Deciphering the subcapsular epithelial cells in human fetal and postnatal thymus

Most papers related to thymus focus on the cortical and medullary epithelial cells whereas the subcapsular layer is ignored. In this thesis, we are providing new informations about the subcapsular thymic epithelial cells (TECs) by comparing them to cortical TECs, medullary TECs, Hassall's corpuscles (HCs) and the epidermis. We have demonstrated that TECs located in the subcapsular region are polarized cells adhering to an organized basement membrane and that they are interconnected in a tridimensional meshwork with all other TECs, including the TECs located in the HCs. We have confirmed that the thymus epithelium has a highly complex architecture that looks like no other epithelium. The 3D structure is certainly important for thymus functionality. However, how the 3D structure impacts T cell instruction remains to be investigated. Additionally, we have demonstrated that the subcapsular TECs express the surface marker EPCAM. Therefore, subcapsular TECs are part of the sorted EPCAM+ TEC population. We have also investigated the expression of proteins important for epidermal morphogenesis and we have unraveled strong similarities between the development of thymic epithelial cells and epidermis. Furthermore, we have shown that epithelial clusters of TP63 positive and Ki67 positive cells are present in the fetal subcortical region. Our work emphasizes that subcapsular TECs are important components of the thymic epithelial network and that they warrant further investigation.