title: The anatomy of T-cell activation and tolerance.
abstract: The mammalian immune system must specifically recognize and eliminate foreign invaders but refrain from damaging the host. This task is accomplished in part by the production of a large number of T lymphocytes, each bearing a different antigen receptor to match the enormous variety of antigens present in the microbial world. However, because antigen receptor diversity is generated by a random mechanism, the immune system must tolerate the function of T lymphocytes that by chance express a self-reactive antigen receptor. Therefore, during early development, T cells that are specific for antigens expressed in the thymus are physically deleted. The population of T cells that leaves the thymus and seeds the secondary lymphoid organs contains helpful cells that are specific for antigens from microbes but also potentially dangerous T cells that are specific for innocuous extrathymic self antigens. The outcome of an encounter by a peripheral T cell with these two types of antigens is to a great extent determined by the inability of naive T cells to enter nonlymphoid tissues or to be productively activated in the absence of inflammation.
authors.affiliation: Department of Microbiology and the Center for Immunology, University of Minnesota Medical School, Minneapolis 55455, USA.
authors.forename: A
authors.initials: A
authors.lastname: Mondino
authors.forename: A
authors.initials: A
authors.lastname: Khoruts
authors.forename: M K
authors.initials: MK
authors.lastname: Jenkins
mesh_terms: D000818:Animals; D000917:Antibody Formation; D000941:Antigens / Q000276:immunology; D001402:B-Lymphocytes / Q000276:immunology; D017637:Clonal Deletion; D006801:Humans; D007108:Immune Tolerance; D008208:Lymphatic System / Q000276:immunology; D008213:Lymphocyte Activation; D011971:Receptors, Immunologic / Q000502:physiology; D013601:T-Lymphocytes / Q000276:immunology*; D013950:Thymus Gland / Q000166:cytology / Q000276:immunology
chemical_list: D000941:Antigens; D011971:Receptors, Immunologic