Suppression of lymphokine production: II. Macrophage-dependent inhibition of production of macrophage activating factor

The ability of different populations of macrophages to affect the production of macrophage activating factor (MAF) by stimulated T lymphocytes was investigated. We found that activated macrophages, infiltrating MSV-induced regressing tumors or macrophages recovered from the peritoneum of mice injected with Corynebacterium parvum, were able to actively suppress the production of MAF. MAF production by antigen-stimulated MSV-immune or -alloimmune spleen cells and by normal spleen cells stimulated by Con A was susceptible to macrophage-dependent suppression to a similar extent. In contrast, resident macrophages or those elicited by light mineral oil or proteose-peptone did not affect MAF production. While suppressor macrophages added at the time of the lymphocyte stimulation inhibited MAF production, the same cells added 4-6 hr after stimulation were ineffective. Therefore, it seems that the macrophages suppressed the early events of lymphocyte activation leading to MAF production. Suppressor macrophages, by inhibiting MAF production, may limit the expansion of the cytotoxic activity. This regulation of macrophage functions, mediated by the effects of suppressor macrophages on T lymphocytes, could be responsible for an insufficient antitumor cytotoxic response by macrophages.