Antigen processing and presentation in the thymus: implications for T cell repertoire selection

•Unique machineries of protein degradation in thymic cortical epithelial cells.•Promiscuous gene expression in thymic medullary epithelial cells.•Roles of antigen processing and presentation in thymic T cell repertoire formation.

The processing and presentation of major histocompatibility complex (MHC)-associated antigens depend on the intracellular digestion of self- and nonself-proteins, the loading of digested peptides onto MHC molecules, and the traffic of peptide-MHC complexes to plasma membrane surface for display to interacting T cells. Recent studies have revealed unique machineries for antigen processing and presentation in thymic antigen-presenting cells that display self-antigens to developing thymocytes for the formation of functionally competent yet self-tolerant T cell repertoire. Here, we briefly summarize those machineries, focusing on the biology of cortical and medullary thymic epithelial cells.