Cellular and molecular analysis of B lymphocyte development and selection

骨髓(BM)以确保造血细胞的速度产生髓系细胞和淋巴样细胞 动态平衡。如何调节造血细胞的产生来控制外周血细胞的大小 细胞隔间还不清楚。在全身感染和/或炎症期间，淋巴生成 在骨髓生成增加时停止，这一过程被称为紧急骨髓生成。多么系统化 炎症信号改变骨髓微环境以实现戏剧性和快速的造血变化也是 很大程度上是未知的。我们建议通过研究B细胞的发育来解决这些基本问题 动态平衡和全身炎症期间。过去6年的研究确定了瘦素受体- 表达间充质祖细胞(Lepr+MPC)作为产生SCF、IL-7和 趋化因子CXCL12，对造血干细胞维持和造血祖细胞至关重要 对淋巴血统的承诺。这种类型的利基组织表明， 造血细胞和Lepr+MPC在体内存在，但到目前为止还没有通过造血细胞传递的特定信号 Lepr+MPC的细胞已被鉴定。在这笔赠款中，我们提供的证据表明，LEPR+MPC表示 淋巴毒素β受体(LTbR)和LTbR信号下调IL-7的产生。成熟的B细胞 通过骨髓自然循环表达LTbR配体LTa1b2。此外，虽然正常的B细胞 祖细胞表达少量LTa1b2，白血病前Preb细胞显著上调LTa1b2，降低IL-7 在体内由Lepr+MPC产生。在目标1中，我们将测试LTbR信号在Lepr+MPC中的假设 调节B细胞室的质量和大小。我们的初步研究结果还显示，LEPR+ MPC以LTbR依赖的方式显著降低全身炎症过程中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，并且 髓系细胞的产生显著减少。值得注意的是，在高剂量李斯特菌的作用下存活下来 单核细胞增多症的感染严重依赖于LTbR信号。通过目标2中描述的实验 我们将验证LTbR信号在Lepr+MPC中是控制MPC的主要分子途径的假设 急诊骨髓再生。最后，由于CXCL12的产生在全身炎症期间迅速减少， 大多数造血细胞从骨髓迅速动员到外周，但成熟的例外 炎症后早期，骨髓中的B细胞数量翻了一番。在目标3中，我们将检验假设 成熟B细胞通过骨髓归巢和相互作用在先天免疫中发挥新的和意想不到的作用 通过Lepr+MPC在这些细胞中传递“指导性的”LTbR信号。我们亦建议研究 机制(S)成熟的B细胞回家，并暂时保留在骨髓在系统性疾病期间 发炎。拟议的目标将为以下目标提供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.