EVOLUTION OF NEUROENDOCRINE THYMUS - STUDIES ON POMC-DERIVED PEPTIDES, CYTOKINES AND APOPTOSIS IN LOWER AND HIGHER VERTEBRATES

In previous papers, we showed that neuroendocrine cells reactive to an ti-POMC-derived peptides and cytokines are present in the thymus of a fish and an anuran amphibian. Here we report that this phenomenon is g eneral, as neuroendocrine cells positive to anti-POMC-derived peptides (ACTH, beta-endorphin, alpha-MSH) and cytokines (IL-1 alpha, IL-2, IL -6, TNF-alpha) are also present in the thymus of chicken and rat. Howe ver, the number and the intrathymic localization and distribution of t hese cells varies in the different species examined. An analysis of ap optotic cells or cells involved in apoptosis, such as interdigitating cells and macrophages, in fish, frog, chicken and rat thymus, using an immunocytochemical method and anti-DNA mAb conjugated with peroxidase (anti-DNA-POD), showed that cell positive to anti-DNA-POD mAb are pre sent in the same thymic areas in which POMC-derived peptides and cytok ines were found. In conclusion, these data on apoptotic cells in the t hymus of lower and higher vertebrates are compatible with the hypothes is that neuroendocrine cells might play a role in the selection and ap optosis of thymic lymphocytes, a phenomenon which could vary slightly in different species and taxa.