Division of Rheumatology, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Division of Rheumatology, Columbia University, College of Physicians and Surgeons, New York, New York, USA.
Ann Rheum Dis. 2016 Nov;75(11):2022-2028. doi: 10.1136/annrheumdis-2015-208529. Epub 2016 Feb 10.
Anti-citrullinated protein antibodies (ACPAs) are the hallmark of rheumatoid arthritis (RA). Protein citrullination is believed to drive autoantigen selection in RA. Nonetheless, several autoantigens in RA are targeted as native (unmodified) proteins. Here, the study of hnRNP A2/B1 (RA33) provides a framework to understand the humoral response to native and citrullinated autoantigens in RA.
RA synovial fluid (SF) cells were analysed by immunoblotting and mass spectrometry. RA33 was cloned from RASF cells and splice variants expressed as recombinant proteins. Antibodies against native and citrullinated RA33 were characterised by ELISA, immunoblotting and immunoprecipitation.
RA33 is citrullinated in the rheumatoid joint and targeted either as a citrullinated or native protein in distinct patient subsets with RA. A novel splice variant (hnRNP B1b) previously associated with disease initiation in experimental arthritis was identified in the RA joint and acts as the major target of the anti-RA33 response. Antibodies exclusively targeting citrullinated RA33 were positively associated with disease duration and erosive disease. In contrast, anti-(native) RA33 antibodies were detected almost exclusively in early RA and identified patients with low radiographic erosion scores. Finally, a unique subset of double-reactive patients demonstrated intermediate severity, but rapid disease progression, suggesting a transitional disease phase in the evolution of an anti-native protein antibody to ACPA response in RA.
These data suggest that native and citrullinated proteins targeted by autoantibodies in RA may be part of a single antibody system and challenge the paradigm of citrullination as the unifying principle underlying loss of tolerance in RA.
抗瓜氨酸化蛋白抗体（ACPAs）是类风湿关节炎（RA）的标志。蛋白瓜氨酸化被认为驱动 RA 中的自身抗原选择。尽管如此，RA 中的几种自身抗原仍被作为天然（未经修饰）蛋白进行靶向。在这里，hnRNP A2/B1（RA33）的研究为理解 RA 中天然和瓜氨酸化自身抗原的体液反应提供了一个框架。
通过免疫印迹和质谱分析 RA 滑膜液（SF）细胞。从 RASF 细胞中克隆 RA33，并作为重组蛋白表达剪接变体。通过 ELISA、免疫印迹和免疫沉淀来表征针对天然和瓜氨酸化 RA33 的抗体。
RA33 在类风湿关节中发生瓜氨酸化，并在具有 RA 的不同患者亚群中作为瓜氨酸化或天然蛋白被靶向。在 RA 关节中鉴定出先前与实验性关节炎发病相关的一种新的剪接变体（hnRNP B1b），并作为抗 RA33 反应的主要靶标。仅靶向瓜氨酸化 RA33 的抗体与疾病持续时间和侵蚀性疾病呈正相关。相比之下，抗（天然）RA33 抗体几乎仅在早期 RA 中检测到，并鉴定出具有低放射学侵蚀评分的患者。最后，一个独特的双反应性患者亚组表现出中等严重程度，但疾病进展迅速，这表明在 RA 中从抗天然蛋白抗体到 ACPA 反应的演变过程中存在过渡性疾病阶段。
这些数据表明，RA 中自身抗体靶向的天然和瓜氨酸化蛋白可能是单一抗体系统的一部分，并挑战了瓜氨酸化作为 RA 中失去耐受的统一原则的范式。
