The pineal gland has been shown to have a strong link with the immune system [Reiter, 1995; Maestroni, 1993]. Inhibited melatonin synthesis and secretion induces states of immunodeficiency. Such states are counteracted by exogenous melatonin. Pinealectomy will result in immunodeficiency and shrinking of the thymus gland [Csaba et al., 1965, 1975, 1976; Becker et al., 1988].

Immunoregulatory properties of melatonin and the pineal sensitivity to thymic hormones suggest that there exists a bidirectional flow of information between the pineal gland and the immune system. The thymus gland has the same superior cervical ganglia nerve connections as the pineal gland. In the discussion of other interrelationships between the pineal gland and peripheral glands, its relationship to the thyroid gland is of interest as it will have relevance to the discussion of the autism-pineal connection. Publications have identified a depressant effect of the pineal gland on the thyroid [DeFronzo and Roth, 1972; Relkin, 1972], and the elimination of the pineal influence has been shown to bring about increased thyroid activity. The work of other researchers [Singh et al., 1969; Relkin, 1972; Mess and Peter, 1975] likewise demonstrated that the pineal exercises control over the hypothalamus-pituitary-thyroid system.

The pineal gland affects the adrenal glands as it does the thyroid, acting as an inhibitory modulator of the adrenal cortex [Dickson et al., 1972; Nir, 1978].