Manifestation of radiation injury of human lymphocytes using PHA mitogenic stimulation in different culture systems

The proliferative response of human lymphocytes to PHA in vitro is affected by X-irradiation. Dose-related changes of mitogenic stimulation of irradiated lymphocytes were compared in two culture systems--cultivation of separated lymphocytes and cultivation of whole blood. In whole blood cultures, the proliferative activity of stimulated lymphocytes was markedly and reproducibly depressed by irradiation. The values of mitogenic response within a dose range from 0 to 2.5 Gy could be fitted with high correlation by an exponential curve. In a modified test where the mitogenic stimulus was given after 24 h delay, depression of the response was even more pronounced. Radiosensitivity of human lymphocytes as determined by means of mitogenic stimulation in whole blood cultures appears to be a characteristic individual feature. The mean D37 value of the radiation-induced depression of mitogenic response in a group of 20 healthy donors was 2.5 Gy in the standard test and 2.0 Gy in the test with a delayed mitogenic stimulus. In contrast, the data obtained from separated lymphocyte cultures were characterized by a high degree of the test-to-test variability and by much lower radiosensitivity. The possible mechanisms of these distinctive manifestations of the same primary radiation injury are discussed.