Properdin is the only positive regulator of the complement system. In this study, we characterize the prevalence, functional consequences and disease associations of autoantibodies against properdin in a cohort of patients with autoimmune disease systemic lupus erythematosus (SLE) suffering from lupus nephritis (LN). We detected autoantibodies against properdin in plasma of 22·5% of the LN patients (16 of 71) by enzyme‐linked immunosorbent assay (ELISA). The binding of these autoantibodies to properdin was dose‐dependent and was validated by surface plasmon resonance. Higher levels of anti‐properdin were related to high levels of anti‐dsDNA and anti‐nuclear antibodies and low concentrations of C3 and C4 in patients, and also with histological signs of LN activity and chronicity. The high negative predictive value (NPV) of anti‐properdin and anti‐dsDNA combination suggested that patients who are negative for both anti‐properdin and anti‐dsDNA will not have severe nephritis. Immunoglobulin G from anti‐properdin‐positive patients’ plasma increased the C3b deposition on late apoptotic cells by flow cytometry. Nevertheless, these IgGs did not modify substantially the binding of properdin to C3b, the C3 convertase C3bBb and the pro‐convertase C3bB, evaluated by surface plasmon resonance. In conclusion, anti‐properdin autoantibodies exist in LN patients. They have weak but relevant functional consequences, which could have pathological significance.

中文翻译：

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狼疮性肾炎患者抗备解素自身抗体的临床和功能后果。

Properdin 是补体系统的唯一正调节剂。在这项研究中，我们描述了一组患有狼疮性肾炎 (LN) 的自身免疫性疾病系统性红斑狼疮 (SLE) 患者中针对备解素的自身抗体的患病率、功能后果和疾病关联。我们通过酶联免疫吸附试验 (ELISA) 在 22·5% 的 LN 患者（71 名中的 16 名）的血浆中检测到针对备解素的自身抗体。这些自身抗体与备解素的结合是剂量依赖性的，并通过表面等离子共振进行了验证。较高水平的抗备解素与患者体内高水平的抗 dsDNA 和抗核抗体以及低浓度的 C3 和 C4 以及 LN 活动和慢性的组织学迹象有关。抗备解素和抗 dsDNA 组合的高阴性预测值 (NPV) 表明，抗备解素和抗 dsDNA 均为阴性的患者不会有严重的肾炎。通过流式细胞术，来自抗备解素阳性患者血浆的免疫球蛋白 G 增加了晚期凋亡细胞上的 C3b 沉积。尽管如此，通过表面等离子体共振评估，这些 IgG 并未显着改变备解素与 C3b、C3 转化酶 C3bBb 和前转化酶 C3bB 的结合。总之，LN 患者存在抗备解素自身抗体。它们具有微弱但相关的功能后果，可能具有病理学意义。通过流式细胞术，来自抗备解素阳性患者血浆的免疫球蛋白 G 增加了晚期凋亡细胞上的 C3b 沉积。然而，通过表面等离子体共振评估，这些 IgG 并未显着改变备解素与 C3b、C3 转化酶 C3bBb 和前转化酶 C3bB 的结合。总之，LN 患者存在抗备解素自身抗体。它们具有微弱但相关的功能后果，可能具有病理学意义。通过流式细胞术，来自抗备解素阳性患者血浆的免疫球蛋白 G 增加了晚期凋亡细胞上的 C3b 沉积。然而，通过表面等离子体共振评估，这些 IgG 并未显着改变备解素与 C3b、C3 转化酶 C3bBb 和前转化酶 C3bB 的结合。总之，LN 患者存在抗备解素自身抗体。它们具有微弱但相关的功能后果，可能具有病理学意义。