SARS-CoV-2感染对人体结构和生理的影响

Structural and physiological changes of the human body upon SARS-CoV-2 infection SARS-CoV-2感染对人体结构和生理的影响 1 2 equal first-author 1 2 equal 1 2 1 2 3 4 5 1 2 4 corresp Jing ZHOU, zhoujing@zju.edu.cn Jing ZHOU, zhoujing@zju.edu.cn zhoujing@zju.edu.cn https://orcid.org/0000-0001-6190-8053 Dr. Li Dak Sum & Yip Yio Chin Center for Stem Cells and Regenerative Medicine, Department of Orthopedic Surgery, the Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou310058, China Dr. Li Dak Sum & Yip Yio Chin Center for Stem Cells and Regenerative Medicine, Department of Orthopedic Surgery, the Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou310058, China Zhejiang University-University of Edinburgh Institute, Key Laboratory of Tissue Engineering and Regenerative Medicine of Zhejiang Province, Zhejiang University School of Medicine, Hangzhou310058, China Zhejiang University-University of Edinburgh Institute, Key Laboratory of Tissue Engineering and Regenerative Medicine of Zhejiang Province, Zhejiang University School of Medicine, Hangzhou310058, China Central Laboratories, School of Stomatology, Peking University, Beijing100871, China Central Laboratories, School of Stomatology, Peking University, Beijing100871, China Department of Sports Medicine, Zhejiang University School of Medicine, Hangzhou310009, China Department of Sports Medicine, Zhejiang University School of Medicine, Hangzhou310009, China Department of Anesthesiology, the First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou310003, China Department of Anesthesiology, the First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou310003, China Since December 2019, the novel coronavirus (severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)) has spread to many countries around the world, developing into a global pandemic with increasing numbers of deaths reported worldwide. To data, although some vaccines have been developed, there are no ideal drugs to treat novel coronavirus pneumonia (coronavirus disease 2019 (COVID-19)). By examining the structure of the coronavirus and briefly describing its possible pathogenesis based on recent autopsy reports conducted by various teams worldwide, this review analyzes the possible structural and functional changes of the human body upon infection with SARS-CoV-2. We observed that the most prominent pathological changes in COVID-19 patients are diffuse alveolar damage (DAD) of the lungs and microthrombus formation, resulting in an imbalance of the ventilation/perfusion ratio and respiratory failure. Although direct evidence of viral infection can also be found in other organs and tissues, the viral load is relatively small. The conclusion that the injuries of the extra-pulmonary organs are directly caused by the virus needs further investigation. 自2019年12月以来，新型冠状病毒（SARS-CoV-2）已蔓延至世界许多国家，目前已发展成为全球大流行，且全世界报告的死亡人数在不断增加。迄今为止，虽然已有一些疫苗研发出来，但仍没有理想的药物来治疗新型冠状病毒性肺炎（COVID-19）。本文通过对冠状病毒结构的研究，并根据世界各国最近的尸检报告简要描述其可能的发病机制，进一步分析了感染SARS-CoV-2后人体可能发生的结构和功能变化。我们观察到COVID-19患者最显著的病理改变是肺部弥漫性肺泡损伤（DAD）和微血栓形成，导致通气/灌注比失衡和呼吸衰竭。虽然在其他器官和组织中也可以发现病毒感染的直接证据，但病毒载量相对较小。肺外器官的损伤是否是由病毒直接引起的，有待进一步研究。 Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Coronavirus disease 2019 (COVID-19) Pathological change Pathogenesis 新型冠状病毒（SARS-CoV-2） 新型冠状病毒性肺炎（COVID-19） 病理改变 发病机制 1 Introduction 1 The novel coronavirus (severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)), which belongs to the β-coronavirus family, is the pathogen of novel coronavirus pneumonia (coronavirus disease 2019 (COVID-19)). Since December 2019, when the initial outbreak of COVID-19 occurred in China, a series of effective preventive control and medical treatment measures have been implemented, and have brought the pandemic under control to a certain extent. However, its incidence is still increasing globally. As of Mar. 14, 2021, there were more than 11.92 million COVID-19 patients worldwide, and the cumulative number of deaths had exceeded 2.6 million ( https://www.dynamed.com/condition/covid-19-and-cardiovascular-disease-patients https://www.dynamed.com/condition/covid-19-and-cardiovascular-disease-patients ). At present, the effects of novel coronavirus infection on the structure and physiology of the human body are still not completely understood, and although the vaccine has been developed, there are currently no ideal specific therapeutic drugs for novel coronavirus pneumonia patients. This paper reviews recent research progress on structural and physiological changes of the human body caused by novel coronavirus infection, so as to provide relevant cues and direction for specific drug research on COVID-19 treatment. 2 Biological traits of coronavirus 1 The coronavirus is circular in shape, with a diameter of about 125 nm ( Malik, 2020 Malik, 2020 ). Because its spike glycoprotein protrudes from the surface, the virus displays a "corona" appearance, hence the name coronavirus. There are four genera of coronavirus: α-coronavirus, β-coronavirus, γ-coronavirus, and δ‍-coronavirus. Mammals are susceptible to α-coronavirus and β-coronavirus, birds to γ-coronavirus, and both mammals and birds to δ-coronavirus ( Naqvi et al., 2020 Naqvi et al., 2020 ). The novel coronavirus (SARS-CoV-2), which leads to COVID-19, belongs to the β-coronavirus genus. For SARS-CoV-2, next-generation sequencing data have shown 79% and 50% homologies to SARS-CoV and Middle East respiratory syndrome coronavirus (MERS-CoV), respectively ( Malik, 2020 Malik, 2020 ). The coronavirus genome is constituted of a single-strand RNA ( Wu F et al., 2020 Wu F et al., 2020 ). Their genome is the largest of all RNA viruses, which usually range between 27 and 32 kb ( Li, 2016 Li, 2016 ). The RNA genome of coronavirus is encapsulated by a nucleocapsid protein (N) and is further enclosed within a lipoprotein envelope. There are at least three structural proteins associated with the viral envelope, in which membrane protein (M) and envelope protein (E) are involved in the assembly of the virus, and spike glycoprotein (S) mediates virus entry into host cells ( Li, 2016 Li, 2016 ; Shi et al., 2020 Shi et al., 2020 ). The S protein is committed to adhering the virus to host cells to initiate infection. It consists of three subunits, S1, S2, and S2' ( Li, 2016 Li, 2016 ), which play different roles in the adhesion of the virus to host cells. The S1 subunit can attach the virus to the host cell membrane via interaction with the angiotensin converting enzyme 2 (ACE2) receptor that initiates the infection process ( Hoffmann et al., 2020 Hoffmann et al., 2020 ). As a fusion protein, the S2 subunit contributes to the fusion of viruses with mammalian cell membranes. The S2 subunit functions as a fusion peptide ( Naqvi et al., 2020 Naqvi et al., 2020 ). In addition to mediating viral entry, spike proteins are the major factors determining the host range and tissue orientation of the virus and are also the main inducers of the host immune response. E proteins contribute to viral assembly and release. E proteins can aggregate on host membranes and form protein-lipid pores which are involved in ion transport and considered to be potential drug targets ( Fehr and Perlman, 2015 Fehr and Perlman, 2015 ). M proteins act simultaneously with E, N, and S proteins and are involved in RNA packaging ( Tang et al., 2020 Tang et al., 2020 ). 3 Pathogenesis of novel coronavirus infection 1 3.1 Invasion and replication of viruses 2 SARS-CoV-2 uses S proteins on its envelope to bind to ACE2 receptors on the cell membrane and relies on the synergistic activation of transmembrane serine protease 2 (TMPRSS2) ( Hoffmann et al., 2020 Hoffmann et al., 2020 ). Subsequently, the virus enters the host cell through membrane fusion ( Offringa et al., 2020 Offringa et al., 2020 ). After entry into the cell, it destroys the endoplasmic reticulum structure, forms a bilayer membrane vesicle structure (double-membrane vesicle (DMV)), and replicates and transcribes within it ( Oudshoorn et al., 2017 Oudshoorn et al., 2017 ). The genome of coronavirus contains a 5' cap structure and a 3' poly(A) tail, similar to eukaryotic messenger RNA (mRNA), so it can be translated just like eukaryotic mRNA ( Fehr and Perlman, 2015 Fehr and Perlman, 2015 ). In the overall process of RNA replication, the replicase is translated firstly and then a replicase complex is assembled. Afterwards, RNA replication and subgenomic RNA synthesis are carried out, and finally mature virus particles are formed. After assembly, the virus is transported to the surface of the cell within vesicles and released by exocytosis ( Malik, 2020 Malik, 2020 ). 3.2 Immunopathological effects of virus infection 2 When a virus enters a cell, its antigen presented by the antigen presentation cells (APCs) is then recognized by the cytotoxic T lymphocytes (CTLs), and stimulates humoral and cellular immunity in the human body ( Li XW et al., 2020 Li XW et al., 2020 ). Acute respiratory distress syndrome (ARDS) is considered to be the leading cause of death in patients with COVID-19 ( Li JZ et al., 2020 Li JZ et al., 2020 ). One of the main mechanisms of ARDS is the cytokine storm, which involves upregulation and activation of many inflammatory cytokines in tissue cells (mainly immune cells) after microbial infection of the body, causing ARDS ( Song et al., 2020 Song et al., 2020 ). Some studies have shown that inflammatory cytokines in serum are significantly increased in most patients with severe COVID-19, including interferon (IFN), interleukin (IL), tumour necrosis factor (TNF), colony-stimulating factor (CSF), IFN-γ-induced protein (IP10), C-reactive protein (CRP), monocyte chemotactic protein-1 (MCP1), and macrophage inflammatory protein 1-‍α (MIP1α) ( Meftahi et al., 2020 Meftahi et al., 2020 ; Zheng et al., 2020 Zheng et al., 2020 ). 3.3 Evasion of the immune system by coronavirus 2 In addition to the direct effects of viral infection and resulting immunopathological damage, immune evasion by the coronavirus is also one of the mechanisms, which promotes disease. Coronavirus has multiple ways to escape immune responses. Viruses are strictly parasitic within cells, thus avoiding the effects of antibodies, the complement system, and drugs. Pattern recognition receptors (PRRs) are mainly expressed on the surface of innate cells and can identify conserved components of exotic microorganisms, namely pathogen-associated molecular patterns (PAMPs). Nevertheless, SARS-CoV and MERS-CoV can induce cells to produce PRR-deficient DMVs and replicate and transcribe within these vesicles, thus avoiding attack by the host immune system ( Snijder et al., 2006 Snijder et al., 2006 ; Oudshoorn et al., 2017 Oudshoorn et al., 2017 ). Interestingly, SAR-CoV-2 can activate the immune response by PRR. Nuclear factor-‍κB (NF-κB), Janus kinase/signal transducers and activators of transcription (JAK/STAT), and other pathways can be activated after the cells are infected by SAR-CoV-2 through recognizing PRRs, thus activating the immune response ( Catanzaro et al., 2020 Catanzaro et al., 2020 ). It is believed that SARS-CoV-2 can achieve immune evasion through the coding of 22 N ‐linked glycosylation sites, the structure of open reading frame 3b (ORF3b), and the methylation of 5' cap of viral RNA ( Tan and Tang, 2021 Tan and Tang, 2021 ). Antigen presentation is also affected by the coronavirus, for example, by down-regulation of gene expression associated with antigen presentation ( Menachery et al., 2018 Menachery et al., 2018 ). ORF8 in SARS-CoV-2 genomes could bind to major histocompatibility complex-1 (MHC-1) to disrupt antigen presentation and initiate immune evasion ( Park, 2020 Park, 2020 ). 4 Damage inflicted by novel coronavirus on the human body 1 After Professor Liang LIU's team of Huazhong University of Science and Technology (Wuhan, China) conducted the first autopsy of a patient who died of COVID-19 in January 2020, other teams and organizations worldwide have also carried out autopsies on deceased COVID-19 patients. We are therefore able to summarize the structural and histological changes caused by SARS-CoV-2 infection observed in these autopsies. 4.1 Respiratory system 2 Gross observations: Dark-red bleeding areas and gray-white lesions were observed in cases with severe inflammatory lesions, which exhibited a patchy shape. The lung tissue felt tough and firm as in diffuse edema, and tissue weight was increased ( Barton et al., 2020 Barton et al., 2020 ; Sekulic et al., 2020 Sekulic et al., 2020 ; Suess and Hausmann, 2020 Suess and Hausmann, 2020 ). White mucus or pink foam could be seen within the bronchial lumen; and in the case of inflammatory lesions, a large amount of viscous secretions overflowed from the alveoli and fibrous cords were observed. There could be mild to moderate pleural effusions on both sides ( Ducloyer et al., 2020 Ducloyer et al., 2020 ; Fox et al., 2020 Fox et al., 2020 ; Suess and Hausmann, 2020 Suess and Hausmann, 2020 ). Microscopic observations: In a minimally invasive autopsy performed on patients who died of COVID-19 ( Xu et al., 2020 Xu et al., 2020 ), diffuse alveolar damage (DAD) was found in the lungs of many patients, but the pathological changes of DAD in different parts of the lung were discordant and often displayed heterogeneity in the same patient ( Sekulic et al., 2020 Sekulic et al., 2020 ). The pathological features of COVID-19-related DAD were not unique, indicating that there may be similar pathogenesis and etiological factors to other DAD ( Konopka et al., 2020 Konopka et al., 2020 ). DAD morphological progress includes three stages: exudation (1‒7 d), proliferation (8‒20 d), and fibrosis (20 d) ( Castro, 2006 Castro, 2006 ). According to available autopsy reports, COVID-19-related DAD was usually at the acute exudation stage or proliferation stage ( Polak et al., 2020 Polak et al., 2020 ), with only a few cases being classified at the fibrosis stage ( Fox et al., 2020 Fox et al., 2020 ). Acute exudative DAD is mainly characterized by diffuse alveolar exudation, with varying degrees of serous and fibrin exudates in the alveolar cavity which may be accompanied by the formation of hyaline membranes. Reactive hyperplasia of type Ⅱ alveolar epithelial cell (AECⅡ) was observed in many cases ( Bradley et al., 2020 Bradley et al., 2020 ). The nuclei of AEC‍Ⅱ were observed to be large and be deeply stained, with strong pleomorphism, suggesting viral cytopathic changes with diffuse epithelial shedding ( Duarte-Neto et al., 2020 Duarte-Neto et al., 2020 ). Capillary dilation and congestion were seen in the alveolar septum, and hyaline thrombosis and mixed thrombosis within blood vessels were also observed ( Polak et al., 2020 Polak et al., 2020 ). Other findings were inflammatory cell infiltration: predominantly monocytes, macrophages and a few multinucleated giant cells, lymphocytes, eosinophils, and neutrophils ( Bradley et al., 2020 Bradley et al., 2020 ). Some areas of interstitial fibrosis occurred in varying degrees, and fibroblast proliferation was seen ( Polak et al., 2020 Polak et al., 2020 ). A major feature of DAD in the hyperplastic stage is the organization of intra-alveolar exudates and alveolar septal fibrosis, which is more common in patients with long-term illness and hospitalization ( Duarte-Neto et al., 2020 Duarte-Neto et al., 2020 ). Cellulose exudation is seen in the alveolar cavity, and the hyaline membrane is replaced by proliferating fibroblasts, with fibroblast thrombus being formed in some alveolar cavities. In COVID-19 autopsies, the alveolar septal was thickened, with fibrosis and massive fibroblast hyperplasia. Local pulmonary tissue consolidation occurred, with infiltration by a small number of monocytes, macrophages, and small lymphocytes. Notably, secondary infection could overlap with viral infection, resulting in suppurative inflammation. A large number of bacteria and fungi were detected in some cases, suggesting that severe bacterial or fungal infections were secondary to DAD caused by coronavirus ( Zhou et al., 2020 Zhou et al., 2020 ). Coronavirus particles were found in the cytoplasm of tracheal and bronchial mucosal epithelial cells and AEC‍Ⅱ, as observed under electron microscopy. The quantitative polymerase chain reaction (qPCR) test for SARS-COV-2 on the tissues in some cases was positive in lung tissues ( Tian et al., 2020 Tian et al., 2020 ). Extensive alveolar injury, exudation, interstitial inflammatory thickening, and thrombosis are the causes of ventilation disorders. Airway epithelial hyperplasia, shedding, and mucus congestion increase ventilation obstruction. These changes are regarded as the pathological basis of fatal respiratory failure ( Bian and The COVID-19 Pathology Team, 2020 Bian and The COVID-19 Pathology Team, 2020 ). 4.2 Circulatory system 2 According to autopsy reports from 23 COVID-19 patients provided by five USA research institutions, the major organ damage in COVID-19 patients is not only in the lungs but also in the heart, which aggravates the circulatory system to enter the procoagulant state ( Buja et al., 2020 Buja et al., 2020 ). Gross observations: the weight of the heart increased slightly or negligibly. Cardiac enlargement and right ventricular dilatation were found. Under microscopy, scattered individual cardiomyocyte necrosis was observed, but no large or confluent area of cardiomyocyte necrosis was observed. There was no significant inflammatory lymphocytic infiltration ( Buja et al., 2020 Buja et al., 2020 ). There is little evidence of direct infection and replication of SARS-CoV-2 in cardiac cells ( Imazio et al., 2020 Imazio et al., 2020 ). Myocardial tissue damage may involve several potential mechanisms, including coronavirus-associated acute myocarditis, increased cytokine secretion, and hypoxia-induced cardiomyocyte apoptosis. Inflammation may be a potential mechanism of myocardial injury ( Buja et al., 2020 Buja et al., 2020 ). Additionally, autopsy reports indicated that blood clots and microangiopathy were present in the small blood vessels and capillaries of the lungs, accompanied by bleeding that caused death ( Ackermann et al., 2020 Ackermann et al., 2020 ). Elevated d-dimer was detected in some patients. This finding may suggest pulmonary vascular endothelial injury. SARS-CoV-2 infects the host through the ACE2 receptor, which is expressed in multiple organs of the human body, including the lung, heart, kidney, and intestine. Endothelial cells also displayed expression of ACE2 receptors. Varga et al. (2020) Varga et al. (2020) found the presence of viral inclusion bodies within endothelial cells in patients with COVID-19, and the accumulation of inflammatory cells associated with endothelial cells was also found in various organs. Both direct infection of endothelial cells by the coronavirus and the recruitment of immune cells mediated by the immune system can lead to extensive endothelial dysfunction with apoptosis. Endothelial dysfunction is the main determinant of microvascular dysfunction. It causes vasoconstriction by changing vascular balance, leading to organ ischemia, tissue edema, and inflammation in a coagulation-promoting state ( Buja et al., 2020 Buja et al., 2020 ). 4.3 Digestive system 2 Histological changes in the liver of COVID-19 patients were limited ( Tian et al., 2020 Tian et al., 2020 ); these could manifest as hepatocyte degeneration, punctate necrosis, fragment necrosis, bridging, or massive necrosis with neutrophil infiltration ( Duarte-Neto et al., 2020 Duarte-Neto et al., 2020 ). Lymphocyte infiltration and slight hepatic sinus dilation were observed within the hepatic lobules of deceased COVID-19 patients ( Tian et al., 2020 Tian et al., 2020 ). The gallbladder was highly filled and the mucosal epithelium was exfoliated ( Duarte-Neto et al., 2020 Duarte-Neto et al., 2020 ). Bile thrombus was seen in the small bile duct ( Bradley et al., 2020 Bradley et al., 2020 ). There was moderate microvascular steatosis and some necrotic hepatocytes were seen around the central vein, but no portal vein inflammation was observed ( Suess and Hausmann, 2020 Suess and Hausmann, 2020 ; Xu et al., 2020 Xu et al., 2020 ). There is no clear positive evidence that SARS-CoV-2 can cause liver injury directly. Drug-induced liver injury, previous history of chronic liver disease, and COVID-19-associated elevated inflammatory response may also cause liver injury. 4.4 Urinary system 2 Under light microscopy, glomerular segmental hyperplasia or necrosis, swelling of endothelial cells, and a small amount of protein exudate were observed in the balloon cavity ( Bian and The COVID-19 Pathology Team, 2020 Bian and The COVID-19 Pathology Team, 2020 ). The renal tubular lumen was widened, while the renal tubular epithelium was flat, exhibiting interstitial edema, mild inflammatory cell infiltration, and fibrous hyperplasia ( Menter et al., 2020 Menter et al., 2020 ). Occasionally, hemosiderin granules, protein tube types, and pigmented tube types were found. The proximal tubules were diffusely damaged. The brush border disappeared, and vacuoles were denatured or even necrotic ( Su et al., 2020 Su et al., 2020 ). Transparent tube type was common in distal tubules. There was noticeable red blood cell aggregation blocking the capillary lumen, and a few cases exhibited diffuse intravascular coagulation and small fibrin thrombus in glomerular capillaries, with hyaline thrombus also in evidence ( Menter et al., 2020 Menter et al., 2020 ). Microscopic examination showed that spherical virus particles with coronavirus characteristics found within proximal tubule epithelial cells and podocytes may be the cause of acute tubular necrosis and proteinuria in some patients. Viral particles in podocytes may be associated with occasional vacuolation, disappearance of pod processes, and detachment of podocytes ( Su et al., 2020 Su et al., 2020 ). Besides the direct toxicity of SARS-CoV-2, factors leading to acute kidney injury include coagulation abnormalities, systemic hypoxia, and possible drug- or hyperventilation-related rhabdomyolysis. Immunohistochemical (IHC) staining revealed no specific aggregation of different inflammatory cells, with T and B cells being mixed in non-specific scar tissues infiltrated by lymphocytes and scattered macrophages. CD235a staining confirmed that microvascular obstructions were mainly composed of red blood cells ( Su et al., 2020 Su et al., 2020 ). 4.5 Nervous system 2 Central nervous system complications have been observed to occur in a deceased COVID-19 patient. The autopsy revealed mild brain swelling and hemorrhagic lesions within the white matter of the cerebral hemisphere. There was axonal damage and accumulation of macrophages around the lesion ( Reichard et al., 2020 Reichard et al., 2020 ). Cerebral hyperemia and edema, and degeneration and ischemic changes of some neurons were also seen in other cases. Some cases showed neurasthenia, perivascular inflammatory cell infiltration, and focal cerebral infarction. A few cases showed brain hernias ( Bian and The COVID-19 Pathology Team, 2020 Bian and The COVID-19 Pathology Team, 2020 ). A number of studies have also shown that after SARS-CoV-2 infection, patients suffered from disorders of smell, taste, or the respiratory center ( Wu YS et al., 2020 Wu YS et al., 2020 ). The detection of viral copies by SARS-CoV-2-specific qPCR showed that the viral load in nerve tissue was relatively low, but the viral load in the olfactory bulb was slightly higher than that in the brain stem, which supported the hypothesis that the virus entered the brain through plates ( Menter et al., 2020 Menter et al., 2020 ). 4.6 Reproductive system 2 Under light microscopy, it was observed that testicular samples of deceased COVID-19 patients exhibited different degrees of spermatogenic cell reduction and injury, obvious damage to the seminiferous tubules, swelling, vacuolation and shedding to the lumen of supporting cells, and decrease of interstitial cells along with interstitial edema and mild inflammation of lymphocytes ( Yang et al., 2020 Yang et al., 2020 ). In some cases, no virus particles were observed by transmission electron microscope (TEM). No virus was detected within testicular samples by qPCR in a majority of patients ( Yang et al., 2020 Yang et al., 2020 ). These findings suggest that although testicular parenchyma is significantly impaired, no virus is present in the testes in most cases. Thus, testicular damage may not be directly caused by the viral infection. 4.7 Hematopoietic system 2 Red blood cells, medullary cells, and megakaryocytes decreased in most cases, with a few cases showing obvious hyperplasia ( Bian and The COVID-19 Pathology Team, 2020 Bian and The COVID-19 Pathology Team, 2020 ). 4.8 Immune system 2 Lymphocyte composition of spleen and lymph nodes was observed to decrease in varying degrees ( Pessoa et al., 2020 Pessoa et al., 2020 ), with CD4 + and CD8 + T cells decreasing significantly ( Bian and The COVID-19 Pathology Team, 2020 Bian and The COVID-19 Pathology Team, 2020 ). Within the spleen, splenic nodules underwent atrophy were decreased or became deficient ( Pessoa et al., 2020 Pessoa et al., 2020 ). Additionally, lymphocyte degeneration and necrosis and macrophage proliferation were observed ( Bradley et al., 2020 Bradley et al., 2020 ). Hemorrhage and anemia infarction were commonly observed in the spleen. Nevertheless, coronavirus particles were observed in the cytoplasm of macrophages in only a few cases under electron microscopy. qPCR detection of 2019 novel coronavirus viral nucleic acids showed mostly negative results ( Pessoa et al., 2020 Pessoa et al., 2020 ). 5 Conclusions 1 COVID-19 infection mainly occurs in the lungs, and the most prominent and important pathological changes are DAD and formation of pulmonary microthrombus, which can easily lead to hypoxia and thus respiratory failure. The disease may also involve various other organs and tissues ( Table 1 Table 1 ). Through qPCR detection of viral nucleic acids, electron microscopy, and IHC staining, SARS-CoV-2 RNA and viral particles have been detected in extrapulmonary tissues such as spleen, heart, liver, gallbladder, kidney, stomach, breast, testis, skin, nasopharynx, and oral mucosa, but the viral load is relatively small and not all COVID-19 patients exhibit direct evidence of viral infection in extrapulmonary tissues. Therefore, the injury of extra-pulmonary tissues may be caused by direct infection of the virus, a serious inflammatory reaction triggered by viral infection, or necrosis of tissue cells caused by hypoxia; or it may arise from the basic medical history of the patient. Elucidation of precise mechanisms requires analysis of more pathological biopsies. Organ Main pathological changes after SARS-CoV-2 infection Reference Lung Inflammatory lesions; different degrees of diffuse alveolar damage Xu et al., 2020 Xu et al., 2020 Heart Procoagulant state and thrombosis Buja et al., 2020 Buja et al., 2020 Liver Hepatocyte degeneration and necrosis, neutrophil and lymphocyte infiltration Duarte-Neto et al., 2020 Duarte-Neto et al., 2020 ; Tian et al., 2020 Tian et al., 2020 Gallbladder Gallbladder filling and mucosal epithelial exfoliation Duarte-Neto et al., 2020 Duarte-Neto et al., 2020 Kidney Glomerular segmental hyperplasia or necrosis; diffuse damage to the proximal tubules; transparent tube type common in distal tubules; inflammatory cell aggregation Bian and The COVID-19 Pathology Team, 2020 Bian and The COVID-19 Pathology Team, 2020 ; Menter et al., 2020 Menter et al., 2020 ; Su et al., 2020 Su et al., 2020 Brain Different degrees of cerebral congestion and edema; some neurons ischemic, degenerative, and infarcted; inflammatory cell aggregation; disorders of smell, taste, or respiratory center Bian and The COVID-19 Pathology Team, 2020 Bian and The COVID-19 Pathology Team, 2020 ; Reichard et al., 2020 Reichard et al., 2020 ; Wu YS et al., 2020 Wu YS et al., 2020 Testes Reduction and injury of parenchymal and stromal cells; mild inflammation Yang et al., 2020 Yang et al., 2020 Hematopoietic system Reduction or proliferation of red blood cells, bone marrow cells and megakaryocytes Bian and The COVID-19 Pathology Team, 2020 Bian and The COVID-19 Pathology Team, 2020 Spleen Hemorrhage and anemia infarction; atrophied, shrunk or absent splenic nodules; lymphocyte degeneration and necrosis Pessoa et al., 2020 Pessoa et al., 2020 References Ackermann M , Verleden SE , Kuehnel M , et al. , 2020 . Pulmonary vascular endothelialitis, thrombosis, and angiogenesis in COVID-19 . N Engl J Med , 383 ( 2 ): 120 - 128 . https://doi.org/10.1056/NEJMoa2015432 https://doi.org/10.1056/NEJMoa2015432 Pulmonary vascular endothelialitis, thrombosis, and angiogenesis in COVID-19 Barton LM , Duval EJ , Stroberg E , et al. , 2020 . COVID-19 autopsies, Oklahoma, USA . Am J Clin Pathol , 153 ( 6 ): 725 - 733 . https://doi.org/10.1093/ajcp/aqaa062 https://doi.org/10.1093/ajcp/aqaa062 COVID-19 autopsies, Oklahoma, USA Bian XW , The COVID-19 Pathology Team , 2020 . Autopsy of COVID-19 patients in China . Nat Sci Rev , 7 ( 9 ): 1414 - 1418 . https://doi.org/10.1093/nsr/nwaa123 https://doi.org/10.1093/nsr/nwaa123 Autopsy of COVID-19 patients in China Bradley BT , Maioli H , Johnston R , et al. , 2020 . Histopathology and ultrastructural findings of fatal COVID-19 infections in Washington State: a case series . Lancet , 396 ( 10247 ): 320 - 332 . https://doi.org/10.1016/s0140-6736(20)31305-2 https://doi.org/10.1016/s0140-6736(20)31305-2 Histopathology and ultrastructural findings of fatal COVID-19 infections in Washington State: a case series Buja LM , Wolf DA , Zhao BH , et al. , 2020 . The emerging spectrum of cardiopulmonary pathology of the coronavirus disease 2019 (COVID-19): report of 3 autopsies from Houston, Texas, and review of autopsy findings from other United States cities . Cardiovasc Pathol , 48 : 107233 . https://doi.org/10.1016/j.carpath.2020.107233 https://doi.org/10.1016/j.carpath.2020.107233 The emerging spectrum of cardiopulmonary pathology of the coronavirus disease 2019 (COVID-19): report of 3 autopsies from Houston, Texas, and review of autopsy findings from other United States cities Castro CY , 2006 . ARDS and diffuse alveolar damage: a pathologist’s perspective . Semin Thorac Cardiovasc Surg , 18 ( 1 ): 13 - 19 . https://doi.org/10.1053/j.semtcvs.2006.02.001 https://doi.org/10.1053/j.semtcvs.2006.02.001 ARDS and diffuse alveolar damage: a pathologist’s perspective Catanzaro M , Fagiani F , Racchi M , et al. , 2020 . Immune response in COVID-19: addressing a pharmacological challenge by targeting pathways triggered by SARS-CoV-2 . Signal Transduct Target Ther , 5 : 84 . https://doi.org/10.1038/s41392-020-0191-1 https://doi.org/10.1038/s41392-020-0191-1 Immune response in COVID-19: addressing a pharmacological challenge by targeting pathways triggered by SARS-CoV-2 Duarte-Neto AN , Monteiro RAA , da Silva LFF , et al. , 2020 . Pulmonary and systemic involvement in COVID-19 patients assessed with ultrasound-guided minimally invasive autopsy . Histopathology , 77 ( 12 ): 186 - 197 . https://doi.org/10.1111/his.14160 https://doi.org/10.1111/his.14160 Pulmonary and systemic involvement in COVID-19 patients assessed with ultrasound-guided minimally invasive autopsy Ducloyer M , Gaborit B , Toquet C , et al. , 2020 . Complete post-mortem data in a fatal case of COVID-19: clinical, radiological and pathological correlations . Int J Legal Med , 134 ( 6 ): 2209 - 2214 . https://doi.org/10.1007/s00414-020-02390-1 https://doi.org/10.1007/s00414-020-02390-1 Complete post-mortem data in a fatal case of COVID-19: clinical, radiological and pathological correlations Fehr AR , Perlman S , 2015 . Coronaviruses: an overview of their replication and pathogenesis . In: Maier HJ, Bickerton E, Britton P (Eds.), Coronaviruses: Methods and Protocols . Humana Press , New York , p. 1 - 23 . https://doi.org/10.1007/978-1-4939-2438-7_1 https://doi.org/10.1007/978-1-4939-2438-7_1 Coronaviruses: an overview of their replication and pathogenesis Fox SE , Akmatbekov A , Harbert JL , et al. , 2020 . Pulmonary and cardiac pathology in African American patients with COVID-19: an autopsy series from New Orleans . Lancet Respir Med , 8 ( 7 ): 681 - 686 . https://doi.org/10.1016/s2213-2600(20)30243-5 https://doi.org/10.1016/s2213-2600(20)30243-5 Pulmonary and cardiac pathology in African American patients with COVID-19: an autopsy series from New Orleans Hoffmann M , Kleine-Weber H , Schroeder S , et al. , 2020 . SARS-CoV-2 cell entry depends on ACE2 and TMPRSS2 and is blocked by a clinically proven protease inhibitor . Cell , 181 ( 2 ): 271 - 280.e1-e5 . https://doi.org/10.1016/j.cell.2020.02.052 https://doi.org/10.1016/j.cell.2020.02.052 SARS-CoV-2 cell entry depends on ACE2 and TMPRSS2 and is blocked by a clinically proven protease inhibitor Imazio M , Klingel K , Kindermann I , et al. , 2020 . COVID-19 pandemic and troponin: indirect myocardial injury, myocardial inflammation or myocarditis? Heart , 106 ( 15 ): 1127 - 1131 . https://doi.org/10.1136/heartjnl-2020-317186 https://doi.org/10.1136/heartjnl-2020-317186 COVID-19 pandemic and troponin: indirect myocardial injury, myocardial inflammation or myocarditis? Konopka KE , Nguyen T , Jentzen JM , et al. , 2020 . Diffuse alveolar damage (DAD) resulting from coronavirus disease 2019 infection is morphologically indistinguishable from other causes of DAD . Histopathology , 77 ( 4 ): 570 - 578 . https://doi.org/10.1111/his.14180 https://doi.org/10.1111/his.14180 Diffuse alveolar damage (DAD) resulting from coronavirus disease 2019 infection is morphologically indistinguishable from other causes of DAD Li F , 2016 . Structure, function, and evolution of coronavirus spike proteins . Annu Rev Virol , 3 ( 1 ): 237 - 261 . https://doi.org/10.1146/annurev-virology-110615-042301 https://doi.org/10.1146/annurev-virology-110615-042301 Structure, function, and evolution of coronavirus spike proteins Li JZ , Gong XB , Wang ZG , et al. , 2020 . Clinical features of familial clustering in patients infected with 2019 novel coronavirus in Wuhan, China . Virus Res , 286 : 198043 . https://doi.org/10.1016/j.virusres.2020.198043 https://doi.org/10.1016/j.virusres.2020.198043 Clinical features of familial clustering in patients infected with 2019 Li XW , Geng MM , Peng YZ , et al. , 2020 . Molecular immune pathogenesis and diagnosis of COVID-19 . J Pharm Anal , 10 ( 2 ): 102 - 108 . https://doi.org/10.1016/j.jpha.2020.03.001 https://doi.org/10.1016/j.jpha.2020.03.001 Molecular immune pathogenesis and diagnosis of COVID-19 Malik YA , 2020 . Properties of coronavirus and SARS-CoV-2 . Malays J Pathol , 42 ( 1 ): 3 - 11 . Properties of coronavirus and SARS-CoV-2 Meftahi GH , Jangravi Z , Sahraei H , et al. , 2020 . The possible pathophysiology mechanism of cytokine storm in elderly adults with COVID-19 infection: the contribution of "inflame-aging" . Inflamm Res , 69 ( 9 ): 825 - 839 . https://doi.org/10.1007/s00011-020-01372-8 https://doi.org/10.1007/s00011-020-01372-8 The possible pathophysiology mechanism of cytokine storm in elderly adults with COVID-19 infection: the contribution of "inflame-aging" Menachery VD , Schafer A , Burnum-Johnson KE , et al. , 2018 . MERS-CoV and H5N1 influenza virus antagonize antigen presentation by altering the epigenetic landscape . Proc Natl Acad Sci USA , 115 ( 5 ): E1012 - E1021 . https://doi.org/10.1073/pnas.1706928115 https://doi.org/10.1073/pnas.1706928115 MERS-CoV and H5N1 influenza virus antagonize antigen presentation by altering the epigenetic landscape Menter T , Haslbauer JD , Nienhold R , et al. , 2020 . Postmortem examination of COVID-19 patients reveals diffuse alveolar damage with severe capillary congestion and variegated findings in lungs and other organs suggesting vascular dysfunction . Histopathology , 77 ( 2 ): 198 - 209 . https://doi.org/10.1111/his.14134 https://doi.org/10.1111/his.14134 Postmortem examination of COVID-19 patients reveals diffuse alveolar damage with severe capillary congestion and variegated findings in lungs and other organs suggesting vascular dysfunction Naqvi AAT , Fatima K , Mohammad T , et al. , 2020 . Insights into SARS-CoV-2 genome, structure, evolution, pathogenesis and therapies: structural genomics approach . Biochim Biophys Acta Mol Basis Dis , 1866 ( 10 ): 165878 . https://doi.org/10.1016/j.bbadis.2020.165878 https://doi.org/10.1016/j.bbadis.2020.165878 Insights into SARS-CoV-2 genome, structure, evolution, pathogenesis and therapies: structural genomics approach Offringa A , Montijn R , Singh S , et al. , 2020 . The mechanistic overview of SARS-CoV-2 using angiotensin-converting enzyme 2 to enter the cell for replication: possible treatment options related to the renin-angiotensin system . Eur Heart J Cardiovasc Pharmacother , 6 ( 5 ): 317 - 325 . https://doi.org/10.1093/ehjcvp/pvaa053 https://doi.org/10.1093/ehjcvp/pvaa053 The mechanistic overview of SARS-CoV-2 using angiotensin-converting enzyme 2 to enter the cell for replication: possible treatment options related to the renin-angiotensin system Oudshoorn D , Rijs K , Limpens RWAL , et al. , 2017 . Expression and cleavage of middle east respiratory syndrome coronavirus nsp3-4 polyprotein induce the formation of double-membrane vesicles that mimic those associated with coronaviral RNA replication . mBio , 8 ( 6 ): e01658 . https://doi.org/10.1128/mBio.01658-17 https://doi.org/10.1128/mBio.01658-17 Expression and cleavage of middle east respiratory syndrome coronavirus nsp3-4 polyprotein induce the formation of double-membrane vesicles that mimic those associated with coronaviral RNA replication Park MD , 2020 . Immune evasion via SARS-CoV-2 ORF8 protein? Nat Rev Immunol , 20 ( 7 ): 408 . https://doi.org/10.1038/s41577-020-0360-z https://doi.org/10.1038/s41577-020-0360-z Immune evasion via SARS-CoV-2 ORF8 protein? Pessoa MSL , Lima CFC , Pimentel ACF , et al. , 2020 . Multisystemic infarctions in COVID-19: focus on the spleen . Eur J Case Rep Intern Med , 7 ( 7 ): 001747 . https://doi.org/10.12890/2020_001747 https://doi.org/10.12890/2020_001747 Multisystemic infarctions in COVID-19: focus on the spleen Polak SB , van Gool IC , Cohen D , et al. , 2020 . A systematic review of pathological findings in COVID-19: a pathophysiological timeline and possible mechanisms of disease progression . Mod Pathol , 33 ( 11 ): 2128 - 2138 . https://doi.org/10.1038/s41379-020-0603-3 https://doi.org/10.1038/s41379-020-0603-3 A systematic review of pathological findings in COVID-19: a pathophysiological timeline and possible mechanisms of disease progression Reichard RR , Kashani KB , Boire NA , et al. , 2020 . Neuropathology of COVID-19: a spectrum of vascular and acute disseminated encephalomyelitis (ADEM)‍-like pathology . Acta Neuropathol , 140 ( 1 ): 1 - 6 . https://doi.org/10.1007/s00401-020-02166-2 https://doi.org/10.1007/s00401-020-02166-2 Neuropathology of COVID-19: a spectrum of vascular and acute disseminated encephalomyelitis (ADEM)‍-like pathology Sekulic M , Harper H , Nezami BG , et al. , 2020 . Molecular detection of SARS-CoV-2 infection in FFPE samples and histopathologic findings in fatal SARS-CoV-2 cases . Am J Clin Pathol , 154 ( 2 ): 190 - 200 . https://doi.org/10.1093/ajcp/aqaa091 https://doi.org/10.1093/ajcp/aqaa091 Molecular detection of SARS-CoV-2 infection in FFPE samples and histopathologic findings in fatal SARS-CoV-2 cases Shi Y , Wang G , Cai XP , et al. , 2020 . An overview of COVID-19 . J Zhejiang Univ-Sci B (Biomed & Biotechnol) , 21 ( 5 ): 343 - 360 . https://doi.org/10.1631/jzus.B2000083 https://doi.org/10.1631/jzus.B2000083 An overview of COVID-19 Snijder EJ , van der Meer Y , Zevenhoven-Dobbe J , et al. , 2006 . Ultrastructure and origin of membrane vesicles associated with the severe acute respiratory syndrome coronavirus replication complex . J Virol , 80 ( 12 ): 5927 - 5940 . https://doi.org/10.1128/JVI.02501-05 https://doi.org/10.1128/JVI.02501-05 Ultrastructure and origin of membrane vesicles associated with the severe acute respiratory syndrome coronavirus replication complex Song PP , Li W , Xie JQ , et al. , 2020 . Cytokine storm induced by SARS-CoV-2 . Clin Chim Acta , 509 : 280 - 287 . https://doi.org/10.1016/j.cca.2020.06.017 https://doi.org/10.1016/j.cca.2020.06.017 Cytokine storm induced by SARS-CoV-2 Su H , Yang M , Wan C , et al. , 2020 . Renal histopathological analysis of 26 postmortem findings of patients with COVID-19 in China . Kidney Int , 98 ( 1 ): 219 - 227 . https://doi.org/10.1016/j.kint.2020.04.003 https://doi.org/10.1016/j.kint.2020.04.003 Renal histopathological analysis of 26 postmortem findings of patients with COVID-19 in China Suess C , Hausmann R , 2020 . Gross and histopathological pulmonary findings in a COVID-19 associated death during self-isolation . Int J Legal Med , 134 ( 4 ): 1285 - 1290 . https://doi.org/10.1007/s00414-020-02319-8 https://doi.org/10.1007/s00414-020-02319-8 Gross and histopathological pulmonary findings in a COVID-19 associated death during self-isolation Tan Y , Tang FQ , 2021 . SARS-CoV-2-mediated immune system activation and potential application in immunotherapy . Med Res Rev , 41 ( 2 ): 1167 - 1194 . https://doi.org/10.1002/med.21756 https://doi.org/10.1002/med.21756 SARS-CoV-2-mediated immune system activation and potential application in immunotherapy Tang T , Bidon M , Jaimes JA , et al. , 2020 . Coronavirus membrane fusion mechanism offers a potential target for antiviral development . Antiviral Res , 178 : 104792 . https://doi.org/10.1016/j.antiviral.2020.104792 https://doi.org/10.1016/j.antiviral.2020.104792 Coronavirus membrane fusion mechanism offers a potential target for antiviral development Tian SF , Xiong Y , Liu H , et al. , 2020 . Pathological study of the 2019 novel coronavirus disease (COVID-19) through postmortem core biopsies . Mod Pathol , 33 ( 6 ): 1007 - 1014 . https://doi.org/10.1038/s41379-020-0536-x https://doi.org/10.1038/s41379-020-0536-x Pathological study of the 2019 novel coronavirus disease (COVID-19) through postmortem core biopsies Varga Z , Flammer AJ , Steiger P , et al. , 2020 . Endothelial cell infection and endotheliitis in COVID-19 . Lancet , 395 ( 10234 ): 1417 - 1418 . https://doi.org/10.1016/s0140-6736(20)30937-5 https://doi.org/10.1016/s0140-6736(20)30937-5 Endothelial cell infection and endotheliitis in COVID-19 Wu F , Zhao S , Yu B , et al. , 2020 . A new coronavirus associated with human respiratory disease in China . Nature , 579 ( 7798 ): 265 - 269 . https://doi.org/10.1038/s41586-020-2008-3 https://doi.org/10.1038/s41586-020-2008-3 A new coronavirus associated with human respiratory disease in China Wu YS , Xu XL , Chen ZJ , et al. , 2020 . Nervous system involvement after infection with COVID-19 and other coronaviruses . Brain Behav Immun , 87 : 18 - 22 . https://doi.org/10.1016/j.bbi.2020.03.031 https://doi.org/10.1016/j.bbi.2020.03.031 Nervous system involvement after infection with COVID-19 and other coronaviruses Xu Z , Shi L , Wang YJ , et al. , 2020 . Pathological findings of COVID-19 associated with acute respiratory distress syndrome . Lancet Respir Med , 8 ( 4 ): 420 - 422 . https://doi.org/10.1016/s2213-2600(20)30076-x https://doi.org/10.1016/s2213-2600(20)30076-x Pathological findings of COVID-19 associated with acute respiratory distress syndrome Yang M , Chen S , Huang B , et al. , 2020 . Pathological findings in the testes of COVID-19 patients: clinical implications . Eur Urol Focus , 6 ( 5 ): 1124 - 1129 . https://doi.org/10.1016/j.euf.2020.05.009 https://doi.org/10.1016/j.euf.2020.05.009 Pathological findings in the testes of COVID-19 patients: clinical implications Zheng Y , Sun LJ , Xu M , et al. , 2020 . Clinical characteristics of 34 COVID-19 patients admitted to intensive care unit in Hangzhou, China . J Zhejiang Univ-Sci B (Biomed & Biotechnol) , 21 ( 5 ): 378 - 387 . https://doi.org/10.1631/jzus.B2000174 https://doi.org/10.1631/jzus.B2000174 Clinical characteristics of 34 COVID-19 patients admitted to intensive care unit in Hangzhou, China Zhou PC , Liu ZG , Chen YH , et al. , 2020 . Bacterial and fungal infections in COVID-19 patients: a matter of concern . Infect Control Hosp Epidemiol , 41 ( 9 ): 1124 - 1125 . https://doi.org/10.1017/ice.2020.156 https://doi.org/10.1017/ice.2020.156 Bacterial and fungal infections in COVID-19 patients: a matter of concern Zhonglin WU, Qi ZHANG, Guo YE, Hui ZHANG, and Boon Chin HENG took the lead in writing the manuscript. Zhonglin WU and Qi ZHANG completed manuscript framework firstly. Yang FEI and Bing ZHAO revised, edited, and checked the final version. Jing ZHOU conceptualized and designed this study. All authors have read and approved the final manuscript and, therefore, have full access to all the data in the study and take responsibility for the integrity and security of the data. This work is supported by the National Key R&D Program of China (No. 2018YFC1105100) and the Zhejiang Provincial Natural Science Foundation of China (No. LY19H090021). 10.1631/jzus.B2000523 1673-1581（2021）04-0310-08 2020-09-02 2021-01-03 2021-03-16 2021-04-15 2022-05-09 © Zhejiang University Press 2021 Zhonglin WU, Qi ZHANG, Guo YE, Hui ZHANG, Boon Chin HENG, Yang FEI, Bing ZHAO, and Jing ZHOU declared that they have no conflict of interest. This article does not contain any studies with human or animal subjects performed by any of the authors. Compliance with ethics guidelines 浙江大学学报（英文版）（B辑：生物医学和生物技术） 4 22