Pattern of Antigen Recognition by Anti-citrullinated Peptide Antibodies in Undifferentiated Arthritis and Rheumatoid Arthritis

The aim of this study were to establish (1) an easy diagnostic criterion for recent-onset arthritis using Rheumatoid Factor (RF) isotypes and anti-cyclic citrullinated peptide (anti-CCP) antibodies. (2) Antigen recognition by anti-citrullinated peptide antibodies (ACPA) in undifferentiated arthritis (UA) and rheumatoid arthritis (RA) patients. This study was conducted on 80 patients of (1) UA (n = 40, < 1 year) and (2) established RA (n = 40, ≥1 year), using blood and Synovial fluid. Controls were (1) SLE patients (n = 15) and (2) Blood bank donors (n = 36). The antigen recognition was judged by serum reactivity to protein extracts. (1) Human Placenta (HP) (2) Synovial Tissue (ST) and (3) Synovial Fluid (SF) using Western blot analysis. Specificity and PPV was 78 and 33%. SF and serum levels of IgA-RF, IgM-RF and anti-CCP antibodies by ELISA showed significant correlation (p<0.01). Association becomes stronger with CCP IgM or CCP IgA-RF (p = 0.0001) 30/55 anti-CCP showed antigen recognition to ~ 55 and ~ 200 kDa. ACPA recognition of citrullinated vimentin seen only in RA patients.