From the Institute for Neurosciences of Montpellier (A.J., A.A., G.T., J.D.), INSERM U1051, Montpellier University, Hôpital Saint Eloi, France; Department of Immunology (A.J.), CHU Montpellier, France ; Department of Neurology (A.A., G.T.), CHU Montpellier, Hôpital Gui de Chauliac, France; Institut de Génomique Fonctionnelle (C.R., J.R., G.T., J.D.), CNRS UMR5203, France; and Neuromuscular Diseases Unit (C.L., I.I., L.Q.), Hospital de la Santa Creu i Sant Pau, Universitat Autónoma de Barcelona, Spain.
Neurol Neuroimmunol Neuroinflamm. 2022 Aug 10;9(5). doi: 10.1212/NXI.0000000000200014. Print 2022 Sep.
IgG4 autoantibodies to neurofascin-155 (Nfasc155) are associated with a subgroup of patients with chronic inflammatory demyelinating polyneuropathy (CIDP), currently named autoimmune nodopathy. We previously demonstrated that those antibodies alter conduction along myelinated axons by inducing Nfasc155 depletion and paranode destruction. In blood, IgG4 have the potency to exchange their moiety with other unrelated IgG4 through a process called Fab-arm exchange (FAE). This process results in functionally monovalent antibodies and may affect the pathogenicity of autoantibodies. Here, we examined this issue and whether FAE is beneficial or detrimental for Nfasc155 autoimmune nodopathy.
The bivalency and monospecificity of anti-Nfasc155 were examined by sandwich ELISA in 10 reactive patients, 10 unreactive CIDP patients, and 10 healthy controls. FAE was induced in vitro using reduced glutathione and unreactive IgG4, and the ratio of the κ:λ light chain was monitored. To determine the pathogenic potential of bivalent anti-Nfasc155 IgG4, autoantibodies derived from patients were enzymatically cleaved into monovalent Fab and bivalent F(ab') or swapped with unreactive IgG4 and then were injected in neonatal animals.
Monospecific bivalent IgG4 against Nfasc155 were detected in the serum of all reactive patients, indicating that a fraction of IgG4 have not undergone FAE in situ. These IgG4 were, nonetheless, capable of engaging into FAE with unreactive IgG4 in vitro, and this decreased the levels of monospecific antibodies and modulated the ratio of the κ:λ light chain. When injected in animals, monovalent anti-Nfasc155 Fab did not alter the formation of paranodes; by contrast, both native anti-Nfasc155 IgG4 and F(ab') fragments strongly impaired paranode formation. The promotion of FAE with unreactive IgG4 also strongly diminished the pathogenic potential of anti-Nfasc155 IgG4 in animals and decreased IgG4 clustering on Schwann cells.
Our findings demonstrate that monospecific and bivalent anti-Nfasc155 IgG4 are detected in patients and that those autoantibodies are the pathogenic ones. The transformation of anti-Nfasc155 IgG4 into monovalent Fab or functionally monovalent IgG4 through FAE strongly decreases paranodal alterations. Bivalency thus appears crucial for Nfasc155 clustering and paranode destruction.
针对神经束蛋白-155（Nfasc155）的 IgG4 自身抗体与慢性炎症性脱髓鞘性多发性神经病（CIDP）的亚组患者有关，目前称为自身免疫性结节病。我们之前证明，这些抗体通过诱导 Nfasc155 耗竭和连接蛋白破坏来改变有髓轴突的传导。在血液中，IgG4 通过称为 Fab 臂交换（FAE）的过程有能力将其部分与其他不相关的 IgG4 交换。该过程导致功能单价抗体，并可能影响自身抗体的致病性。在这里，我们检查了这个问题，以及 FAE 是否有利于或不利于 Nfasc155 自身免疫性结节病。
通过夹心 ELISA 在 10 名反应性患者、10 名无反应性 CIDP 患者和 10 名健康对照中检查抗 Nfasc155 的二价和单特异性。使用还原型谷胱甘肽和无反应性 IgG4 在体外诱导 FAE，并监测 κ：λ 轻链的比值。为了确定单价抗 Nfasc155 IgG4 的致病潜力，从患者中获得的自身抗体被酶切为单价 Fab 和二价 F(ab')，或与无反应性 IgG4 交换，然后注入新生动物。
在所有反应性患者的血清中均检测到针对 Nfasc155 的单特异性二价 IgG4，表明 IgG4 的一部分尚未在原位发生 FAE。然而，这些 IgG4 能够在体外与无反应性 IgG4 发生 FAE，这降低了单特异性抗体的水平并调节了 κ：λ 轻链的比值。当注入动物时，单价抗 Nfasc155 Fab 不会改变连接蛋白的形成；相比之下，天然抗 Nfasc155 IgG4 和 F(ab')片段强烈损害连接蛋白的形成。与无反应性 IgG4 一起促进 FAE 也强烈降低了抗 Nfasc155 IgG4 在动物中的致病性，并减少了 IgG4 在 Schwann 细胞上的聚集。
我们的发现表明，在患者中检测到单特异性和二价抗 Nfasc155 IgG4，并且这些自身抗体是致病性的。通过 FAE 将抗 Nfasc155 IgG4 转化为单价 Fab 或功能单价 IgG4 强烈降低连接蛋白的改变。因此，二价对于 Nfasc155 聚集和连接蛋白破坏似乎至关重要。
