Adaptive response induction and variation in human lymphoblastoid cell lines.

Adaptive response is a term used to describe the ability of a low, priming dose of ionizing radiation to modify the effects of a subsequent higher, challenge dose, but it has been observed to be highly variable in both presence and magnitude. To examine this variability, 10 human lymphoblastoid cell lines were screened for adaptability to 137Cs radiation by determining the frequency of micronuclei in binucleated cells. Of these, six adapted, three did not adapt and one was synergistic. The assay was then repeated on each of the cell lines to test for reproducibility. Five cell lines showed the same result both times; four of these adapted and one did not. To determine whether fluctuations in the cell cycle distribution in the irradiated population of cells could alter the adaptive response, and therefore explain some of the observed variability, two of the cell lines were tested for adaptation after enriching the population, by synchronization, for a given cell cycle stage. In both cell lines, the direction of the response was altered when the distribution of cells within the cell cycle was changed, suggesting that the adaptive response can be affected by cell cycle stage at the time of irradiation.