title: A requirement for IL-2/IL-2 receptor signaling in intrathymic negative selection.
abstract: The nature of the signals that influence thymocyte selection and determine the fate of CD4(+)8(+) (double positive) thymocytes remains unclear. Cytokines produced locally in the thymus may modulate signals delivered by TCR-MHC/peptide interactions and thereby influence the fate of double-positive thymocytes. Because the IL-2/IL-2R signaling pathway has been implicated in thymocyte and peripheral T cell survival, we investigated the possibility that IL-2/IL-2R interactions contribute to the deletion of self-reactive, Ag-specific thymocytes. By using nontransgenic and transgenic IL-2-sufficient and -deficient animal model systems, we have shown that during TCR-mediated thymocyte apoptosis, IL-2 protein is expressed in situ in the thymus, and apoptotic thymocytes up-regulate expression of IL-2RS: IL-2R(+) double-positive and CD4 single-positive thymocytes undergoing activation-induced cell death bind and internalize IL-2. IL-2-deficient thymocytes are resistant to TCR/CD3-mediated apoptotic death, which is overcome by providing exogenous IL-2 to IL-2(-/-) mice. Furthermore, disruption or blockade of IL-2/IL-2R interactions in vivo during Ag-mediated selection rescues some MHC class II-restricted thymocytes from apoptosis. Collectively, these findings provide evidence for the direct involvement of the IL-2/IL-2R signaling pathway in the deletion of Ag-specific thymocyte populations and suggest that CD4 T cell hyperplasia and autoimmunity in IL-2(-/-) mice is a consequence of ineffective deletion of self-reactive T cells.
authors.affiliation: Department of Clinical Studies, University of Pennsylvania, School of Veterinary Medicine, Philadelphia, PA 19014, USA.
authors.forename: H
authors.initials: H
authors.lastname: Bassiri
authors.forename: S R
authors.initials: SR
authors.lastname: Carding
mesh_terms: D000818:Animals; D019138:Antibodies, Blocking / Q000494:pharmacology; D017209:Apoptosis / Q000276:immunology; D017637:Clonal Deletion / Q000276:immunology*; D018984:Epitopes, T-Lymphocyte / Q000096:biosynthesis; D007106:Immune Sera / Q000494:pharmacology; D007376:Interleukin-2 / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D011485:Protein Binding / Q000276:immunology; D017260:Receptor-CD3 Complex, Antigen, T-Cell / Q000502:physiology; D011948:Receptors, Antigen, T-Cell / Q000276:immunology / Q000378:metabolism; D015375:Receptors, Interleukin-2 / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction / Q000276:immunology*; D016176:T-Lymphocyte Subsets / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D013950:Thymus Gland / Q000166:cytology* / Q000276:immunology / Q000378:metabolism*
chemical_list: D019138:Antibodies, Blocking; D018984:Epitopes, T-Lymphocyte; D007106:Immune Sera; D007376:Interleukin-2; D017260:Receptor-CD3 Complex, Antigen, T-Cell; D011948:Receptors, Antigen, T-Cell; D015375:Receptors, Interleukin-2