To investigate the significance of citrullinated collagen type II and its antibodies in the pathogenesis and diagnosis of rheumatoid arthritis (RA).
Serum samples were obtained from 175 patients with RA, 112 patients with systemic lupus erythematosus (SLE), 37 patients with osteoarthritis (OA), and 160 healthy controls. Arginine residues of bovine collagen type II (bCII) were converted to citrulline residues by peptidylarginine deiminase (PAD). The presence of antibodies against citullinated bCII (Cit-bCII) and bCII, a substrate protein of PAD, were examined by using enzyme-linked immunosorbent assay (ELISA) and Western blotting. The levels of anti-cyclic citrullinated peptide (CCP) antibodies, C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and rheumatoid factor (RF) in the above patients were detected.
The positive rate of anti-CitbCII antibodies of the RA patients was 50.3% (88/175), significantly higher than those of the SLE patients (17.9%, 20/112), OA patients (18.9%, 7/37), and healthy controls (2.5%, 4/160). The positive rate of anti-b of the RA patients was 33.7% (59/175), significantly lower than that of the CII antibodies. The levels of anti-CitbCII and anti-bCII antibodies were not statistically different from SLE and OA patients. There was a close correlation between anti-CitbCII and anti-CCP antibodies. Spearman correlation analysis showed that anti-CitbCII antibodies were positively correlated with anti-CCP antibodies, and CRP, ESR, RF, X ray imaging, course of disease, and age were not associated with anti-CitbCII antibodies.
Anti-citrullinated bCII antibody is relatively RA-specific. Citrullination appears to be important in RA.