VARIABILITY IN ADAPTIVE RESPONSE TO LOW-DOSE RADIATION IN HUMAN BLOOD-LYMPHOCYTES - CONSISTENT RESULTS FROM CHROMOSOME-ABERRATIONS AND MICRONUCLEI

The frequencies of chromosome aberrations and micronuclei were evaluat ed to assess the induction of adaptive response to low dose ionizing r adiation in each of the blood samples collected from eight different i ndividuals. Following stimulation with phytohemagglutinin, the cells w ere exposed to an adaptive dose of 1 cGy X-radiation at 24 hours and a challenge dose of 150 cGy gamma radiation at 48 hours. Lymphocytes we re fixed at 54 hours to examine the incidence of chromosome aberration s and at 72 hours to examine the frequency of micronuclei in cytokines is-blocked binucleated cells. Lymphocytes from five donors, i.e., ''re sponders'', exhibited the induction of adaptive response; their lympho cytes, which were pre-treated with 1 cGy had significantly fewer chrom osome aberrations and micronuclei induced by the challenge dose of 150 coy gamma radiation, as compared to the cells which did not receive t he pre-treatment with 1 cGy. Such an induction of adaptive response wa s not observed in the remaining three donors, i.e., ''non-responders'' ; the incidence of chromosome aberrations and micronuclei induced by t he challenge dose of 150 cGy was not significantly different between t he cells which were pre-exposed and un-exposed to 1 cGy. In all eight individuals, there was a strong positive correlation between the incid ence of chromosome aberrations and micronuclei. Hence, whether or not an individual is a 'responder' or 'non-responder' could be assessed us ing either chromosome aberrations or micronuclei as the end-point. The overall pattern of response confirms the heterogeneity in adaptive re sponse between individuals to ionizing radiation, which may in part be genetically controlled. Because of the simplicity of the technique an d rapid assessment of the binucleated cells, we suggest the use of the micronucleus test as an alternative procedure in large scale populati on studies related to the adaptive response.