Molecular pathogenesis of anti-glomerular basement membrane nephritis

描述(申请人提供)：肾小球基底膜(GBM)是血液滤过屏障的重要组成部分，也是抗GBM抗体介导的侵袭性肾小球肾炎的主要损伤部位。致病抗体由自身免疫或同种异体免疫机制引起，并针对主要的GBM成分a3a4a5(IV)胶原蛋白上的特定部位。这些位点位于非胶原(NC1)结构域中，这些结构域介导IV型胶原链的特异性组装成四级结构，在自然组织中形成NC1六聚体。目前尚不完全清楚的是，对IV型胶原链的免疫耐受的分子机制通常是在健康人群中建立的，在自身免疫性抗GBM疾病中被打破，或在移植后Alport肾炎中选择性地缺乏。这个项目的目标是在分子水平上确定适应性免疫系统如何异常参与，启动抗GBM肾炎。前提是，IV型胶原链组装成四元结构深刻地影响健康和疾病中对这种抗原的获得性免疫反应，因为NC1六聚体的形成：a)隐藏隐蔽的B细胞表位，同时创建新的四元表位；b)影响T细胞表位的处理和呈现；c)通过确定哪些IV型胶原链与组织中的天然结构相关联来形成免疫耐受。抗GBM抗体是这一提议的主要焦点，因为它们将抗原特异性B细胞和T细胞的激活偶联到导致组织损伤的效应途径。我们假设致病抗体的形成是由抗原的分子结构和宿主遗传背景(抗原缺乏或抗原不足)共同决定的。反复出现的主题是，抗GBM抗体的肾原性取决于它们与GBM中可接近的部位结合并参与炎症效应的能力。这项提案中提出的目标将通过追求四个具体目标来实现。目的1将描述仅在患者肾脏中发现的抗GBM自身抗体的新亚型，并通过被动转移研究确定它们的致病意义。目的2鉴定引起X连锁Alport患者移植后肾炎的激发同种异体抗原和抗GBM同种异体抗体的致病决定因素。目的3研究决定小鼠抗肾小球基底膜肾炎发生的抗原和抗体的分子特征及其作用机制。目的4将通过鉴定抗原敲除小鼠中异常的B细胞和T细胞对IV型胶原的反应，来确定Alport综合征IV型胶原链的遗传缺陷如何允许致病的同种免疫反应。鉴定a3a4a5(IV)胶原蛋白上新的自体和同种异体抗原性位点，鉴定抗GBM抗体的致病决定因素和作用机制，将有助于开发针对人类抗GBM肾炎的预防、检测和治疗的靶向策略。公共卫生相关性一种非常侵袭性的、危及生命的肾脏疾病是由以肾小球基底膜(GBM)为靶点的异常产生的抗体引起的，GBM是肾脏血液滤过屏障的重要组成部分。对致病抗体攻击的特定GBM成分的详细了解，以及在实验室小鼠或大鼠中产生的类似疾病的研究，将有助于我们理解导致严重肾小球疾病的事件序列中的个别步骤。这些研究可能会确定增加患病风险的因素，建议如何避免高危人群患病，并为既定疾病提供更好的治疗方法。

DESCRIPTION (provided by applicant): The glomerular basement membrane (GBM) is an essential part of the blood filtration barrier and the primary site of injury in aggressive forms of glomerulonephritis mediated by anti-GBM antibodies. Pathogenic antibodies are elicited by autoimmune or alloimmune mechanisms and target specific sites on a3a4a5(IV) collagen, the major GBM component. These sites are located within the non- collagenous (NC1) domains, which mediate the specific assembly of collagen IV chains into quaternary structures, forming NC1 hexamers in the native tissues. Incompletely understood are the molecular mechanisms by which immune tolerance to collagen IV chains is normally established in health, broken in autoimmune anti-GBM disease, or selectively deficient in alloimmune Alport post-transplant nephritis. The objective of this project is to determine at molecular level how the adaptive immune system is abnormally engaged, initiating anti-GBM nephritis. The premise is that assembly of collagen IV chains into quaternary structures profoundly affects adaptive immune responses to this antigen in health and disease, because the formation of NC1 hexamers: a) hides cryptic B cell epitopes while creating novel quaternary epitopes; b) affects the processing and presentation of T cell epitopes; and c) shapes immune tolerance by determining which collagen IV chains associate and their native structure in tissues. Anti-GBM antibodies are the major focus of this proposal because they couple the activation of antigen-specific B and T cells to effector pathways causing tissue damage. We hypothesize that the formation of pathogenic antibodies is determined by both molecular structure of the antigen and the host genetic background (antigen-deficient or -sufficient). The recurring theme is that the nephritogenicity of anti-GBM antibodies is contingent upon their ability to bind to accessible sites in the GBM and engage inflammatory effectors. The objective set forth in this proposal will be achieved by pursuing four specific aims. Aim 1 will characterize novel subsets of anti-GBM autoantibodies found only in the patient kidneys and determine their pathogenic significance by passive transfer studies. Aim 2 will identify the pathogenic determinants of the inciting alloantigen and of the anti-GBM alloantibodies causing post-transplant nephritis in X-linked Alport patients. Aim 3 will characterize the molecular features of the antigen and antibodies determining the development of anti-GBM nephritis in mouse models, and their effector mechanisms. Aim 4 will establish how genetic deficiency of collagen IV chains in Alport syndrome is permissive for pathogenic alloimmune responses by identifying abnormal B cell and T cell responses to collagen IV in antigen-knockout mice. The characterization of novel autoantigenic and alloantigenic sites on a3a4a5(IV) collagen and the identification of pathogenic determinants and effector mechanisms of anti-GBM antibodies will facilitate the development of targeted strategies for prevention, detection, and treatment of human anti-GBM nephritis. PUBLIC HEALTH RELEVANCE A very aggressive, life-threatening form of kidney disease is caused by abnormally produced antibodies that target the glomerular basement membrane (GBM), an important part of the blood filtration barrier in the kidneys. Detailed knowledge of the specific GBM components attacked by disease-producing antibodies and studies of a similar illness produced in laboratory mice or rats will helps us understand individual steps in the sequence of events leading to severe glomerular disease. These studies may identify factors that increase the risk of disease, suggest how to avoid disease in people at risk, and yield better treatments of established disease.