title: Tumour necrosis factor alpha-driven IL-32 expression in rheumatoid arthritis synovial tissue amplifies an inflammatory cascade.
abstract: OBJECTIVE
  To investigate the interplay between IL-32 and tumour necrosis factor alpha (TNFα) during the chronic inflammation of rheumatoid arthritis (RA) and to assess whether anti-TNFα treatment of RA patients modulates synovial IL-32 expression.
  
  
  METHODS
  Induction of IL-32γ by Pam3Cys, lipopolysaccharide, IL-1β or TNFα was investigated in human fibroblast-like synoviocytes (FLS). Stimulation of TNFα production by IL-32γ was studied by adenoviral overexpression of IL-32γ (AdIL-32γ) and lipopolysaccharide stimulation of THP1 cells. Silencing of endogenous IL-32 was employed to study cytokine regulation in FLS. AdIL-32γ followed by TNFα stimulation was performed in FLS to investigate cytokine induction. Immunohistochemistry was applied to study IL-32 expression in synovial biopsies from RA patients.
  
  
  RESULTS
  TNFα potently induced IL-32γ expression in FLS. Increased TNFα, IL-1β, IL-6 and CXCL8 production was observed after IL-32γ overexpression and lipopolysaccharide stimulation of THP1 cells. TNFα stimulation of FLS after silencing IL-32γ resulted in diminished IL-6 and CXCL8 production, whereas IL-32γ overexpression resulted in enhanced IL-6 and CXCL8 levels. Remarkably, the mechanism through which IL-32γ overexpression induced TNFα, IL-1β and CXCL8 was by counteracting messenger RNA decay. Importantly, treatment of RA patients with anti-TNFα resulted in significant reduction of IL-32 protein in synovial tissue.
  
  
  CONCLUSIONS
  TNFα is a potent inducer of endogenous IL-32 expression and IL-32 itself contributes to prolonged TNFα production, thus inducing an important auto-inflammatory loop. Treatment of RA patients with anti-TNFα antibodies diminished IL-32 expression in synovial tissue. The potent anti-inflammatory effect of TNFα blockade in RA patients may be partly due to the reduction of synovial IL-32 expression.
authors.affiliation: Rheumatology Research and Advanced Therapeutics, Department of Rheumatology, Radboud University Nijmegen Medical Centre, PO Box 9101, 6500HB, Nijmegen, The Netherlands. s.heinhuis@reuma.umcn.nl
authors.forename: Bas
authors.initials: B
authors.lastname: Heinhuis
authors.forename: Marije I
authors.initials: MI
authors.lastname: Koenders
authors.forename: Piet L
authors.initials: PL
authors.lastname: van Riel
authors.forename: Fons A
authors.initials: FA
authors.lastname: van de Loo
authors.forename: Charles A
authors.initials: CA
authors.lastname: Dinarello
authors.forename: Mihai G
authors.initials: MG
authors.lastname: Netea
authors.forename: Wim B
authors.initials: WB
authors.lastname: van den Berg
authors.forename: Leo A B
authors.initials: LA
authors.lastname: Joosten
mesh_terms: D018501:Antirheumatic Agents / Q000494:pharmacology; D001172:Arthritis, Rheumatoid / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D002478:Cells, Cultured; D005347:Fibroblasts / Q000378:metabolism; D020868:Gene Silencing; D006801:Humans; D018836:Inflammation Mediators / Q000378:metabolism; D053583:Interleukin-1beta / Q000096:biosynthesis / Q000235:genetics; D015850:Interleukin-6 / Q000096:biosynthesis; D016209:Interleukin-8 / Q000096:biosynthesis / Q000235:genetics; D007378:Interleukins / Q000096:biosynthesis*; D008070:Lipopolysaccharides / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics; D013583:Synovial Membrane / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*
chemical_list: D018501:Antirheumatic Agents; C508606:CXCL8 protein, human; C496971:IL32 protein, human; C508600:IL6 protein, human; D018836:Inflammation Mediators; D053583:Interleukin-1beta; D015850:Interleukin-6; D016209:Interleukin-8; D007378:Interleukins; D008070:Lipopolysaccharides; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha