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 chrom osomal aberrations have been performed with proliferating lymphocytes. It is known that lymphocytes have variable cell cycle transit times a nd it has been pointed out that in such cases aberration scores obtain ed from a single harvest are not very meaningful because cells harvest ed together in metaphase at any one time after irradiation were in dif ferent parts of the cell cycle at the time of irradiation. The scored sample will thus always contain a mixture of cells having different ra diosensitivities and any variations of cell proliferation will influen ce the aberration score. In order to get a more representative aberrat ion score a multiple fixation regimen was applied to lymphocytes of tw o human donors. Cells receiving the adapting + challenging and the cha llenging dose were fixed at three intervals after the challenge. In ly mphocytes of donor 1 no adaptive response was seen at any fixation tim e 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 radi ation resistance.