Inhibitory receptors in early B cell development

描述（由申请人提供）：免疫系统的正常功能需要开发一种B细胞库，该细胞库识别广泛的外源抗原，但仍保持自身耐受性。为此，B细胞发育通过一系列有序的事件进行，其中免疫球蛋白（IG）重链和轻链依次重排并测试功能性和自身反应性。在大前B细胞阶段，已成功重排IG重链基因的细胞响应于来自IL-7和前BCR的信号而经历增殖性扩增。这用于扩增表达任何给定功能性重链的细胞库。当细胞分化成小的前体细胞时， B期并失去对IL-7的反应性。在此阶段，前BCR信号和IL-7信号的缺乏都促进了IG轻链重排。这一过渡受到严格控制， 其破坏导致小鼠和人类的免疫缺陷和恶性肿瘤。因此，了解调控这些早期B细胞发育的分子机制可能对这些潜在的致命疾病具有重要的治疗意义。 成熟的外周B细胞的活化受到含有抑制性受体的ITIM的限制，ITIM主要通过磷酸酶SHIP或SHP-1起作用。虽然已知SHIP也在前B细胞中起作用，但SHP-1依赖性抑制性受体在早期阶段的作用是不确定的。 B细胞发育尚未被探索。该家族的几个成员由骨髓中的前B细胞和未成熟B细胞表达。有趣的是，SHP-1已在B细胞系和其他细胞类型中显示出抑制IL-7和前BCR信号传导途径的几种关键组分。来自mev/mev小鼠的祖细胞B细胞系显示出分化能力受损和对细胞因子信号传导的应答增加的迹象。更令人感兴趣的是，缺乏ITIM区的抑制性受体CD 22的突变形式最近已显示在B细胞祖细胞白血病中具有致病作用。我们的初步数据表明，gp 49 B（一种已知在其他细胞类型中通过SHP-1起作用的抑制性受体）的过表达可以限制IL-7中前B细胞的增殖或存活。因此，我们假设SHP-1偶联的抑制性受体抑制大的前B细胞的扩增和/或促进它们分化成小的前B细胞。为了验证这一假设，我们将确定SHP-（Aim 1）和SHP-1偶联抑制性受体（Aim 2）在前B细胞增殖和分化中的作用。我们还将确定抑制性受体和磷酸酶（Aim 3）靶向IL-7和前B信号通路的哪些组分。 这些研究将揭示以前未探索的机制，通过该机制调节从大前B细胞向小前B细胞的转变，并可能阐明由该过程中断引起的疾病的新治疗靶点，包括免疫缺陷和恶性肿瘤。 公共卫生相关性：B淋巴细胞在早期发育阶段不能适当地转变导致人和小鼠中的B细胞免疫缺陷和/或恶性肿瘤。拟议的研究将定义和表征控制这些发育转变的新机制，从而可能阐明这些潜在致命疾病的新治疗方法。

DESCRIPTION (provided by applicant): Proper function of the immune system requires the development of a B cell repertoire that recognizes a wide range of foreign antigens yet remains self-tolerant. To this end, B cell development proceeds via an ordered series of events in which the immunoglobulin (Ig) heavy and light chains are sequentially rearranged and tested for functionality and self-reactivity. At the large pre-B cell stage, cells that have successfully rearranged an Ig heavy chain gene undergo a proliferative expansion in response to signals from IL-7 and the pre-BCR. This serves to expand the pool of cells expressing any given functional heavy chain. Proliferation eventually ceases as the cells differentiate to the small pre B stage and lose responsiveness to IL-7. At this stage, both pre-BCR signals and the absence of IL-7 signaling promote Ig light chain rearrangement. This transition is under tight control, and its disruption leads to both immunodeficiency and malignancy in mice and humans. Thus, understanding the molecular mechanisms that regulate these early stages of B cell development is likely to have important therapeutic implications for these potentially fatal diseases. The activation of mature peripheral B cells is limited by ITIM containing inhibitory receptors, which act primarily through the phosphatases SHIP or SHP-1. While SHIP is known to act in pre-B cells as well, a role for SHP-1 dependent inhibitory receptors in earlier stages of B cell development has not been explored. Several members of this family are expressed by pre-B and immature B cells in the bone marrow. Intriguingly, SHP-1 has been shown in B cell lines and other cell types to inhibit several critical components of IL-7 and pre- BCR signaling pathways. Progenitor B cell lines from mev/mev mice show signs of impaired ability to differentiate and increased response to cytokine signaling. Of further interest, a mutant form of the inhibitory receptor CD22 that lacks the ITIM region has recently been shown to have a pathogenic role in B cell progenitor leukemia. Our preliminary data show that overexpression of gp49B, an inhibitory receptor known to act through SHP-1 in other cell types, can limit the proliferation or survival of pre-B cells in IL-7. Thus, we hypothesize that SHP-1 coupled inhibitory receptors restrain the expansion of large pre-B cells and/or promote their differentiation into small pre-B cells. To test this hypothesis, we will determine the role of SHP- (Aim 1) and SHP-1 coupled inhibitory receptors (Aim 2) in the proliferation and differentiation of pre-B cells. We will also determine which components of IL-7 and pre-B signaling pathways are targeted by inhibitory receptors and phosphatases (Aim 3). These studies will shed light on a previously unexplored mechanism by which the transition from large pre-B to small pre-B cells is regulated and may illuminate novel therapeutic targets for diseases caused by disruption of this process, including immunodeficiency and malignancy. PUBLIC HEALTH RELEVANCE: Failure of B lymphocytes to transition appropriately through early developmental stages results in B cell immunodeficiency and/or malignancy in both humans and mice. The proposed studies will define and characterize a novel mechanism that controls these developmental transitions and may thus illuminate new therapeutic approaches for these potentially fatal diseases.