Development and Function of Natural Autoreactive B Cells

描述（由申请人提供）：尽管广泛认为具有自身反应性的B细胞被删除或使其功能失活，但在健康动物的血清中可以发现称为“天然自身抗体”的自身反应性抗体。这种天然自身抗体是由一小部分B细胞产生的，其具有细胞表面糖蛋白CD 5的独特表达。这些CD 5+自身反应性B细胞比成人骨髓中的那些更频繁地从胎儿B细胞前体产生，作为“B-1”B细胞发育的一部分。胎儿/新生儿天然自身抗体在保护性免疫中的重要性由T15独特型阳性抗磷酸胆碱抗体例证，T15独特型阳性抗磷酸胆碱抗体是对强毒肺炎球菌感染最具保护性的抗体，在感染后迅速产生。我们的研究探索了为什么这种自身反应性B细胞自然存在，它们发育的机制以及它们失调的潜力。通过建立和研究表达天然抗Thy-1自身抗体（ATA）的小鼠天然自身反应性B细胞模型，我们发现自身抗原对于CD 5 + ATA自身反应性B-1 B细胞积累具有重要作用，相对较高的B细胞受体（BCR）信号强度介导正选择过程。相反，在脾中从骨髓前体发育的常规B细胞（“B-2”）过程中，表达相同BCR的细胞发生负选择。在这次更新中，我们将全面了解这种B细胞亚群的发育机制。我们将首先研究卵泡B细胞成熟和维持B-2 B细胞发育的机制。将检查由其他淋巴细胞、T细胞和B-1 B细胞提供的非BCR信号传导对于缺乏BCR交联信号的B细胞成熟的意义，以及细菌产物在B细胞存活中的作用（目的1）。为了理解为什么自身反应性B-1阳性选择发生在胎儿B细胞发育中，我们将鉴定“胎儿B-1特征”，我们假设该特征反映了决定BCR信号传导阈值差异的独特细胞机制，相对于骨髓B-2发育。这种早期产生的B-1细胞的命运将在Lysmd 2-GFP报告小鼠中进行检查，这是基于我们最近将该基因鉴定为胎儿B-1特征的组成部分（Aim 2）。实现这些目标将大大推进我们对B细胞发育的理解，以及自身抗原和微环境在建立完全胜任的免疫系统中的重要性。在人类中，CD 5表达是晚期发展的慢性B细胞白血病（B CLL）的标志。全面了解B细胞的发育及其维持机制对于未来设计此类失调的CD 5 + B细胞的合理疗法至关重要。 公共卫生责任：免疫系统在对感染因子的急性反应中起关键作用，天然自身反应性B-1 B细胞在该系统中起关键作用，快速产生抗体以根除微生物。然而，在某些自身免疫小鼠品系中，B-1 B细胞的异常扩增可随着年龄的增长而发生，有时进展为CD 5 + B白血病/淋巴瘤。如本申请中所提出的，全面理解B细胞发育的机制，并确定天然自身反应性B-1 B细胞如何正常调节和发挥功能，对于设计感染性疾病的合理疗法和治疗可能导致癌症的失调的B细胞扩增都是至关重要的。

DESCRIPTION (provided by applicant): Although it is widely accepted that B cells with self-reactivity are deleted or rendered functionally inactive, self-reactive antibodies, referred to as "natural autoantibodies" can be found in the serum of healthy animals. Such natural autoantibodies are produced by a small fraction of B cells with distinctive expression of the cell surface glycoprotein CD5. These CD5+ autoreactive B cells are more frequently generated from fetal B cell precursors as a part of "B-1" B cell development than those in the adult bone marrow. The importance of fetal/neonatal natural autoantibodies in protective immunity is exemplified by T15 idiotype positive anti-phosphorylcholine antibody, the most protective antibody to virulent pnuemococcal infection, rapidly produced after infection. Our research explores why such autoreactive B cells exist naturally, the mechanism whereby they develop, and their potential for dysregulation. By establishing and investigating mouse natural autoreactive B cell models expressing natural anti-Thy-1 autoantibody (ATA), we found that self-antigen is important for CD5+ ATA autoreactive B-1 B cell accumulation with relatively higher B cell receptor (BCR) signal intensity mediating a positive selection process. In contrast, negative selection occurs for cells expressing the identical BCR during conventional B cell ("B-2") development in spleen from bone marrow precursors. In this renewal, we will obtain a comprehensive understanding of the mechanism for development of this B cell subset . We will first investigate the mechanism of follicular B cell maturation and maintenance in B-2 B cell development. The significance of non-BCR signaling, provided by other lymphocytes, T cells and B-1 B cells, for the maturation of B cells that lack a BCR crosslinking signal, and a role for bacterial products in B cell survival will be examined (Aim 1). To understand why autoreactive B-1 positive selection occurs from fetal B cell development, we will identify a "fetal B-1 signature" that we hypothesize reflects distinctive cellular machinery determining a difference in the BCR signaling threshold, relative to bone marrow B-2 development. The fate of such earlygenerated B-1 cells will be examined in Lysmd2-GFP reporter mice, based on our recent identification of this gene as a component of the fetal B-1 signature (Aim 2). Accomplishing these aims will significantly advance our understanding of B cell development, and the importance of self-antigen and microenvironment in establishing a fully competent immune system. In humans, CD5 expression is a hallmark of late developing chronic B cell leukemia ( B CLL). Arriving at a comprehensive understanding of B cell development and the mechanism of their maintenance will be critically important for designing rational therapies of such dysregulated CD5+ B cells in the future. PUBLIC HEALTH RELLEVANCE: The immune system plays a crucial role in the acute response to infectious agents and natural autoreactive B-1 B cells play a key role in this system, rapidly producing antibodies to eradicate microorganisms. However, abnormal expansions of B-1 B cells can occur with age in certain autoimmune mouse strains, sometimes progressing to CD5+ B leukemia/lymphoma. Arriving at a comprehensive understanding of the mechanism(s) of B cell development, and establishing how natural autoreactive B-1 B cell are normally regulated and function, as proposed in this application, will be critically important both for designing rational therapies of infectious disease and for treating dysregulated B cell expansions that may lead to cancer.