title: Anti-myeloperoxidase antibodies in patients with rheumatoid arthritis: prevalence, clinical correlates, and IgG subclass.
abstract: OBJECTIVE
  To determine the prevalence and clinical associations of autoantibodies to myeloperoxidase (MPO) in an unselected series of well-characterised outpatients with rheumatoid arthritis (RA) and to compare the distribution of IgG subclasses of anti-MPO antibodies in these patients with that in patients with systemic vasculitis.
  
  
  METHODS
  A study was made of 97 patients with RA, who have been seen regularly in this department for up to 20 years, and 29 patients with anti-neutrophil cytoplasmic antibody (ANCA) positive systemic vasculitis. Anti-MPO antibodies were detected using a direct-binding enzyme-linked immunosorbent assay (ELISA) with MPO from human granulocytes as antigen. The IgG subclass of anti-MPO antibodies was determined by ELISA using isotype specific monoclonal antibodies.
  
  
  RESULTS
  Anti-MPO antibodies were detected in 12% of patients with RA. Six sera contained IgG anti-MPO antibodies only, 1 IgM only and 5 antibodies of both classes. In the patients with RA the predominant subclasses were IgG1 and IgG3: only 2 sera contained detectable IgG4 antibodies. This was in contrast to patients with vasculitis, in whom most sera contained IgG1, IgG3 and IgG4 anti-MPO antibodies. Anti-MPO antibodies in sera from both patient groups bound only to the native protein. None of the patients studied with RA had evidence of vasculitis affecting the nerves or kidney: three patients (1 positive for anti-MPO antibodies and 2 negative) had cutaneous vasculitis. In the patients with RA, positivity for anti-MPO antibodies was associated with nodules and number of active joints. Three patients with anti-MPO antibodies, and none without, had pulmonary fibrosis.
  
  
  CONCLUSIONS
  Twelve per cent of a group of unselected outpatients with RA, but without evidence of major systemic vasculitis, had anti-MPO antibodies in their serum. Positivity for anti-MPO antibodies was more common in patients with nodular disease and lung involvement but not in patients with cutaneous vasculitis. IgG4 sub-class anti-MPO antibodies were present in 90% of sera from patients with ANCA-positive vasculitis and only 2/11 (18%) of anti-MPO antibody containing sera from patients with RA.
authors.affiliation: Department of Immunology, University College London Medical School, United Kingdom.
authors.forename: G
authors.initials: G
authors.lastname: Cambridge
authors.forename: M
authors.initials: M
authors.lastname: Williams
authors.forename: B
authors.initials: B
authors.lastname: Leaker
authors.forename: M
authors.initials: M
authors.lastname: Corbett
authors.forename: C R
authors.initials: CR
authors.lastname: Smith
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019268:Antibodies, Antineutrophil Cytoplasmic; D001172:Arthritis, Rheumatoid / Q000097:blood / Q000276:immunology*; D001323:Autoantibodies / Q000097:blood*; D015153:Blotting, Western; D005260:Female; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood* / Q000276:immunology; D007075:Immunoglobulin M / Q000097:blood / Q000276:immunology; D008297:Male; D008875:Middle Aged; D009195:Peroxidase / Q000276:immunology*; D014657:Vasculitis / Q000097:blood / Q000276:immunology*
chemical_list: D019268:Antibodies, Antineutrophil Cytoplasmic; D001323:Autoantibodies; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D009195:Peroxidase