The Effect of Radiation Upon Lymphocyte Response to Pha

Abstract. The proliferative response of lymphocytes to phytohaemagglutinin has been studied following incremental doses of ⁶⁰Co gamma radiation delivered at the beginning of culture. A dose-dependent inhibition of ³H-thymidine uptake is apparent in 48 hr and 72 hr cultures throughout the 250–2000 rad range, and the effect appears more marked at the later labelling time. Parallel autoradiographic studies have revealed changes in the cell cycle kinetics of irradiated cultures which underlie the effects observed at the whole-culture level. Irradiation reduces the number of cells reaching the first period of DNA synthesis and causes dose-dependent delays at specific points in the cycle of proliferating cells.