Table_1_Complement Activation via the Lectin and Alternative Pathway in Patients With Severe COVID-19.xlsx

Complement plays an important role in the direct defense to pathogens, but can also activate immune cells and the release of pro-inflammatory cytokines. However, in critically ill patients with COVID-19 the immune system is inadequately activated leading to severe acute respiratory syndrome (SARS) and acute kidney injury, which is associated with higher mortality. Therefore, we characterized local complement deposition as a sign of activation in both lungs and kidneys from patients with severe COVID-19. Using immunohistochemistry we investigated deposition of complement factors C1q, MASP-2, factor D (CFD), C3c, C3d and C5b-9 as well as myeloperoxidase (MPO) positive neutrophils and SARS-CoV-2 virus particles in lungs and kidneys from 38 patients who died from COVID-19. In addition, tissue damage was analyzed using semi-quantitative scores followed by correlation with complement deposition. Autopsy material from non-COVID patients who died from cardiovascular causes, cerebral hemorrhage and pulmonary embolism served as control (n=8). Lung injury in samples from COVID-19 patients was significantly more pronounced compared to controls with formation of hyaline membranes, thrombi and edema. In addition, in the kidney tubular injury was higher in these patients and correlated with lung injury (r=0.361*). In autopsy samples SARS-CoV-2 spike protein was detected in 22% of the lungs of COVID-19 patients but was lacking in kidneys. Complement activation was significantly stronger in lung samples from patients with COVID-19 via the lectin and alternative pathway as indicated by deposition of MASP-2, CFD, C3d and C5b9. Deposits in the lung were predominantly detected along the alveolar septa, the hyaline membranes and in the alveolar lumina. In the kidney, complement was significantly more deposited in patients with COVID-19 in peritubular capillaries and tubular basement membranes. Renal COVID-19-induced complement activation occurred via the lectin pathway, while activation of the alternative pathway was similar in both groups. Furthermore, MPO-positive neutrophils were found in significantly higher numbers in lungs and kidneys of COVID-19 patients and correlated with local MASP-2 deposition. In conclusion, in patients who died from SARS-CoV-2 infection complement was activated in both lungs and kidneys indicating that complement might be involved in systemic worsening of the inflammatory response. Complement inhibition might thus be a promising treatment option to prevent deregulated activation and subsequent collateral tissue injury in COVID-19.

补体（Complement）在病原体直接防御过程中发挥关键作用，同时可激活免疫细胞并促进促炎细胞因子的释放。然而，新型冠状病毒肺炎（COVID-19）重症患者的免疫系统被过度激活，引发严重急性呼吸综合征（SARS）与急性肾损伤，且与更高的死亡率相关。因此，本研究以重症新冠患者肺部与肾脏的局部补体沉积作为补体激活的标志物，对其进行了表征。我们采用免疫组织化学法，对38例因新冠死亡患者的肺部及肾脏组织中的补体因子C1q、MASP-2、D因子（CFD）、C3c、C3d及C5b-9的沉积情况，以及髓过氧化物酶（MPO）阳性中性粒细胞与新型冠状病毒（SARS-CoV-2）病毒颗粒进行了检测。此外，通过半定量评分对组织损伤程度进行分析，并将其与补体沉积情况开展相关性研究。以因心血管疾病、脑出血及肺栓塞死亡的非新冠患者的尸检组织作为对照（n=8）。相较于对照组，新冠患者的肺部损伤更为显著，可见透明膜、血栓及水肿形成。此类患者的肾小管损伤程度更高，且与肺部损伤呈正相关（r=0.361*）。尸检样本中，新冠患者肺部的SARS-CoV-2刺突蛋白检出率为22%，但肾脏组织中未检测到该蛋白。新冠患者肺部的补体激活通过凝集素途径与替代途径实现，其激活程度显著高于对照组，具体体现为MASP-2、CFD、C3d及C5b-9的沉积。肺部补体沉积主要分布于肺泡隔、透明膜及肺泡腔内。在肾脏组织中，新冠患者的补体在肾小管周围毛细血管与肾小管基底膜中的沉积量显著更高。新冠诱导的肾脏补体激活通过凝集素途径发生，而两组的替代途径激活程度相似。此外，新冠患者肺部与肾脏中的MPO阳性中性粒细胞数量显著更高，且与局部MASP-2沉积情况呈正相关。综上，在因SARS-CoV-2感染死亡的患者中，其肺部与肾脏均出现补体激活，表明补体可能参与了炎症反应的全身性恶化。因此，补体抑制或许可作为一种极具前景的治疗策略，用以预防新冠患者体内补体的失调激活及其后续引发的附带组织损伤。