title: CD69 expression discriminates MHC-dependent and -independent stages of thymocyte positive selection.
abstract: In the thymus, phenotypically and functionally mature single positive cells are generated from immature CD4+8+ precursors by a process known as positive selection. Although this event is known to involve alphabetaTCR ligation by peptide/MHC complexes expressed on thymic stromal cells, it is clear that positive selection is a multistage process involving transition through an intermediate CD4+8+69+ phase as well as subsequent postselection phases. By analyzing the development of preselection CD4+8+69- and intermediate CD4+8+69+ thymocytes in the presence of MHC class I-deficient, MHC class II-deficient, and MHC double-deficient thymic stromal cells, we investigated the role of MHC molecules at three distinct points during positive selection. Although the initiation of positive selection is critically dependent upon MHC interactions, we find the that later stages of maturation, involving the differentiation of CD4+8- and CD4-8+ cells from CD4+8+69+ thymocytes, occur in the absence of MHC molecules. Moreover, an analysis of the postselection proliferation of newly generated CD4+8- and CD4-8+ thymocytes shows that this also occurs independently of MHC molecules. Thus, our data provide direct evidence that, although positive selection is a multistage process initiated by TCR-MHC interactions, continuation of this process and subsequent postselection events are independent of ongoing engagement of the TCR.
authors: Department of Anatomy, University of Birmingham Medical School, Edgbaston, United Kingdom. k.j.hare@bham.ac.uk
authors: K J
authors: KJ
authors: Hare
authors: E J
authors: EJ
authors: Jenkinson
authors: G
authors: G
authors: Anderson
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D015703:Antigens, CD / Q000096:biosynthesis*; D000945:Antigens, Differentiation, T-Lymphocyte / Q000096:biosynthesis*; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology / Q000378:metabolism; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology / Q000378:metabolism; D002449:Cell Aggregation / Q000276:immunology; D002455:Cell Division / Q000276:immunology; D004847:Epithelial Cells / Q000276:immunology / Q000378:metabolism; D037181:Lectins, C-Type; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009924:Organ Culture Techniques; D011948:Receptors, Antigen, T-Cell / Q000235:genetics; D013234:Stem Cells / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D016176:T-Lymphocyte Subsets / Q000166:cytology* / Q000276:immunology / Q000378:metabolism; D013950:Thymus Gland / Q000166:cytology* / Q000276:immunology / Q000378:metabolism; D000099192:CD69 Antigens
chemical_list: D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; D037181:Lectins, C-Type; D011948:Receptors, Antigen, T-Cell; D000099192:CD69 Antigens