DataSheet_1_Circulating Memory B Cells in Early Multiple Sclerosis Exhibit Increased IgA+ Cells, Globally Decreased BAFF-R Expression and an EBV-Related IgM+ Cell Signature.docx

Multiple sclerosis (MS) is an immune-mediated inflammatory disease of the central nervous system that results in demyelination of axons, inefficient signal transmission and reduced muscular mobility. Recent findings suggest that B cells play a significant role in disease development and pathology. To further explore this, B cell profiles in peripheral blood from 28 treatment-naive patients with early MS were assessed using flow cytometry and compared to 17 healthy controls. Conventional and algorithm-based analysis revealed a significant increase in MS patients of IgA+ memory B cells (MBC) including CD27+, CD27- and Tbet+ subsets. Screening circulating B cells for markers associated with B cell function revealed a significantly decreased expression of the B cell activation factor receptor (BAFF-R) in MS patients compared to controls. In healthy controls, BAFF-R expression was inversely associated with abundance of differentiated MBC but this was not observed in MS. Instead in MS patients, decreased BAFF-R expression correlated with increased production of proinflammatory TNF following B cell stimulation. Finally, we demonstrated that reactivation of Epstein Barr Virus (EBV) in MS patients was associated with several phenotypic changes amongst MBCs, particularly increased expression of HLA-DR molecules and markers of a T-bet+ differentiation pathway in IgM+ MBCs. Together, these data suggest that the B cell compartment is dysregulated in MS regarding aberrant MBC homeostasis, driven by reduced BAFF-R expression and EBV reactivation. This study adds further insights into the contribution of B cells to the pathological mechanisms of MS, as well as the complex role of BAFF/BAFF-R signalling in MS.

多发性硬化（Multiple sclerosis, MS）是一种中枢神经系统免疫介导的炎性疾病，可导致轴突脱髓鞘、信号传导效率低下以及肌肉活动能力下降。近期研究表明，B细胞在该病的发生发展与病理进程中均发挥重要作用。为进一步探究该机制，本研究通过流式细胞术分析了28例初治早期多发性硬化患者的外周血B细胞谱，并与17名健康对照者进行对比。常规分析与基于算法的分析均显示，多发性硬化患者体内的IgA+记忆B细胞（memory B cells, MBC）——包括CD27+、CD27-及Tbet+亚群——占比显著升高。通过筛查循环B细胞的B细胞功能相关标志物，本研究发现，与健康对照相比，多发性硬化患者体内B细胞活化因子受体（BAFF-R）的表达水平显著降低。在健康对照者中，BAFF-R的表达水平与分化型记忆B细胞的丰度呈负相关，但这一关联在多发性硬化患者中并未观察到。反之，在多发性硬化患者体内，BAFF-R表达降低与B细胞受刺激后促炎性肿瘤坏死因子（TNF）的分泌增加呈显著相关。最后，本研究证实，多发性硬化患者体内EB病毒（Epstein Barr Virus, EBV）的再激活与记忆B细胞的多项表型改变密切相关，尤其在IgM+记忆B细胞中，可见人类白细胞抗原-DR（HLA-DR）分子表达上调，以及T-bet+分化通路标志物的升高。综上，上述数据表明，多发性硬化患者的B细胞池存在稳态失调，表现为记忆B细胞稳态异常，这一异常由BAFF-R表达降低与EB病毒再激活共同驱动。本研究进一步阐明了B细胞在多发性硬化病理机制中的作用，以及BAFF/BAFF-R信号通路在该病中发挥的复杂调控功能。