Figure 2.

General scheme of thymocyte selection and emigration to the peripheral lymphoid compartment. CD4^-CD8^- (DN) cells expressing pre-TCR undergo divisions and become αβTCR⁺CD4⁺CD8⁺ (DP) at which stage they interact with self-peptides presented by class I and II MHC molecules expressed on thymic stromal cells. Those thymocytes whose TCRs interact with high affinity to pMHC undergo apoptosis, while those bound to pMHC with low affinity mature to become MHC class I-restricted CD8⁺ SP or class II-restricted CD4⁺ SP cells. These mature thymocytes then emigrate to the periphery aided by different egress-related mechanisms.