Evidence of melatonin synthesis and release by mast cells. Possible modulatory role on inflammation.

Mast cells take part of armamentarium immunologic for host defense against parasitic and bacterial infections. They are derived from bone marrow progenitors and can be activated by immunological and chemical stimuli in order to get its degranulation. The activation of mast cells generates a signalling cascade leaded to the rapid release of vasoactives and pro-inflammatory mediators. Melatonin (N-acetyl-5-methoxytryptamine) is a molecule with antioxidant, cytoprotective and immunomodulatory actions. It was initially known to be produced exclusively in the pineal gland but melatonin synthesis has been found in different sites of the organism, and a major source of extrapineal melatonin is the immune system. The aim of the present study was to prove if the rat mast cell line (RBL-2H3) synthesizes and releases melatonin, also to explain its possible mechanism of action. We report that both resting and stimulated mast cells synthesize and release melatonin. We also report that the necessary machinery to synthesize melatonin is present in mast cells and that these cells showed the presence of MT1 and MT2 melatonin membrane receptors. Those results indicated that the melatonin would be able to exert a regulatory effect on inflammatory reactions mediated by mast cells.