title: Activation events during thymic selection.
abstract: During their differentiation in the mouse thymus, CD4+8- cells undergo several of the sequential changes observed upon normal activation of mature, peripheral CD4+ lymphocytes. Expression of CD69, an early activation marker, is first observed on a minority of cells at the T cell receptor (TCR)lo/med double-positive stage, is maximal (50-90%) on heat-stable antigen (HSA)hi TCRhi double-positive, HSAhi TCRmed CD4+8lo, and HSAhi TCRhi CD4+8- cells, and is downmodulated at the mature HSAlo CD4+8- stage. In contrast, CD44, a late activation marker, is selectively expressed at the HSAlo stage. The set of lymphokines that CD4+8- thymocytes can produce upon stimulation also characteristically expands from mainly interleukin 2 (IL-2) at the HSAhi stage, to IL-2 and very large amounts of IL-4, IL-5, IL-10, and interferon gamma (IFN-gamma) at the HSAlo stage. 1 in 30 HSAlo CD4+8- adult thymocytes secrete IL-4 upon stimulation through their TCR. This frequency is 25% of the frequency of IL-2 producers, about 100-fold above that of peripheral (mainly resting) CD4+ T cells. With time after their generation in organ culture, CD4+8- thymocytes lose their capacity to secrete IL-4, IL-5, and IFN-gamma, but not IL-2. Similarly, the frequency of IL-4, but not of IL-2, producers progressively decreases after emigration to the periphery as judged by direct comparison between thymic and splenic CD4+ cells in newborns, or by following the fate of intrathymically labeled CD4+8- cells in adults after their migration to the spleen. This sequence suggests that thymic selection results from an activation process rather than a simple rescue from death at the double-positive stage, and shows that the functional changes induced after intrathymic activation, although transient, are still evident after export to the periphery.
authors.affiliation: Laboratory of Cellular and Molecular Immunology, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland 20892.
authors.forename: A
authors.initials: A
authors.lastname: Bendelac
authors.forename: P
authors.initials: P
authors.lastname: Matzinger
authors.forename: R A
authors.initials: RA
authors.lastname: Seder
authors.forename: W E
authors.initials: WE
authors.lastname: Paul
authors.forename: R H
authors.initials: RH
authors.lastname: Schwartz
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000276:immunology; D000945:Antigens, Differentiation, T-Lymphocyte / Q000276:immunology; D015704:CD4 Antigens / Q000032:analysis; D016827:CD8 Antigens / Q000032:analysis; D002454:Cell Differentiation; D005333:Fetus; D007371:Interferon-gamma / Q000378:metabolism; D007376:Interleukin-2 / Q000378:metabolism; D015847:Interleukin-4 / Q000378:metabolism; D037181:Lectins, C-Type; D008213:Lymphocyte Activation / Q000502:physiology*; D051379:Mice; D008806:Mice, Inbred AKR; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D009924:Organ Culture Techniques; D013154:Spleen / Q000166:cytology; D013601:T-Lymphocytes / Q000276:immunology*; D013950:Thymus Gland / Q000166:cytology* / Q000196:embryology; D000099192:CD69 Antigens
chemical_list: D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; D015704:CD4 Antigens; D016827:CD8 Antigens; D007371:Interferon-gamma; D007376:Interleukin-2; D015847:Interleukin-4; D037181:Lectins, C-Type; D000099192:CD69 Antigens