Neuroendocrinology of the thymus.

The neuropeptides oxytocin (OT) and vasopressin (VP) are synthesized in the human thymus in a similar way as in the hypothalamo-neurophypophyseal system. Immunocytochemistry with polyclonal and monoclonal antibodies revealed that immunoreactive OT- and VP-producing cells are localized in the subcapsular cortex and medulla of human and murine thymuses. The epithelial nature of the neuroendocrine thymic cells is demonstrated by their immunostaining with a monoclonal antibody against cytokeratin. An original example of a neuroendocrine-immune microenvironment is given by the thymic nurse cells which are composed of a large neuroendocrine epithelial cell enclosing numerous mitotic immature thymocytes. These observations and the previously reported mitogenic and immunomodulatory properties of VP and OT upon mature T cells and thymocytes strongly support the existence of a neuroendocrine thymo-lymphoid axis and an active role of thymic VP and OT in T cell differentiation and activation.