| Abstrakt: |
Introduction The thymus gland develops from three different sources. The thymic epithelial anlage is a derivative of the foregut endoderm. The branching epithelial cords of thymic primordium grow into the surrounding mesenchyme of neural crest (NC) origin. This epithelial- mesenchyme primordium is finally colonized by hemopoietic cells. The blood vessels reach the thymic tissue from the capsule and interlobular trabaeculae, the latter developing from the NC cells. The epithelial framework of the thymus consists of reticular epithelial cells (RECs). The anti-cytokeratin immunostaining identifies two sub- compartments in the medulla. One is continuous with the cortical epithelial cells, which expresses keratin (keratin positive network-KPN) and the other does not show keratin staining (keratin negative area-KNA) and is devoid of RECs. The connective tissue space of interlobular septae is continuous with KNA, that is "a dilation" of the septae. Aim The precise origin of the KNA is unknown, so our aim is to show its NC origin and characterize the changes in thymic development of cranial NC ablated and transplanted chicken embryos. Methods To investigate the possibility of NC origin of KNA we applied chicken NC ablation and chicken-quail NC chimera technique. The chicken NC was unilaterally ablated from the level of the 1st somite until the 5th somite ideally during stage 10 according to Hamburger-Hamilton. For creating the chimera this ablated segment was transplanted from quail into chicken. After 2 weeks of incubation the development of the thymus primordium was followed up by immunocytochemistry staining. Results After the NC ablation the cortex showed absence of epithelial cells, bood vessels and CD8 positive T-cells. In the NC-grafted chicken thymus NC-derived cells were detected in the capsule, trabaeculae and in the medulla. Conclusions The thymic epithelial progenitor cells do not differentiate into medullary thymic epithelial cells. The development of the thymic lobes and the normal KPN/KNA pattern is perturbed, the medulla is not developed. The cortical capillarisation and the development of T cells are disturbed. The result of the ablation supports the hypothesis of NC origin of the NKA. In accordance with this finding, the grafting reveals NC-derived cells in the medulla. [ABSTRACT FROM AUTHOR] |
