Loss of B Cell Tolerance in Primary Immunodeficiencies

抗体是在B细胞发育早期通过免疫球蛋白(Ig)基因片段的随机连接而产生的。免疫球蛋白基因重组可导致自身反应性抗体或B细胞受体(BCR)的组装。产生自我反应性受体的B细胞可以通过三种机制之一沉默：删除、无能和受体编辑。虽然缺失和无能最终消除了自我反应性B细胞，但受体编辑通过取代自身反应性抗体来拯救它们。我们通过跟踪B细胞发育过程中产生自身抗体的B细胞的进化，分析了人类对B细胞的耐受性是如何建立的。我们发现，55-75%的早期B细胞前体细胞表达自反应性抗体，并产生自身抗体 健康捐献者的B细胞在两个不同的检查点被从人群中移除。这个 沉默这些自身反应性B细胞的机制尚不清楚，抗体特异性和bcr信号在调节缺失、无能和受体编辑之间的平衡方面的作用也知之甚少。然而，系统性红斑狼疮和常见的可变免疫缺陷(CVID)患者的B细胞中发现了BCR信号的缺陷，这表明BCR信号可能在反选择自身反应性B细胞中发挥作用。 这项拟议研究的长期目标是通过分析BCR信号改变的原发免疫缺陷患者B细胞来阐明BCR在调节B细胞耐受中的作用。工作假设是，BCR信号在建立B细胞耐受性方面是必不可少的，当它受到影响时，自身反应性B细胞不会被沉默，而是可以迁移到外周。该项目的第一个目标将包括从X连锁无丙种球蛋白血症患者的血液中克隆单个B细胞的抗体，并确定修改后的BTK基因缺陷B细胞中BCR信号的阈值是否影响B细胞耐受机制。该项目的第二部分将分析CD40等BCR辅助受体如何影响高IgM患者B细胞耐受的建立和维持。该项目的第三部分将 研究CVID患者的B细胞耐受性。这些研究对于理解如何在保持或不保持自我耐受的情况下产生自我反应性B细胞具有重要意义。

Antibodies are generated during early B cell development by random joining of immunoglobulin (Ig) gene segments. Ig gene recombination can result in the assembly of self-reactive antibodies or B cell receptors (BCR). B cells that develop self-reactive receptors can be silenced by one of three mechanisms: deletion, anergy; and receptor editing. Whereas deletion and anergy ultimately eliminate self-reactive B cells, receptor editing rescues them by replacing autoreactive antibodies. We analyzed how B cell tolerance was established in humans by following the evolution of autoantibody-producing B cells during B cell development. We found that 55-75% of early B cell precursors expressed self-reactive antibodies and that autoantibodyproducing B cells in healthy donors were removed from the population at two discrete checkpoints. The mechanisms that prevail in silencing these autoreactive B cells remain to be characterized, and little is known about the effect of antibody specificity and BCR signaling in regulating the balance between deletion, anergy, and receptor editing. However, defects in BCR signaling have been reported in B cells from patients with systemic lupus erythematosus and common variable immunodeficiency (CVID) who frequently develop autoimmunity suggesting that BCR signaling may play a role in counterselecting self-reactive B cells. The long range goal of the proposed research is to elucidate the role of BCR in the regulation of B cell tolerance by analyzing primary immunodeficient patient B cells with altered BCR signaling. The working hypothesis is that BCR signaling is essential in establishing B cell tolerance and when it is affected, autoreactive B cells are not silenced and can migrate to the periphery. The first aim of the project will consist of cloning antibodies from single B cells from the blood of X-linked agammaglobulinemia patients and determine whether modified threshold of BCR signaling in btk gene-deficient B cells impacts B cell tolerance mechanisms. The second part of the project will analyze how BCR co-receptors such as CD40 influence the establishment and the maintenance of B cell tolerance in hyper-IgM patients. The third part of the project will study B cell tolerance in CVID patients. These studies have significant implications for understanding how self-reactive B cells may be produced with or without maintaining self-tolerance.