Immunoactive peptides, FK 156 and FK 565. IV. Activation of mouse macrophages.

We investigated the effects of the immunoactive peptides, FK 156 and FK 565, on functions of mouse macrophages. FK 156 and FK 565 given parenterally or orally to mice enhanced spreading of peritoneal macrophages, phagocytosis of latex particles and intracellular killing of bacteria by peritoneal macrophages. FK 156 and FK 565 also enhanced the production of superoxide anion and lysosomal enzyme activities of macrophages. The peptides also activated mouse spleen macrophages, and the kinetics of this activation differed from that of the peritoneal macrophages. In addition, both drugs directly enhanced the production of superoxide anion by mouse peritoneal macrophages treated in vitro and enhanced the functions of peritoneal macrophages of athymic nude mice. Both these phenomena suggest that direct activation might be one of the mechanisms of macrophage activation by the peptides.