Barra Lillian, Saunders Sheri, Mangion Mathias, Paré Guillaume, Maaroufi Halim, Garnier Alain, Cairns Ewa, Fernandes Maria J
Department of Microbiology and Immunology, Western University, London, Ontario, Canada.
Department of Medicine, Division of Rheumatology, Western University, London, Ontario, Canada.
J Transl Autoimmun. 2025 Apr 15;10:100287. doi: 10.1016/j.jtauto.2025.100287. eCollection 2025 Jun.
Rheumatoid arthritis is an autoimmune disease characterized by anti-citrullinated protein antibodies (ACPA). The pathogenic and protective roles of ACPA of distinct specificities are emerging and remains poorly understood. Thus, it is crucial to define the range of ACPA specificities and determine their contribution to disease and their potential clinical relevance. Since extracellular citrullination occurs in RA, we investigated whether autoantibodies in RA patients bind a citrullinated form of the cell-surface receptor CLEC12A that is expressed on neutrophils, the most abundant leukocyte in inflamed joints.
We generated a FLAG-tagged, recombinant form of the extracellular portion of human CLEC12A. After purification, the tag was removed prior to citrullination by PAD2 that was confirmed by mass spectrometry. We developed an ELISA for citrullinated CLEC12A to screen for seropositivity in sera of 68 RA patients and 36 healthy controls. Potential associations between these autoantibodies and clinical variables were determined.
In our cohort, 40 % of RA patients were positive for anti-citrullinated CLEC12A autoantibodies. Those seropositive patients were younger than RA patients that tested negative for these autoantibodies (p = 0.0058). Most patients had antibodies to multiple citrullinated and homocitrullinated antigens; 17 % of patients negative for other ACPA were positive for anti-citrullinated CLEC12A autoantibodies.
This is the first report of seropositivity towards citrullinated CLEC12A in RA patients. A validation cohort will confirm our findings and identify additional correlations between these autoantibodies and clinical parameters. Citrullination may be a mechanism through which CLEC12A's inhibitory function is altered to exacerbate inflammation in RA. Identifying citrullinated neoantigens advances our understanding of the diverse molecular mechanisms that contribute to RA pathogenesis.
类风湿性关节炎是一种以抗瓜氨酸化蛋白抗体（ACPA）为特征的自身免疫性疾病。不同特异性的ACPA的致病和保护作用正在显现，但仍知之甚少。因此，确定ACPA特异性的范围并确定它们对疾病的贡献及其潜在的临床相关性至关重要。由于细胞外瓜氨酸化发生在类风湿性关节炎中，我们研究了类风湿性关节炎患者的自身抗体是否结合在中性粒细胞（炎症关节中最丰富的白细胞）上表达的细胞表面受体CLEC12A的瓜氨酸化形式。
我们生成了人CLEC12A细胞外部分的FLAG标签重组形式。纯化后，在通过质谱确认的PAD2进行瓜氨酸化之前去除标签。我们开发了一种针对瓜氨酸化CLEC12A的酶联免疫吸附测定（ELISA），以筛查68例类风湿性关节炎患者和36例健康对照血清中的血清阳性。确定了这些自身抗体与临床变量之间的潜在关联。
在我们的队列中，40%的类风湿性关节炎患者抗瓜氨酸化CLEC12A自身抗体呈阳性。那些血清阳性的患者比这些自身抗体检测呈阴性的类风湿性关节炎患者年轻（p = 0.0058）。大多数患者对多种瓜氨酸化和高瓜氨酸化抗原有抗体；17%对其他ACPA呈阴性的患者抗瓜氨酸化CLEC12A自身抗体呈阳性。
这是关于类风湿性关节炎患者对瓜氨酸化CLEC12A血清阳性的首次报告。一个验证队列将证实我们的发现，并确定这些自身抗体与临床参数之间的其他相关性。瓜氨酸化可能是一种机制，通过该机制CLEC12A的抑制功能被改变，从而加剧类风湿性关节炎中的炎症。识别瓜氨酸化新抗原有助于我们进一步了解导致类风湿性关节炎发病机制的多种分子机制。
