title: AhR mediates an anti-inflammatory feedback mechanism in human Langerhans cells involving FcεRI and IDO.
abstract: BACKGROUND
  Aryl hydrocarbon receptor (AhR), an important regulator of immune responses, is activated by UVB irradiation in the skin. Langerhans cells (LC) in the epidermis of patients with atopic dermatitis (AD) carry the high-affinity receptor for IgE, FcεRI, and are crucially involved in the pathogenesis of AD by inducing inflammatory responses and regulating tolerogenic processes.
  
  
  OBJECTIVE
  We investigated AhR and AhR repressor (AhRR) expression and functional consequences of AhR activation in human ex vivo skin cells and in in vitro-generated LC.
  
  
  METHODS
  Epidermal cells from healthy skin were analyzed for their expression of AhR and AhRR. LC generated from CD34+hematopoietic stem cells (CD34LC) were treated with the UV photoproduct and AhR ligand 6-formylindolo[3,2-b]carbazole (FICZ). Cell surface receptors, transcription factors, and the tolerogenic tryptophan-degrading enzyme indoleamine 2,3-dioxygenase (IDO) were analyzed using flow cytometry and quantitative PCR.
  
  
  RESULTS
  Epidermal LC and CD34LC express AhR and AhRR. AhR was also found in keratinocytes, which lack AhRR. AhR activation of LC by FICZ caused downregulation of FcεRI in CD34LC without affecting their maturation. AhR-mediated regulation of FcεRI did not involve any known transcription factors related to this receptor. Furthermore, we could show upregulation of IDO mediated by AhR engagement.
  
  
  CONCLUSIONS
  Our study shows that AhR activation by FICZ reduces FcεRI and upregulates IDO expression in LC. This AhR-mediated anti-inflammatory feedback mechanism may dampen the allergen-induced inflammation in AD.
authors.affiliation: Department of Dermatology and Allergy, Christine Kühne - Center for Allergy Research and Education (CK-CARE), University of Bonn, Bonn, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Koch
authors.affiliation: Department of Dermatology and Allergy, Christine Kühne - Center for Allergy Research and Education (CK-CARE), University of Bonn, Bonn, Germany.
authors.forename: T J
authors.initials: TJ
authors.lastname: Stroisch
authors.affiliation: LIMES Institute, Immunology and Environment, University of Bonn, Bonn, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Vorac
authors.affiliation: Department of Dermatology and Allergy, Christine Kühne - Center for Allergy Research and Education (CK-CARE), University of Bonn, Bonn, Germany.
authors.forename: N
authors.initials: N
authors.lastname: Herrmann
authors.affiliation: Department of Dermatology and Allergy, Christine Kühne - Center for Allergy Research and Education (CK-CARE), University of Bonn, Bonn, Germany.
authors.forename: N
authors.identifier: http://orcid.org/0000-0002-4795-5010
authors.initials: N
authors.lastname: Leib
authors.affiliation: Department of Dermatology and Allergy, Christine Kühne - Center for Allergy Research and Education (CK-CARE), University of Bonn, Bonn, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Schnautz
authors.affiliation: Department of Dermatology and Allergy, Christine Kühne - Center for Allergy Research and Education (CK-CARE), University of Bonn, Bonn, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Kirins
authors.affiliation: LIMES Institute, Immunology and Environment, University of Bonn, Bonn, Germany.
authors.forename: I
authors.initials: I
authors.lastname: Förster
authors.affiliation: LIMES Institute, Immunology and Environment, University of Bonn, Bonn, Germany.|Innate Immunity and Extrinsic Skin Aging, IUF - Leibniz Research Institute for Environmental Medicine, Düsseldorf, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Weighardt
authors.affiliation: Department of Dermatology and Allergy, Christine Kühne - Center for Allergy Research and Education (CK-CARE), University of Bonn, Bonn, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Bieber
mesh_terms: D000328:Adult; D051792:Basic Helix-Loop-Helix Proteins / Q000502:physiology*; D003876:Dermatitis, Atopic / Q000276:immunology*; D025461:Feedback, Physiological / Q000502:physiology*; D005260:Female; D006801:Humans; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase / Q000378:metabolism; D007249:Inflammation / Q000276:immunology*; D007801:Langerhans Cells / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D018336:Receptors, Aryl Hydrocarbon / Q000502:physiology*; D017455:Receptors, IgE / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; D018336:Receptors, Aryl Hydrocarbon; D017455:Receptors, IgE; D012097:Repressor Proteins; C111235:AHR protein, human
keywords: Ah receptor; Fc epsilon receptor; Langerhans cells; atopic dermatitis; indoleamine 2,3-dioxygenase