Thymus machinery for T-cell selection.

An immunocompetent and self-tolerant pool of naive T cells is formed in the thymus through the process of repertoire selection. T cells that are potentially capable of responding to foreign antigens are positively selected in the thymic cortex and are further selected in the thymic medulla to help prevent self-reactivity. The affinity between T-cell antigen-receptors (TCRs) expressed by newly generated T cells and self-peptide-MHC complexes displayed in the thymic microenvironments plays a key role in determining the fate of developing T cells during thymic selection. Recent advances in our knowledge of the biology of thymic epithelial cells have revealed unique machinery that contributes to positive and negative selection in the thymus. In this article, we summarize recent findings on thymic T-cell selection, focusing on the machinery unique to thymic epithelial cells.