Analysis of CD4/CD8 Lineage Commitment by Pronase Treatment and Reexpression Assay

During the developmental process of T cells in the thymus, immature CD4CD8 double positive thymocytes (DP) are subject to undergo positive selection process to become either CD4 single positive (SP) or CD8-SP mature cells (1 –3 ). Since both CD4-SP and CD8-SP mature T cells are the progeny of immature DP thymocytes, positive selection requires a lineage commitment step in which synthesis of one or the other coreceptor molecule is terminated. The mechanism of CD4/8 lineage commitment process, i.e., how does thymocyte stop one or the other coreceptor synthesis, is still unclear although many types of models have been presented (4 –10 ).