title: Only rheumatoid factor-positive subset of anti-citrullinated peptide/protein antibody-negative rheumatoid arthritis may seroconvert to anti-citrullinated peptide/protein antibody-positive.
abstract: OBJECTIVE
  Anti-citrullinated peptide/protein antibody (ACPA) has been reported to occur in about 60% of patients with early rheumatoid arthritis (RA), and about 80% in patients with established RA. While ACPA seroconversion is possible, previous reports have shown that it rarely occurs. We retrospectively determined the proportion of patients who underwent ACPA seroconversion and described the clinical characteristics of these cases.
  
  
  METHODS
  ACPA-negative RA patients who had undergone ACPA assessment more than once with an interval of 3 months or longer were investigated for ACPA seroconversion. The clinical characteristics of seroconverted patients were assessed.
  
  
  RESULTS
  In 149 ACPA-negative RA patients, only eight patients (5.4%) converted to ACPA-positive during follow-up. We found that all eight of the seroconverted cases were positive for rheumatoid factor (RF) and showed bone erosions by X-ray. Of 56 ACPA-negative RF-positive RA patients, 14.3% of them seroconverted to ACPA-positive. None of the ACPA-negative RF-negative RA patients seroconverted to ACPA-positive.
  
  
  CONCLUSIONS
  The proportion of total RA patients who experienced seroconversion from ACPA-negative to ACPA-positive was 5.4%. When ACPA-negative RA patients were subdivided into RF-negative and RF-positive subsets, only the RF-positive subset seroconverted to ACPA-positive. These results imply that RF-negative and RF-positive patients are distinct subsets within ACPA-negative RA patients.
authors.affiliation: Department of Rheumatology and Clinical Immunology, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Ryosuke
authors.initials: R
authors.lastname: Hiwa
authors.affiliation: Department of Rheumatology and Clinical Immunology, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Koichiro
authors.initials: K
authors.lastname: Ohmura
authors.affiliation: Department of Rheumatology and Clinical Immunology, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Shuichiro
authors.initials: S
authors.lastname: Nakabo
authors.affiliation: Center for Genomic Medicine, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Chikashi
authors.initials: C
authors.lastname: Terao
authors.affiliation: Department of Rheumatology and Clinical Immunology, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Kosaku
authors.initials: K
authors.lastname: Murakami
authors.affiliation: Department of Rheumatology and Clinical Immunology, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Ran
authors.initials: R
authors.lastname: Nakashima
authors.affiliation: Department of Rheumatology and Clinical Immunology, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Imura
authors.affiliation: Department of Rheumatology and Clinical Immunology, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Naoichiro
authors.initials: N
authors.lastname: Yukawa
authors.affiliation: Department of Rheumatology and Clinical Immunology, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Hajime
authors.initials: H
authors.lastname: Yoshifuji
authors.affiliation: Department of the Control for Rheumatic Diseases, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Motomu
authors.initials: M
authors.lastname: Hashimoto
authors.affiliation: Department of the Control for Rheumatic Diseases, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Moritoshi
authors.initials: M
authors.lastname: Furu
authors.affiliation: Department of the Control for Rheumatic Diseases, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Hiromu
authors.initials: H
authors.lastname: Ito
authors.affiliation: Department of the Control for Rheumatic Diseases, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Takao
authors.initials: T
authors.lastname: Fujii
authors.affiliation: Department of Rheumatology and Clinical Immunology, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Tsuneyo
authors.initials: T
authors.lastname: Mimori
mesh_terms: D000328:Adult; D000368:Aged; D000075422:Anti-Citrullinated Protein Antibodies / Q000097:blood*; D001172:Arthritis, Rheumatoid / Q000097:blood / Q000175:diagnosis / Q000276:immunology*; D015415:Biomarkers / Q000097:blood; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010456:Peptides, Cyclic / Q000276:immunology*; D012189:Retrospective Studies; D012217:Rheumatoid Factor / Q000097:blood*; D000069078:Seroconversion; D012698:Serologic Tests; D013997:Time Factors
chemical_list: D000075422:Anti-Citrullinated Protein Antibodies; D015415:Biomarkers; D010456:Peptides, Cyclic; C487763:cyclic citrullinated peptide; D012217:Rheumatoid Factor
keywords: anti-citrullinated peptide/protein antibody; rheumatoid arthritis; rheumatoid factor; seroconversion