The Thymus: Key Organ between Endocrinologic and Immunologic Systems

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Abstract
Our data permitted us to postulate an immunoregulatory circuit linking the neuroendocrine structure and the immune system via hormones secreted by the thymus which permit differentiation of T cells. In our first approach we have considered the thymus as a key organ; it exerts its function upon the two systems. We can also consider the thymus a key organ because a major part of the lymphoid cells responsible for the secretion of immunotransmitters or described as target cells for immunohormones or opioids are mature T cells; these T cells have had contact--either cellular (nurse cells) or humoral (thymic hormones)--with thymus during ontogeny. We hypothesize that during this differentiation the properties of secreting hormones or opioids and of receiving an endocrine message appear. Concerning the effect of TF V, the different thymosin properties led us to postulate that among the TF V polypeptides some could exert their effects on the immune system and some on the endocrine system directly or indirectly, either in synergism or in antagonism with classical hormones. There is no doubt that neurotransmitters and hormones can modulate in vivo ontogenesis, differentiation, and expression of the immune response. We believe that the thymus via its hormonal function is one factor in this modulation and one of the main channels of this bidirectional action between the immune and the endocrine systems. We have summarized our hypothesis in Figure 2.