Differential stimulation of macrophages for tumor cytostasis and monokine production

We have investigated whether antitumor activity could be expressed independently of cytokine production. Resident macrophages treated with interferon-γ (IFN-γ), lipopolysaccharide (LPS) plus muramyldipeptide (MDP) expressed a cytostatic activity against P815 tumor cells and released interleukin 6 (IL-6) and nitrite but produced neither IL-1 nor tumor necrosis factor (TNF). Thioglycollate-elicited macrophages required only LPS plus IFN-γ for cytostatic activity which was expressed concomitantly with the release of high levels of TNF, IL-1 and IL-6, whereas C3H HeJ macrophages produced low levels of monokines and were not cytostatic. LPS, alone, was sufficient for triggering Concanavalin A-primed macrophages leading to a full cytostatic activity, even in C3HM HeJ macrophages that was expressed, for these latter, in the absence of monokine production. TNF did not appear to play a role either in autocrine stimulation of macrophages or in the cytostatic process because anti-TNF antiserum affected neither the cytostatic activity nor the nitrite production.