INHIBITORY EFFECT OF MELATONIN ON PRODUCTION OF IFN-GAMMA OR TNF-ALPHA IN PERIPHERAL-BLOOD MONONUCLEAR-CELLS OF SOME BLOOD-DONORS

Melatonin, the main pineal hormone, has been shown to influence many b iological functions, including the immune response and cancer growth. The purpose of this study was to examine the effect of melatonin on th e production of interferon gamma (IFN gamma) and tumor necrosis factor alpha (TNF alpha) by peripheral blood mononuclear cells (PBMC) in cul ture. Melatonin at physiological concentrations fails to induce produc tion of IFN or TNF by PBMC in culture but causes a dose-related inhibi tion of production of both cytokines if the PBMC are stimulated with p hytohaemagglutinin. This inhibitory effect occurs in only 22% of cases (melatonin-sensitive) but disappears when the cells are stored at 4 d egrees C for 4 days. The effect of melatonin appears not to be mediate d by opiates nor to be correlated with the age, sex, or blood group of donors, but seems to be influenced by the seasonal time of blood coll ection. These results provide further evidence for an interaction betw een melatonin and the immune system and suggest that the effect of mel atonin on production of IFN and TNF may be mediated by various factors not yet fully understood.