Antigen presentation in the thymus for positive selection and central tolerance induction.

Understanding how thymic selection imparts self-peptide-MHC complex restriction and a high degree of self tolerance on the T cell repertoire requires a detailed description of the parameters that shape the MHC ligand repertoire of distinct thymic antigen-presenting cells and of how these cells communicate with T cells. Several recent discoveries pertaining to cortex-specific pathways of antigen processing, the heterogeneity of thymic dendritic cells and the intercellular transfer of self antigens have uncovered surprising and unique aspects of antigen presentation in the thymic microenvironment. Here, we discuss these new findings in the context of how individual thymic stromal cell types support T cell selection in a cooperative rather than a redundant manner.