Assessment of melatonin's ability to regulate cytokine production by macrophage and microglia cell types

Evidence in support of melatonin's role as an immunomodulator is incomplete and, in some cases, contradictory. The present studies determined whether melatonin modulates the activity of stimulated macrophages. In vitro lipopo lysaccharide (LPS, 10-1000 ng/ml) treatment of alveolar, splenic and perito neal macrophages isolated from mice and/or rats resulted in a dose-dependen t increase in interleukin-1 beta (IL-1 beta) and tumor necrosis factor (TNF -alpha) secretion. Treatment with melatonin (10(-10)-10(-6) M) prior to the addition of LPS, had no effect on IL-1 beta or TNF-alpha release. Addition ally, melatonin had no effect on stimulated BV2 microglial cell line cytoki ne secretion. To determine whether melatonin had an indirect effect on macr ophage cytokine release via T cells, melatonin was added to unfractionated mouse spleen cells. Again, melatonin showed no priming effect on LPS-stimul ated spleen cells. These results suggest that melatonin has no direct or in direct effect on mouse and rat macrophages. In vivo studies, where melatoni n was continuously available in the drinking water, showed that melatonin d id not have a priming effect on LPS-stimulated mouse peritoneal macrophages . These findings suggest that melatonin is not an important modulator of ma crophage and microglia function. (C) 2001 Elsevier Science B.V. All rights reserved.