A CHARACTERIZATION OF THE IN-VIVO IMMUNOMODULATION BY MET-ENKEPHALIN IN MICE

Single intraperitoneal injections of Met-enkephalin (MENK) into CBA mi ce decreased the phagocytic activity of peritoneal macrophages, Con-A- induced proliferation and NK-activity of spleen cells. Conversely, in mice which had been immunized with sheep erythrocytes, treatment with MENK was associated with enhancement of phagocytosis, and no effect on lymphoid proliferation and NK-cytotoxicity of spleen cells. MENK-indu ced inhibition of cellular functions in nonimmunized mice was associat ed with a decrease of plasma ACTH level, whereas MENK-induced stimulat ion of phagocytosis in immunized mice was paralleled with an elevation of ACTH, suggesting a role of corticoids in immunomodulation by MENK. MENK-induced modulation (suppression and stimulation) of phagocytosis , as well as inhibition of spleen cell proliferation, was not observab le in adrenalectomized mice, although a reduced NK-cytotoxicity was st ill present.