Department of Neurology, Yale University School of Medicine, New Haven, CT, USA.
Department of Immunobiology, Yale University School of Medicine, New Haven, CT, USA.
Brain. 2019 Jun 1;142(6):1598-1615. doi: 10.1093/brain/awz106.
Neuromyelitis optica spectrum disorders (NMOSD) constitute rare autoimmune disorders of the CNS that are primarily characterized by severe inflammation of the spinal cord and optic nerve. Approximately 75% of NMOSD patients harbour circulating pathogenic autoantibodies targeting the aquaporin-4 water channel (AQP4). The source of these autoantibodies remains unclear, but parallels between NMOSD and other autoantibody-mediated diseases posit compromised B cell tolerance checkpoints as common underlying and contributing factors. Using a well established assay, we assessed tolerance fidelity by creating recombinant antibodies from B cell populations directly downstream of each checkpoint and testing them for polyreactivity and autoreactivity. We examined a total of 863 recombinant antibodies. Those derived from three anti-AQP4-IgG seropositive NMOSD patients (n = 130) were compared to 733 antibodies from 15 healthy donors. We found significantly higher frequencies of poly- and autoreactive new emigrant/transitional and mature naïve B cells in NMOSD patients compared to healthy donors (P-values < 0.003), thereby identifying defects in both central and peripheral B cell tolerance checkpoints in these patients. We next explored whether pathogenic NMOSD anti-AQP4 autoantibodies can originate from the pool of poly- and autoreactive clones that populate the naïve B cell compartment of NMOSD patients. Six human anti-AQP4 autoantibodies that acquired somatic mutations were reverted back to their unmutated germline precursors, which were tested for both binding to AQP4 and poly- or autoreactivity. While the affinity of mature autoantibodies against AQP4 ranged from modest to strong (Kd 15.2-559 nM), none of the germline revertants displayed any detectable binding to AQP4, revealing that somatic hypermutation is required for the generation of anti-AQP4 autoantibodies. However, two (33.3%) germline autoantibody revertants were polyreactive and four (66.7%) were autoreactive, suggesting that pathogenic anti-AQP4 autoantibodies can originate from the pool of autoreactive naïve B cells, which develops as a consequence of impaired early B cell tolerance checkpoints in NMOSD patients.
视神经脊髓炎谱系疾病（NMOSD）构成了中枢神经系统罕见的自身免疫性疾病，主要表现为严重的脊髓和视神经炎症。大约 75%的 NMOSD 患者存在针对水通道蛋白 4（AQP4）的循环致病性自身抗体。这些自身抗体的来源尚不清楚，但 NMOSD 与其他自身抗体介导的疾病之间的相似之处表明，B 细胞耐受检查点受损是共同的潜在和促成因素。我们使用一种成熟的检测方法，通过从每个检查点的下游 B 细胞群中创建重组抗体，并测试它们的多反应性和自身反应性，来评估耐受保真度。我们总共检查了 863 种重组抗体。从 3 名抗 AQP4-IgG 阳性 NMOSD 患者（n = 130）中获得的抗体与 15 名健康供体的 733 种抗体进行了比较。与健康供体相比，NMOSD 患者的新移民/过渡性和成熟幼稚 B 细胞的多反应性和自身反应性频率显著升高（P 值 <0.003），从而确定了这些患者的中枢和外周 B 细胞耐受检查点均存在缺陷。我们接下来探讨了致病性 NMOSD 抗 AQP4 自身抗体是否可以源自存在于 NMOSD 患者幼稚 B 细胞群中的多反应性和自身反应性克隆池中。我们将六个获得体细胞突变的人抗 AQP4 自身抗体返回到它们的未突变种系前体，然后测试它们与 AQP4 的结合以及多反应性或自身反应性。虽然成熟自身抗体与 AQP4 的亲和力从适度到强（Kd 15.2-559 nM）不等，但没有一个种系返变体显示出与 AQP4 的任何可检测结合，表明体细胞超突变是产生抗 AQP4 自身抗体所必需的。然而，两个（33.3%）种系自身抗体返变体是多反应性的，四个（66.7%）是自身反应性的，这表明致病性抗 AQP4 自身抗体可以源自自身反应性幼稚 B 细胞池，这是 NMOSD 患者早期 B 细胞耐受检查点受损的结果。
