title: Elevated IL-6 levels in the synovial fluid of osteoarthritis patients stem from plasma cells.
abstract: OBJECTIVE
  To analyse the levels of interleukin-6 (IL-6) in the synovial fluids and sera of patients with osteoarthritis (OA) and to identify the IL-6-secreting cells.
  
  
  METHODS
  Serum, synovial fluid, synovial tissue, and articular cartilage samples were collected from 49 OA patients with end-stage knee or hip OA who underwent joint replacement surgery. Serum and synovial fluid levels of IL-6 were measured by enzyme-linked immunosorbent assay (ELISA) and IL-6-secreting cells were identified by immunohistochemistry.
  
  
  RESULTS
  Eight out of 49 patients (16%) exhibited elevated IL-6 levels in the synovial fluids, averaging at 2022+/-526 pg/mL, while the levels in the rest of the patients averaged at 132+/-19 pg/mL. The sera levels of all patients were comparable in the 10 pg/mL range. Immunohistochemical analyses revealed plasma cells in the synovial lining of the high producers as the source of IL-6.
  
  
  CONCLUSIONS
  Synovial fluid IL-6 levels may help to classify OA patients and may point to a subgroup with a particular impact from their immune system.
authors.affiliation: Institute of Immunology, Medical Faculty, University of Rostock, Berlin.
authors.forename: F
authors.initials: F
authors.lastname: Doss
authors.forename: J
authors.initials: J
authors.lastname: Menard
authors.forename: M
authors.initials: M
authors.lastname: Hauschild
authors.forename: H-J
authors.initials: HJ
authors.lastname: Kreutzer
authors.forename: T
authors.initials: T
authors.lastname: Mittlmeier
authors.forename: M
authors.initials: M
authors.lastname: Müller-Steinhardt
authors.forename: B
authors.initials: B
authors.lastname: Müller
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D015850:Interleukin-6 / Q000097:blood / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000276:immunology*; D020370:Osteoarthritis, Knee / Q000276:immunology*; D010950:Plasma Cells / Q000378:metabolism*; D013582:Synovial Fluid / Q000737:chemistry* / Q000276:immunology; D013583:Synovial Membrane / Q000276:immunology / Q000378:metabolism*
chemical_list: D015415:Biomarkers; D015850:Interleukin-6