Role of PLA2R and anti-PLA2R in idiopathic membranous nephropathy

描述（由申请人提供）：该项目将解决三个问题，以便更好地了解m型磷脂酶A2受体（PLA2R）作为特发性膜性肾病（MN）的主要靶抗原的作用，以及在该疾病患者中特异性检测到的抗PLA2R抗体的特性。1. PLA2R1基因变异是否与特发性MN易感性有关？这一目的是基于抗PLA2R自身抗体鉴定的PLA2R表位是构象依赖的这一发现；甘露糖受体/PLA2R家族的其他成员以弯曲或延伸构型存在的已知倾向；PLA2R在正常和MN肾组织中的免疫反应性差异；PLA2R1中存在几个非同义snp，包括包含表位的N端区域内的8个，其中至少有3个被预测会影响PLA2R结构。假设：PLA2R1的变异可以解释MN致病性表位的独特特性。方法：将来自特发性MN患者的PLA2R1基因组变异与匹配对照进行比较，以确定是否存在与该疾病共分离的独特snp。将特别注意那些预计会影响PLA2R结构或功能的变异。2. 抗pla2r自身抗体是否激活补体，如果是，哪个IgG亚类负责，哪个途径被激活？这个目的将解决一个明显的悖论，即IgG4，特发性MN的主要IgG亚类和主要抗pla2r亚类，不能激活经典的补体途径，但补体成分通常存在于特发性MN的肾小球免疫沉积物中。甘露聚糖结合凝集素（MBL）和活化C4的存在，但免疫沉积物中不存在C1q，表明凝集素途径可能参与其中。值得注意的是，在Fc - n连接的聚糖上缺乏末端半乳糖的免疫球蛋白已被证明可以激活MBL。假设：IgG4抗pla2r自身抗体可能通过凝集素途径激活补体。方法：评估PLA2R IgG亚类激活补体的能力。如果IgG4激活补体，将确定其结合和激活MBL的能力，并检查其糖基化状态。3. 移植肾复发性MN与循环抗pla2r相关吗？特发性MN经常在移植肾中复发，并伴有同种异体移植肾丢失的高风险。目前还没有办法预测哪些病人有可能复发。假设：循环中抗pla2r的存在可预测MN的复发。方法：对特发性MN患者的移植前和移植后血清进行检测，以确定抗pla2r抗体的存在是否早于MN的复发并预示MN的复发。

DESCRIPTION (provided by applicant): This program will address three questions in order to better understand the role of the M-type phospholipase A2 receptor (PLA2R) as a major target antigen in idiopathic membranous nephropathy (MN) and the properties of the anti-PLA2R antibodies that are specifically detected in patients with the disease. 1. Do variants in the PLA2R1 gene account for susceptibility to idiopathic MN? This aim is based on the finding that the PLA2R epitope identified by anti-PLA2R autoantibodies is conformation dependent; the known propensity for other members of the mannose receptor/PLA2R family to exist in bent or extended configurations; differences in immunoreactivity between PLA2R in normal and MN kidney tissues; and the presence of several non-synonymous SNPs in PLA2R1, including eight within the N- terminal region that contains the epitope, at least three of which are predicted to affect PLA2R structure. Hypothesis: Variants in PLA2R1 may explain the unique properties of the pathogenic epitope in MN. Approach: Genomic variants in PLA2R1 from patients with idiopathic MN will be compared to matched controls to determine if there are unique SNPs that co-segregate with the disease. Particular attention will be paid to those variants that are predicted to affect PLA2R structure or function. 2. Do anti-PLA2R autoantibodies activate complement and, if so, which IgG subclass is responsible and which pathway is activated? This aim will address the apparent paradox that IgG4, the major IgG subclass in idiopathic MN and predominant anti-PLA2R subclass, is incapable of activating the classical complement pathway, yet complement components are commonly present in the glomerular immune deposits in idiopathic MN. The presence of mannan-binding lectin (MBL) and activated C4 but absent C1q in the immune deposits suggests that the lectin pathway may be involved. It is noteworthy that immunoglobulins lacking terminal galactose on Fc N-linked glycans have been shown to activate MBL. Hypothesis: IgG4 anti-PLA2R autoantibodies may activate complement via the lectin pathway. Approach: The ability of PLA2R IgG subclasses to activate complement will be assessed. If IgG4 activates complement, its ability to bind and activate MBL will be determined and its glycosylation state examined. 3. Is recurrent MN in transplanted human kidneys associated with circulating anti-PLA2R? Idiopathic MN frequently recurs in the transplanted kidney and is associated with a high risk of allograft loss. There is presently no way to predict which patients are likely to recur. Hypothesis: The presence of circulating anti-PLA2R will predict the recurrence of MN. Approach: Pretransplant and serial post-transplant sera from patients with idiopathic MN will be tested to determine if the presence of anti-PLA2R antibodies predates and presages the recurrence of MN.