Positive and negative selection of the alpha beta T-cell repertoire in vivo.

The selection of developing and mature alpha beta T cells, by intrathymic and extra-thymic ligands expressed on cells of hemopoietic and other origins, has been studied in a variety of systems. These experiments have increased our knowledge of the selection of alpha beta T cells in the thymus, in the presence or absence of specific peptides bound to MHC, and also made clear that additional selective mechanisms exist outside the thymus that can be exploited to silence mature T cells.