Complement plays a role in both hepatic ischemia reperfusion (IR) injury (IRI) and liver regeneration, but it is not clear how complement is activated in either process. We investigated the role of self‐reactive immunoglobulin M (IgM) antibodies in activating complement after hepatic IR and liver resection. Natural IgM antibodies that recognize danger‐associated molecular patterns (neoepitopes) activate complement following both hepatic IR and liver resection. Antibody‐deficient Rag1–/– mice were protected from hepatic IRI, but had increased hepatic injury and an impaired regenerative response after 70% partial hepatectomy (PHx). We identified two IgM monoclonal antibodies (mAbs) that specifically reversed the effect of Rag1 deficiency in both models; B4 (recognizes Annexin IV) and C2 (recognizes subset of phospholipids). Focusing on the B4‐specific response, we demonstrated sinusoidal colocalization of IgM and C3d in Rag1–/– mice that were reconstituted with B4 mAb, and furthermore that the Annexin IV neoepitope is specifically and similarly expressed after both hepatic IR and PHx in wild‐type (WT) mice. A single‐chain antibody construct (scFv) derived from B4 mAb blocked IgM binding and reduced injury post‐IR in WT mice, although, interestingly, B4scFv did not alter regeneration post‐PHx, indicating that anti‐Annexin IV antibodies are sufficient, but not necessary, for the regenerative response in the context of an entire natural antibody repertoire. We also demonstrated expression of the B4 neoepitope in postischemic human liver samples obtained posttransplantation and a corollary depletion in IgM recognizing the B4 and C2 neoepitopes in patient sera following liver transplantation. Conclusion: These data indicate an important role for IgM in hepatic IRI and regeneration, with a similar cross‐species injury‐specific recognition system that has implications for the design of neoepitope targeted therapeutics. (Hepatology 2018;67:721‐735).

中文翻译：

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天然 IgM 启动炎症反应，对肝缺血再灌注损伤和再生都很重要

补体在肝缺血再灌注 (IR) 损伤 (IRI) 和肝再生中都起作用，但尚不清楚补体在这两个过程中是如何被激活的。我们研究了自身反应性免疫球蛋白 M (IgM) 抗体在肝 IR 和肝切除术后激活补体中的作用。识别危险相关分子模式（新表位）的天然 IgM 抗体在肝 IR 和肝切除术后激活补体。抗体缺陷的 Rag1–/– 小鼠免受肝脏 IRI 的影响，但在 70% 部分肝切除术 (PHx) 后，肝损伤增加，再生反应受损。我们鉴定了两种 IgM 单克隆抗体 (mAb)，它们在两种模型中特异性地逆转了 Rag1 缺陷的影响；B4（识别膜联蛋白 IV）和 C2（识别磷脂）。专注于 B4 特异性反应，我们证明了 IgM 和 C3d 在用 B4 mAb 重组的 Rag1–/– 小鼠中的正弦共定位，此外，在野生型中，在肝脏 IR 和 PHx 后，膜联蛋白 IV 新表位特异性且相似地表达。型 (WT) 小鼠。源自 B4 mAb 的单链抗体构建体 (scFv) 在 WT 小鼠中阻断了 IgM 结合并减少了 IR 后损伤，尽管有趣的是，B4scFv 没有改变 PHx 后的再生，表明抗膜联蛋白 IV 抗体就足够了，但是对于整个天然抗体库的情况下的再生反应，这不是必需的。我们还证明了 B4 新表位在移植后获得的缺血后人类肝脏样本中的表达，以及在肝移植后识别患者血清中 B4 和 C2 新表位的 IgM 的必然消耗。结论：这些数据表明 IgM 在肝脏 IRI 和再生中的重要作用，具有类似的跨物种损伤特异性识别系统，对新表位靶向治疗的设计有影响。（肝病学 2018 年；67：721-735）。