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Anti-cyclic citrullinated peptide (anti-CCP) antibody is a highly specific biomarker for rheumatoid arthritis (RA), and is recognised as a predictor of the development of RA.1 2 It has been demonstrated that some HLA-DRB1 alleles, such as shared epitope (SE) alleles, significantly contribute to the positivity of anti-CCP antibody and the susceptibility of anti-CCP antibody-positive RA.3 4 However, the quantitative effect of HLA-DRB1 alleles on anti-CCP antibody levels in RA patients is controversial.3 5 6 Therefore, we carried out a large-scale study to study the quantitative effects of HLA-DRB1 alleles on anti-CCP antibody levels in Japanese patients with RA.
A total of 2384 Japanese patients with RA was recruited through several medical institutes of Japan under the support of the BioBank Japan Project7 (age 61.5±11.8 years (mean±SD), 81.2% were women). All patients fulfilled the American College of Rheumatology revised criteria for RA, and provided written informed consent. Serum anti-CCP antibody levels were assayed using the second-generation anti-CCP ELISA kit (DIASTAT Anti-CCP; MBL, Nagoya, Japan) with …