Abstract
It is important for radiation risk estimation to study the adaptive response triggered by low-dose ionizing radiation. In this study, we tried to detect the adaptive response as genetic change on the chromosome by using the LOH (Loss of heterozygosity) detection system, which we have already established in human lymphoblastoid cell TK6. The priming doses of X-rays were 2.5 , 5, or 10 cGy , the challenging X-ray dose was fixed at 2 Gy and the interval between two irradiations were changed from 1 to 12 hr. An approximately 30 % recovery from the lethal effect of 2 Gy exposure was observed with the 5 cGy pre-irradiaiton at 3hr before the challenging exposure, but this recovery rate was not statistically significant. While the 6 hr proceeded 5 cGy pre-irradiation decreased the mutation frequency in thymidine kinase (TK) gene locus to about half of non-pre-irradiation level. The LOH analyses of the obtained TK mutants provided an interesting finding as follows; homozygous LOH events in the restricted chromosome region, probably caused by the non-homologous end-joining repair of DNA double-strand break, were observed only after the pre-irradiation although these events rarely occurred. The mechanisms responsible for this particular type of LOH events are now under the study.
