Neuropeptides and thymic hormones in the Xenopus thymus.

T-cell development is characterised by a complex series of events in the thymus, which results in the development of self-restricted immunocompetent lymphocytes. We have previously reported the expression of neuropeptides in the thymus of various species, highlighting the evolutionary importance of neuroendocrine interactions in thymocyte development. Despite the many physiological and functional similarities in their immune systems, no study has addressed the importance of neuropeptides and thymic hormones in T-cell development in Xenopus. Immunohistochemical analysis revealed that the neuropeptides substance P, neuropeptide Y, somatostatin, calcitonin gene related peptide, and vasoactive intestinal polypeptide and the thymic hormones thymosin alpha1, thymosin beta4, and thymopoietin are found in the Xenopus thymus. This was further corroborated by RT-PCR. Furthermore, double staining revealed that neuropeptides and thymic hormones are coexpressed within the epithelial cell component of the thymus. These results show that neuropeptides and thymic hormones are expressed in the thymus of Xenopus, and suggest that they are likely to play a role in T-cell development.