胸腺调节B细胞功能缺陷在AChR中枢失耐受、MG发病中的作用及其机制研究

Regulatory cells are important for the maintenance of immunological homeostasis. Regulatory B cells (Breg) have been identified to a specific subsets of B cells with negative regulation in the immune system in mice and human recently. Accumulating data indicated defective Breg was related closely to the pathogenesis of several autoimmune disorders. Myasthenia gravis (MG) is a typical autoimmune disease and the pathogenesis of MG is closely related to abnormal immune response within thymus. Our studies firstly identified IL-10-producing CD19+CD24hiCD38hiBreg in human thymus, and this population of B cells suppressed CD4+ T cells proliferation, suggesting it might be involved in the central tolerance. However, the frequency of CD19+CD24hiCD38hiBreg and IL-10 expression were decreased in MG thymus compared with normal thymus, and the propotion of IL-10+ Breg was negatively correlated with disease severity, indicating defective thymic Breg were implicated in the pathogenesis of MG. Therefore, we will deeply study the role of human thymic Breg in the central tolerance; on this basis, further clarify the relationship between defective thymic Breg and the broken of central AChR self-tolerance, abnormal immune response within MG thymus, hoping restore central tolerance via Breg and provide a new therapeutic strategy for MG.

调节细胞对于免疫系统稳态维持具有举足轻重的作用；近年来，人们在人类和小鼠体内发现具有负向免疫调控功能的B细胞亚群-调节B细胞（Breg）。越来越多的证据表明：Breg功能缺陷与自身免疫性疾病的发生密切相关。重症肌无力（MG）是典型的自身免疫性疾病，其发生、发展与胸腺内异常免疫应答直接相关。我们研究首次发现人类胸腺存在表达IL-10的CD19+CD24hiCD38hiBreg，该群细胞可抑制胸腺CD4+T细胞增殖，提示其可能参与中枢耐受；然而，MG胸腺CD19+CD24hiCD38hiBreg比例及IL-10表达较健康胸腺明显下降，且与疾病的严重程度呈负相关，提示其功能缺陷可能参与MG发病。因此，本课题拟深入研究人类胸腺Breg在中枢免疫耐受中的作用；在此基础上，阐明MG胸腺Breg功能缺陷与AChR中枢失耐受、胸腺异常免疫应答的关系；有望通过Breg恢复中枢耐受，为MG提供新的治疗策略！

重症肌无力（MG）是由乙酰胆碱受体（AChR）抗体介导、细胞免疫依赖、补体参与的神经肌肉接头传递障碍的自身免疫性疾病。越来越多的证据表明重症肌无力的发生、发展与胸腺密切相关，调节B细胞（Breg）的负向免疫调节功能障碍参与了多种自身免疫性疾病的发病。我们研究发现：CD19+CD24hiCD38hi B细胞为主要分泌IL-10的细胞亚群，可作为Breg细胞表型，MG患者外周血和胸腺的Breg细胞比例均较正常人显著下降，且与疾病的严重程度呈负相关。MG胸腺Breg细胞不能有效抑制CD4+T细胞增殖及促炎细胞因子分泌，提示MG胸腺Breg功能缺陷。进一步研究发现：胸腺单细胞悬液在CD40单抗刺激下CD19+CD24hiCD38hi B细胞亚群中的磷酸化STAT3（p-STAT3）表达低于健康对照，提示MG患者胸腺STAT3信号通路受损可能参与Breg细胞功能缺陷。此外，将anti-CD40 mAb活化的CD19+CD24hiCD38hi B细胞输注EAMG小鼠，其肌无力症状明显改善。进一步分析发现Breg细胞可降低EAMG小鼠外周血促炎细胞因子的水平（IFN-γ、TNF-α），增加抑炎细胞因子Il-10水平。本研究首次确定胸腺Breg表型、明确了胸腺Breg功能缺陷在MG发病中的作用，初步探讨了胸腺Breg功能缺陷的机制；恢复Breg细胞数量或逆转其功能将为MG患者的免疫治疗提供新策略，具有重要的临床应用前景。