EFFECTS OF LOW-DOSE (2-CGY) X-RAY ON CELL-CYCLE KINETICS AND ON INDUCED MITOTIC DELAY IN HUMAN LYMPHOCYTE

Experiments were carried out with human lymphocytes to test the effect of low-dosage X-ray irradiation (2 cGy) on cell-cycle kinetics and on the mitotic delay induced by the conditioning pretreatment alone or b y a subsequent high dose of X-ray. All the tests were performed using lymphocytes from two donors who had previously displayed considerable differences in the interaction between a low and a high dose of ionizi ng radiation. A dose of 2 cGy led to significant variations in mitotic indices (MI) which differed for the two donors in relation to variati ons in the times of irradiation and fixation after stimulation with PH A. Moreover in one of the two donors 4-6 h after challenge the pretrea ted cultures have a higher MI that the controls; on the other hand, co nditioning treatment alone induces in the other donor an extension of both G(2) and of the time taken by cells in S at the time of challenge to reach mitosis. These findings could in the future provide some ins ight into the problem of the variability of the adaptive response in h uman lymphocytes.