Elucidation of the physiological impact of regulatory B cells and regulatory B cell-derived IgA on mucosal immunity by employing novel genetic animal models

越来越多的临床证据将最近描述的免疫调节性B细胞与人类疾病联系起来。然而，关于这些调节性B细胞的细胞性质和功能机制的许多基本问题仍然是未知的。在这项后续应用中，我们解决了迄今为止尚未解决的调节性B细胞的免疫调节机制问题，并旨在通过使用新的遗传动物模型阐明这些细胞及其后代对慢性肠道炎症和炎症相关肿瘤发生的生理影响。在我们之前的研究中，我们分析了调节性B细胞（Bregs）的功能特征，并确定了Bregs向IgA浆细胞分化的固有能力。此外，我们的研究表明，breg来源的IgA抗体在慢性结肠炎和结肠炎相关结直肠癌的进展过程中促进了有益微生物组成的发展。基于我们在上一个资助期发现的这些有趣的调节B细胞生物学新方面，我们的目标是通过建立创新的il -10谱系追踪报告小鼠模型，进一步表征breg衍生的IgA在控制肠道微生物群中的生理功能。该报告模型将使我们第一次能够在整个动物系统中明确识别breg衍生的产生iga的浆细胞，并研究它们在正常和患病条件下的诱导和归巢特性。这些研究还将包括克隆重组breg来源的IgA抗体，方法是利用breg来源的IgA浆细胞的单细胞bcr -库谱分析，并表征其抗原特异性及其对肠道微生物群的功能活性。此外，之前的dfg资助使我们能够在B细胞上产生特异性过表达“breg调节剂”Fcmr（Toso）的转基因小鼠。根据我们之前的研究，预计这些小鼠的Bregs数量会减少甚至不存在，从而为研究Bregs在炎症性疾病发展中的生理相关性提供了一个独特的动物模型。由于fmr (Toso)-过表达与B细胞恶性肿瘤密切相关，这些小鼠也可能作为一种新的癌症模型。因此，在我们研究的第二部分，我们将对这些新型转基因小鼠进行详细的表型表征，特别关注慢性炎症免疫疾病的发展，以及B细胞相关的肿瘤发生。总之，我们提出的研究结果将导致我们对控制慢性炎症的调节性B细胞介导的保护机制的理解的主要概念进展，甚至可能开辟使用breg衍生的IgA抗体治疗炎症性疾病的新治疗前景。

Increasing clinical evidence links recently described immunoregulatory B cells to human disease. However, many of the basic questions on the cellular nature and mechanism of function of these regulatory B cells are still largely unknown. In this follow-up application, we address so far unresolved questions of the immunomodulatory mechanisms of regulatory B cells and aim to elucidate the physiological impact of these cells and their descendants on chronic intestinal inflammation and inflammation-associated tumorigenesis by using novel genetic animal models. In our previous studies, we analyzed functional characteristics of regulatory B cells (Bregs) and identified an inherent capacity of Bregs to differentiate into IgA plasma cells. Furthermore, our studies indicate that Breg-derived IgA antibodies promote the development of a beneficial microbial composition during the progression of chronic colitis and colitis-associated colorectal cancer. Building up on these intriguing new aspects of regulatory B cell biology that we uncovered in the previous funding period, we here aim to further characterize the physiological function of Breg-derived IgA in controlling the intestinal microbiota by establishing an innovative IL-10-lineage-tracing reporter mouse model. This reporter model will enable us for the first time to unequivocally identify Breg-derived IgA-producing plasma cells in vivo in a whole animal system and to study their induction and homing characteristics under normal and diseased conditions. These studies will also include the cloning of recombinant Breg-derived IgA antibodies by employing single-cell BCR-repertoire profiling of Breg-derived IgA plasma cells and characterization of their antigen-specificity as well as their functional activities on the intestinal microbiota. Furthermore, the previous DFG-funding enabled us to generate a transgenic mouse that specifically overexpresses the ‘Breg-regulator’ Fcmr(Toso) on B cells. Based on our previous studies, these mice are expected to have reduced numbers or even absence of Bregs and, thus, provide a unique animal model to study the physiological relevance of Bregs in the development of inflammatory disease. As Fcmr(Toso)-overexpression is tightly associated with B cell malignancy, these mice may also serve as a novel cancer model. Therefore, in the second part of our studies, we will perform a detailed phenotypical characterization of these novel transgenic mice with specific focus on the development of chronic inflammatory immune disorders, as well as B cell-related tumorigenesis. Together, the results from our proposed studies will lead to principal conceptual advances in our understanding of regulatory B cell-mediated protective mechanisms in the control of chronic inflammation and may even open up novel therapeutic prospects of using Breg-derived IgA antibodies in inflammatory disease.