title: Multiple antibody reactivities to citrullinated antigens in sera from patients with rheumatoid arthritis: association with HLA-DRB1 alleles.
abstract: BACKGROUND
  Autoantibodies to cyclic citrullinated peptides (anti-CCP) are present in most patients with rheumatoid arthritis (RA), and associate with HLA-DRB1 shared epitope (SE) alleles.
  
  
  OBJECTIVE
  To investigate reactivities of anti-CCP to various citrullinated proteins/peptides, which represent potential autoantigens in RA, and to examine the relationship between such antibodies, and their association with genetic variants within HLA-DRB1 SE alleles.
  
  
  METHODS
  Serum samples from 291 patients with established RA and 100 sex- and age-matched healthy subjects were included in this study. Sera were first analysed for presence of anti-CCP antibodies and further for IgG and IgA antibodies towards candidate autoantigens in both their native and citrullinated form including: fibrinogen, alpha-enolase peptide-1 and the C1-epitope of type II collagen (C1(III)). Antibody specificity was confirmed by cross-reactivity tests. HLA-DR genotyping was performed.
  
  
  RESULTS
  72% of patients with RA were anti-CCP positive. Among the candidate autoantigens examined, IgG antibodies to citrullinated fibrinogen were found in 66% of patients' sera and in 41% for both citrullinated alpha-enolase peptide-1 and citrullinated C1(III). These antibodies were mainly seen in the anti-CCP-positive patient group; they were specific for their respective antigen and displayed limited cross reactivity. IgA responses were also detected, but less frequently than IgG. Anti-CCP and anti-citrullinated protein antibodies were associated with HLA-DRB1*04 rather than with HLA-DRB1*01 alleles.
  
  
  CONCLUSIONS
  Antibodies directed against several citrullinated antigens are present in CCP-positive RA, with many patients displaying multireactivity. All specific reactivities were primarily associated with the HLA-DRB1*04 alleles, suggesting common pathways of anti-citrulline immunity.
authors.affiliation: Department of Medicine, Rheumatology Unit, Karolinska University Hospital, Karolinska Institute, Solna, Stockholm, Sweden.
authors.forename: O
authors.initials: O
authors.lastname: Snir
authors.forename: M
authors.initials: M
authors.lastname: Widhe
authors.forename: C
authors.initials: C
authors.lastname: von Spee
authors.forename: J
authors.initials: J
authors.lastname: Lindberg
authors.forename: L
authors.initials: L
authors.lastname: Padyukov
authors.forename: K
authors.initials: K
authors.lastname: Lundberg
authors.forename: A
authors.initials: A
authors.lastname: Engström
authors.forename: P J
authors.initials: PJ
authors.lastname: Venables
authors.forename: J
authors.initials: J
authors.lastname: Lundeberg
authors.forename: R
authors.initials: R
authors.lastname: Holmdahl
authors.forename: L
authors.initials: L
authors.lastname: Klareskog
authors.forename: V
authors.initials: V
authors.lastname: Malmström
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000483:Alleles; D001172:Arthritis, Rheumatoid / Q000235:genetics / Q000276:immunology*; D001323:Autoantibodies / Q000097:blood*; D001324:Autoantigens / Q000276:immunology; D014408:Biomarkers, Tumor / Q000276:immunology; D002956:Citrulline / Q000276:immunology; D024043:Collagen Type II / Q000276:immunology; D003429:Cross Reactions; D004268:DNA-Binding Proteins / Q000276:immunology; D005260:Female; D005340:Fibrinogen / Q000276:immunology; D005838:Genotype; D006684:HLA-DR Antigens / Q000235:genetics*; D059811:HLA-DRB1 Chains; D006801:Humans; D007070:Immunoglobulin A / Q000096:biosynthesis; D008297:Male; D008875:Middle Aged; D010456:Peptides, Cyclic / Q000276:immunology*; D010751:Phosphopyruvate Hydratase / Q000276:immunology; D025521:Tumor Suppressor Proteins / Q000276:immunology; D055815:Young Adult
chemical_list: D001323:Autoantibodies; D001324:Autoantigens; D014408:Biomarkers, Tumor; D024043:Collagen Type II; D004268:DNA-Binding Proteins; D006684:HLA-DR Antigens; D059811:HLA-DRB1 Chains; D007070:Immunoglobulin A; D010456:Peptides, Cyclic; D025521:Tumor Suppressor Proteins; C487763:cyclic citrullinated peptide; D002956:Citrulline; D005340:Fibrinogen; C095157:ENO1 protein, human; D010751:Phosphopyruvate Hydratase