Different roles of fetal- and adult-derived IgA secreting cells against GI infection

摘要 伊加是在肠的固有层（LP）中产生的最丰富的免疫球蛋白，并且保护肠粘膜。 宿主通过包被和排斥它们来抵抗微生物侵入肠粘膜。选择性伊加缺乏症 是最常见的免疫缺陷，超过50%的患者是无症状的。但其他 患者发展出各种疾病，例如炎症性肠病、过敏、自身免疫性疾病， 反复感染。尽管伊加的重要作用，它仍然是未知的是什么原因导致不同的临床表现， 这种疾病的表现。理解选择性伊加缺乏症病理学的障碍之一是 关于IgA分泌细胞发育起源的异质性的知识缺口。我们的长期 我们的目标是填补这一知识空白，并确定不同来源的伊加+细胞在粘膜中的作用， 免疫力 已知产生伊加分泌细胞的途径有两种：T细胞非依赖性（TI）和T细胞依赖性 (TD)途径。TI-IgA是一种低亲和力的多克隆抗体，可覆盖细菌并维持微生物组 在某些实施方案中，TD-IgA具有体内平衡，而TD-IgA经历体细胞超突变并与特异性抗原反应。的 这些TI-和TD-IgA的前体一直存在争议，但最近已经证明TI伊加+ 细胞来源于腹膜B-1 B细胞，而TD伊加+细胞来源于生发中心B-2细胞。一般 认为这些B-1 B和B-2细胞最终是由造血干细胞（HSC）产生的， 骨髓（BM）。然而，我们和其他人先前的工作已经表明，B-1 B细胞也是由 胚胎发育过程中的HSC非依赖性胎儿祖细胞。我们的谱系追踪数据表明，伊加+ 固有层（LP）中的细胞来源于胚胎第7.5天（E）的内皮细胞（EC）， 胚胎中第一个HSC的产生。我们的谱系追踪系统使用EC衍生的（Cdh 5CreERT 2）和HSC- 衍生的（Fgd 5CreERT 2）使我们能够分离不同来源的LP中的伊加+细胞。因此，中央 该项目的假设是LP中的伊加+细胞由不同来源的细胞组成：胎儿（EC）-和HSC-。 不同来源的伊加+细胞对肠道损伤和感染具有不同的作用。来测试我们 假设，在Aim 1中，我们将检查胎儿和HSC衍生的B细胞的TI-和TD-类别转换。我们还将 使用scRNA测序和BCR库可视化这些胎儿和HSC衍生的TI-和伊加+细胞。 测序并将显示这些细胞的分子差异。在目标2中，我们将检查 胎儿和HSC来源的伊加+细胞对C.啮齿动物。 本研究结果将为伊加+细胞的发育起源建立一个新的范式 以及它们在肠道内稳态和感染中的作用。

Abstract IgA is the most abundant immunoglobulin produced in the lamina propria (LP) of the intestine and protects the host against microbial invasions into intestinal mucosa by coating and excluding them. Selective IgA deficiency is the most common immunodeficiency, and more than 50% of patients are asymptomatic. However, other patients develop various diseases such as inflammatory bowel diseases, allergies, autoimmune diseases, and recurrent infections. Despite the essential roles of IgA, it still remains unknown what causes the different clinical manifestations of this disease. One of the barriers to understanding the pathology of selective IgA deficiency is a gap of knowledge about the heterogeneity of developmental origin of the IgA-secreting cells. Our long-term goal is to fill this knowledge gap and to determine the roles of IgA+ cells of different origins in the mucosal immunity. There are two known pathways in producing IgA secreting cells: T-cell independent (TI) and T-cell dependent (TD) pathways. TI-IgA is a low-affinity polyclonal antibody that coats bacteria and maintains the microbiome homeostasis, while TD-IgA undergoes somatic hypermutation and reacts against specific antigens. The precursors of these TI- and TD-IgA have been controversial, but it has recently been demonstrated that TI IgA+ cells are derived from peritoneal B-1b cells while TD IgA+ cells are from germinal center B-2 cells. It is generally considered that these B-1b and B-2 cells are ultimately produced by hematopoietic stem cells (HSCs) that reside in the bone marrow (BM). However, our and others' prior work has shown that B-1b cells are also produced by HSC-independent fetal progenitors during embryonic development. Our lineage tracing data indicated that IgA+ cells in the lamina propria (LP) are derived from embryonic day (E) 7.5 endothelial cells (ECs), three days before the first HSC production in the embryo. Our lineage tracing system using EC-derived (Cdh5CreERT2) and HSC- derived (Fgd5CreERT2) enables us to segregate IgA+ cells in the LP of different origins. Thus, the central hypothesis of this project is that IgA+ cells in the LP consists of cells with different origins: fetal (EC)- and HSC- derived and that IgA+ cells of different origins have different roles against gut injury and infections. To test our hypothesis, in Aim1, we will examine TI- and TD- class switching of fetal- and HSC-derived B cells. We will also visualize these fetal- and HSC-derived TI- and TD- IgA+ cells using scRNA-sequencing and BCR repertoire- sequencing and will display the molecular differences of these cells. In Aim 2, we will examine the protective roles of fetal- and HSC-derived IgA+ cells against GI infection with C. rodentium. The results obtained from this proposal will establish a new paradigm of the developmental origin of IgA+ cells and their functions in the gut homeostasis and infections.