The amount of citrullinated proteins in synovial tissue is related to serum anti-cyclic citrullinated peptide (anti-CCP) antibody levels.

The objective of this study was to determine the relationship between citrullinated proteins in synovial tissue with peripheral anti-citrullinated peptides autoantibodies (ACPA) and peptidylarginine deiminase and messenger RNA (mRNA) expressions in synovial tissue and fibroblast-like synoviocytes in rheumatoid arthritis (RA) patients. Eleven RA and 12 osteoarthritis (OA) patients who underwent knee replacement surgery were studied. We detected citrullinated proteins in synovial tissue homogenates by western blot and serum ACPA by ELISA to anti-cyclic citrullinated peptide (anti-CCP) antibodies, and duanyu1563I2, duanyu1563I3, and duanyu1563I4 mRNA expressions in synovial tissue and in fibroblast-like synoviocytes. Patients with high amount of citrullinated proteins in synovial tissue (3 out of 7) have high levels of anti-CCP in serum. However, in the remaining 4 patients, the amount of synovial citrullinated proteins was minimal and their sera showed low levels of anti-CCP antibodies. Furthermore, we observed an increase in mRNA expression in RA synovial tissue compared with OA patients (p = 0.02). We detected mRNA in the synovial tissue of RA patients, but not in the tissue of OA patients. Even though fibroblast-type synoviocytes in RA are not the main source of in the synovial tissue, they express duanyu1563I2 mRNA moderately, duanyu1563I4 mRNA weakly, while there is no detectable expression of duanyu1563I3 mRNA. In conclusion, we found a variety of citrullinated proteins in the synovial tissue of RA patients and the amount of such proteins is related to serum concentration of anti-CCP antibodies. We identified the presence mRNA expression in synovial tissue and duanyu1563I2 and duanyu1563I4 mRNA expressions in fibroblast-like synoviocytes from patients with RA.

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