Changes in peripheral blood lymphocyte subsets in patients undergoing radiotherapy

Purpose: To investigate the changes in peripheral blood lymphocyte subpopulations in patients undergoing radiotherapy. Materials and methods: In 8 patients undergoing external beam radiotherapy to the pelvis, the different lymphocyte subpopulations were followed during treatment. The lymphocyte populations were determined using two-colour flow cytometry. The study comprises the T-helper, T-suppressor/cytotoxic cells, the B-lymphocytes and natural killer (NK) cells. Results: The B-cells were characterized by a steep decrease at the beginning of the radiotherapy. They reached their lowest level at an equivalent total body dose of 1.5Gy and remained constant during the rest of the therapy (10% of the initial level). In T-cells (both T-helper and T-suppressor subsets) the steep decrease was less pronounced. T-lymphocytes reached a base level at 2.5Gy equivalent total body dose (20% of the initial level). No significant differences between the T-helper and the T-suppressor/cytotoxic cells were observed. NK cells were characterized by a weak decline during the first weeks of therapy, being less pronounced than in the other populations. Near the end of therapy, the NK cells reached the level of the T-lymphocytes. Conclusion: In vivo, NK cells were the most radioresistant and B-cells the most radiosensitive lymphocytes. No significant differences between T-helper and T-suppressor/cytotoxic cells were observed. These data are in agreement with the differences in apoptosis induction in peripheral blood lymphocyte subpopulations after in vitro gamma-irradiation of whole blood lymphocytes.