Figure 5.

Diagram illustrating changes in the expression of different markers during thymocyte maturation and related molecular events. Immature cells entering the cortex did not express CD4, CD8, or CD3 (triple-negative stage, TN). During cortical thymocyte maturation, CD4 and CD8 were coexpressed (double-positive stage, DP), like CD3, which was primarily cytoplasmic (cCD3) before being located at the cell surface (sCD3). Mature thymocytes in the medulla express either CD4 or CD8 (simple-positive stage, SP). CD6 expression appeared at a late DP stage. RAG-1 and RAG-2 were first involved in TCRβ chain rearrangements; their levels were substantially repressed during population expansion, which took place at the DP stage and then increased to induce α chain rearrangements. PBR and Bcl-2 expression were also bimodal, and increased, especially during DP to SP transition concomitantly with the selection process.