Vaccination prepartum enhances the beneficial effects of melatonin on the immune response and reduces platelet responsiveness in sheep

The experiments were carried out in peripartum sheep from a farm located in an area of Mediterranean-type ecosystem. Plasma melatonin levels were determined by ELISA and sheep platelet aggregation was monitored using an aggregometer. Here we demonstrated for the first time that plasma melatonin concentration were higher in pregnant (125？pg/mL) than in non-pregnant sheep (15？pg/mL; P？<？0.05). Administration of melatonin prepartum did not significantly modify platelet function but significantly improved the immune response to vaccination against C. perfringens.Administration of melatonin as an adjuvant provides a significant improvement in the immune response to vaccine administration prepartum against C. perfringens.Melatonin (N-acetyl-5-methoxy-tryptamine), a hormone produced in the pineal gland and a number of other cells and organs, regulates a number of physiological processes either by its powerful ability to scavenge reactive oxygen species, interaction with intracellular molecules or via activation of the G protein-coupled melatonin receptors, MT1 and MT2 [1-3]. Melatonin regulates the immune system by affecting cytokine production, enhancing the production of several T helper cytokines and modulating the IL-2/IL-2R system [4-6]. Melatonin has been shown to exert a positive effect as an adjuvant of a number of vaccines [7-11]. Platelet function is also regulated by melatonin binding to high-affinity sites [12], which results in enhanced platelet responsiveness to physiological agonist and inducing beneficial effects on platelet function and haemostasis [8].Enterotoxemia, caused by Clostridium perfringens, is one of the most frequently occurring diseases in all species of domestic animals and humans inducing gastrointestinal and enterotoxemic diseases in animals [13-15]. The bacterium is a normal inhabitant of the intestine where it produces small amounts of toxin that, under normal conditions, are removed by gut movements or are inactivated by circulating anti