Increased yields of exchanges but not of deletions in X-irradiated human peripheral lymphocytes following phytohemagglutinin stimulation

We have irradiated human peripheral lymphocytes after various intervals of phytohemagglutinin stimulation to determine the time course for exchange induction and to determine whether or not deletion yields increase with increasing intervals of stimulation. We found no increase in deletion yields for intervals up to 12 hr, and rings and dicentric yields increased by about 60% in the interval between 0 and 6 hr but then reached a plateau. We also measured induced unscheduled DNA synthesis during the same interval and found it generally increased during the first 6 hr like exchange yields, but then tended to decrease again.