Molecular pathogenesis of anti-glomerular basement membrane nephritis

描述（由申请人提供）：肾小球基底膜（glomerular basal membrane， 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。致病性抗体是由自身免疫或同种免疫机制引起的，针对的是GBM的主要成分a3a4a5（IV）胶原蛋白上的特定位点。这些位点位于非胶原（NC1）结构域，介导胶原IV链的特异性组装成四级结构，在天然组织中形成NC1六聚体。对IV型胶原链的免疫耐受通常在健康中建立，在自身免疫性抗gbm疾病中破坏，或在同种免疫移植后肾炎中选择性缺乏的分子机制尚不完全清楚。该项目的目的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。前提是胶原IV链组装成四级结构深刻影响健康和疾病中对该抗原的适应性免疫反应，因为NC1六聚体的形成：a)隐藏了隐性B细胞表位，同时产生了新的四级表位；b)影响T细胞表位的加工和提呈；c)通过确定哪些IV型胶原链相关及其在组织中的天然结构来形成免疫耐受。抗gbm抗体是这一建议的主要焦点，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上。我们假设病原性抗体的形成是由抗原的分子结构和宿主遗传背景（抗原缺乏或充足）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中可接近的位点结合并参与炎症效应物的能力。这项建议所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自身抗体的新亚群，并通过被动转移研究确定其致病意义。目的2将确定引起x连锁Alport患者移植后肾炎的同种异体抗原和抗gbm同种异体抗体的致病决定因素。目的3将描述小鼠模型中决定抗gbm肾炎发展的抗原和抗体的分子特征及其效应机制。目的4将通过鉴定抗原敲除小鼠中对IV型胶原的异常B细胞和T细胞反应，确定Alport综合征中IV型胶原链的遗传缺陷是如何允许致病性同种免疫反应的。a3a4a5（IV）胶原蛋白上新的自身抗原和同种抗原位点的表征，以及抗gbm抗体的致病决定因素和效应机制的鉴定，将有助于制定人类抗gbm肾炎的预防、检测和治疗的靶向策略。肾小球基底膜（肾小球基底膜是肾脏血液滤过屏障的重要组成部分）是一种非常具有侵袭性、危及生命的肾脏疾病，它是由异常产生的抗体引起的。详细了解由致病抗体攻击的特定GBM成分，以及对实验室小鼠或大鼠产生的类似疾病的研究，将有助于我们了解导致严重肾小球疾病的事件序列中的各个步骤。这些研究可以确定增加疾病风险的因素，建议如何在有风险的人群中避免疾病，并为现有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.