Thymic selection

The ability of T celss to recognize foreign antigens, distinguish them from self antigens, and regulate immune responses depends largely on which of the vast array of different T-cell receptors they display on their surface, the so called T-cell repertoire. Two selection processes, positive and negative selection, operate on developing T cells and allow only a subset of all possible T cells to differentiate. New developments in transgenic mouse technology and the study of T-cell signalling are unravelling these fascinating processes.