Polymorphism in the Sp1 binding site in the first intron of the COL1A1 gene has been related to increased risk of osteoporosis in several populations. To overcome the difficulties associated with the use of mismatch oligonucleotide primers in the original method for its detection, we developed a procedure involving PCR amplification of a 598-base pair sequence from the intron and its digestion with the restriction enzyme Van 91 I. The more frequent allele is recognized by the enzyme, whereas the reaction is abolished in the less frequent allele. Two convenience samples from the population in northern Finland, consisting altogether of 173 individuals, were studied. The overall frequencies were 0.864 for the G and 0.136 for the T allele, with a heterozygocity of 27.2%. The frequency of the T allele is towards the lower end of the range observed for other European populations.
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).
We compared the ability of assay for cross-linked carboxyterminal telopeptide of type I collagen (ICTP) and CrossLaps assay to reflect increased pathological degradation of type I collagen in serum and synovial fluid samples of patients with rheumatoid arthritis (RA; n = 40). ICTP and CrossLaps concentrations were correlated with each other and with markers of collagen synthesis (PINP and PIIINP, amino terminal propeptides of type I and type III procollagens, respectively) and with markers of inflammation, i.e., C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR). Serum ICTP was increased in half of the RA patients, whereas CrossLaps assays were increased only occasionally. Serum ICTP correlated with the other markers of collagen metabolism as well as with CRP and ESR. Serum CrossLaps correlated only with PINP and ICTP, but not with serum PIIINP, CRP or ESR. Two patients had false-positive reactions in the CrossLaps assay due to the rheumatoid factor. The ICTP and CrossLaps antigens were clearly separate peaks in gel filtration analysis. The CrossLaps assay is able to detect the same ICTP antigen, but not vice versa. The ICTP assay reflects increased matrix metalloproteinase-mediated collagen degradation in joints in RA. In contrast, the physiological cathepsin K-mediated bone resorption measured by the CrossLaps assay was only occasionally increased.
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.