Immuno-derived opioids as mediators of the immuno-enhancing and anti-stress action of melatonin.

The pineal neurohormone melatonin was shown to stimulate the release of opioid peptides from activated CD4+, T lymphocytes. These immuno-derived opioids or "lymphomorphins" crossreact with anti-beta-endorphin and anti-metenkephalin antisera, bind to opioid receptors in the thymus and are the mediators of the immunoenhancing and anti-stress action of endogenous and/or exogenous melatonin. These findings proved the existence of a novel immunoneuroendocrine physiological mechanism which may be related for the long range maintenance of the immune homeostasis in spite of the unavoidable stress and/or infectious events occurring during the span of life in a normal unprotected environment.