title: Promiscuous Foxp3-cre activity reveals a differential requirement for CD28 in Foxp3⁺ and Foxp3⁻ T cells.
abstract: Costimulatory signals by CD28 are critical for thymic regulatory T-cell (Treg) development. To determine the functional relevance of CD28 for peripheral Treg post thymic selection, we crossed the widely used Forkhead box protein 3 (Foxp3)-CreYFP mice to mice bearing a conditional Cd28 allele. Treg-specific CD28 deficiency provoked a severe autoimmune syndrome as a result of a strong disadvantage in competitive fitness and proliferation of CD28-deficient Tregs. By contrast, Treg survival and lineage integrity were not affected by the lack of CD28. This data demonstrate that, even after the initial induction requirement, Treg maintain a higher dependency on CD28 signalling than conventional T cells for homeostasis. In addition, we found the Foxp3-CreYFP allele to be a hypomorph, with reduced Foxp3 protein levels. Furthermore, we report here the stochastic activity of the Foxp3-CreYFP allele in non-Tregs, sufficient to recombine some conditional alleles (including Cd28) but not others (including R26-RFP). This hypomorphism and 'leaky' expression of the Foxp3-CreYFP allele should be considered when analysing the conditionally mutated Treg.
authors.affiliation: 1] Autoimmune Genetics Laboratory, VIB, Leuven, Belgium [2] Department of Microbiology and Immunology, University of Leuven, Leuven, Belgium.
authors.forename: Dean
authors.initials: D
authors.lastname: Franckaert
authors.affiliation: 1] Autoimmune Genetics Laboratory, VIB, Leuven, Belgium [2] Department of Microbiology and Immunology, University of Leuven, Leuven, Belgium.
authors.forename: James
authors.initials: J
authors.lastname: Dooley
authors.affiliation: 1] Autoimmune Genetics Laboratory, VIB, Leuven, Belgium [2] Department of Microbiology and Immunology, University of Leuven, Leuven, Belgium.
authors.forename: Evelyne
authors.initials: E
authors.lastname: Roos
authors.affiliation: Department of Experimental Immunology, Helmholtz Centre for Infection Research, Braunschweig, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Floess
authors.affiliation: Department of Experimental Immunology, Helmholtz Centre for Infection Research, Braunschweig, Germany.
authors.forename: Jochen
authors.initials: J
authors.lastname: Huehn
authors.affiliation: 1] Centre d'Immunologie de Marseille-Luminy (CIML), UM2 Aix-Marseille Université, Marseille Cedex 9, France [2] INSERM U1104, Marseille Cedex 9, France [3] CNRS UMR7280, Marseille Cedex 9, France.
authors.forename: Herve
authors.initials: H
authors.lastname: Luche
authors.affiliation: Institute of Immunology, University Clinics Ulm, Ulm, Germany.
authors.forename: Hans Joerg
authors.initials: HJ
authors.lastname: Fehling
authors.affiliation: 1] Autoimmune Genetics Laboratory, VIB, Leuven, Belgium [2] Department of Microbiology and Immunology, University of Leuven, Leuven, Belgium.
authors.forename: Adrian
authors.initials: A
authors.lastname: Liston
authors.affiliation: Lymphocyte Signalling and Development, Babraham Institute, Babraham Research Campus, Cambridge, UK.
authors.forename: Michelle A
authors.initials: MA
authors.lastname: Linterman
authors.affiliation: 1] Autoimmune Genetics Laboratory, VIB, Leuven, Belgium [2] Department of Microbiology and Immunology, University of Leuven, Leuven, Belgium.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Schlenner
mesh_terms: D000818:Animals; D015551:Autoimmunity / Q000235:genetics; D018106:CD28 Antigens / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation / Q000235:genetics; D019070:Cell Lineage / Q000235:genetics; D002470:Cell Survival / Q000235:genetics; D060966:Clonal Selection, Antigen-Mediated / Q000235:genetics; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D006706:Homeostasis; D051379:Mice; D008822:Mice, Transgenic; D015398:Signal Transduction / Q000235:genetics; D016176:T-Lymphocyte Subsets / Q000502:physiology*; D050378:T-Lymphocytes, Regulatory / Q000502:physiology*
chemical_list: D018106:CD28 Antigens; D051858:Forkhead Transcription Factors; C498833:Foxp3 protein, mouse