Melatonin--a pleiotropic molecule involved in pathophysiological processes following organ transplantation.

Mammals adjust their physiology in response to seasonal changes to environment (i.e. photoperiod, temperature, food availability). These changes are thought to predominantly occur for the conservation of energy during winter, by pervasive changes such as the inhibition of reproduction. Previous reports have suggested that circannual changes also occur to the immune system. In mammals, this chronological effect may be dependent on photoperiod, and evidence exists to suggest that there is a great deal of immune variation in response to light, or circadian rhythm. This is a clinically relevant, yet under-reported area of human transplantation. The aim of this review is to discuss immune variation, with specific emphasis on melatonin secretion, in the context of organ rejection, infection, neoplasia formation, and immunosuppression.