title: Serum antibodies against intact human collagen IX are elevated at onset of rheumatoid arthritis but are not related to development of erosions.
abstract: OBJECTIVE
  To measure the presence of autoantibodies binding to intact human recombinant collagen IX and assess their usefulness as a diagnostic marker and an indicator of disease activity in rheumatoid arthritis (RA).
  
  
  METHODS
  Recombinant human full-length collagen IX (rCIX) was produced in a baculovirus expression system and purified for use in ELISA developed to detect antibodies to native and denatured collagen IX. Fifty-three patients with recent-onset rheumatoid factor-seropositive RA were analyzed for the presence of rCIX antibodies of the IgG type at the time of initial diagnosis and after 3, 6, 12, and 24 months of followup. The RA sera were accompanied by 30 controls. Associations were determined between patients' antibody titers, development of erosions in the hands and feet, and various clinical and laboratory markers.
  
  
  RESULTS
  Serum antibody levels among patients with RA at time of diagnosis were 1.78 times higher against native rCIX (p < 0.001) and 1.71 times higher against denatured rCIX (p < 0.001) than in the controls, and they remained high during the followup. No correlation was seen between antibody levels and clinical and laboratory findings.
  
  
  CONCLUSIONS
  Our data show that patients with recent-onset RA have significantly elevated levels of autoantibodies to human rCIX. These autoantibodies were observed already at the early stages of the disease, which may reflect their diagnostic potential in RA.
authors.affiliation: Collagen Research Unit, Biocenter Oulu, Oulu, Finland.
authors.forename: Juha
authors.initials: J
authors.lastname: Jäälinoja
authors.forename: Martti
authors.initials: M
authors.lastname: Nissilä
authors.forename: Markku J
authors.initials: MJ
authors.lastname: Kauppi
authors.forename: Markku
authors.initials: M
authors.lastname: Hakala
authors.forename: Kari
authors.initials: K
authors.lastname: Laiho
authors.forename: Riitta
authors.initials: R
authors.lastname: Karttunen
authors.forename: Sohvi
authors.initials: S
authors.lastname: Hörkkö
authors.forename: Leena
authors.initials: L
authors.lastname: Ala-Kokko
mesh_terms: D000328:Adult; D000918:Antibody Specificity / Q000276:immunology; D001172:Arthritis, Rheumatoid / Q000175:diagnosis / Q000276:immunology* / Q000503:physiopathology; D001323:Autoantibodies / Q000097:blood*; D015551:Autoimmunity / Q000276:immunology; D016367:Baculoviridae / Q000235:genetics; D016022:Case-Control Studies; D024081:Collagen Type IX / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood*; D008297:Male; D008875:Middle Aged; D011994:Recombinant Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D012720:Severity of Illness Index; D014162:Transfection
chemical_list: D001323:Autoantibodies; D024081:Collagen Type IX; D007074:Immunoglobulin G; D011994:Recombinant Proteins