Melatonin mediates seasonal adjustments in immune function

In addition to seasonal changes in reproductive function, seasonal changes in immune function are mediated by the pineal hormone, melatonin. Melatonin affects immune function both indi- rectly, acting through other hormones, and directly by acting on components of the immune sys- tem. Melatonin also affects tumorigenesis and tumor development. We hypothesize that many of the indirect effects of melatonin on immune function are mediated through glucocorticoids, and appear to be part of an integrated series of adaptations to manage energy. Direct effects of mela- tonin on immune function appear to be mediated by melatonin receptors on lymphatic tissue or on immune cells in circulation. Winter is energetically demanding and stressful; thermoregulatory demands typically increase when food availability decreases. Individuals would enjoy a survival advantage if seasonally recurring stressors could be anticipated and countered by bolstering immune function. To summarize, melatonin may be part of an integrative system to coordinate reproductive, immunologic and other physiological processes to cope successfully with energetic stressors dur- ing winter. © Inra/Elsevier, Paris melatonin / seasonality / thermoregulation / energetics / metabolism / photoperiod Rsum ― La mlatonine traduit les variations saisonnires de fonction immunitaire. Comme pour les variations saisonnires de reproduction, l'hormone pinale, mlatonine, traduit les chan- gements saisonniers de fonction immunitaire. La mlatonine modifie la fonction immunitaire la fois indirectement, par l'intermdiaire d'autres hormones, et directement en agissant sur des lments du systme immunitaire. La mlatonine influence galement la gense et le dveloppement des tumeurs. Nous mettons l'hypothse que la plupart des effets indirects de la mlatonine sur la fonction immu- nitaire impliquent les glucocorticodes, et semblent faire partie d'un ensemble de mcanismes adaptatifs intgrs destins grer l'nergie. Les effets directs de la mlatonine sur la fonction immuni- taire semblent impliquer des rcepteurs la mlatonine sur le tissu lymphatique ou sur les cellules immunitaires de la circulation sanguine. L'hiver est coteux sur le plan nergtique et il est source