Melatonin in relation to the antioxidative defense and immune systems: possible implications for cell and organ transplantation

Melatonin, a molecule synthesized and secreted by the mammalian (including human) pineal gland, has a variety of seemingly unrelated functions in organisms. In photoperiodically-dependent seasonal breeders, the changing melatonin signal imparts seasonal information to the species thereby regulating the annual cycle of reproduction [1]. Melatonin also is involved in a number of 24 h rhythms and is believed to be an important component of the circadian system [2, 3]. More recently, melatonin was found to relate to immune function [4] in organisms and to be an effective antioxidant [5]. As an antioxidant melatonin would appear to provide substantial protection against free radicals which are generated under a variety of experimental corrections, including ischemia/reperfusion injury [6, 7]. These latter two functions of melatonin, i.e., as an immune system modulator and as an antioxidant, both may have applicability to cell and organ transplantation [8–11].