title: Increased levels of interleukin 34 in serum and synovial fluid are associated with rheumatoid factor and anticyclic citrullinated peptide antibody titers in patients with rheumatoid arthritis.
abstract: OBJECTIVE
  Interleukin 34 (IL-34) is a recently discovered cytokine that binds macrophage colony-stimulating factor (M-CSF) receptor. Rheumatoid arthritis (RA) is characterized by increased osteoclastogenesis. To identify the significance of IL-34 in RA, the IL-34 concentration was measured in serum and synovial fluid (SF).
  
  
  METHODS
  IL-34 concentrations were measured in serum from patients with RA (n = 113), patients with osteoarthritis (OA; n = 56), and controls (n = 36), and in SF isolated from patients with RA (n = 36) or OA (n = 24). Correlations between serum IL-34 levels and clinical features in RA were assessed. The levels of IL-1β, IL-6, IL-17α, interferon-γ-induced protein 10, receptor activator of nuclear factor κB ligand (RANKL), and Dickkopf-1 were also measured.
  
  
  RESULTS
  Patients with RA had a higher mean serum level of IL-34 than did patients with OA and controls (188.0 ± 550.3, 36.6 ± 38.0, and 49.1 ± 78.5 pg/ml, respectively). Similarly, SF IL-34 concentration was higher in patients with RA than in those with OA. IL-34 levels were positively associated with IL-6 levels in serum from patients with RA and OA. SF IL-34 concentration correlated significantly with IL-6 and RANKL levels only in RA. The serum level of IL-34 was not correlated with systemic osteoporosis and radiographic joint damage in RA. IL-34 levels in the serum from patients with RA were positively correlated with rheumatoid factor and anticyclic citrullinated peptide antibody titers (r = 0.282 and 0.491, respectively).
  
  
  CONCLUSIONS
  Circulating IL-34 levels in RA correlated with autoantibody production. Further investigations of localized and systemic effects of IL-34 are warranted to elucidate RA pathogenesis.
authors.affiliation: From the Division of Rheumatology, Department of Internal Medicine, School of Medicine, The Catholic University of Korea, Seoul, South Korea.
authors.forename: Su-Jin
authors.initials: SJ
authors.lastname: Moon
authors.forename: Yeon-Sik
authors.initials: YS
authors.lastname: Hong
authors.forename: Ji Hyeon
authors.initials: JH
authors.lastname: Ju
authors.forename: Seung-Ki
authors.initials: SK
authors.lastname: Kwok
authors.forename: Sung-Hwan
authors.initials: SH
authors.lastname: Park
authors.forename: Jun-Ki
authors.initials: JK
authors.lastname: Min
mesh_terms: D000328:Adult; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000097:blood / Q000276:immunology / Q000378:metabolism*; D001323:Autoantibodies / Q000097:blood*; D005260:Female; D006801:Humans; D007378:Interleukins / Q000097:blood / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D010456:Peptides, Cyclic / Q000276:immunology*; D012217:Rheumatoid Factor / Q000097:blood*; D013582:Synovial Fluid / Q000378:metabolism*
chemical_list: D001323:Autoantibodies; C529076:IL34 protein, human; D007378:Interleukins; D010456:Peptides, Cyclic; C487763:cyclic citrullinated peptide; D012217:Rheumatoid Factor
keywords: ANTICYCLIC CITRULLINATED ANTIBODIES; INTERLEUKIN 34; OSTEOPOROSIS; RHEUMATOID ARTHRITIS; RHEUMATOID FACTOR