Laboratory of "Epidermis Differentiation and Rheumatoid Autoimmunity", UMR 5165 CNRS-Toulouse III University, Purpan Hospital, Place du Dr Baylac, TSA 40031, 31059 Toulouse cedex 9, France.
J Autoimmun. 2011 Dec;37(4):263-72. doi: 10.1016/j.jaut.2011.07.003. Epub 2011 Aug 27.
The major targets of the disease-specific autoantibodies to citrullinated proteins (ACPA) in synovium of rheumatoid arthritis (RA) patients are borne by the citrullinated α- and β-chains of fibrin. We demonstrated that ACPA target a limited set of citrullinated fibrin peptides and particularly four multicitrullinated peptides which present the major epitopes. In this study, we established the clear immunodominance of the peptides α36-50Cit(38,42) and β60-74Cit(60,72,74) which were recognised by 51/81 (63%) and 61/81 (75%) of ACPA-positive patients, respectively, more than 90% recognising one, the other or both peptides. We also identified the citrullyl residues αCit(42), βCit(72) and βCit(74) as essential for antigenicity, and at a lesser degree αCit(38). Then, we assayed on overlapping 7-mer peptides encompassing the sequences of the two peptides, 3 series of sera recognising either α36-50Cit(38,42) or β60-74Cit(60,72,74) or both peptides. In each series, the reactivity profiles of the sera, largely superimposable, allowed identification of the two 4/5-mer overlapping epitopes (α: VECit(42)HQ and α': Cit(38)VVE), and the single 5-mer epitope (β: GYCit(72)ACit(74)), all located to a flexible globular domain of fibrin on a topological 3D model. In conclusion, we demonstrated that only 3 immunodominant epitopes are targeted by ACPA on citrullinated fibrin stressing their actual oligoclonality. However, the reactivity to the 3 epitopes distinguishes three subgroups of patients. The closely restricted antigen specificity suggests that the autoimmune reaction to citrullinated fibrin is antigen-driven. The accessibility of the epitopes reinforces the hypothesis of a pathogenic role for ACPA via immune complexe formation in the synovial tissue.
类风湿关节炎患者滑膜中的瓜氨酸化蛋白自身抗体（ACPA）的主要靶标是纤维蛋白的瓜氨酸化 α-和 β-链。我们证明 ACPA 靶向一组有限的瓜氨酸化纤维蛋白肽，特别是四个多瓜氨酸化肽，这些肽呈现主要表位。在这项研究中，我们确定了肽 α36-50Cit(38,42)和 β60-74Cit(60,72,74)的明显免疫优势，分别有 51/81（63%）和 61/81（75%）的 ACPA 阳性患者识别它们，超过 90%的患者识别一个、另一个或两个肽。我们还确定了瓜氨酸残基 αCit(42)、βCit(72)和 βCit(74)是抗原性所必需的，而 αCit(38)的程度较低。然后，我们在包含这两个肽序列的重叠 7 聚肽上进行检测，3 系列血清识别 α36-50Cit(38,42)或 β60-74Cit(60,72,74)或两者的肽。在每个系列中，血清的反应性谱，在很大程度上是重叠的，允许鉴定两个 4/5 -mer 重叠表位（α：VECit(42)HQ 和 α'：Cit(38)VVE）和单个 5-mer 表位（β：GYCit(72)ACit(74)），它们都位于纤维蛋白的一个灵活的球状结构域上，根据拓扑 3D 模型。总之，我们证明只有 3 个免疫显性表位被 ACPA 靶向瓜氨酸化纤维蛋白，强调了它们的实际寡克隆性。然而，对这 3 个表位的反应区分了 3 组患者。抗原特异性的紧密限制表明，对瓜氨酸化纤维蛋白的自身免疫反应是抗原驱动的。表位的可及性增强了 ACPA 通过在滑膜组织中形成免疫复合物在致病中的作用假说。
