Effects of cyclooxygenase inhibitors and prostaglandin E2 on macrophage activation in vitro

The effect of the cyclooxygenase inhibitors, indomethacin and diclofenac, and of PGE2 on either resting or stimulated macrophages was investigated. Peritoneal macrophages were obtained from untreated mice and cultured for 10 days. Macrophage activation was induced by zymosan phagocytosis and was monitored by testing for plasminogen activator secretion and the cellular levels of lactate dehydrogenase, beta-glucuronidase and alkaline phosphodiesterase I. It was found that cyclooxygenase inhibitors activate resting macrophages and enhance the degree of activation obtained after zymosan phagocytosis. Addition of exogenous PGE2, on the other hand, had the opposite effect, it suppressed activation induced either by cyclooxygenase inhibitors, phagocytosis or a combination of both. Cyclooxygenase inhibitors and PGE2 did not affect the hexose monophosphate shunt activity of resting macrophages and had only a minor effect on the respiratory burst occurring during zymosan phagocytosis. It appears, therefore, that the observed changes in the state of activation of the macrophages are not related to hexose monophosphate shunt activity. The described effects suggest that PGE2 and possibly other cyclooxygenase products may function as inhibitory feed-back regulators of macrophage activation.