title: Soluble HLA class I antigens in serum and synovial fluid from patients with rheumatoid arthritis and other arthropathies.
abstract: OBJECTIVE
  To investigate the presence of soluble HLA class I (s-HLA) antigens in serum and synovial fluid (SF) from a large cohort of rheumatic patients.
  
  
  METHODS
  We studied clinical and analytical data and serum samples from 300 patients [122 patients with rheumatoid arthritis (RA), 38 with osteoarthritis or osteoporosis, 29 with seronegative spondyloarthropathies, 45 patients with other rheumatic diseases] and 66 healthy controls. In addition, we studied 25 paired samples of serum and SF from these groups of subjects. In RA patients, we examined whether the levels of s-HLA in serum and SF were related to the activity of the disease.
  
  
  RESULTS
  The mean concentrations of s-HLA molecules in serum were slightly higher in RA patients (1.2 microg/ml) than in the other four groups (1.08, 1.01, 1.09 and 0.94 microg/ml respectively). We found no correlation between serum s-HLA levels and any variable of inflammatory disease activity in RA patients. s-HLA molecules were found in SF and at levels that correlated with those found in serum (P=0.04; r=0.4). Furthermore, s-HLA levels were higher in SF from patients with RA (1.3 microg/ml) or crystal-induced arthritis (0.98 microg/ml) than in SF from those with osteoarthritis (0.38 microg/ml) (P<0.05 and P<0.005 respectively), and these levels were correlated inversely and significantly with the score on the visual analogue scale of pain (P=0.02), the number of painful joints (P=0.05) and the level of C-reactive protein (P=0.03) in RA patients.
  
  
  CONCLUSIONS
  This is the first report to demonstrate the presence of s-HLA molecules in SF at levels that correlate with serum levels. The mean levels of s-HLA molecules were significantly higher in SF from patients with RA and crystal-induced arthritis than in SF from cases of osteoarthritis, and correlated inversely with certain variables of disease activity in RA patients.
authors.affiliation: Rheumatology Unit, Hospital Universitario La Paz, Universidad Autónoma de Madrid, Madrid, Spain.
authors.forename: S
authors.initials: S
authors.lastname: Muñoz-Fernández
authors.forename: J
authors.initials: J
authors.lastname: Martín
authors.forename: E
authors.initials: E
authors.lastname: Martín-Mola
authors.forename: M C
authors.initials: MC
authors.lastname: García-Rodriguez
authors.forename: M
authors.initials: M
authors.lastname: Cantalejo
authors.forename: G
authors.initials: G
authors.lastname: Fontán
authors.forename: A
authors.initials: A
authors.lastname: Ferreira
mesh_terms: D000328:Adult; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000097:blood* / Q000276:immunology; D015331:Cohort Studies; D005260:Female; D015395:Histocompatibility Antigens Class I / Q000032:analysis* / Q000097:blood*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010003:Osteoarthritis / Q000097:blood / Q000276:immunology; D010024:Osteoporosis / Q000097:blood / Q000276:immunology; D012995:Solubility; D025241:Spondylarthritis / Q000097:blood / Q000276:immunology; D013582:Synovial Fluid / Q000737:chemistry*
chemical_list: D015395:Histocompatibility Antigens Class I