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

摘要 免疫球蛋白是肠道固有层(LP)产生的最丰富的免疫球蛋白，它能保护 宿主通过包被和排除微生物来防止微生物入侵肠道粘膜。选择性IgA缺乏症 是最常见的免疫缺陷，超过50%的患者没有症状。然而，其他 患者会患上各种疾病，如炎症性肠病、过敏、自身免疫性疾病和 反复感染。尽管免疫球蛋白A具有重要的作用，但目前仍不清楚是什么导致了不同的临床症状。 这种疾病的表现。了解选择性IgA缺乏症的病理障碍之一是 关于IgA分泌细胞发育来源的异质性的认识差距。我们的长期合作 目的是填补这一知识空白，并确定不同来源的IgA+细胞在粘膜中的作用 豁免权。 已知的产生IgA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)路径。TI-IgA是一种低亲和力的多克隆抗体，它包裹细菌并维持微生物群 动态平衡，而TD-IgA经历体细胞的超突变，并与特定的抗原发生反应。这个 这些TI-和TD-IgA的前体一直存在争议，但最近证明TI IgA+ 细胞来源于腹膜B-1b细胞，而TD-IgA+细胞来源于生发中心B-2细胞。它一般都是 认为这些B-1b和B-2细胞最终是由居住在 在骨髓(BM)中。然而，我们和其他人之前的工作表明，B-1b细胞也是由 胚胎发育过程中不依赖于HSC的胎儿祖细胞。我们的血统追踪数据表明，IgA+ 固有层(LP)中的细胞来源于胚胎期(E)7.5天的内皮细胞(ECs)，三天前 第一次在胚胎中产生HSC。我们的血统追踪系统使用EC派生的(CDH5CreERT2)和HSC- 衍生的(Fgd5CreERT2)使我们能够分离不同来源的LP中的IgA+细胞。因此，中央 这个项目的假设是，LP中的IgA+细胞由不同来源的细胞组成：胎儿(EC)-和HSC-- 不同来源的IgA+细胞对肠道损伤和感染有不同的作用。测试我们的 假设，在Aim1中，我们将研究胎儿和HSC来源的B细胞的TI和TD类转换。我们还将 使用scRNA测序和BCR谱系显示这些来自胎儿和HSC的TI-和TD-IgA+细胞。 测序，并将显示这些细胞的分子差异。在目标2中，我们将研究保护 胎儿和肝星状细胞来源的IgA+细胞在抗胃肠道感染中的作用 从这一提议中获得的结果将建立关于IgA+细胞发育起源的新范式 以及它们在肠道动态平衡和感染中的作用。

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.