Frequency of CD59 mutations induced in human-hamster hybrid A(L) cells by low-dose X-irradiation

Determination of the genotoxic effects of ionizing radiation, especially at , low-doses, is of great importance for risk assessment, e.g, in radiologic al diagnostics. The human-hamster hybrid A(L) cell line has been shown prev iously to be a well-suited in vitro model fur the study of mutations induce d by various mutagens. The A(L) cells contain a standard set of hamster chr omosomes and a single human chromosome 11, which confers the expression of the human cell surface protein CD59. Using CD59 specific antibodies, cells mutated in the CD59 gene can be detected and quantified by the loss of the cell surface marker. In contrast to previous studies, prior to irradiation we removed spontaneous mutants by magnetic cell separation (MACS) which all ows analysis of radiation-induced mutation events only. We exposed A(L) cel ls to 100 kV X-rays at 0.1 to 5 Gy. The proportions of X-irradiation-induce d CD59(-) mutants were quantified by Row cytometry after immunofluorescence labeling. Between 0.2 and 5 Gy the yield of CD59 mutants was a linear func tion of dose. The molecular analysis of individual CD59-negative clones ind uced after exposure of 1, 3 and 5 Gy of X-ray revealed a dose-dependent lin ear increase of large deletions (> 6 Mbp), whereas, point mutations could b e seen only in spontaneous CD59 mutants or after low-dose exposure (less th an or equal to 1 Gy), We conclude that the modified A(L) assay presented he re is appropriate for detection and quantification of non-lethal DNA lesion s induced by low-dose ionizing radiation. (C) 2001 Elsevier Science B.V. Al l rights reserved.