Department of Rheumatology, Aarhus University Hospital, Aarhus, Denmark.
Institute of Clinical Medicine, Aarhus University, Aarhus, Denmark.
Front Immunol. 2018 Mar 26;9:581. doi: 10.3389/fimmu.2018.00581. eCollection 2018.
INTRODUCTION/OBJECTIVES: In 2012, hypocomplementemia was included in the classification criteria of systemic lupus erythematosus (SLE). The suggested measurement of C3 or C4 often reflect disease activity poorly. Our objective was to establish an assay measuring C3dg, which is generated following complement activation, and to evaluate the assay in a cross-sectional SLE cohort.
We included SLE patients ( = 169) and controls ( = 170) and developed a modified C3dg assay where C3dg fragments were separated from the large plasma proteins by polyethylene glycol (PEG), and the supernatant containing the C3dg fragment was used for analysis in an antibody-based sandwich-type assay. Gel permeation chromatography and western blotting were used to establish the optimal conditions for PEG precipitation.
16% PEG was optimal for separating C3dg from C3 and the larger protein fragments. The assay showed a high degree of stability when using EDTA plasma, and measurements correlated well with commercially available complement activation assays. SLE patients had higher concentrations in plasma of C3dg than controls ( < 0.05). ROC analysis showed that the C3dg activation fragment of C3 with an AUC of 0.96 (CI 0.94-0.98) was superior to C3 (AUC 0.52) in differentiating between patients and controls.
Our results present a modified assay for the measurement of C3dg. We demonstrate that C3dg was superior to conventional C3 measurements in discriminating SLE patients from controls. We suggest that C3dg should be considered as a complement activation measurement in the SLE classification criteria.
简介/目的：2012 年，低补体血症被纳入系统性红斑狼疮（SLE）的分类标准。C3 或 C4 的检测通常不能很好地反映疾病活动度。我们的目的是建立一种检测 C3dg 的方法，C3dg 是补体激活后产生的，并用该方法检测一个 SLE 横断面队列。
我们纳入了 SLE 患者（ = 169）和对照组（ = 170），并开发了一种改良的 C3dg 检测方法，该方法通过聚乙二醇（PEG）将 C3dg 片段与大的血浆蛋白分离，并用抗体夹心型检测法分析上清液中的 C3dg 片段。凝胶渗透色谱和 Western blot 用于建立 PEG 沉淀的最佳条件。
16%PEG 是分离 C3dg 与 C3 和较大蛋白片段的最佳浓度。该检测方法使用 EDTA 血浆时具有高度稳定性，并且与商业上可用的补体激活检测方法具有良好的相关性。SLE 患者的血浆 C3dg 浓度高于对照组（ < 0.05）。ROC 分析表明，C3 的 C3dg 激活片段的 AUC 为 0.96（CI 0.94-0.98），优于区分患者和对照组的 C3（AUC 0.52）。
我们的结果提供了一种改良的 C3dg 检测方法。我们证明，C3dg 在区分 SLE 患者与对照组方面优于传统的 C3 检测。我们建议 C3dg 应被视为 SLE 分类标准中的补体激活标志物。
