Positive selection of thymocytes: the long and winding road

Positive selection is a crucial stage in T-cell development because it is h ere that CD4(+)CD8(+) cells bearing T-cell receptors that interact with sel f-major histocompatibility complex molecules are rescued from cell death, r esulting in the generation of mature T cells. Here, Graham Anderson and col leagues review recent studies indicating that positive selection is a multi stage process involving interactions with thymic epithelium.