Cytogenetic and survival adaptive responses in G1 phase human lymphocytes.

Human lymphocytes from six donors were treated with 5 cGy of X-rays followed by 200 or 400 cGy in the first G1 phase after PHA stimulation, and assayed for cytogenetic aberrations and cell survival. Four donors showed cytogenetic adaptive responses with 400 cGy, and one with both 200 cGy and 400 cGy. Both exchanges and deletions were reduced, indicating that the cytogenetic adaptive response acts by restitution of chromosome breaks. Good correlations were found between nonaberrant cells and survival, although the former were often higher than the later, especially with the 400 cGy dose. In four of six donors, 5 cGy alone had significant effects on cell survival; however, this was independent of the 5 cGy effect on high-dose-induced responses. Two donors had survival adaptive responses with 5 + 200 cGy, while none were found with the 5 + 400 cGy treatment. The comparisons between the cytogenetic and survival responses suggests that a survival adaptive response will only be seen with a sufficient increase in nonaberrant cells. To date, adaptive responses to ionizing radiation have been reported to occur in G0, G1 and late S/early G2 human lymphocytes.