Kupffer cell dysfunction in liver cirrhosis leads to uncontrolled infection

感染是肝硬化患者高死亡率的主要原因。肝硬化相关免疫功能障碍是一种一方面对病原体免疫应答不足，另一方面基础免疫激活增加，导致免疫系统多方面紊乱的病症。从生理学上讲，肝脏是防止病原体通过肠道屏障系统性传播的第一道防线。枯否细胞是肝脏内的巨噬细胞，具有独特的捕获循环病原体的能力，因此对肝脏的过滤功能有重要贡献。本研究旨在阐明肝硬化免疫功能障碍的机制。我们假设肝硬化枯否细胞受损，因此细菌清除和有效抗菌免疫力降低。将使用不同的肝损伤模型，例如损伤肝细胞的CCl 4模型、胆管结扎模型和胆管损伤的DDC模型，诱导小鼠实验性肝硬化。一旦建立了肝硬化，小鼠将感染临床相关的病原体（肠球菌属物种，E.大肠杆菌、非肠球菌链球菌、葡萄球菌。 aureus)具有良好的抗菌活性。通过使用复杂的活体成像技术来可视化肝脏血管系统中枯否细胞捕捉细菌的情况，我们希望能更好地了解肝硬化的潜在机制。初步数据表明枯否细胞对病原体捕获的显著损害，提高了某些对病原体捕获至关重要的分子（例如CRIg、TLR-4）下调的可能性。这将使用流式细胞术和质谱细胞术进一步检查。接下来我们将分析肝硬化中枯否细胞与中性粒细胞的相互作用。 肝硬化患者中性粒细胞的募集和中性粒细胞胞外捕集器（NET）的形成可能受到损害。Kubes实验室最近发现了一种腹膜修复巨噬细胞非血管募集的新机制，但尚不清楚腹膜巨噬细胞是否在感染中发挥作用。第三步，我们将研究腹腔巨噬细胞在健康和损伤肝脏感染中的作用。病理性细菌易位是肝硬化患者感染的重要来源。在拟议研究的第二部分，我们计划用荧光细菌在肝硬化小鼠的肠道中定殖。这些小鼠的肠、引流淋巴结和肝脏的活体成像将揭示病原体在穿过肠上皮屏障和可能的全身性扩散至其他器官后所采取的途径。通过对肝脏进行成像，重点关注枯否细胞和中性粒细胞，我们将探索肝硬化肝脏屏障功能缺陷的可能机制。明确其机制将有助于恢复促炎和抗炎免疫应答的平衡，从而改善患者的预后。

Infections contribute substantially to high mortality in patients with liver cirrhosis. Cirrhosis-associated immune dysfunction is a condition of insufficient immune response to pathogens on the one hand and increased basal immune activation on the other hand resulting in a multifaceted disturbance of the immune system. Physiologically the liver serves as a first-line defence to prevent systemic spreading of pathogens overcoming the intestinal barrier. Kupffer cells are liver resident macrophages with the unique capability to capture circulating pathogens, thus contributing essentially to the hepatic filtering function. The aim of the proposed research is to elucidate mechanisms of immune dysfunction in cirrhosis. We hypothesize that Kupffer cells in cirrhosis are impaired and therefore bacterial clearance and effective antibacterial immunity are reduced. Experimental cirrhosis in mice will be induced using different models of liver injury, e.g. CCl4 model which injures hepatocytes, bile duct ligation model and the DDC model of biliary injury. Once cirrhosis is established, mice will be infected with clinically relevant pathogens (Enterococcus species, E. coli, non-enterococcal streptococci, Staph. aureus). By using sophisticated intravital imaging to visualize Kupffer cells catching bacteria within the liver vasculature we hope to gain a better understanding of the underlying mechanisms in cirrhosis. Preliminary data suggest a significant impairment in pathogen catching by Kupffer cells, raising the possibility that certain molecules critical for pathogen catching (e.g. CRIg, TLR-4) are downregulated. This will be examined further using flow cytometry and mass cytometry. Next we will analyse the interplay of Kupffer cells with neutrophils in cirrhosis. Recruitment of neutrophils and formation of neutrophil extracellular traps (NETs) could be impaired in cirrhosis. The Kubes laboratory has recently identified a new mechanism of non-vascular recruitment of peritoneal repair macrophages, but it is unknown whether peritoneal macrophages have a role in infection. In a third step we will investigate the role of peritoneal macrophages in infection in healthy and injured livers. Pathological bacterial translocation is an important source of infections in patients with cirrhosis. For the second part of the proposed research, we plan to colonize the gut of cirrhotic mice with fluorescent bacteria. Intravital imaging of the intestine, draining lymph nodes and the liver of these mice will reveal the route pathogens take after crossing the epithelial barrier of the intestine and possibly systemic spreading to other organs. By imaging the liver with a focus on Kupffer cells and neutrophils we will explore a possible mechanism of defective barrier function of the liver in cirrhosis. Identifying the mechanisms will help to restore the balance of pro- and anti-inflammatory immune responses and as a result improve patients' prognosis.