Supplementary Material for: Another Piece of the Puzzle of Podocyte B7-1 Expression: Lupus Nephritis

<b><i>Background/Aims:</i></b> Lupus nephritis (LN) is a frequent complication and a major predictor of poor prognosis of systemic lupus erythematosus. Immune complex deposition and T cell infiltration are crucial events in LN pathogenesis. B7-1 (CD80), normally expressed by antigen-presenting cells, is one of the major co-stimulators of T-cell activation through the binding with its counter-receptors CD28 and cytotoxic T-lymphocyte antigen-4. Unexpectedly, B7-1 induction was described at the podocyte level in patients affected by different renal diseases, including LN. These observations suggested a novel exciting function for B7-1 as a biomarker of podocyte injury, and hence that B7-1 inhibitory drugs could serve as podocyte-targeted treatment of intractable renal diseases. However, subsequent studies hardly questioned the reliability of B7-1 detection assays and the therapeutic efficacy of B7-1 blockade in proteinuric patients, casting doubts on B7-1 expression by podocytes. Here, we thoroughly investigated whether B7-1 was indeed expressed by podocytes in LN, before even considering employing B7-1 blockade in patients with severe manifestations of LN and unfavourable prognosis. <b><i>Methods:</i></b> Applying different immunohistochemical assays with 4 primary antibodies, we analysed kidney biopsies from 42 LN patients at different stages of the disease, and from NZB/NZW mice, an LN model. <b><i>Results:</i></b> B7-1 was not induced in podocytes in human and murine LN; instead its expression was confined to infiltrating inflammatory cells. <b><i>Conclusion:</i></b> B7-1 is not expressed by podocytes in LN. A renoprotective effect of B7-1 blockade in LN patients cannot be ruled out but, if confirmed, cannot be the result of an effect on podocyte B7-1.

<b><i>背景与目的:</i></b> 狼疮肾炎（Lupus nephritis, LN）是系统性红斑狼疮（systemic lupus erythematosus）常见的并发症，也是其预后不良的主要预测因素。免疫复合物沉积与T细胞浸润（T cell infiltration）是狼疮肾炎发病机制中的关键事件。B7-1（CD80）通常由抗原呈递细胞（antigen-presenting cells）表达，是通过与其共受体CD28和细胞毒性T淋巴细胞抗原-4（cytotoxic T-lymphocyte antigen-4, CTLA-4）结合介导T细胞活化（T-cell activation）的主要共刺激因子之一。令人意外的是，有研究报道在包括狼疮肾炎在内的多种肾脏疾病患者的足细胞（podocyte）中可检测到B7-1的诱导表达。上述发现提示B7-1有望作为足细胞损伤的新型生物标志物（biomarker），因此B7-1抑制类药物或可成为针对难治性肾脏疾病的足细胞靶向治疗手段。然而后续研究对B7-1检测方法的可靠性以及B7-1阻断治疗在蛋白尿患者中的疗效提出了质疑，也对足细胞表达B7-1这一结论产生了争议。本研究在考虑对出现严重临床表现且预后不良的狼疮肾炎患者使用B7-1阻断治疗之前，首先对狼疮肾炎患者足细胞是否确实表达B7-1进行了全面探究。<b><i>方法:</i></b> 本研究采用4种一抗（primary antibodies）开展多组免疫组化检测（immunohistochemical assays），分析了42例不同疾病阶段的狼疮肾炎患者的肾活检样本，以及狼疮肾炎模型小鼠NZB/NZW（NZB/NZW mice）的相关组织。<b><i>结果:</i></b> 无论是人类还是小鼠狼疮肾炎，其足细胞中均未检测到B7-1的诱导表达；B7-1的表达仅局限于浸润的炎症细胞。<b><i>结论:</i></b> 狼疮肾炎患者的足细胞并不表达B7-1。B7-1阻断治疗对狼疮肾炎患者的肾脏保护作用虽无法完全排除，但即便该疗效得到证实，其作用机制也并非通过靶向作用于足细胞的B7-1。