The long term effects of radiation on T and B lymphocytes in the peripheral blood after regional irradiation

The long term alterations of T and B lymphocytes in the peripheral blood of patients treated with regional irradiation for various malignancies were examined. Eighty patients were tested at various intervals after the completion of irradiation. Absolute lymphocyte counts, the percentages of T cells and B cells, and the blastogenic response to phytohemagglutinin (PHA) or to allogeneic lymphocytes in the mixed lymphocyte reaction (MLR) were determined. Nearly all patients initially had absolute lymphocytopenia and one‐third of the patients tested 3 years after completion of irradiation had lymphocyte counts which were more than two standard deviations below the normal range. The depression was not specific for either the T‐ or B‐lymphocyte subpopulations. The PHA response was impaired for extended periods of time after the completion of irradiation. Differences in the mean response of lymphocytes to PHA were noted for all concentrations of the mitogen, but were most marked with sub‐optimal concentrations of PHA. The MLR was below the lower limits of normal in 70% of the recently irradiated patients. There was a gradual recovery of the ability to respond in the MLR, and all patients tested more than 4.5 years after the completion of therapy had a normal response. These results were compared with those obtained in patients treated with total lymphoid irradiation for Hodgkin's disease. Although there appeared to be a difference in the effect of radiation on lymphocyte subpopulations in the two groups, the effects on lymphocyte function were similar.