Figure 1.

Mouse thymocyte development scheme. Mouse T cells develop in the thymus from early thymic progenitors (ETPs) to mature thymocytes that are single positive for CD4 (SP4) or CD8 (SP8). (A) shows the maturational pathway from the ETPs to the intermediate CD8 single positives (ISPs). (B) shows the maturation from the ISP stage to the most mature single positive stages. DP = double positive for CD4 and CD8, DN = double negative for CD4 and CD8, TCR = T cell receptor. Surface antigens used to discriminate the subsets and important developmental events are noted. Thymocyte subsets not directly in the T cell lineage are not depicted. Non-T-lineage markers (Lin) used for discrimination are also not depicted.