Selecting and maintaining a diverse T-cell repertoire

To provide a T-cell population that will respond promptly to foreign antige n, the immune system looks inward, using the variety of self-antigens to se lect and maintain a diverse repertoire of receptors. A protective Immune sy stem must include a T-lymphocyte population that is poised to respond to fo reign antigenic peptides presented by self-major histocompatibility complex molecules. As the organism cannot predict the precise pathogen-derived ant igens that will he encountered, the system uses the diverse array of self-p eptides bound to self-major histocompatibility complex molecules, not only to select a receptor repertoire in the thymus, but also to keep naive T cel ls alive and 'ready for action' in the periphery.