Myelin Basic Protein-Induced Production of Tumor Necrosis Factor-α and Interleukin-6, and Presentation of the Immunodominant Peptide MBP85-99 by B Cells from Patients with Relapsing-Remitting Multiple Sclerosis

B cells are involved in driving relapsing-remitting multiple sclerosis (RRMS), as demonstrated by the positive effect of therapeutic B-cell depletion. Aside from producing antibodies, B cells are efficient antigen-presenting and cytokine-secreting cells. Diverse polyclonal stimuli have been used to study cytokine production by B cells, but here we used the physiologically relevant self-antigen myelin basic protein (MBP) to stimulate B cells from untreated patients with RRMS and healthy donors. Moreover, we took advantage of the unique ability of the monoclonal antibody MK16 to recognize the immunodominant peptide MBP85-99 presented on HLA-DR15, and used it as a probe to directly study B-cell presentation of self-antigenic peptide. The proportions of B cells producing TNF-α or IL-6 after stimulation with MBP were higher in RRMS patients than in healthy donors, indicating a pro-inflammatory profile for self-reactive patient B cells. In contrast, polyclonal stimulation with PMA + ionomycin and MBP revealed no difference in cytokine profile between B cells from RRMS patients and healthy donors. Expanded disability status scale (EDSS) as well as multiple sclerosis severity score (MSSS) correlated with reduced ability of B cells to produce IL-10 after stimulation with MBP, indicative of diminished B-cell immune regulatory function in patients with the most severe disease. Moreover, EDSS correlated positively with the frequencies of TNF-α, IL-6 and IL-10 producing B cells after polyclonal stimulation. Patient-derived, IL-10-producing B cells presented MBP85-99 poorly, as did IL-6-producing B cells, particulary in the healthy donor group. B cells from MS patients thus present antigen to T cells in a pro-inflammatory context. These findings contribute to understanding the therapeutic effects of B-cell depletion in human autoimmune diseases, including MS.

B细胞（B cells）参与驱动复发缓解型多发性硬化（relapsing-remitting multiple sclerosis, RRMS），该结论已通过治疗性B细胞耗竭的积极疗效得到验证。除分泌抗体外，B细胞同时是高效的抗原呈递细胞与细胞因子分泌细胞。既往已有多种多克隆刺激剂被用于探究B细胞的细胞因子产生能力，但本研究采用生理相关的自身抗原髓鞘碱性蛋白（myelin basic protein, MBP），对未接受治疗的RRMS患者及健康捐献者的B细胞进行刺激。此外，本研究利用单克隆抗体MK16的独特特性——其可识别HLA-DR15分子呈递的免疫显性肽段MBP85-99——将其作为探针，直接研究B细胞对自身抗原肽的呈递过程。经MBP刺激后，RRMS患者体内产生肿瘤坏死因子-α（TNF-α）或白细胞介素-6（IL-6）的B细胞比例显著高于健康捐献者，提示自身反应性患者B细胞呈现促炎表型。与之相反，采用佛波醇酯（PMA）与离子霉素（ionomycin）联合MBP进行多克隆刺激时，RRMS患者与健康捐献者的B细胞在细胞因子谱上未表现出显著差异。扩展残疾状态量表（Expanded Disability Status Scale, EDSS）与多发性硬化严重程度评分（Multiple Sclerosis Severity Score, MSSS）均与MBP刺激后B细胞产生白细胞介素-10（IL-10）的能力降低呈显著相关，表明病情最重的患者其B细胞的免疫调节功能出现损伤。此外，EDSS与多克隆刺激后产生TNF-α、IL-6及IL-10的B细胞频率呈正相关。患者来源的产生IL-10的B细胞呈递MBP85-99的能力较弱，产生IL-6的B细胞亦存在类似现象，该表型在健康捐献者组中尤为显著。综上，多发性硬化（multiple sclerosis, MS）患者的B细胞可在促炎环境下向T细胞（T cells）呈递抗原。本研究结果有助于阐明B细胞耗竭疗法在包括MS在内的人类自身免疫性疾病中的治疗作用。