Higher frequency of chromosome aberrations in late-arising first-division metaphases than in early-arising metaphases after exposure of human lymphocytes to X-rays in G 0

Abstract

Purpose : To determine whether metaphases arising at different times after mitogen stimulation of G 0 lymphocytes differ in frequencies of X-ray-induced chromosome aberrations. Materials and methods : Human G 0 lymphocytes from peripheral blood exposed to 0, 1.5 or 3.0 Gy X-rays were stimulated to divide with the mitogen phytohaemagglutinin (PHA). First-division metaphases were distinguished from second and third divisions by chromatid labelling with 5-bromodeoxyuridine (BUdR) and staining with Giemsa or DAPI. Cultures harvested 48, 70 and 94 h after mitogen stimulation were analysed for unstable aberrations on Giemsa-stained slides and for stable and unstable aberrations by fluorescence in situ hybridization (FISH) with painting probes for chromosomes 1, 2 and 4. Results : Frequencies of aberrations declined at the later culture periods, as expected on the basis of unstable aberrations being lost in mitotic division. When scoring was restricted to first-division metaphases, however, aberration frequencies were higher in 94-h cultures than in 48-h cultures. Conclusions : Frequencies of radiation-induced chromosome aberrations in first-division metaphases increase with culture time after mitogen stimulation. Possible explanations for this finding are a delay of damaged cells in mitogenic response or progression through divisions and heterogeneity among lymphocytes in culture kinetics and radiosensitivity. The data argue against the common assumption that all first-division cells are equivalent as indicators of radiation-induced chromosome aberrations.