Development and Function of Natural Autoreactive B Cells

描述(由申请人提供)：尽管人们普遍接受具有自我反应的B细胞被删除或功能不活跃，但在健康动物的血清中仍可发现被称为“天然自身抗体”的自我反应性抗体。这种天然自身抗体是由一小部分独特表达细胞表面糖蛋白CD5的B细胞产生的。与成人骨髓相比，这些CD5+自体反应性B细胞更多地来自胎儿B细胞前体细胞，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的例证是T15独特型阳性的抗磷胆碱抗体，这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，它们发展的机制，以及它们调节失调的可能性。通过建立和研究表达天然抗Thy-1自身抗体(ATA)的小鼠自然自身反应性B细胞模型，我们发现自身抗原对于CD5+ATA自身反应性B-1B细胞的聚集是重要的，并且B细胞受体(BCR)信号强度相对较高，介导了阳性选择过程。相反，在传统的B细胞(“B-2”)发育过程中，表达相同bcr的细胞从骨髓前体细胞中进行负选择。在这次更新中，我们将对这个B细胞亚群的发展机制有一个全面的了解。我们将首先研究B-2B细胞发育过程中滤泡B细胞成熟和维持的机制。将研究由其他淋巴细胞、T细胞和B-1B细胞提供的非BCR信号对缺乏BCR交联信号的B细胞成熟的意义，以及细菌产物在B细胞生存中的作用(目标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信号”，我们假设它反映了独特的细胞机制，决定了BCR信号阈值相对于骨髓B-2发育的不同。这种早期生成的B-1细胞的命运将在Lysmd2-GFP报告小鼠中进行检查，这是基于我们最近发现该基因是胎儿B-1信号的一个组成部分(目标2)。实现这些目标将极大地促进我们对B细胞发育的理解，以及自我抗原和微环境在建立完全合格的免疫系统中的重要性。在人类中，CD5的表达是慢性B细胞白血病(B CLL)晚期发展的标志。全面了解B细胞的发育及其维持机制，对于今后设计合理的CD5+B细胞治疗方案具有重要意义。 公共卫生研究结果：免疫系统在对感染物的急性反应中起着至关重要的作用，而天然的自身反应性B-1B细胞在这一系统中起着关键作用，它能迅速产生抗体来清除微生物。然而，在某些自身免疫小鼠品系中，随着年龄的增长，B-1B细胞会发生异常扩张，有时会进展为CD5+B白血病/淋巴瘤。全面了解B细胞发育的机制(S)，并确定本申请中提出的自然自身反应性B-1 B细胞是如何正常调节和功能的，对于设计合理的感染性疾病治疗方案和治疗可能导致癌症的调节失调的B细胞扩张都至关重要。

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.