Cell cycle analysis and properties of two sub-populations in PHA responding lymphocytes. A comparison of 21-trisomic and normal cells

Age related change in the frequency of ara C-induced chromosome aberrations in human peripheral blood lymphocytes

1-beta-D-Arabinofuranosylcytosine (ara C) has been known to inhibit repair replication in the G1 phase of cell cycle and to convert certain types of DNA damage into chromosome-type exchanges: e.g., dicentric or ring chromosomes. It is then considered to be a useful cytogenetic method to investigate the frequency of ara C-induced dicentric and ring chromosomes (dic and ring) for estimating cellular DNA damage or capacity to repair it. Peripheral blood lymphocytes from donors ranging from newborn to 91 years old were treated with 10 microM ara C in their G1 phase and the resulting disc and ring were observed to investigate whether age-related change in peripheral lymphocytes would be present in the amount of spontaneous DNA damage or in the capacity to repair it. Chromatid-type (Ct) aberrations and sister chromatid exchanges (SCEs) were also scored for additional cytogenetic indices of DNA damage in the lymphocytes. The results showed that the frequency of dic and ring had a negatively linear correlation with the logarithm of the age of the blood donors, but that the frequencies of Ct aberrations and SCEs were not influenced by the age. The present study suggests the presence of age-related change in the amount or in the capacity to repair certain types of DNA damage in the G1 phase of human peripheral lymphocytes. Other possible explanations for the present results are also discussed.

Proliferative kinetics of human lymphocytes in culture measured by autoradiography and sister chromatid differential staining

A simple combination of autoradiography, to determine when a cell synthesized DNA, and sister chromatid differential staining, to determine how many times a cell has divided, was used to follow up the proliferating fate of human lymphocytes in culture. Cells were incubated continuously with 5-bromodeoxyuridine (BrdU) and pulse-labelled with 0.1 muCi/ml [3H]thymidine at various times after stimulation with phytohemagglutinin (PHA). The cells were then harvested at 4 h intervals up to 72 h, and the percentage of labelled mitoses was determined separately in first, second, or third division cells. The data showed that the cycling cells, whether they began cycling at earlier or later times after stimulation, had about the same generation times of 12--14 h. This confirms that the heterogeneity of cell generations seen in short-term lymphocyte cultures is in large part due to the difference in the times when cells began cell cycling in response to PHA.

Bleomycin-induced chromosomal aberrations in Down's syndrome lymphocytes

Blood samples from 4 Down's syndrome (DS) patients with a 47,XY,21 + karyotype and from 4 normal male probands were cultured for 72 h in the presence of BrdU and lymphocytes analysed at their first mitosis for chromosomal aberrations. The frequencies of spontaneous aberrations and the proportions of cells in the first or later mitoses in culture were not different between the groups. Treatment with various doses of bleomycin in vitro resulted in similar delays in cell development for both DS and normal lymphocytes and dose-dependent increases in the incidence of chromosome-type aberrations. However, the induction of both dicentric aberrations and acentric fragments was significantly enhanced in DS cells relative to cells of normal karyotype.

Lymphocyte proliferation in Down's syndrome measured by sister chromatid differential staining

Lymphocyte proliferation in PHA stimulated cultures from Down's syndrome patients and normals was measured by the BrdU/Giemsa method for demonstrating sister chromatid differential staining. Both Down's syndrome patients and normals had 1st, 2nd and 3rd divisions present. However, Down's syndrome patients had more 3rd division metaphases and fewer 2nd division metaphases than the normals. There was no difference in the mitotic index between the two groups.