Reciprocal interdependence between pineal gland and avian immune system. NEL Review

The immune system of mammals and birds exhibits the same basic anatomical and functional organization, including dichotomy into the cellular and humoral immune response. Specificities of avian immune system may be, however, very useful for understanding numerous phylogenetic and evolutionary mysteries. Similarities and differences between mammals and birds in terms of several pineal gland functions are well known, and they seem to include the immunomodulatory activity of melatonin (MEL) as well. Embryonic pinealectomy of the chicken demonstrated functional interrelationships between the development of the pineal gland, immune system and/or neuroendocrine network, and embryonic bursectomy influenced the diurnal rhythm of the pineal gland function and abolished the effect of immunization on serum MEL level. Also immunization with a thymo-dependent antigen (SRBC) evoked some changes in the chicken nocturnal pineal NAT activity. We have found that the pineal gland and MEL control the diurnal rhythm of immunity in the chicken, but we were not able to demonstrate any immunostimulatory and anti-glucocorticoid MEL effects, regardless of the chicken's age, sex, season, and hormone dose used. The existence of functional connections between the pineal gland and the immune system in chickens was, however, confirmed in other experimental approaches. Specific and reversible binding of 2-[125I]iodoMEL to the membrane preparations from lymphoid glands was demonstrated in several avian species. In vitro MEL diminished lymphocyte proliferation stimulated by the common T-cell mitogens, while alone failed to influence the blast formation. Reciprocal functional connections between the avian immune system and the pineal gland seem to be well documented, but the mechanism(s) involved have to be elucidated.