Proposed pathway for the discharge of immature thymocytes from thymuses of E
-injected female B6A mice. The top diagram (A) depicts the typical thymocyte maturation pathway, beginning with the sub-capsular entry of prothymocytes into the cortex and the expression of Thy-1. Maturation continues through CD3-CD4-CD8- triple negative (TN) stages and the development of the T cell receptor (TcR). Subsequent expression of CD3 produces CD3+CD4- CD8- double negative (DN) cells with αβ TcR. After expression of CD4 and CD8, the CD4+CD8+ double positive (DP) cells undergo the process of positive selection. Surviving DP cells pass through the corticomedullary junction into the medulla. Here, they are transformed into CD4+ (SP) and CD8+ (SP) T cells, and in the process, autoreactive T cells are eliminated. Mature SP T cells then exit the thymus at the corticomedullary junction. The bottom diagram (B) shows how the E2-induced increase in vascular permeability is proposed to affect thymocyte maturation. Thymocytes, rather than expressing CD4+ and CD8+ and continuing into the medulla, exit the thymus at the corticomedullary junction. Maturation into SP T cells then takes place in the sinusoids of the liver.