Data_Sheet_1_In Human Autoimmunity, a Substantial Component of the B Cell Repertoire Consists of Polyclonal, Barely Mutated IgG+ve B Cells.pdf

B cells are critical for promoting autoimmunity and the success of B cell depletion therapy in rheumatoid arthritis (RA) confirms their importance in driving chronic inflammation. Whilst disease specific autoantibodies are useful diagnostically, our understanding of the pathogenic B cell repertoire remains unclear. Defining it would lead to novel insights and curative treatments. To address this, we have undertaken the largest study to date of over 150 RA patients, utilizing next generation sequencing (NGS) to analyze up to 200,000 BCR sequences per patient. The full-length antigen-binding variable region of the heavy chain (IgGHV) of the IgG B cell receptor (BCR) were sequenced. Surprisingly, RA patients do not express particular clonal expansions of B cells at diagnosis. Rather they express a polyclonal IgG repertoire with a significant increase in BCRs that have barely mutated away from the germline sequence. This pattern remains even after commencing disease modifying therapy. These hypomutated BCRs are expressed by TNF-alpha secreting IgG+veCD27−ve B cells, that are expanded in RA peripheral blood and enriched in the rheumatoid synovium. A similar B cell repertoire is expressed by patients with Sjögren's syndrome. A rate limiting step in the initiation of autoimmunity is the activation of B cells and this data reveals that a sizeable component of the human autoimmune B cell repertoire consists of polyclonal, hypomutated IgG+ve B cells, that may play a critical role in driving chronic inflammation.

B细胞（B cells）在介导自身免疫反应中发挥关键作用，而类风湿关节炎（rheumatoid arthritis, RA）患者接受B细胞耗竭治疗的临床疗效，证实了其在驱动慢性炎症过程中的重要性。尽管疾病特异性自身抗体在临床诊断中具有应用价值，但目前学界对致病性B细胞库（pathogenic B cell repertoire）的认知仍较为有限。明确该B细胞库的特征，将为相关研究带来全新视角，并助力开发治愈性治疗手段。为解决这一问题，本研究开展了迄今规模最大的相关队列研究，纳入超过150名类风湿关节炎患者，并采用下一代测序（next generation sequencing, NGS）技术对每名患者的多达20万条B细胞受体（B cell receptor, BCR）序列进行分析。本研究对IgG型B细胞受体（IgG B cell receptor, BCR）的重链抗原结合可变区（IgGHV）进行了全长测序。令人意外的是，类风湿关节炎患者在确诊时并未出现特定的B细胞克隆扩增现象。反之，患者体内呈现多克隆IgG型B细胞库，且与胚系序列差异极小的BCR占比显著升高。即使在开始接受改善病情抗风湿治疗后，该特征仍持续存在。这些低突变BCR由分泌肿瘤坏死因子α（TNF-α）的IgG阳性、CD27阴性B细胞表达，这类细胞在类风湿关节炎患者的外周血中存在扩增，并在类风湿滑膜中富集。干燥综合征（Sjögren's syndrome）患者体内也存在类似的B细胞库特征。自身免疫启动的一个限速步骤是B细胞活化，本研究数据显示，人类自身免疫性B细胞库中有相当一部分由多克隆、低突变的IgG阳性B细胞组成，这类细胞可能在驱动慢性炎症过程中发挥关键作用。