Figure 1.

Stages of T cell selection during the establishment of central tolerance. T cell precursor double-negative (DN) T cells enter the cortex of the thymus through a blood vessel to undergo positive selection. Due to the interaction between antigen-presenting cells (APCs) present on cortical thymic epithelial cells (cTECs) and migratory dendritic cells (DCs), double-positive (DP) T cells are differentiated into CD4⁺ or CD8⁺ single-positive (SP) T cells and migrate to the medulla of the thymus to undergo negative selection. As they interact with APCs (medulla thymic epithelial cells (mTECs), migratory or resident DCs, and B cells), CD4⁺ T cells become CD4⁺ naïve T cells or T regulatory cells (Tregs) and leave the thymus. Negative selection is schematically shown only for SP CD4⁺ T cells.