INTRODUCTION The complement system, an essential part of the innate immune system, is involved in various autoimmune diseases. Activation of the complement system by autoantibodies results in immune activation and tissue damage. At the moment little is known about the role of the complement system in autoimmune liver disease, including primary biliary cholangitis (PBC), primary sclerosing cholangitis (PSC) and autoimmune hepatitis (AIH). Since inhibition of the complement system is currently being tested in several autoimmune diseases as a therapeutic option, its role in autoimmune liver disease requires further clarification. METHODS A review of the literature was performed on studies investigating complement activation in PBC, PSC and AIH. Since data on AIH were lacking immunohistochemical staining for IgG, C1q, C3d, C4d and C5b9 was performed on liver tissue of nine AIH patients, two healthy controls and one positive control (acute liver failure caused by paracetamol intoxication). RESULTS Immunohistochemical analysis in AIH revealed increased production of C3 and C4 by hepatocytes. Despite a strong staining for IgG in the immune infiltrate in AIH, C3d, C4d and C5b9 deposition was only present in one AIH patient and the deposition was restricted to the interface between portal tracts and liver parenchyma. No deposition was found in all other AIH patients or healthy controls. Literature review showed raised plasma C3 and C4 levels in AIH, PBC and PSC patients compared to healthy controls. For PBC and PSC no complement depositions at the bile ducts were reported. CONCLUSION AND DISCUSSION Although complement is involved in various autoimmune diseases, the role of complement in autoimmune liver disease seems limited. Therefore it is unlikely that complement inhibition will become a novel treatment option for these diseases.

中文翻译：

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补体激活在自身免疫性肝病中的作用。

简介补体系统是先天免疫系统的重要组成部分，涉及多种自身免疫性疾病。自身抗体激活补体系统会导致免疫激活和组织损伤。目前，关于补体系统在自身免疫性肝病（包括原发性胆源性胆管炎（PBC），原发性硬化性胆管炎（PSC）和自身免疫性肝炎（AIH））中的作用还知之甚少。由于补体系统的抑制作用目前正在几种自身免疫性疾病中作为治疗选择进行测试，因此其在自身免疫性肝病中的作用需要进一步阐明。方法对研究PBC，PSC和AIH中补体激活的研究进行了文献综述。由于有关AIH的数据缺乏针对IgG，C1q，C3d的免疫组织化学染色，在9例AIH患者，2个健康对照和1个阳性对照（对乙酰氨基酚中毒引起的急性肝衰竭）的肝脏组织上进行了C4d和C5b9的检测。结果AIH的免疫组织化学分析显示肝细胞产生C3和C4的增加。尽管AIH的免疫浸润液中IgG染色很强，但仅一名AIH患者存在C3d，C4d和C5b9沉积，并且沉积局限于门道与肝实质之间的界面。在所有其他AIH患者或健康对照者中均未发现沉积物。文献综述显示，与健康对照组相比，AIH，PBC和PSC患者血浆C3和C4水平升高。对于PBC和PSC，在胆管中没有补体沉积的报道。结论与讨论尽管补体参与多种自身免疫性疾病，补体在自身免疫性肝病中的作用似乎是有限的。因此，补体抑制不可能成为这些疾病的新颖治疗选择。