Increased radiosensitivity of stimulator cells in the human mixed leucocyte culture reaction and the secondary response of primed lymphocytes.

In chessboard mixed leucocyte culture (MLR) experiments we have identified three unrelated healthy blood donors of lymphocytes which showed low stimulatory capacity with apparently MLR-incompatible and HLA-D-non-identical responder lymphocytes. This was due to increased sensitivity to X-irradiation of stimulators which was demonstrable in both MLR and secondary PLT responses. On the other hand, lymphocytes from these donors exhibited normal radiosensitivity when tested as responders in MLR and phytohaemagglutinin- and pokeweed mitogen-induced blastogenesis. The results of family studies of a low stimulator donor suggested that the radiosensitivity of stimulator cells may be under some genetic control which is probably not linked to HLA.