Time factor in PHA responsiveness of human blood lymphocytes after in vitro irradiation.

Previous investigations (BARAL & BLOMCREN 1976, SCHREK & STEFANI 1964, CIRKOVIC 1969, BRAEMAN & MOORE 1974) have demonstrated that exposure of human peripheral lymphocytes to increasing doses of roentgen rays reduces their PHA-responsiveness as a two-phased function. A steep fall of the PHA-reactivity is recorded up to 8 Gy, followed by a plateau phase at higher doses. This observation may be interpreted in several ways. One possibility could be that there exists a true difference in sensitivity to radiation between two lymphocyte subpopulations. An alternative explanation could be that there are two subpopulations of PHAreactive cells: one which is activated rapidly by PHA and thereby builds up a repair system for the structures injured by irradiation, and another subpopulation which is activated more slowly by PHA and that dies in interphase. In this investigation this question has been explored by varying the sequence and time intervals between radiation exposure and PHA-stimulation.