Inhibitory receptors in early B cell development

说明(申请人提供)：免疫系统的正常功能需要发展一种B细胞谱系，能够识别广泛的外来抗原，同时保持自我耐受。为此，B细胞的发育通过一系列有序的事件进行，在这些事件中，免疫球蛋白(Ig)的重链和轻链被顺序地重新排列，并测试其功能性和自我反应性。在大的前B细胞阶段，成功重排Ig重链基因的细胞在IL-7和前BCR信号的响应下经历增殖扩张。这有助于扩大表达任何给定功能重链的细胞池。随着细胞分化为小的Pre，增殖最终停止 B期，对IL-7失去反应性。在这一阶段，Pre-BCR信号和IL-7信号的缺失都促进了Ig轻链重排。这种过渡受到了严格的控制，而且 它的破坏会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B细胞发育早期阶段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。成熟外周B细胞的激活受到含有抑制性受体的ITIM的限制，这些受体主要通过磷酸酶SHIP或SHP-1发挥作用。虽然SHIP已知也作用于前B细胞，但SHP-1依赖的抑制性受体在慢性粒细胞白血病早期阶段的作用 B细胞的发育还没有被探索过。这个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已经在B细胞系和其他类型的细胞中被证明可以抑制IL-7和BCR前信号通路的几个关键成分。来自MEV/MEV小鼠的祖细胞B细胞系表现出分化能力受损和对细胞因子信号的反应增强的迹象。更令人感兴趣的是，最近发现一种缺乏ITIM区域的抑制性受体CD22的突变形式在B细胞前体白血病中具有致病作用。我们的初步数据显示，gp49B的过度表达可以限制前B细胞在IL-7中的增殖或存活。gp49B是一种已知在其他细胞类型中通过SHP-1发挥作用的抑制性受体。因此，我们假设SHP-1偶联的抑制性受体抑制大的前B细胞的扩张和/或促进其向小的前B细胞的分化。为了验证这一假说，我们将确定SHP-(Aim 1)和SHP-1偶联抑制受体(Aim 2)在前B细胞增殖和分化中的作用。我们还将确定抑制受体和磷酸酶以IL-7和Pre-B信号通路的哪些成分为靶点(目标3)。这些研究将揭示一种以前未探索的机制，通过该机制调节从大的前B细胞到小的前B细胞的转变，并可能阐明这一过程中断所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：在人类和小鼠中，B淋巴细胞未能在早期发育阶段适当过渡会导致B细胞免疫缺陷和/或恶性。拟议的研究将定义和描述一种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.