title: Border control: Anatomical origins of the thymus medulla.
abstract: The thymus is an anatomically compartmentalized primary lymphoid organ that fosters the production of self-tolerant T cells. The thymic cortex provides a specialized microenvironment in which cortical thymic epithelial cells (cTECs) support the positive selection and further differentiation of self-MHC-restricted thymocytes. Following their migration into the medulla, positively selected thymocytes are further screened for self-reactivity, which involves both negative selection and Foxp3(+) regulatory T cell generation via interactions with medullary thymic epithelial cells (mTECs). Given the importance of both cortical and medullary microenvironments for T cell development, studies that address the developmental origins of cTECs and mTECs are important in understanding the processes that shape the developing T cell receptor repertoire, and reduce the frequency of self-reactive T cells that initiate autoimmune disease. In this issue of the European Journal of Immunology, Onder et al. [Eur. J. Immunol. 2015. 45: 2218-2231] identified a subset of podoplanin(+) mTECs in mice that reside at the corticomedullary junction (CMJ), show that their development is important to establish self-tolerance, and require the presence of self-reactive T cells. Collectively, their findings highlight the CMJ as a potential repository for precursors of the mTEC lineage, and provide a better understanding of thymus medulla formation.
authors.affiliation: MRC Centre for Immune Regulation, Institute for Biomedical Research, Medical School, University of Birmingham, Birmingham, UK.
authors.forename: Graham
authors.initials: G
authors.lastname: Anderson
authors.affiliation: MRC Centre for Immune Regulation, Institute for Biomedical Research, Medical School, University of Birmingham, Birmingham, UK.
authors.forename: William E
authors.initials: WE
authors.lastname: Jenkinson
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000276:immunology*; D004847:Epithelial Cells / Q000276:immunology*; D008562:Membrane Glycoproteins / Q000276:immunology*; D016328:NF-kappa B / Q000276:immunology*; D015398:Signal Transduction / Q000276:immunology*; D013234:Stem Cells / Q000276:immunology*; D013950:Thymus Gland / Q000276:immunology*
chemical_list: D008562:Membrane Glycoproteins; D016328:NF-kappa B
keywords: Central tolerance; Epithelial cells; Stem cells; T cell; Thymus