title: TCR signaling for initiation and completion of thymocyte positive selection has distinct requirements for ligand quality and presenting cell type.
abstract: Thymocyte selection involves signaling by TCR engaging diverse self-peptide:MHC molecule ligands on various cell types in the cortex and medulla. Here we separately analyze early and late stages of selection to better understand how presenting cell type, ligand quality, and the timing of TCR signaling contribute to intrathymic differentiation. TCR transgenic CD4+CD8+ thymocytes (double positive (DP)) from MHC-deficient mice were stimulated using various presenting cells and ligands. The resulting CD69high cells were isolated and evaluated for maturation in reaggregate cultures with wild-type or MHC molecule-deficient thymic stroma with or without added hemopoietic dendritic cells (DC). Production of CD4+ T cells required TCR signaling in the reaggregates, indicating that transient recognition of self-ligands by DP is inadequate for full differentiation. DC bearing a potent agonist ligand could initiate positive selection, producing activated thymocytes that matured into agonist-responsive T cells in reaggregates lacking the same ligand. DC could also support the TCR signaling necessary for late maturation. These results argue that despite the negative role assigned to DC in past studies, neither the peptide:MHC molecule complexes present on DC nor any other signals provided by these cells stimulate only thymocyte death. These findings also indicate that unique epithelial ligands are not necessary for positive selection. They provide additional insight into the role of ligand quality in selection events and support the concept that following initiation of maturation from the DP state, persistent TCR signaling is characteristic of and perhaps required by T cells.
authors.affiliation: Lymphocyte Biology Section, Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: K
authors.initials: K
authors.lastname: Yasutomo
authors.forename: B
authors.initials: B
authors.lastname: Lucas
authors.forename: R N
authors.initials: RN
authors.lastname: Germain
mesh_terms: D000818:Animals; D000938:Antigen-Presenting Cells / Q000145:classification* / Q000201:enzymology / Q000276:immunology / Q000378:metabolism; D015703:Antigens, CD / Q000096:biosynthesis; D000945:Antigens, Differentiation, T-Lymphocyte / Q000096:biosynthesis; D015704:CD4 Antigens / Q000096:biosynthesis; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D016827:CD8 Antigens / Q000096:biosynthesis; D002449:Cell Aggregation / Q000276:immunology; D002454:Cell Differentiation / Q000276:immunology; D002470:Cell Survival / Q000276:immunology; D002478:Cells, Cultured; D003574:Cytochrome c Group / Q000276:immunology / Q000378:metabolism; D003713:Dendritic Cells / Q000201:enzymology / Q000276:immunology / Q000378:metabolism; D000949:Histocompatibility Antigens Class II / Q000378:metabolism; D016130:Immunophenotyping; D037181:Lectins, C-Type; D008024:Ligands; D008213:Lymphocyte Activation; D008285:Major Histocompatibility Complex / Q000276:immunology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D010455:Peptides / Q000819:agonists / Q000276:immunology / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000819:agonists / Q000096:biosynthesis; D011948:Receptors, Antigen, T-Cell / Q000502:physiology*; D015398:Signal Transduction / Q000276:immunology*; D017154:Stromal Cells / Q000276:immunology / Q000378:metabolism; D016176:T-Lymphocyte Subsets / Q000166:cytology* / Q000276:immunology / Q000378:metabolism*; D013950:Thymus Gland / Q000166:cytology* / Q000276:immunology / Q000378:metabolism*; D015854:Up-Regulation / Q000276:immunology; D000099192:CD69 Antigens
chemical_list: D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; D015704:CD4 Antigens; D016827:CD8 Antigens; D003574:Cytochrome c Group; D000949:Histocompatibility Antigens Class II; D037181:Lectins, C-Type; D008024:Ligands; D010455:Peptides; D019253:Proto-Oncogene Proteins c-bcl-2; D011948:Receptors, Antigen, T-Cell; D000099192:CD69 Antigens; C024138:I-E-antigen