title: Role of CTLA-4 in the activation of single- and double-positive thymocytes.
abstract: CTLA-4, a homologue of CD28, is a negative regulator of T cell activation in the periphery and is transiently expressed on the cell surface after T cell activation. However, the role of CTLA-4 in T cell activation in the thymus is not clear. This investigation was initiated to determine the role of CTLA-4 in the activation of CD4(+)CD8(+) double-positive (DP) and CD4(+)CD8(-) and CD4(-)CD8(+) single-positive (SP) thymocytes using fetal thymic organ cultures (FTOC) of MHC class II-restricted, OVA(323-339)-restricted TCR transgenic mice (DO11.10). We found that treatment of the FTOC with anti-CTLA-4-blocking Ab during activation with OVA(323-339) increased the proportion and number of DP thymocytes, but decreased the proportion and number of SP thymocytes compared with OVA(323-339)-stimulated FTOC without anti-CTLA-4 Ab treatment. In addition, anti-CTLA-4 Ab treatment inhibited OVA(323-339)-induced expression of the early activation marker, CD69, in DP thymocytes, but increased CD69 in SP thymocytes. Similarly, CTLA-4 blockage decreased phosphorylation of ERK in DP thymocytes by Ag-specific TCR engagement, but increased phosphorylation of ERK in SP thymocytes. CTLA-4 blockage inhibited deletion of DP thymocytes treated with a high dose of OVA(323-339), whereas CTLA-4 blockage did not inhibit deletion of DP thymocytes treated with a low dose of OVA(323-339). We conclude that CTLA-4 positively regulates the activation of DP thymocytes, resulting in their deletion, whereas blocking CTLA-4 suppresses the activation of DP thymocytes, leading to inhibition of DP thymocyte deletion. In contrast, CTLA-4 negatively regulates the activation of SP thymocytes.
authors.affiliation: Julia McFarlane Diabetes Research Center, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Hyokjoon
authors.initials: H
authors.lastname: Kwon
authors.forename: Hee-Sook
authors.initials: HS
authors.lastname: Jun
authors.forename: Lee-Yong
authors.initials: LY
authors.lastname: Khil
authors.forename: Ji-Won
authors.initials: JW
authors.lastname: Yoon
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019138:Antibodies, Blocking / Q000494:pharmacology; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D015704:CD4 Antigens / Q000096:biosynthesis*; D016827:CD8 Antigens / Q000096:biosynthesis*; D060908:CTLA-4 Antigen; D017637:Clonal Deletion; D015536:Down-Regulation / Q000276:immunology; D018984:Epitopes, T-Lymphocyte / Q000276:immunology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D005260:Female; D008213:Lymphocyte Activation / Q000276:immunology*; D018655:Lymphocyte Count; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D009924:Organ Culture Techniques; D011948:Receptors, Antigen, T-Cell / Q000276:immunology / Q000378:metabolism; D015398:Signal Transduction / Q000276:immunology; D016176:T-Lymphocyte Subsets / Q000201:enzymology / Q000276:immunology* / Q000378:metabolism*; D013950:Thymus Gland / Q000166:cytology / Q000201:enzymology / Q000276:immunology* / Q000378:metabolism*; D015854:Up-Regulation / Q000276:immunology
chemical_list: D019138:Antibodies, Blocking; D015703:Antigens, CD; D000943:Antigens, Differentiation; D015704:CD4 Antigens; D016827:CD8 Antigens; D060908:CTLA-4 Antigen; C556707:Ctla4 protein, mouse; D018984:Epitopes, T-Lymphocyte; D011948:Receptors, Antigen, T-Cell; D048049:Extracellular Signal-Regulated MAP Kinases