title: CTLA-4 (CD152) controls homeostasis and suppressive capacity of regulatory T cells in mice.
abstract: OBJECTIVE
  CD4+CD25+ regulatory T cells (known as Treg cells) suppress unwanted and autoreactive T cell responses. Treg cells express the costimulatory molecule CTLA-4 intracellularly, but the mechanisms by which Treg cells exploit CTLA-4 signaling remain unclear. The present study was undertaken to investigate the role of CTLA-4 in controlling the homeostasis and suppressive function of Treg cells.
  
  
  METHODS
  Murine Treg cells were analyzed by flow cytometry for coexpression of CTLA-4 and typical Treg cell-expressed molecules, and the influence of CTLA-4 on T cell proliferation, suppression, and apoptosis was investigated by in vitro assays. To analyze the importance of CTLA-4 in Treg cell-mediated suppression in vivo, wild-type Treg cells were transferred into CTLA-4-deficient mice displaying lymphoproliferation, and survival was monitored over time.
  
  
  RESULTS
  A strong correlation between expression of forkhead box P3 and ex vivo expression of CTLA-4 in Treg cells was observed. Inhibition of CTLA-4 signaling in Treg cells during in vitro stimulation increased cell cycling and led to enhanced activation-induced cell death (AICD), which was mediated by CD95/CD95 ligand-induced activation of caspases. Blockade of CTLA-4 signaling resulted in impairment of the suppressive capacity of Treg cells. Despite these effects, high amounts of Treg cells persisted in CTLA-4-deficient mice. Results of transfer experiments in CTLA-4-deficient mice showed that the mice had a significantly prolonged lifespan when CTLA-4-competent Treg cells were injected.
  
  
  CONCLUSIONS
  Expression of CTLA-4 on Treg cells serves to control T cell proliferation, to confer resistance against AICD, and to maintain the suppressive function of Treg cells.
authors.affiliation: Deutsches Rheuma-Forschungszentrum Berlin, and Charité-University Hospital, Berlin, Germany.
authors.forename: Paula
authors.initials: P
authors.lastname: Kolar
authors.forename: Karin
authors.initials: K
authors.lastname: Knieke
authors.forename: J Kolja E
authors.initials: JK
authors.lastname: Hegel
authors.forename: Dagmar
authors.initials: D
authors.lastname: Quandt
authors.forename: Gerd-R
authors.initials: GR
authors.lastname: Burmester
authors.forename: Holger
authors.initials: H
authors.lastname: Hoff
authors.forename: Monika C
authors.initials: MC
authors.lastname: Brunner-Weinzierl
mesh_terms: D019264:Adoptive Transfer; D000818:Animals; D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism*; D015704:CD4 Antigens / Q000378:metabolism; D060908:CTLA-4 Antigen; D016923:Cell Death / Q000276:immunology; D002455:Cell Division / Q000276:immunology; D002470:Cell Survival / Q000276:immunology; D002478:Cells, Cultured; D005434:Flow Cytometry; D051858:Forkhead Transcription Factors / Q000378:metabolism; D006706:Homeostasis / Q000276:immunology*; D053645:Interleukin-2 Receptor alpha Subunit / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D015398:Signal Transduction / Q000276:immunology*; D050378:T-Lymphocytes, Regulatory / Q000166:cytology / Q000378:metabolism*
chemical_list: D015703:Antigens, CD; D015704:CD4 Antigens; D060908:CTLA-4 Antigen; C556707:Ctla4 protein, mouse; D051858:Forkhead Transcription Factors; C498833:Foxp3 protein, mouse; C508018:Il2ra protein, mouse; D053645:Interleukin-2 Receptor alpha Subunit