Vogt Leonie M, Talens Simone, Kwasniewicz Ewa, Scavenius Carsten, Struglics André, Enghild Jan J, Saxne Tore, Blom Anna M
Division of Medical Protein Chemistry, Department of Translational Medicine, Lund University, Skåne County Council, S-20502 Malmö, Sweden.
Department of Molecular Biology and Genetics, Aarhus University, 8000 Aarhus, Denmark.
J Immunol. 2017 Aug 1;199(3):1113-1121. doi: 10.4049/jimmunol.1700018. Epub 2017 Jun 21.
The aim of this study was to identify molecules that trigger complement activation in rheumatic joints. C4d, the final cleavage product of C4 activation, is found in the diseased joint and can bind covalently to complement-activating molecules. By using a highly specific Ab against a cleavage neoepitope in C4d, several molecules that were specifically bound to C4d were identified from pooled synovial fluid (SF) from four rheumatoid arthritis (RA) patients. One of these molecules, pigment epithelium-derived factor (PEDF), is a broadly expressed multifunctional member of the serine proteinase inhibitor family. Using ELISA, we confirmed the presence of various amounts of complexes between PEDF and C4d in the SF from 30 RA patients, whereas none were detected in SF from control subjects. Correlation analyses suggested that, in arthritis patients, C4d-PEDF complexes found in sera arise from the joints, as well as from other tissues, and levels of the complexes did not differ in sera of RA patients and healthy controls. When immobilized, recombinant PEDF expressed in eukaryotic cells activated the classical complement pathway but not the alternative or lectin pathways. C1q protein was demonstrated to bind immobilized PEDF, and PEDF was shown to bind to immobilized C1q, in particular its head regions, which are known to interact with other activators of the classical pathway. Our results call for further investigation into the role of PEDF in inflammatory processes in the joint, which, in combination with classical complement activation, appears to be part of a (patho-)physiologic response.
本研究的目的是鉴定引发风湿性关节中补体激活的分子。C4d是C4激活的最终裂解产物，在患病关节中可检测到，并且能够与补体激活分子共价结合。通过使用针对C4d中裂解新表位的高度特异性抗体，从4例类风湿关节炎（RA）患者的滑膜液（SF）混合样本中鉴定出几种与C4d特异性结合的分子。其中一种分子，色素上皮衍生因子（PEDF），是丝氨酸蛋白酶抑制剂家族中广泛表达的多功能成员。使用酶联免疫吸附测定（ELISA），我们证实了30例RA患者的SF中存在不同数量的PEDF与C4d的复合物，而在对照受试者的SF中未检测到。相关性分析表明，在关节炎患者中，血清中发现的C4d-PEDF复合物来源于关节以及其他组织，并且RA患者血清和健康对照血清中复合物的水平没有差异。当固定时，真核细胞中表达的重组PEDF激活经典补体途径，但不激活替代途径或凝集素途径。已证明C1q蛋白可结合固定化的PEDF，并且PEDF可结合固定化的C1q，特别是其头部区域，已知该区域可与经典途径的其他激活剂相互作用。我们的结果要求进一步研究PEDF在关节炎症过程中的作用，其与经典补体激活相结合，似乎是（病理 - ）生理反应的一部分。
