OBJECTIVE Anti-citrullinated protein antibodies (ACPAs) and rheumatoid factor (RF) are commonly present in rheumatoid arthritis (RA) without a clear rationale for their coexistence. Moreover, autoantibodies develop against proteins with different posttranslational modifications and native proteins without obvious unifying characteristics of the antigens. We undertook this study to broadly evaluate autoantibody binding in seronegative and seropositive RA to identify novel features of reactivity. METHODS An array was created using a total of 172,828 native peptides, citrulline-containing peptides, and homocitrulline-containing peptides derived primarily from proteins citrullinated in the rheumatoid joint. IgG and IgM binding to peptides were compared between cyclic citrullinated peptide (CCP)-positive RF+, CCP+RF-, CCP-RF+, and CCP-RF- serum from RA patients (n = 48) and controls (n = 12). IgG-bound and endogenously citrullinated peptides were analyzed for amino acid patterns and predictors of intrinsic disorder, i.e., unstable 3-dimensional structure. Binding to IgG-derived peptides was specifically evaluated. Enzyme-linked immunosorbent assay confirmed key results. RESULTS Broadly, CCP+RF+ patients had high citrulline-specific IgG binding to array peptides and CCP+RF- and CCP-RF+ patients had modest citrulline-specific IgG binding (median Z scores 3.02, 1.42, and 0.75, respectively; P < 0.0001). All RA groups had low homocitrulline-specific binding. CCP+RF+ patients had moderate IgG binding to native peptides (median Z score 2.38; P < 0.0001). The highest IgG binding was to citrulline-containing peptides, irrespective of protein identity, especially if citrulline was adjacent to glycine or serine, motifs also seen in endogenous citrullination in the rheumatoid joint. Highly bound peptides had multiple features predictive of disorder. IgG from CCP+RF+ patients targeted citrulline-containing IgG-derived peptides. CONCLUSION Disordered antigens, which are frequently citrullinated, and common epitopes for ACPAs and RF are potentially unifying features for RA autoantibodies.

中文翻译：

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类风湿性关节炎中抗瓜氨酸蛋白抗体和类风湿因子之间的无序抗原和表位重叠。

目的 抗瓜氨酸蛋白抗体 (ACPA) 和类风湿因子 (RF) 在类风湿性关节炎 (RA) 中普遍存在，但没有明确的共存理由。此外，自身抗体针对具有不同翻译后修饰的蛋白质和天然蛋白质产生，而抗原没有明显的统一特征。我们进行了这项研究，以广泛评估血清阴性和血清阳性 RA 中自身抗体的结合，以确定反应性的新特征。方法 使用总共 172,828 种天然肽、含瓜氨酸的肽和含高瓜氨酸的肽创建了一个阵列，这些肽主要来源于类风湿关节中瓜氨酸化的蛋白质。在环状瓜氨酸肽 (CCP) 阳性 RF+、CCP+RF-、CCP-RF+、来自 RA 患者 (n = 48) 和对照组 (n = 12) 的 CCP-RF- 血清。分析了 IgG 结合和内源性瓜氨酸肽的氨基酸模式和内在疾病的预测因子，即不稳定的 3 维结构。专门评估了与 IgG 衍生肽的结合。酶联免疫吸附试验证实了关键结果。结果 总体而言，CCP+RF+ 患者与阵列肽具有较高的瓜氨酸特异性 IgG 结合，而 CCP+RF- 和 CCP-RF+ 患者具有适度的瓜氨酸特异性 IgG 结合（中位 Z 评分分别为 3.02、1.42 和 0.75；P < 0.0001 ）。所有 RA 组均具有低同型瓜氨酸特异性结合。CCP+RF+ 患者与天然肽有中度 IgG 结合（中位 Z 评分 2.38；P < 0.0001）。最高的 IgG 结合是与含瓜氨酸的肽，无论蛋白质身份如何，特别是如果瓜氨酸与甘氨酸或丝氨酸相邻，则在类风湿关节的内源性瓜氨酸化中也可以看到基序。高度结合的肽具有预测疾病的多种特征。来自 CCP+RF+ 患者的 IgG 靶向含瓜氨酸的 IgG 衍生肽。结论 经常被瓜氨酸化的无序抗原以及 ACPA 和 RF 的共同表位可能是 RA 自身抗体的统一特征。