouse lymphoma cells in culture was obtained with 10(-3)M ouabain, 1.65 X 10(-3)M thymidine, 1.8 X 10(-4)M thioguanine and 10(-6)M cytosine arabinoside. The toxicity of methotrexate was dependent upon cell density and this compound was excluded from further study. The expression time before addition of the selective agent was important for detecting EMS induced resistant variants. Ouabain-resistant variants appeared immediately after treatment and were present over a broad time span. No excess thymidine- or thioguanine-resistant variants were seen initially; a peak in variant numbers was seen for excess thymidine resistance at 48-96 h and for thioguanine resistance at 144-192 h. Using induced mutation frequencies at optimum expression times, equal EMS treatments yielded substantially more variants resistant to thioguanine than to ouabain. It is suggested that this difference may have origin in possible constraints in the classes of mutants which are permissible in a vital function, maintenance of the Na+/K+ balance, when compared with a non-vital function, salvage purine biosynthesis. Some data are presented on the stability in culture of resistant variants. A limited number of observations were made following treatment in the peritoneal cavity of the mouse which were in broad agreement with the above results.

Possible association between mutant frequency in peripheral lymphocytes and domestic radon concentrations.

To investigate whether previously found geographical correlations between leukaemia incidence and exposure to radon are reflected in a detectable mutagenic effect on individuals, the frequency of mutations in the hypoxanthine guanine phosphoribosyl transferase gene (hprt) in peripheral blood T lymphocytes was measured in subjects with known domestic radon concentrations. These concentrations were measured in December, 1989, in houses in Street, Somerset, UK, by passive alpha-track radon detectors. 20 non-smoking subjects aged 36-55 years were selected from the patient list at the local health centre on the basis of the radon concentrations in their homes--the range selected varied by a factor of ten. Blood samples for preparation of T lymphocytes were taken in July, 1990. There was a significant association between the log mutant frequency and radon concentration (t = 3.47, p less than 0.01). A second analysis of a further set of radon measurements (October, 1990, to January, 1991), in both living rooms and bedrooms, and repeated mutant frequency determinations also showed a significant relation, which remained significant even after exclusion of the highest frequency and adjustment for subjects age and cloning efficiency. These data must be regarded as preliminary and further more extensive studies should be done to determine whether the observed association is causal.

Detection of somatic mutants in man: HPRT mutations in lymphocytes and hemoglobin mutations in erythrocytes

In this paper, results obtained with a new detection method which combines use of a polyclonal monospecific fluorescent antibody against sickle cell hemoglobin (HbS) (due to a transversion mutation, codon GAG in the normal globin gene is replaced by GTG in the sickle-cell gene, which results in replacement of glutamic acid by valine at position 6 of the globin gene) are presented. A newly developed highly automated image analysis system, built for this purpose, is described

Comparative Human Cellular Radiosensitivity: III. γ-radiation Survival of Cultured Skin Fibroblasts and Resting T-lymphocytes from the Peripheral Blood of the Same Individual

Skin and blood samples were obtained from 34 donors, for whom there was no indication of abnormal radiosensitivity. From these, in 33 cases both fibroblast and T-lymphocyte cultures were obtained and in 26 cases at least three fibroblast and at least two G0 (resting) T-lymphocyte survival assays were possible. Within this set of results, differences in radiosensitivity between donors were significant for fibroblasts but not T-lymphocytes, although the range of radiosensitivity was similar for the two cell types (D 0.90-1.68 Gy for fibroblasts; 1.26-2.15 Gy for T-lymphocytes). Furthermore, there was little evidence for a correlation in radiosensitivity between the two cell types. These results suggest limitations in the predictive value of conventional measurement of cell survival.

A comparison of the agar cloning and microtitration techniques for assaying cell survival and mutation frequency in L5178Y mouse lymphoma cells

Microtitration methods for assaying cell survival and mutation frequency to ouabain resistance, 6-thioguanine resistance and 1-beta-D-arabinofuranosyl cytosine resistance in L5178Y mouse lymphoma cells were compared to the standard agar cloning technique. The two methods gave essentially similar results for untreated cells, and after treatment with ethyl methanesulphonate and 4-nitroquinoline 1-oxide. Potential advantages of the microtitration method as a routine assay system are discussed.