Stimulation of thymocyte mitogenic protein secretion and of cytostatic activity of mouse peritoneal macrophages by trehalose dimycolate and muramyldipeptide.

Immunomodulators of bacterial origin, such as muramyl-dipeptide (MDP) and trehalose dimycolate, are able to stimulate some important biological functions of macrophages, such as their capacity to secrete a monokine, the thymocyte mitogenic protein (TMP), and to limit the growth of mastocytoma cells in vitro. Adherent cells from the peritoneal cavity of untreated mice do not secrete significant amounts of TMP and are not cytostatic. In contrast, adherent peritoneal cells from mice injected with trehalose dimycolate (emulsified in water) secrete TMP and are strongly cytostatic for P815 cells. Trehalose dimycolate is also active when added in vitro: (a) it enhances the cytostatic action of thioglycollate-elicited macrophages; (b) alone or in sequence with MDP, it induces an appreciable cytostatic activity in resident macrophages; (c) it limits the decline of the strong cytostatic action of trehalose-dimycolate-elicited macrophages occurring during in vitro cultivation. MDP also stimulates the cytostatic activity of the macrophages in vitro. The most interesting effect of MDP is its capacity to induce a strong secretion of TMP after a short contact (1 h) with elicited macrophages.