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 IgG₁, IgG₃, and IgG₄, 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，表现为与神经肌肉接头 (NMJ) 蛋白抗体相关的肌肉无力和疲劳。最常见的自身抗体靶点是乙酰胆碱受体 (AChR)。假设自身抗体可能干扰神经传递的三种机制：直接拮抗受体、补体介导的突触后膜破坏以及增强受体的内化。这些机制很可能不止一种同时发挥作用。剖析自身抗体介导的病理机制需要源自患者的单克隆抗体。使用膜抗原捕获激活细胞分选 (MACACS)，我们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 特异性抗体均发生超突变，包括同种型 IgG ₁ 、IgG ₃和 IgG ₄ ，并识别 AChR 的不同亚基。尽管有明显的结合，但没有一种抗体对体外神经肌肉突触模型中测量的 AChR 或 AChR 依赖性补体激活表现出显着的拮抗作用，并且它们在体内不会诱导肌无力症状。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诱导严重的无力，这与肌肉中的 NMJ 破坏和补体激活有关。最强的补体激活是由针对 AChR 不同亚基的抗体组合介导的，这种组合还在体外诱导活细胞表面形成大的 AChR 簇。 我们认为不同表位特异性的抗体之间的协同作用是该疾病的基本特征，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相互作用的重要性可以解释众所周知的血清抗 AChR 滴度和临床严重程度之间的差异，并对目前正在研究的治疗策略产生影响。