We developed sensitive assay methods for autoantibodies recognizing the citrullinated synthetic peptides derived from type I and type II collagens in patients with rheumatoid arthritis (RA). These peptides were tested with the chemiluminescence method (Nichols Advantage® System). In 44 RA patients out of 120, the sera showed increased binding of citrullinated synthetic C-telopeptide derived from the α1 chain of type I collagen (p=0.003 compared to controls). For a corresponding C-telopeptide pair from the α1 chain of type II collagen, 35 patient sera bound the citrullinated peptide more strongly than the arginine peptide, but the difference compared to the controls was not significant (p=0.074). Correlation between the two carboxy-telopeptides was r=0.473 (p<0.001). The anti-CCP assay (antibodies against citrullinated filaggrin sequence-derived peptides) was positive in 59% of our RA patients. There was no relationship between the anti-CCP results and the antibodies against collagen C-telopeptides, but both are increased in RA patients. We demonstrated autoantibodies in RA patients that bound citrullinated C-telopeptides derived from type I and type II collagen antigens. The peptide sequences detected (-YYXA and -YMXA) were different from that based on the cyclic filaggrin antigen (-STXG-, where X represents citrulline).
Background: The aim of the study was to describe automated immunoassays for autoantibodies to homocitrulline or citrulline containing telopeptides of type I and II collagen in various disease categories in an early arthritis series.
Methods: Serum samples were collected from 142 patients over 16 years of age with newly diagnosed inflammatory joint disease. All samples were analyzed with an automated inhibition chemiluminescence immunoassay (CLIA) using four different peptide pairs, each consisting of a biotinylated antigen and an inhibiting peptide. Assays were performed with an IDS-iSYS analyzer. Autoantibodies binding to homocitrulline and citrulline containing C-telopeptides of type I (HTELO-I, TELO-I) and type II collagens (HTELO-II, TELO-II) were analyzed.
Results: The mean ratio of HTELO-I inhibition in seropositive and seronegative rheumatoid arthritis (RA) was 3.07 (95% CI 1.41–11.60), p=0.003, and in seropositive and seronegative undifferentiated arthritis (UA) 4.90 (1.85–14.49), p<0.001. The respective mean ratios in seropositive and seronegative RA and UA were in TELO-I 8.72 (3.68–58.01), p<0.001 and 3.13 (1.49–6.16), p=0.008, in HTELO-II 7.57 (3.18–56.60), p<0.001 and 2.97 (1.23–6.69), p=0.037, and in TELO-II 3.01 (1.30–9.51), p=0.002 and 3.64 (1.86–7.65), p=0.008. In reactive arthritis, ankylosing spondylitis, psoriatic arthritis and unspecified spondyloarthritis the inhibition levels were similar to those observed in seronegative RA or UA.
Conclusions: Autoantibodies binding to homocitrulline or citrulline containing telopeptides of type I and II collagen did not differ significantly. They were highest among patients with seropositive disease and they differentiated seropositive and seronegative arthritis.