Development and Function of Natural Autoreactive B Cells

描述（由申请人提供）：尽管人们普遍认为具有自身反应性的B细胞被删除或功能失活，但在健康动物的血清中可以发现被称为“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具有细胞表面糖蛋白CD5独特表达的B细胞产生的。这些CD5+自身反应性B细胞更频繁地由胎儿B细胞前体产生，作为B-1 B细胞发育的一部分，而不是成人骨髓中的B细胞。T15独特型阳性抗磷胆碱抗体是抗肺炎球菌感染最具保护性的抗体，在感染后迅速产生，说明了胎儿/新生儿天然自身抗体在保护性免疫中的重要性。我们的研究探讨了为什么这种自身反应性B细胞自然存在，它们发展的机制，以及它们失调的可能性。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，我们发现自身抗原在CD5+ ATA自身反应性B细胞积累中具有重要作用，具有相对较高的B细胞受体（BCR）信号强度，介导阳性选择过程。相反，在骨髓前体的常规B细胞（“B-2”）在脾脏中发育过程中，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B-2 B细胞发育过程中卵泡B细胞成熟和维持的机制。由其他淋巴细胞、T细胞和B-1 B细胞提供的非BCR信号对于缺乏BCR交联信号的B细胞成熟的重要性，以及细菌产物在B细胞存活中的作用将被研究（目的1）。为了理解为什么自体反应性B-1阳性选择发生在胎儿B细胞发育过程中，我们将确定一个“胎儿B-1特征”，我们假设它反映了与骨髓B-2发育相关的BCR信号阈值差异的独特细胞机制。这些早期生成的B-1细胞的命运将在Lysmd2-GFP报告小鼠中进行检验，基于我们最近鉴定出该基因是胎儿B-1特征的一个组成部分（目的2）。实现这些目标将大大提高我们对B细胞发育的理解，以及自身抗原和微环境在建立一个完全胜任的免疫系统中的重要性。在人类中，CD5表达是晚期慢性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合理的CD5+ B细胞失调疗法至关重要。

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.