Dual effect of normal and stimulated macrophages and their conditioned media on target cell proliferation

Normal (resident) and peritoneal macrophage populations that were from male BALB/c mice and induced by five stimuli were tested for their regulatory activity on the proliferation of virus-infected and virus-transformed fibroblast cell lines. Cell proliferation was assessed with a quantitative method correlating the binding of methylene blue to adherent cells with the number of cells. At a low surface density and short coculture periods, macrophage monolayers of normal macrophages and thioglycollate-, concanavalin A (Con A)-, and BCG-stimulated macrophages enhanced target cell proliferation, whereas at a high density and relatively long (46 hr) coculture periods they markedly inhibited growth. Corynebacterium parvum-stimulated macrophages showed strong cytotoxic (cytostatic and/or cytolytic) effects under all coculture conditions. All macrophage populations possessed arginase activity, and their cultivation led to depletion of arginine from culture medium to a variable degree. Although extraneous arginine supply is essential for target cell proliferation, the addition of arginine to macrophage-target cell cocultures at 12-hour Intervals did not reverse the growth inhibition effect appreciably. Conditioned medium (CM) derived from 17-hour cultures of normal and thloglycollate-stimulated macrophages enhanced target cell proliferation, whereas CM derived from Con A-and C. parvum-stimulated macrophages exhibited strong cytotoxic effects. Arginine supplementation abrogated growth inhibition mediated by CM derived from Con A-stimulated macrophages, whereas CM derived from C. parvum-stimulated macrophages was not affected. Thus normal and stimulated macrophage populations have a dual effect on target cell proliferation, stimulation, and inhibition, which are determined by culture conditions as well as by a differential expression of these activities in the various populations. Macrophage-mediated arginine depletion from culture medium could not be the only factor determining the cytotoxic effect.—JNCI 63: 1009–1016, 1979.