B1 cell-mediated immunity in Human Immune System mice

描述（由申请方提供）：为了了解解决菌血症所需的保护性免疫应答的细胞基础，我们一直在研究赫氏疏螺旋体感染的小鼠模型。使用这个实验系统，我们已经确定了B1 b细胞亚群在保护性免疫中的独特作用。具体地说，我们发现B1 B细胞与B的消退同时扩增。hermsii菌血症和扩增的细胞在恢复期小鼠中持续相当长的时间，并有助于新的T细胞非依赖性B细胞记忆。这一开创性的发现已经被几种重要的人类病原体所概括。有趣的是，在这些细菌感染系统中，B1 b细胞识别的抗原不仅包括多糖，还包括细菌外膜蛋白。虽然小鼠模型在阐明免疫机制方面的能力是毋庸置疑的，但尚不清楚B1 b细胞介导的免疫功能是否存在于人类中。最近，在人脐带血和成人外周血中鉴定出一种新的B细胞群（CD 19 + CD 20 + CD 27 + CD 43 + CD 70-CD 69-），其具有鼠B1细胞的几个关键特征。为了研究人B1细胞的功能，我们利用CD 34+人造血干细胞（HSC）移植的NOD/SCID/IL-2 R？空（NSG）小鼠，称为“人免疫系统”小鼠（HIS小鼠）。我们已经发现，HIS小鼠产生包括B1细胞在内的人B细胞的几个亚群，这表明鼠微环境能够支持人HSC向人B1细胞的发育。我们还发现，B. HIS小鼠中的赫姆氏菌感染导致菌血症的反复发作，这是回归热的标志。此外，初次菌血症发作的消退与B的产生同时发生。hermsii特异性人IgM应答。在鼠感染模型中，B1 B细胞对因子H结合蛋白A（FhBA）（B的外膜蛋白）产生特异性抗体应答。赫姆斯。有趣的是，来自B. hermsii感染的个体或来自B. hermsii感染的HIS小鼠显示出相同的FhBA反应性。抗人CD 20在HI小鼠中耗尽B细胞导致B丧失。hermsii和FhBA特异性抗体应答和持续性菌血症。总之，这些发现表明，在人类和HIS小鼠中存在小鼠B1 b细胞的功能等同物。虽然B. HIS小鼠中的hermsii感染反映了人回归热的感染，但不知道人B细胞的哪些亚群在功能上负责控制B。赫姆斯。本建议的目的是：（1）鉴定HIS小鼠中鼠B1 B细胞的人等效物和（2）确定HIS小鼠中扩增的人B细胞群是否持续存在并赋予对B的增强的保护性应答。赫姆斯。研究HIS小鼠中B细胞亚群赋予的保护性TI应答的基础不仅将验证我们目前基于小鼠模型对B1 B细胞的理解，而且还将作为一个翻译平台，这可以帮助我们探索B1 B细胞在人类许多细菌感染中的潜在作用。

DESCRIPTION (provided by applicant): To understand the cellular basis for the protective immune responses required for the resolution of bacteremia, we have been studying the murine model of Borrelia hermsii infection. Using this experimental system we have identified a unique role for B1b cell subset in protective immunity. Specifically we found that B1b cells expand concurrent with the resolution of B. hermsii bacteremia and the expanded cells persist in convalescent mice for a remarkably long time and contribute to a novel T cell-independent B cell memory. This seminal finding has been recapitulated using several important human pathogens. Interestingly, the antigens recognized by B1b cells in these bacterial infection systems include not only polysaccharides, but also bacterial outer-membrane proteins. Although the power of murine models in elucidating immunological mechanisms is unquestioned, it is not known whether a functional equivalent of B1b cell-mediated immunity exists in humans. Recently, a novel population of B cells (CD19+CD20+CD27+CD43+CD70-CD69-) was identified in human umbilical cord blood and adult peripheral blood that has several key characteristics of murine B1 cells. To investigate the function of human B1 cells, we have utilized CD34+ human hematopoeitic stem cell (HSC)-engrafted NOD/SCID/IL-2R??null (NSG) mice, referred to as "Human Immune System" mice (HISmice). We have found that HISmice generate several subsets of human B cells including B1 cells suggesting that the murine microenvironment is capable of supporting the development of human B1 cells from human HSCs. We also found that B. hermsii infection in HISmice results in recurrent episodes of bacteremia, a hallmark of relapsing fever. Moreover, the resolution of the primary episode of bacteremia was concurrent with the generation of a B. hermsii-specific human IgM response. In the murine infection model, B1b cells mount a specific antibody response to Factor H binding protein A, (FhBA), an outer-membrane protein of B. hermsii. Interestingly, IgM from B. hermsii-infected individuals or from B. hermsii-infected HISmice display an identical FhBA reactivity. Depletion of B cells by anti- human CD20 in HISmice results in loss of B. hermsii- and FhBA-specific antibody responses and in persistent bacteremia. Together, these findings suggest that functional equivalents of murine B1b cells exist in humans and HISmice. Although the characteristics of B. hermsii infection in HISmice mirror those of human relapsing fever, it is not known which subsets of human B cells are functionally responsible for controlling B. hermsii. The Aims of this proposal are to: (1) identify the human equivalents of murine B1b cells in HISmice and (2) to determine whether expanded human B cell population in HISmice persist and confer a heightened protective response to B. hermsii. Investigating the basis for protective TI responses conferred by B cell subsets in HISmice will not only validate our current understanding of B1b cells based on murine models, but will also serve as a translational platform, which can help us to explore the potential role for B1b cells in a number of bacterial infections in humans.