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 by 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 ionizing radiation. A dose of 2 cGy led to significant variations in mitotic indices (MI) which differed for the two donors in relation to variations in the times of irradiation and fixation after stimulation with PHA. Moreover in one of the two donors 4–6 h after challenge the pretreated cultures have a higher MI that the controls; on the other hand, conditioning treatment alone induces in the other donor an extension of both G2 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 insight into the problem of the variability of the adaptive response in human lymphocytes.