Intrathymic Tfh/B Cells Interaction Leads to Ectopic GCs Formation and Anti-AChR Antibody Production: Central Role in Triggering MG Occurrence

Myasthenia gravis is a typical acetylcholine receptor (AChR) antibody-mediated autoimmune disease in which thymus frequently presents follicular hyperplasia or thymoma. It is now widely accepted that the thymus is probably the site of AChR autosensitization and autoantibody production. However, the exact mechanism that triggers intrathymic AChR antibody production is still unknown. T follicular helper cells, recently identified responsible for B cell maturation and antibody production in the secondary lymphoid organs, were involved in many autoimmune diseases. Newly studies found T follicular helper (Tfh) cells increased in the peripheral blood of myasthenia gravis (MG). Whether it appears in the thymus of MG and its role in the intrathymic B cells help and autoantibody production is unclear. Therefore, this study aims to determine in more detail whether Tfh/B cell interaction exist in MG thymus and to address its role in the ectopic germinal centers (GCs) formation and AChR antibody production. We observed the frequency of Tfh cells and its associated transcription factor Bcl-6, key cytokine IL-21 enhanced both in the thymocytes and peripheral blood mononuclear cells (PBMCs) of MG patients. In parallel, we also showed increased B cells and autoantibody titers in MG peripheral blood and thymus. Confocal microscope results demonstrated Tfh and B cells co-localized within the ectopic GCs in MG thymus, suggesting putative existence of Tfh/B cells interaction. In vitro studies further showed dynamic behavior of Tfh/B cells interaction and Tfh cells induced autoantibody secretion might through its effector cytokine IL-21. Altogether, our data demonstrated that intrathymic Tfh/B cells interaction played a key role in thymic ectopic GCs formation and anti-AChR antibody production, which might trigger MG occurrence.

重症肌无力是一种典型的由乙酰胆碱受体（AChR）抗体介导的自身免疫性疾病，其胸腺常呈现滤泡增生或胸腺瘤。现在人们普遍认为，胸腺可能是AChR自身致敏和自身抗体产生的部位。然而，触发胸腺内AChR抗体产生的确切机制仍然未知。T滤泡辅助细胞最近被确定在次级淋巴器官中负责B细胞成熟和抗体产生，它参与了许多自身免疫性疾病。新的研究发现，重症肌无力（MG）患者外周血中T滤泡辅助（Tfh）细胞增多。它是否出现在MG患者的胸腺中以及它在胸腺内B细胞辅助和自身抗体产生中的作用尚不清楚。因此，本研究旨在更详细地确定MG胸腺中是否存在Tfh/B细胞相互作用，并探讨其在异位生发中心（GCs）形成和AChR抗体产生中的作用。我们观察到MG患者的胸腺细胞和外周血单个核细胞（PBMCs）中Tfh细胞的频率及其相关转录因子Bcl - 6、关键细胞因子IL - 21均升高。同时，我们还发现MG患者外周血和胸腺中的B细胞和自身抗体滴度升高。共聚焦显微镜结果显示，Tfh细胞和B细胞在MG胸腺的异位GCs内共定位，提示可能存在Tfh/B细胞相互作用。体外研究进一步表明了Tfh/B细胞相互作用的动态行为，并且Tfh细胞诱导自身抗体分泌可能是通过其效应细胞因子IL - 21。总之，我们的数据表明，胸腺内Tfh/B细胞相互作用在胸腺异位GCs形成和抗AChR抗体产生中起关键作用，这可能引发MG的发生。