Ligand-Stimulated Signaling Events in Immature CD4+CD8+Thymocytes ExpressingCompetent T-Cell Receptor Complexes

摘要

During thymic selection of the developing T-cell repertoire, the fate ofindividual CD4+CD8+thymocytes is determined by the specificity of the T-cell antigen receptors (TCRs) they express. Paradoxically, most CD4+CD8+thymocytes express few TRC molecules, and those they express are essentially incapable of transducing intracellular signals as measured by intracellular calcium mobilization. However, both TCR number and calcium signaling capability are significantly induced in CD4+CD8+thymocytes when the cells are released from intrathymic inhibitory signals that are mediated by their CD4 molecules. In the thymus, developing CD4+CD8+thymocytes encounter Ia thymic epithelial cells that engage their CD4 molecules and induce intracellular signals that contribute to the low surface T-cell antigen receptor (TCR) phenotype of most immature CD4+CD8+thymocytes.