Functional connections between the pineal gland and immune system.

Experimental findings which support a functional connection between the pineal gland and immune system in mammals and birds are summarized. Developmental and age-related changes in pineal gland function appear, at least partially, to be related with immune system efficiency. Mechanisms whereby melatonin influences immune system function are complex, but include participation of mediators (endogenous opioids, cytokines, hormones, zinc pool) as well as specific binding sites on the immune cells. Melatonin, as a highly lyophilic compound, may also penetrate immune cells without mediation of specific receptors and act within as a potent free radical scavenger and as an anti-aging and oncostatic factor. The immune system may, in turn, via synthesis and secretion of soluble factors, cytokines, influence pineal gland function, thereby closing the information loop to maintain homeostasis in order to face the harmful environment.