Cellular and molecular analysis of B lymphocyte development and selection

骨髓（BM）产生髓样和淋巴样细胞的速度，确保造血细胞 体内平衡如何调节造血细胞的产生以控制外周造血细胞的大小 细胞室不了解。在全身感染和/或炎症期间，淋巴样物质的产生是 在骨髓生成增加时停止，这一过程被称为紧急骨髓生成。如何系统化 炎症信号改变BM微环境，使造血发生显著而快速的变化， 大部分未知。我们建议通过研究B细胞的发育来解决这些基本问题， 稳态和全身炎症期间。过去6年的研究发现瘦素受体- 表达间充质祖细胞（Lepr+ MPC）作为产生SCF、IL-7的主要细胞， 趋化因子CXCL 12，其对于造血干细胞维持和造血前体细胞的形成至关重要。 进入淋巴系统。这种类型的利基组织表明， 体内存在造血细胞和Lepr+ MPC，但迄今为止还没有造血细胞传递特异性信号 已经鉴定了Lepr+ MPC的细胞。在这项授权中，我们提供的证据表明，Lepr+ MPC表达 研究表明，IL-7的产生与光毒素β受体（LTbR）有关，并且LTbR信号传导下调IL-7的产生。成熟的B细胞 通过BM自然再循环表达LTbR配体LTa 1b 2。此外，虽然正常B细胞 白血病前B细胞显著上调LTa 1b 2表达，降低IL-7水平 由Lepr+ MPC在体内产生。在目的1中，我们将检验Lepr+ MPC中LTbR信号转导的假设， 调节B细胞区室的质量和大小。我们的初步研究结果还表明，Lepr+ MPC以LTbR依赖性方式显著降低全身炎症期间IL-7的表达。 重要的是，当Lepr+ MPC不能关闭IL-7的产生时，B淋巴细胞继续产生， 骨髓细胞的产生显著减少。值得注意的是，抵抗高剂量李斯特菌的存活率 单核细胞增多症感染严重依赖于LTbR信号传导。通过目标2中所述的实验 我们将检验Lepr+ MPC中的LTbR信号传导是控制Lepr+ MPC的主要分子途径的假设。 紧急骨髓增生最后，由于CXCL 12的产生在全身炎症过程中迅速减少， 大多数造血细胞从骨髓迅速动员到外周，成熟的造血细胞除外。 在炎症后的最初几小时内，BM中的B细胞数量增加一倍。在目标3中，我们将检验假设 成熟的B细胞通过BM归巢和相互作用在先天免疫中发挥了新的和未预料到的作用 与Lepr+ MPC一起用于在这些细胞中递送“指导性”LTbR信号传导。我们亦建议研究 成熟B细胞在全身性疾病期间归巢并暂时保留在BM中的机制 炎症拟议的目标将提供一个广泛的概念和机制框架， 了解骨髓基质细胞如何影响细胞谱系决定。

The bone marrow (BM) produces myeloid and lymphoid cells at a rate that ensures hematopoietic cell homeostasis. How hematopoietic cell production is regulated to control the size of the peripheral hematopoietic cell compartment is not understood. During systemic infection and/or inflammation, lymphoid production is halted while myelopoiesis is increased, a process that is known as emergency myelopoiesis. How systemic inflammatory signals alter the BM microenvironment to enable dramatic and quick hematopoietic shifts is also largely unknown. We propose to address these fundamental questions by studying B cell development under homeostasis and during systemic inflammation. Studies over the past 6 years identified Leptin receptor- expressing mesenchymal progenitor cells (Lepr+ MPCs) as the major cells producing SCF, IL-7, and the chemokine CXCL12, that are critical for hematopoietic stem cell maintenance and hematopoietic precursor commitment into the lymphoid lineage. This type of niche organization suggests that cross-talk between hematopoietic cells and Lepr+ MPCs occurs in vivo, but so far no specific signals delivered by hematopoietic cells to Lepr+ MPCs have been identified. In this grant we provide evidence showing that Lepr+ MPCs express Lymphotoxin beta receptor (LTbR) and that LTbR signaling downregulates IL-7 production. Mature B cells that naturally recirculate through BM express the LTbR ligand LTa1b2. Furthermore, while normal B cell progenitors express little LTa1b2, pre-leukemic preB cells significantly up-regulate LTa1b2 and reduce IL-7 produced by Lepr+ MPCs in vivo. In aim 1 we will test the hypothesis that LTbR signaling in Lepr+ MPCs regulates the quality and size of the B cell compartment. Our preliminary findings also revealed that Lepr+ MPCs significantly reduce IL-7 expression during systemic inflammation in a LTbR-dependent manner. Importantly, when Lepr+ MPCs cannot shut-down IL-7 production, B lymphocytes continue to be made, and myeloid cell production is significantly reduced. Remarkably, survival against a high dose of Listeria monocytogenes infection is critically dependent on LTbR signaling. Through experiments described in Aim 2 we will test the hypothesis that LTbR signaling in Lepr+ MPCs is the major molecular pathway controlling emergency myelopoiesis. Finally, as CXCL12 production is quickly reduced during systemic inflammation, most hematopoietic cells are rapidly mobilized from BM into the periphery, with the notable exception of mature B cells that double in number in BM in the early hours after inflammation. In Aim 3, we will test the hypothesis that mature B cells play a novel and unsuspected role in innate immunity through BM homing and interaction with Lepr+ MPCs for delivery of “instructive” LTbR signaling in these cells. We also propose to study the mechanism(s) used by mature B cells to home and be temporarily retained in BM during systemic inflammation. The proposed aims will provide a broad conceptual and mechanistic framework for understanding how bone marrow stromal cells influence cell lineage decisions.