Identification of novel citrullinated antigens in rheumatoid arthritis (RA) and the role of anti-CCP antibody in the pathogenesis of RA

抗环瓜氨酸肽（CCP）抗体是类风湿关节炎（RA）早期诊断和预测关节破坏的有效血清学指标。然而，抗CCP抗体在RA发病机制中的作用尚未确定。因此，目前尚不清楚类风湿性滑膜炎是否会产生抗CCP抗体，以及肽基精氨酸脱亚胺酶（PADI）对推定自身抗原的刺激和随后诱导的抗CCP抗体是否参与了RA的关节破坏。到目前为止，瓜氨酸化形式的纤维蛋白原、聚丝蛋白、波形蛋白已被认为是RA的推定自身抗原。本研究利用类风湿性关节炎滑膜细胞裂解液、重组p53和合成的纤维蛋白原肽建立了一种全新的ELISA检测抗瓜氨酸肽抗体的方法。虽然本ELISA系统的灵敏度低于市售抗CCP 2试剂盒，但根据我们的抗瓜氨酸肽抗体结果，可以对RA患者进行分类。我们还确定了瓜氨酸肽类风湿关节炎患者滑液中的鱼精蛋白结合部分。我们进一步鉴定了类风湿滑液中特异性的瓜氨酸化纤维蛋白原。进一步的研究检查我们已经鉴定的瓜氨酸化抗原的生物化学和免疫学性质及其免疫原性，将有助于阐明RA的发病机制。

Anti-CCP (cyclic citrullinated peptides) antibody has been demonstrated to be a useful serological marker for early diagnosis as well as prediction of joint destruction of rheumatoid arthritis (RA). However, the role of anti-CCP antibody in the pathogenesis of RA has not been established. Thus it is not known whether anti-CCP is produced as a result of rheumatoid synovitis and whether cirtrullination of putative autoantigens by peptidylarginine deiminases (PADIs) and subsequent induction of anti-CCP antibody is involved for the joint destruction in RA. So far, citrullinated forms of fibrinogen, filaggrin, vimentin have been implicated as putative autoantigens in RA. However, the specific presence of such citrullinated antigens in rheumatoid synovium has remained to be elucidated.In this study we established a brand-new ELISA system to detect anti-citrullinated peptide antibody using citrullinated form of rheumatoid synovial cell lysate, recombinant p53 and synthetic fibrinogen peptide. Although the sensitivity of the present ELISA system was inferior to the commercially available anti-CCP2 kit, it was possible to classify RA patients according to the results of our anti-citrullinated peptide antibodies. We also identified citrullinated peptides as a protamine-binding fraction of synovial fluids from RA patients. We further identified citrullinated form of fibrinogen specifically in rheumatoid synovial fluids. Further studies examining biochemical and immunological nature of the citrullinated antigens that we have identified and their immunogenicity would be warranted for elucidation of the pathogenesis of RA.