Orlando R A, Kerjaschki D, Farquhar M G
Division of Cellular and Molecular Medicine, University of California, San Diego, La Jolla 92093, USA.
J Am Soc Nephrol. 1995 Jul;6(1):61-7. doi: 10.1681/ASN.V6161.
The Heymann nephritis antigenic complex (HNAC) consists of two glycoproteins, megalin (gp330), and the receptor-associated protein (RAP). HNAC is expressed on the surface of the glomerular epithelium where it plays a primary role in the pathogenesis of Heymann nephritis (HN). Several models were previously proposed describing how antibody binding epitopes in HNAC may contribute to the initiation and progression of HN. Although these models suggest that nephritogenic epitopes capable of initiating HN are present in both megalin and RAP, the structural relationship between these epitopes has not been established. Previously a nephritogenic epitope was identified and characterized in RAP that initiates immune complex formation in HN. In this report, the immunologic relationship between nephritogenic epitopes in megalin and RAP were examined to determine whether these epitopes are immunologically distinct or antigenically related. To this end, a polyclonal antibody to megalin was generated that does not recognize RAP by immunoblotting or immunoprecipitation and whether this antibody is capable of inducing passive HN was determined. It was found that antimegalin antibodies devoid of RAP cross-reactivity induced the formation of subepithelial immune deposits (passive HN) when injected into rats. Antibodies eluted from glomeruli of the injected rats recognized only megalin by immunoblotting a cortical extract and did not recognize a RAP fusion protein or any other renal protein. In addition, the eluted antibodies immunoprecipitated two proteolytic fragments of megalin (140 and 75 kd) identifying a pathogenic epitope within a smaller fragment of megalin.(ABSTRACT TRUNCATED AT 250 WORDS)
海曼肾炎抗原复合物（HNAC）由两种糖蛋白组成，即巨膜蛋白（gp330）和受体相关蛋白（RAP）。HNAC表达于肾小球上皮细胞表面，在海曼肾炎（HN）的发病机制中起主要作用。此前曾提出几种模型来描述HNAC中的抗体结合表位如何促成HN的起始和进展。尽管这些模型表明能够引发HN的致肾炎表位存在于巨膜蛋白和RAP中，但这些表位之间的结构关系尚未确定。此前在RAP中鉴定并表征了一个致肾炎表位，它可引发HN中的免疫复合物形成。在本报告中，研究了巨膜蛋白和RAP中致肾炎表位之间的免疫学关系，以确定这些表位在免疫学上是不同的还是抗原相关的。为此，制备了一种针对巨膜蛋白的多克隆抗体，通过免疫印迹或免疫沉淀法该抗体不识别RAP，并确定了该抗体是否能够诱导被动性HN。结果发现，缺乏RAP交叉反应性的抗巨膜蛋白抗体注入大鼠后可诱导上皮下免疫沉积物的形成（被动性HN）。从注射大鼠的肾小球洗脱的抗体通过对皮质提取物进行免疫印迹仅识别巨膜蛋白，不识别RAP融合蛋白或任何其他肾蛋白。此外，洗脱的抗体免疫沉淀了巨膜蛋白的两个蛋白水解片段（140和75kd），从而在巨膜蛋白的一个较小片段中确定了一个致病表位。（摘要截短于250字）
