title: Divergent expression of IL-1 receptor antagonists in CD34⁺ fibrocytes and orbital fibroblasts in thyroid-associated ophthalmopathy: contribution of fibrocytes to orbital inflammation.
abstract: BACKGROUND
  Thyroid-associated ophthalmopathy (TAO) manifests as inflammation of orbital connective tissue. Bone marrow-derived CD34⁺ fibrocytes infiltrate the orbit in TAO where they become CD34⁺ orbital fibroblasts. They express thyroid-specific antigens and thus may contribute to inflammation. Evidence suggests that orbital susceptibility to TAO may involve IL-1, which is modulated by IL-1 receptor antagonists, designated secreted (sIL-1RA) and intracellular (icIL-1RA).
  
  
  OBJECTIVE
  We sought to characterize the expression of sIL-1RA and icIL-1RA in TAO orbital fibroblasts compared to CD34⁺ fibrocytes.
  
  
  METHODS
  Patients with TAO and healthy donors were recruited from an academic medical center clinical practice.
  
  
  METHODS
  Real-time PCR, cytokine-specific ELISA, gene promoter activities, transcriptional analysis, mRNA stability, and cytometric cell sorting were performed.
  
  
  RESULTS
  Orbital fibroblasts treated with IL-1β exhibit greater inductions of IL-1α, IL-1β, and prostaglandin endoperoxide H synthase-2 transcripts than do fibrocytes. Fibrocytes express dramatically higher basal levels of both icIL-1RA and sIL-1RA. When treated with IL-1β, icIL-1RA is induced in orbital fibroblasts but not sIL-1RA, whereas in fibrocytes, sIL-1RA is dominantly up-regulated. These inductions result from increased steady-state levels of respective mRNAs, enhanced transcript stabilities, and modestly increased gene transcription.
  
  
  CONCLUSIONS
  Robust responses of TAO orbital fibroblasts to IL-1β are a consequence of low-level sIL-1RA expression. This results in poorly opposed actions of IL-1β. In contrast, circulating fibrocytes express high levels of sIL-1RA, which are diminished as these cells transition to orbital fibroblasts. These findings identify an explanation for the inflammatory phenotype exhibited by TAO orbital fibroblasts and provide a potential target for altering disease susceptibility.
authors: Department of Ophthalmology and Visual Sciences, University of Michigan Medical School, Ann Arbor, Michigan 48105, USA.
authors: Bin
authors: B
authors: Li
authors: Terry J
authors: TJ
authors: Smith
mesh_terms: D018952:Antigens, CD34 / Q000378:metabolism*; D054338:Cell Transdifferentiation; D002478:Cells, Cultured; D051546:Cyclooxygenase 2 / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D004198:Disease Susceptibility; D005347:Fibroblasts / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D005786:Gene Expression Regulation; D049970:Graves Ophthalmopathy / Q000276:immunology / Q000378:metabolism* / Q000473:pathology / Q000601:surgery; D006801:Humans; D053590:Interleukin 1 Receptor Antagonist Protein / Q000235:genetics / Q000378:metabolism*; D053582:Interleukin-1alpha / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D053583:Interleukin-1beta / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D007962:Leukocytes / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D009915:Orbit / Q000276:immunology / Q000378:metabolism* / Q000473:pathology / Q000601:surgery; D011401:Promoter Regions, Genetic; D020871:RNA Stability; D012333:RNA, Messenger / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism
chemical_list: D018952:Antigens, CD34; C508584:IL1A protein, human; C508585:IL1B protein, human; C507763:IL1RN protein, human; D053590:Interleukin 1 Receptor Antagonist Protein; D053582:Interleukin-1alpha; D053583:Interleukin-1beta; D012333:RNA, Messenger; D011994:Recombinant Proteins; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human
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