van den Beukel M D, Zhang L, van der Meulen S, Borggreven N V, Nugteren S, Brouwer M C, Pouw R B, Gelderman K A, de Ru A H, Janssen G M C, van Veelen P A, Knevel R, Parren P W H I, Trouw L A
Leiden University Medical Center, Department of Immunology, Leiden, the Netherlands.
Sanquin Research, and Landsteiner Laboratory, Amsterdam UMC, University of Amsterdam, Amsterdam, the Netherlands.
J Autoimmun. 2025 Jul;155:103444. doi: 10.1016/j.jaut.2025.103444. Epub 2025 Jun 23.
Autoimmune diseases, such as rheumatoid arthritis (RA), are characterized by the presence of autoantibodies including those targeting self-proteins modified by post-translational modifications (PTMs). The complement system is known for its role in innate immune defense, but also in clearing debris and induction of antibody responses. We therefore hypothesized that complement could directly bind to PTMs and target PTM-modified proteins for clearance, or stimulate (chronic) inflammation and development of anti-PTM autoimmunity.
Six PTMs were investigated: nitration (Nt), citrullination (Cit), carbamylation (Ca), acetylation (Ac), malondialdehyde-acetaldehyde adducts (MAA) and advanced glycation end-products (AGE). We used mass spectrometry and plate-bound assays to analyze binding of serum proteins to PTM-modified proteins. The impact of complement activation on cellular uptake was studied in phagocytosis assays. The relationship between complement SNPs, and presence of anti-PTM autoantibodies was analyzed in 587 RA patients.
Mass spectrometry analysis revealed a strong binding of complement to proteins modified with Ca, Ac, MAA and AGE but not to Nt and Cit. These observations were confirmed by plate-bound assays revealing that Ca-, MAA- and AGE-modified proteins activated the classical pathway, without involving antibodies. Ac activated the lectin pathway through ficolin-3. Complement activation on Ca-, Ac-, MAA- and AGE-coupled beads enhanced phagocytosis. SNPs in complement genes, associated with higher complement activity, were strongly associated with the presence of anti-PTM antibodies in RA patients.
Proteins containing the PTMs Ca, Ac, MAA or AGE activate complement. These complement opsonized PTMs increase phagocytosis and may lead to the development of anti-PTM antibodies.
自身免疫性疾病，如类风湿关节炎（RA），其特征是存在自身抗体，包括那些靶向经翻译后修饰（PTM）修饰的自身蛋白的抗体。补体系统以其在先天性免疫防御中的作用而闻名，但也参与清除碎片和诱导抗体反应。因此，我们推测补体可能直接结合PTM并靶向PTM修饰的蛋白进行清除，或刺激（慢性）炎症和抗PTM自身免疫的发展。
研究了六种PTM：硝化（Nt）、瓜氨酸化（Cit）、氨甲酰化（Ca）、乙酰化（Ac）、丙二醛-乙醛加合物（MAA）和晚期糖基化终产物（AGE）。我们使用质谱和板结合试验分析血清蛋白与PTM修饰蛋白的结合。在吞噬试验中研究了补体激活对细胞摄取的影响。在587例RA患者中分析了补体单核苷酸多态性（SNP）与抗PTM自身抗体存在之间的关系。
质谱分析显示补体与经Ca、Ac、MAA和AGE修饰的蛋白有强烈结合，但与Nt和Cit修饰的蛋白无结合。板结合试验证实了这些观察结果，显示经Ca、MAA和AGE修饰的蛋白激活经典途径，不涉及抗体。Ac通过纤维胶凝蛋白-3激活凝集素途径。补体在Ca、Ac、MAA和AGE偶联珠上的激活增强了吞噬作用。与较高补体活性相关的补体基因SNP与RA患者中抗PTM抗体的存在密切相关。
含有Ca、Ac、MAA或AGE等PTM的蛋白激活补体。这些补体调理的PTM增加吞噬作用，并可能导致抗PTM抗体的产生。
