肠道微生物与致病性缺糖IgA1及抗糖抗体产生在IgA肾病发病中的作用研究

Recent studies have indicated that autoimmune factors including the galactose-deficient IgA1(GdIgA1) and circulating autoantibodies directed against GdIgA1 play important roles in the development of IgA nephropathy (IgAN). However, the source of GdIgA1 and autoantibodies remains still unknown. Previous studies have indicated gut-associated lymphoid tissue (GALT) plays a major role in the development of IgAN. So we speculate that GALT stimulated by some microbiotas could promote the production of GdIgA1. Our previous data showed that some of the microbiotas have similar amino acid sequence and galactose-deficient O-glycosylation with the hinge region of human IgA1, anti-glycan antibodies against the proteins from these microbiotas were detected, based on these data we inferred that anti-glycan antibodies against the microbiotas may have cross reaction with GdIgA1. So we put forward the hypotheses stimulated by some microbiotas, higher levels of GdIgA1 and anti-glycan antibodies against GdIgA1 were produced, which involved in the pathogenesis of IgAN. In this study, we aim to identify the specific microbiotas associated with the higher levels of GdIgA1, and then identify microbiotas with galactose-deficient peptides and can produce anti-glycan antibodies with cross-reaction with GdIgA1, the results will provide evidence and clues for further studies in exploration the role of microbiota on mucosal immune system and new treatment strategy in IgAN.

近年来的研究已经证实半乳糖缺失IgA1及其抗糖抗体是IgA肾病发病的重要始动环节，但其具体产生机制仍不清楚。既往研究提示微生物诱导肠道黏膜免疫可能与循环高水平半乳糖缺失IgA1产生有关，我们前期研究发现一些黏膜感染微生物与IgA1铰链区氨基酸序列高度同源且存在半乳糖缺失，因此我们提出这些微生物感染人体可以诱发抗糖抗体并与半乳糖缺失IgA1存在交叉反应，最终促进循环中多聚IgA1免疫复合物形成，从而参与IgA肾病发病的研究假说。本研究通过肠道微生物多样性与半乳糖缺失IgA1相关性分析，筛选与半乳糖缺失IgA1相关的微生物，检索UniProt数据库、免疫印迹、O-糖质谱分析筛选鉴定存在半乳糖缺失可与缺糖IgA1产生交叉反的肠道微生物，并进行独立人群验证，最终明确与IgA肾病半乳糖缺失IgA1及抗糖抗体产生有关的肠道微生物，为黏膜免疫参与IgA肾病发病机制研究及IgA肾病新的治疗策略提供线索。

IgA肾病发病机制仍不清楚，但既往研究提示肠道粘膜免疫可能参与IgA肾病中半乳糖缺失IgA1的产生。本研究通过对77例IgA肾病、22例IgA肾病患者健康家属及39例健康对照粪便16s rDNA测序，PCoA分析发现IgA肾病患者肠道菌群构成与健康家属对照及其他健康对照在属水平存在显著差异，而健康对照家属与其他健康对照菌群构成存在很大重叠。LEfSef分析提示在IgA肾病患者中特异高丰度的主要菌群有志贺氏大肠杆菌属，拟杆菌属、脆弱拟杆菌，多形类杆菌等，健康人特异性的主要菌群有巨型球菌属、毛螺菌属、普氏菌属。Indicator指示物种分析提示志贺氏大肠杆菌属拟杆菌、志贺氏大肠杆菌、活泼瘤胃球菌可作为IgA肾病的指示物种，志贺氏大肠杆菌用于区分健康对照及IgA肾病患者ROC曲线下面积为0.826。且高丰度的志贺氏大肠杆菌属与缺糖IgA1水平正相关(r=0.36，p<0.01)，活泼瘤胃球菌与血浆 GdIgA1(r=0.25，p=0.01) 及poly-IgA1(r=0.23，p=0.02)均正相关。而健康人粪便中高丰度的巨形球菌属、琥珀酸菌属与致病性GdIgA1及多聚IgA1负相关。IgA肾病患者肠道中产IgA蛋白酶可降解IgA1的共生菌丰度明显低于健康对照。综上结果提示IgA肾病患者肠道菌群构成异于健康人，患者含有高丰度志贺氏大肠杆菌及活泼瘤胃球菌与GdIgA1及多聚IgA1产生相关，同时合并低丰度的表达降解IgA1酶共生菌，以上因素可能导致患者体内存在高水平GdIgA1及多聚IgA1,继而参与IgA肾病的发生。