In vitro X-ray irradiation of human peripheral blood T lymphocytes enhances suppressor function

We studied the effect of in vitro X-ray irradiation on human peripheral blood T lymphocytes, with regard to their suppressor activity related to the concanavalin A (Con A)-induced suppressor system. To generate suppressor T lymphocytes, purified human T lymphocytes were incubated for 3 days in the first culture, with or without Con A. These lymphocytes were irradiated with various doses of X-ray before, mid or after the culture. After doing a second culture for 6 days, we measured the suppressive influence of these cells on T lymphocyte proliferation rates stimulated with allogeneic mononuclear cells, and B lymphocyte proliferation rates stimulated with pokeweed mitogen. Irradiation (1,000 rad) of cultures to which Con A had not been added induced much the same level of suppressor activity as seen in the cultures with Con A. The suppressor activity gradually increased with lapse of time from the irradiation to the suppressor cell assay. Suppressor T lymphocytes were resistant to X-ray irradiation and independent of DNA synthesis. On the other hand, irradiation-induced enhancement was minimal in cultures incubated with Con A, regardless of the irradiation time. As irradiation of human peripheral blood T lymphocytes was found to induce a suppressor function in vitro, clinical and experimental applications of irradiation in cases of a suppressed T lymphocyte function may be feasible.