title: CTLA-4 overexpression inhibits T cell responses through a CD28-B7-dependent mechanism.
abstract: CTLA-4 has been shown to be an important negative regulator of T cell activation. To better understand its inhibitory action, we constructed CTLA-4 transgenic mice that display constitutive cell surface expression of CTLA-4 on CD4 and CD8 T cells. In both in vivo and in vitro T cell responses, CTLA-4 overexpression inhibits T cell activation. This inhibition is dependent on B7 and CD28, suggesting that overexpressed CTLA-4 inhibits responses by competing with CD28 for B7 binding or by interfering with CD28 signaling. In addition, expression of the transgene decreases the number of CD25+Foxp3+ T cells in these mice, but does not affect their suppressive ability. Our data confirm the activity of CTLA-4 as a negative regulator of T cell activation and that its action may be by multiple mechanisms.
authors.affiliation: Division of Immunology, Howard Hughes Medical Institute, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
authors.forename: John J
authors.initials: JJ
authors.lastname: Engelhardt
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Sullivan
authors.forename: James P
authors.initials: JP
authors.lastname: Allison
mesh_terms: D000818:Animals; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000096:biosynthesis* / Q000235:genetics* / Q000502:physiology; D018122:B7-1 Antigen / Q000378:metabolism / Q000502:physiology*; D001667:Binding, Competitive / Q000235:genetics / Q000276:immunology; D018106:CD28 Antigens / Q000378:metabolism / Q000502:physiology*; D060908:CTLA-4 Antigen; D002454:Cell Differentiation / Q000235:genetics / Q000276:immunology; D002478:Cells, Cultured; D015536:Down-Regulation / Q000235:genetics* / Q000276:immunology*; D004681:Encephalomyelitis, Autoimmune, Experimental / Q000235:genetics / Q000276:immunology / Q000517:prevention & control; D018984:Epitopes, T-Lymphocyte / Q000235:genetics / Q000276:immunology; D006801:Humans; D008198:Lymph Nodes / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D008213:Lymphocyte Activation / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D018345:Mice, Knockout; D008822:Mice, Transgenic; D016192:Resting Phase, Cell Cycle / Q000235:genetics / Q000276:immunology; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology; D016176:T-Lymphocyte Subsets / Q000166:cytology / Q000276:immunology* / Q000378:metabolism*
chemical_list: D015703:Antigens, CD; D000943:Antigens, Differentiation; D018122:B7-1 Antigen; D018106:CD28 Antigens; D060908:CTLA-4 Antigen; C556706:CTLA4 protein, human; C556707:Ctla4 protein, mouse; D018984:Epitopes, T-Lymphocyte