APPLICATION OF A MULTIPLE FIXATION REGIMEN TO STUDY THE ADAPTIVE RESPONSE TO IONIZING-RADIATION IN LYMPHOCYTES OF 2 HUMAN DONORS

The majority of experiments studying the adaptive response using chromosomal aberrations have been performed with proliferating lymphocytes. It is known that lymphocytes have variable cell cycle transit times and it has been pointed out that in such cases aberration scores obtained from a single harvest are not very meaningful because cells harvested together in metaphase at any one time after irradiation were in different parts of the cell cycle at the time of irradiation. The scored sample will thus always contain a mixture of cells having different radiosensitivities and any variations of cell proliferation will influence the aberration score. In order to get a more representative aberration score a multiple fixation regimen was applied to lymphocytes of two human donors. Cells receiving the adapting + challenging and the challenging dose were fixed at three intervals after the challenge. In lymphocytes of donor 1 no adaptive response was seen at any fixation time in two experiments. In lymphocytes of donor 2, however, a reduction of aberration frequencies was seen, but at different fixation times in the two experiments. In a third experiment, no adaptive response was detected. It is concluded that the response observed at some fixation times in lymphocytes of donor 2 is rather a result of some phenomenon associated with variations of cell cycle kinetics than of induced radiation resistance.