Impact of regulatory T cells on human peripheral B cell tolerance

描述(由申请人提供)：免疫功能受损导致原发免疫缺陷通常与矛盾的自身免疫并发症相关。患有原发免疫缺陷的患者提供了难得的机会来研究特定缺陷基因对人类B细胞耐受性的调节和对发展中的自身反应性B细胞的去除的影响。在缺乏功能性BTK、CD19或介导TLR信号的分子如IRAK4、MyD88和UNC93B的患者中，B细胞受体(BCR)信号通路的改变导致中央检查点缺陷和未能反选发育中的自身反应性B细胞(1，2)。事实上，自身抗原与自身反应性BCR和TLR的结合未能诱导耐受机制，因为所有这些患者的B细胞中的受体信号阈值增加，自身反应性B细胞从骨髓渗漏到外周(1，2)。我们最新的研究表明，中枢B细胞耐受缺陷是许多自身免疫性疾病的主要原因，包括类风湿性关节炎(RA)、系统性红斑狼疮(SLE)和1型糖尿病(T1D)，它是与自身免疫分离的遗传因素的结果，并编码干扰BCR信号的变体(3-5)。然而，我们最近发现，多发性硬化(MS)患者仅表现出外周B细胞耐受缺陷，而中枢B细胞耐受通常是正常建立的。在CD40L和MHC II类缺陷患者中也观察到了类似的观察结果，他们指出调节性T细胞(Treg)和血清B细胞激活因子(BAFF)在清除外周发育的自身反应性B细胞方面具有潜在作用(6)。有趣的是，据报道多发性硬化症患者的Treg细胞功能存在缺陷。因此，通过对免疫缺陷、多内分泌病、肠病、X连锁综合征(IPEX)和自身免疫性多内分泌病-念珠菌病-外胚叶营养不良(APECED)患者的研究，建议在R21应用中分析Treg细胞作为第二轴控制外周B细胞耐受性的建立和维持，这些患者表现出Treg细胞室缺陷并患有自身免疫状况和许多自身反应性抗体的分泌。这项拟议研究的长期目标是确定调节健康人外周B细胞耐受性的机制，但在IPEX和APECED患者中可能存在缺陷。工作假说是，影响Treg细胞功能的遗传缺陷不仅干扰了外周自身反应性B细胞的移除，还可能导致它们的激活，从而潜在地有利于自身免疫的发展。与CD40L缺陷患者类似，我们预计发现FOXP3和AIRE缺陷的Treg细胞功能异常的患者将显示正常的中枢B细胞耐受检查点，但外周B细胞耐受检查点存在缺陷。我们还将评估Treg细胞可能诱导自身反应性B细胞死亡和有助于B细胞动态平衡调节的机制。总之，这项拟议的研究旨在证明Treg细胞在抑制外周自身反应性B细胞中的作用。 与公共卫生相关：这项建议旨在通过分析Foxp3和AIRE缺陷的Treg细胞频率和功能改变的患者，并评估Treg细胞可能阻止自身反应性B细胞在外周扩张的机制，来证明Treg细胞在外周清除自身反应性B细胞中的作用。

DESCRIPTION (provided by applicant): Impaired immune functions leading to primary immunodeficiencies often correlate with paradoxical autoimmune complications. Patients with primary immunodeficiencies provide rare opportunities to study the impact of specific defective genes on the regulation of B cell tolerance and the removal of developing autoreactive B cells in humans. Alterations in B cell receptor (BCR) signaling pathways in patients lacking functional BTK, CD19, or molecules mediating TLR signaling such as IRAK4, MyD88, and UNC93B result in a defective central checkpoint and a failure to counterselect developing autoreactive B cells (1, 2). Indeed, the binding of self-antigens to autoreactive BCRs and TLRs fail to induce tolerance mechanisms due to increase receptor signaling thresholds in all these patients' B cells and autoreactive B cells leaks from the bone marrow into the periphery (1, 2). Our latest investigations revealed that central B cell tolerance defects are primary to many autoimmune diseases including rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) and type 1 diabetes (T1D) and result from genetic factors segregating with autoimmunity and which encode variants interfering with BCR signaling (3-5). However, we recently found that patients with multiple sclerosis (MS) only displayed peripheral B cell tolerance defects whereas central B cell tolerance was often established normally. Similar observations were observed in CD40L- and MHC class II-deficient patients, who pointed to a potential role for regulatory T (Treg) cells and serum B-cell activating factor (BAFF) in the removal of developing autoreactive B cells in the periphery (6). Interestingly, Treg cell functions have been reported to be defective in MS patients. Hence, Treg cells as second axis controlling the establishment and the maintenance of B cell tolerance in the periphery is proposed to be analyzed in this R21 application by studying immune deficiency, polyendocrinopathy, enteropathy, X-linked syndrome (IPEX) and autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) patients, who display a defective Treg cell compartment and suffer from autoimmune condition and the secretion of many self-reactive antibodies. The long range goal of the proposed research is to determine the mechanisms that regulate peripheral B cell tolerance in healthy humans but may be defective in IPEX and APECED patients. The working hypothesis is that genetic defects impacting Treg cell functions not only interfere with the removal of autoreactive B cells in the periphery but may lead to their activation, thereby potentially favoring the development of autoimmunity. Similarly to CD40L-deficient patients, we expect to find that FOXP3- and AIRE-deficient patients with abnormal Treg cell functions will display normal central yet defective peripheral B cell tolerance checkpoints. We will also assess the mechanisms by which Treg cells may induce autoreactive B cell death and contribute to B cell homeostasis regulation. Altogether, the proposed study intends to demonstrate a role for Treg cells in the restraining autoreactive B cells in the periphery. PUBLIC HEALTH RELEVANCE: This proposal intends to demonstrate a role for Treg cells in the peripheral removal of autoreactive B cells by analyzing Foxp3- and AIRE-deficient patients with altered Treg cell frequencies and functions, and assessing mechanisms by which Treg cells may prevent autoreactive B cell expansion in the periphery.