In vitro cellular regulation of monocyte function: Evidence for a radiosensitive suppressor

Radiation was used in the following studies to better define and understand the interaction between human killer monocytes and their suppressor lymphocytes in a cytotoxic assay. Human mononuclear leukocytes become spontaneously cytotoxic to a variety of red blood cell targets after 7 days of in vitro culture. This phenomenon was independent of exogenous stimulus by Ag, Ab, or mitogen. Monocytes appeared to be the cytotoxic cell and were controlled by lymphocyte suppressor cells. In the present study, X-irradiation enhanced the magnitude of monocyte-mediated cytotoxicity generated and stimulated an earlier appearance of this cytotoxicity when compared with that of unirradiated mononuclear leukocytes. The effect of X-irradiation (150 to 600 R) on separated populations of mononuclear leukocytes enriched for either lymphocytes or monocytes was examined; this enhanced cytotoxicity appeared to be secondary to inactivation of the lymphocyte suppressor cells.