Department of Biomedicine, University Hospital Basel and University of Basel, Basel, Switzerland.
Neurologic Clinic and Policlinic and MS Center, University Hospital Basel, University of Basel, Basel, Switzerland.
Acta Neuropathol. 2022 Nov;144(5):1005-1025. doi: 10.1007/s00401-022-02493-6. Epub 2022 Sep 8.
Myasthenia gravis is an autoimmune disorder defined by muscle weakness and fatigability associated with antibodies against proteins of the neuromuscular junction (NMJ). The most common autoantibody target is the acetylcholine receptor (AChR). Three mechanisms have been postulated by which autoantibodies might interfere with neurotransmission: direct antagonism of the receptor, complement-mediated destruction of the postsynaptic membrane, and enhanced internalization of the receptor. It is very likely that more than one of these mechanisms act in parallel. Dissecting the mechanisms of autoantibody-mediated pathology requires patient-derived, monoclonal antibodies. Using membrane antigen capture activated cell sorting (MACACS), we isolated AChR-specific B cells from patients with myasthenia gravis, and produced six recombinant antibodies. All AChR-specific antibodies were hypermutated, including isotypes IgG, IgG, and IgG, and recognized different subunits of the AChR. Despite clear binding, none of the individual antibodies showed significant antagonism of the AChR measured in an in vitro neuromuscular synapse model, or AChR-dependent complement activation, and they did not induce myasthenic signs in vivo. However, combinations of antibodies induced strong complement activation in vitro, and severe weakness in a passive transfer myasthenia gravis rat model, associated with NMJ destruction and complement activation in muscle. The strongest complement activation was mediated by combinations of antibodies targeting disparate subunits of the AChR, and such combinations also induced the formation of large clusters of AChR on the surface of live cells in vitro. We propose that synergy between antibodies of different epitope specificities is a fundamental feature of this disease, and possibly a general feature of complement-mediated autoimmune diseases. The importance of synergistic interaction between antibodies targeting different subunits of the receptor can explain the well-known discrepancy between serum anti-AChR titers and clinical severity, and has implications for therapeutic strategies currently under investigation.
重症肌无力是一种自身免疫性疾病，其特征为肌肉无力和易疲劳，与神经肌肉接头（NMJ）的蛋白抗体有关。最常见的自身抗体靶标是乙酰胆碱受体（AChR）。已经提出了三种机制，即自身抗体可能干扰神经递质传递：受体的直接拮抗、补体介导的突触后膜破坏以及受体的内化增强。很可能这些机制中的一种以上并行作用。剖析自身抗体介导的病理学机制需要使用患者来源的单克隆抗体。我们使用膜抗原捕获激活细胞分选（MACACS），从重症肌无力患者中分离出 AChR 特异性 B 细胞，并产生了六种重组抗体。所有 AChR 特异性抗体均高度突变，包括 IgG、IgG 和 IgG 同种型，并且识别 AChR 的不同亚基。尽管有明确的结合，但在体外神经肌肉突触模型中，没有一种单独的抗体显示出对 AChR 的明显拮抗作用，也没有 AChR 依赖性补体激活作用，并且在体内也没有引起肌无力症状。然而，抗体组合在体外诱导强烈的补体激活，并在被动转移重症肌无力大鼠模型中引起严重的虚弱，伴有 NMJ 破坏和肌肉补体激活。最强的补体激活是由针对 AChR 不同亚基的抗体组合介导的，并且这种组合还诱导了体外活细胞表面 AChR 的大簇形成。我们提出，不同表位特异性抗体之间的协同作用是该疾病的一个基本特征，并且可能是补体介导的自身免疫性疾病的一般特征。针对受体不同亚基的抗体之间协同作用的重要性可以解释血清抗 AChR 滴度与临床严重程度之间的明显差异，并对目前正在研究的治疗策略具有重要意义。
