Blk as a Master Regulator of Marginal Zone B Cell Development and Activation

描述（由申请人提供）：对血源性病原体的体液反应是由脾脏B细胞的一个特殊亚群介导的，称为边缘区（MZ） B细胞。当外来抗原进入脾脏时，这些细胞被战略性地安置在抵抗外来抗原的位置，迅速产生有效的抗体反应，因此，它们代表了抵抗血源性病原体的第一道防线。虽然已知MZ B细胞的发育和功能依赖于多种表面受体的信号传导，包括B细胞抗原受体（BCR）、Notch、肿瘤坏死因子受体（TNFR）家族、g蛋白偶联受体（GPCR）家族、toll样受体（TLR）家族和1型干扰素受体（IFNR）家族，但仍不清楚这些不同的信号通路如何以及何时相互作用以产生功能性MZ B细胞。在最近发表的一项研究中，我们报道了Blk，酪氨酸激酶Src家族（SFKs）的B细胞特异性成员，在成熟脾B细胞亚群中差异表达，MZ B细胞表达的Blk是卵泡B细胞的两倍。重要的是，这种Blk表达水平的差异反映了MZ和FO B细胞发育对Blk的不同需求，因为Blk缺陷和Blk单倍体不足的小鼠在MZ而非FO B细胞发育中都表现出缺陷。此外，尽管与Blk+/+小鼠相比，Blk+/-和Blk-/-小鼠的MZ B细胞较少，但在体外和体内，Blk突变型MZ B细胞对BCR刺激都有超反应。总之，这些数据证明了Blk在MZ B细胞的发育和激活中的作用。我们的长期目标是确定高水平的Blk控制mzb细胞发育和功能的机制。由于sfk参与多种信号通路，我们假设增加Blk水平可以提高不同类型表面受体对其的利用，从而为多种信号通路之间的交流提供了一种机制，这些信号通路有助于MZ B细胞的产生和维持。本R21基金申请的目的是通过确定在MZ B细胞发育过程中哪些信号通路上调Blk表达以及在MZ B细胞发育和激活过程中哪些信号通路需要Blk活性来验证这一新的假设。我们期望这项研究不仅能确定Blk是否是BCR、Notch、GPCR、TNFR、TLR和IFNR信号通路的关键成分，还能阐明这些不同的信号通路在MZ B细胞发育和激活过程中如何以及何时相互作用。这项研究很重要，因为通过了解它们正常发育和功能的分子要求，它将促进专门针对MZ B细胞的疫苗和疗法的开发。

DESCRIPTION (provided by applicant): Humoral responses to blood-borne pathogens are mediated by a specialized subset of splenic B cells known as marginal zone (MZ) B cells. These cells, which are strategically positioned to encounter foreign antigen as it enters the spleen, rapidly produce an effective antibody response and, therefore, represent a first line of defense against blood-borne pathogens. While it is known that MZ B cell development and function are dependent on signaling through a variety of surface receptors including the B cell antigen receptor (BCR), Notch, the tumor necrosis factor receptor (TNFR) family, the G-protein-coupled receptor (GPCR) family, the toll-like receptor (TLR) family, and the type 1 interferon receptor (IFNR) family, it is still not understood how and when these diverse signaling pathways interact to generate functional MZ B cells. In a recently published study, we reported that Blk, a B cell-specific member of the Src family of tyrosine kinases (SFKs), is differentially expressed in mature splenic B cell subsets, with MZ B cells expressing twice as much Blk as follicular (FO) B cells. Importantly, this difference in Blk expression levels reflected a differential requirement fr Blk in MZ and FO B cell development, as both Blk-deficient and Blk-haploinsufficient mice exhibited defects in the development of MZ but not FO B cells. Moreover, although there were fewer MZ B cells in Blk+/- and Blk-/- mice compared to Blk+/+ mice, Blk mutant MZ B cells were hyper-responsive to BCR stimulation, both in vitro and in vivo. Together, these data demonstrate a previously undocumented role for Blk in the development and activation of MZ B cells. Our long-term goal is to determine the mechanism(s) by which high levels of Blk control MZ B cell development and function. Since SFKs participate in a multitude of signaling pathways, we hypothesize that increasing Blk levels improves its utilization by different classes of surface receptors, thereby providing a mechanism for communication among the diverse signaling pathways that contribute to the generation and maintenance of MZ B cells. The objective of this R21 grant application is to test this novel hypothesis by determining which signaling pathways upregulate Blk expression during MZ B cell development and which require Blk activity during MZ B cell development and activation. We expect that the proposed study will not only determine whether Blk is a key component in the BCR, Notch, GPCR, TNFR, TLR and type IFNR signaling pathways but will also shed light on how and when these diverse signaling pathways interact during MZ B cell development and activation. This study is important because, by understanding the molecular requirements for their proper development and function, it will facilitate development of vaccines and therapies that specifically target MZ B cells. PUBLIC HEALTH RELEVANCE: It is expected that this study will provide important information about the biology of a specialized set of B cells known as marginal zone B cells. As these cells contribute to host defense against blood-borne pathogens and to the development/pathogenesis of autoimmune disease, this knowledge will aid in the design of vaccines and therapies that specifically target this B cell subset.