A SARS-CoV-2-Related Virus from Malayan Pangolin Causes Lung Infection without Severe Disease in Human ACE2-Transgenic Mice.

Coronavirus disease 2019 (COVID-19), which is caused by the novel coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is the most severe emerging infectious disease in the current century. The discovery of SARS-CoV-2-related coronaviruses (SARSr-CoV-2) in bats and pangolins in South Asian countries indicates that SARS-CoV-2 likely originated from wildlife. To date, two SARSr-CoV-2 strains have been isolated from pangolins seized in Guangxi and Guangdong by the customs agency of China, respectively. However, it remains unclear whether these viruses cause disease in animal models and whether they pose a transmission risk to humans. In this study, we investigated the biological features of a SARSr-CoV-2 strain isolated from a smuggled Malayan pangolin (Manis javanica) captured by the Guangxi customs agency, termed MpCoV-GX, in terms of receptor usage, cell tropism, and pathogenicity in wild-type BALB/c mice, human angiotensin-converting enzyme 2 (ACE2)-transgenic mice, and human ACE2 knock-in mice. We found that MpCoV-GX can utilize ACE2 from humans, pangolins, civets, bats, pigs, and mice for cell entry and infect cell lines derived from humans, monkeys, bats, minks, and pigs. The virus could infect three mouse models but showed limited pathogenicity, with mild peribronchial and perivascular inflammatory cell infiltration observed in lungs. Our results suggest that this SARSr-CoV-2 virus from pangolins has the potential for interspecies infection, but its pathogenicity is mild in mice. Future surveillance among these wildlife hosts of SARSr-CoV-2 is needed to monitor variants that may have higher pathogenicity and higher spillover risk. IMPORTANCE SARS-CoV-2, which likely spilled over from wildlife, is the third highly pathogenic human coronavirus. Being highly transmissible, it is perpetuating a pandemic and continuously posing a severe threat to global public health. Several SARS-CoV-2-related coronaviruses (SARSr-CoV-2) in bats and pangolins have been identified since the SARS-CoV-2 outbreak. It is therefore important to assess their potential of crossing species barriers for better understanding of their risk of future emergence. In this work, we investigated the biological features and pathogenicity of a SARSr-CoV-2 strain isolated from a smuggled Malayan pangolin, named MpCoV-GX. We found that MpCoV-GX can utilize ACE2 from 7 species for cell entry and infect cell lines derived from a variety of mammalian species. MpCoV-GX can infect mice expressing human ACE2 without causing severe disease. These findings suggest the potential of cross-species transmission of MpCoV-GX, and highlight the need of further surveillance of SARSr-CoV-2 in pangolins and other potential animal hosts.

Metabolic dysfunction associated fatty liver disease and coronavirus disease 2019: clinical relationship and current management.

The coronavirus disease 2019 (COVID-19) is caused by the severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2). At present, the COVID-19 has been prevalent worldwide for more than a year and caused more than four million deaths. Liver injury was frequently observed in patients with COVID-19. Recently, a new definition of metabolic dysfunction associated fatty liver disease (MAFLD) was proposed by a panel of international experts, and the relationship between MAFLD and COVID-19 has been actively investigated. Several previous studies indicated that the patients with MAFLD had a higher prevalence of COVID-19 and a tendency to develop severe type of respiratory infection, and others indicated that liver injury would be exacerbated in the patients with MAFLD once infected with COVID-19. The mechanism underlying the relationship between MAFLD and COVID-19 infection has not been thoroughly investigated, and recent studies indicated that multifactorial mechanisms, such as altered host angiotensin converting enzyme 2 (ACE2) receptor expression, direct viral attack, disruption of cholangiocyte function, systemic inflammatory reaction, drug-induced liver injury, hepatic ischemic and hypoxic injury, and MAFLD-related glucose and lipid metabolic disorders, might jointly contribute to both of the adverse hepatic and respiratory outcomes. In this review, we discussed the relationship between MAFLD and COVID-19 based on current available literature, and summarized the recommendations for clinical management of MAFLD patients during the pandemic of COVID-19.

HIGH HEPARANASE LEVEL IN SURVIVORS OF COVID-19 - INDICATOR OF VASCULAR AND PULMONARY RECOVERY?

ABSTRACT: Background: Severe progression of coronavirus disease 2019 (COVID-19) causes respiratory failure and critical illness. Recently, COVID-19 has been associated with heparanase (HPSE)-induced endothelial barrier dysfunction and inflammation, so called endothelitis, and therapeutic treatment with heparin or low-molecular-weight heparin (LMWH) targeting HPSE has been postulated. Because, up to this date, clinicians are unable to measure the severity of endothelitis, which can lead to multiorgan failure and concomitant death, we investigated plasma levels of HPSE and heparin-binding protein (HBP) in COVID-19 intensive care patients to render a possible link between endothelitis and these plasma parameters. Therefore, a prospective prolonged cohort study was conducted, including 47 COVID-19 patients from the intensive care unit. Plasma levels of HPSE, and HBP were measured daily by enzyme-linked immunosorbent assay in survivors (n = 35) and nonsurvivors (n = 12) of COVID-19 from admission until discharge or death. All patients were either treated with heparin or LMWH, aiming for an activated partial thromboplastin time of ≥60 seconds or an anti-Xa level of >0.8 IU/mL using enoxaparin, depending on the clinical status of the patient (patients with extracorporeal membrane oxygenation or >0.1 µg/kg/min noradrenaline received heparin, all others enoxaparin). Results: We found significantly higher plasma levels of HPSE and HBP in survivors and nonsurvivors of COVID-19, compared with healthy controls. Still, interestingly, plasma HPSE levels were significantly higher ( P < 0.001) in survivors compared with nonsurvivors of COVID-19. In contrast, plasma HBP levels were significantly reduced ( P < 0.001) in survivors compared with nonsurvivors of COVID-19. Furthermore, when patients received heparin, they had significantly lower HPSE ( P = 2.22 e - 16) and significantly higher HBP ( P = 0.00013) plasma levels as when they received LMWH. Conclusion: Our results demonstrated that patients, who recover from COVID-19-induced vascular and pulmonary damage and were discharged from the intensive care unit, have significantly higher plasma HPSE level than patients who succumb to COVID-19. Therefore, HPSE is not suitable as marker for disease severity in COVID-19 but maybe as marker for patient's recovery. In addition, patients receiving therapeutic heparin treatment displayed significantly lower heparanse plasma level than upon therapeutic treatment with LMWH.

Spike and nsp6 are key determinants of SARS-CoV-2 Omicron BA.1 attenuation.

The SARS-CoV-2 Omicron variant is more immune evasive and less virulent than other major viral variants that have so far been recognized1-12. The Omicron spike (S) protein, which has an unusually large number of mutations, is considered to be the main driver of these phenotypes. Here we generated chimeric recombinant SARS-CoV-2 encoding the S gene of Omicron (BA.1 lineage) in the backbone of an ancestral SARS-CoV-2 isolate, and compared this virus with the naturally circulating Omicron variant. The Omicron S-bearing virus robustly escaped vaccine-induced humoral immunity, mainly owing to mutations in the receptor-binding motif; however, unlike naturally occurring Omicron, it efficiently replicated in cell lines and primary-like distal lung cells. Similarly, in K18-hACE2 mice, although virus bearing Omicron S caused less severe disease than the ancestral virus, its virulence was not attenuated to the level of Omicron. Further investigation showed that mutating non-structural protein 6 (nsp6) in addition to the S protein was sufficient to recapitulate the attenuated phenotype of Omicron. This indicates that although the vaccine escape of Omicron is driven by mutations in S, the pathogenicity of Omicron is determined by mutations both in and outside of the S protein.

Neonatal imprinting of alveolar macrophages via neutrophil-derived 12-HETE.

Resident-tissue macrophages (RTMs) arise from embryonic precursors1,2, yet the developmental signals that shape their longevity remain largely unknown. Here we demonstrate in mice genetically deficient in 12-lipoxygenase and 15-lipoxygenase (Alox15-/- mice) that neonatal neutrophil-derived 12-HETE is required for self-renewal and maintenance of alveolar macrophages (AMs) during lung development. Although the seeding and differentiation of AM progenitors remained intact, the absence of 12-HETE led to a significant reduction in AMs in adult lungs and enhanced senescence owing to increased prostaglandin E2 production. A compromised AM compartment resulted in increased susceptibility to acute lung injury induced by lipopolysaccharide and to pulmonary infections with influenza A virus or SARS-CoV-2. Our results highlight the complexity of prenatal RTM programming and reveal their dependency on in trans eicosanoid production by neutrophils for lifelong self-renewal.

Lung Organoids as Model to Study SARS-CoV-2 Infection.

Coronavirus disease-2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has become a global pandemic and has severely affected socio-economic conditions and people's life. The lung is the major target organ infected and (seriously) damaged by SARS-CoV-2, so a comprehensive understanding of the virus and the mechanism of infection are the first choices to overcome COVID-19. Recent studies have demonstrated the enormous value of human organoids as platforms for virological research, making them an ideal tool for researching host-pathogen interactions. In this study, the various existing lung organoids and their identification biomarkers and applications are summarized. At the same time, the seven coronaviruses currently capable of infecting humans are outlined. Finally, a detailed summary of existing studies on SARS-CoV-2 using lung organoids is provided and includes pathogenesis, drug development, and precision treatment. This review highlights the value of lung organoids in studying SARS-CoV-2 infection, bringing hope that research will alleviate COVID-19-associated lung infections.

3D Ex vivo tissue platforms to investigate the early phases of influenza a virus- and SARS-CoV-2-induced respiratory diseases.

Pandemic outbreaks of viruses such as influenza virus or SARS-CoV-2 are associated with high morbidity and mortality and thus pose a massive threat to global health and economics. Physiologically relevant models are needed to study the viral life cycle, describe the pathophysiological consequences of viral infection, and explore possible drug targets and treatment options. While simple cell culture-based models do not reflect the tissue environment and systemic responses, animal models are linked with huge direct and indirect costs and ethical questions. Ex vivo platforms based on tissue explants have been introduced as suitable platforms to bridge the gap between cell culture and animal models. We established a murine lung tissue explant platform for two respiratory viruses, influenza A virus (IAV) and SARS-CoV-2. We observed efficient viral replication, associated with the release of inflammatory cytokines and the induction of an antiviral interferon response, comparable to ex vivo infection in human lung explants. Endolysosomal entry could be confirmed as a potential host target for pharmacological intervention, and the potential repurposing potentials of fluoxetine and interferons for host-directed therapy previously seen in vitro could be recapitulated in the ex vivo model.

Elevated Myl9 reflects the Myl9-containing microthrombi in SARS-CoV-2-induced lung exudative vasculitis and predicts COVID-19 severity.

The mortality of coronavirus disease 2019 (COVID-19) is strongly correlated with pulmonary vascular pathology accompanied by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection-triggered immune dysregulation and aberrant activation of platelets. We combined histological analyses using field emission scanning electron microscopy with energy-dispersive X-ray spectroscopy analyses of the lungs from autopsy samples and single-cell RNA sequencing of peripheral blood mononuclear cells to investigate the pathogenesis of vasculitis and immunothrombosis in COVID-19. We found that SARS-CoV-2 accumulated in the pulmonary vessels, causing exudative vasculitis accompanied by the emergence of thrombospondin-1-expressing noncanonical monocytes and the formation of myosin light chain 9 (Myl9)-containing microthrombi in the lung of COVID-19 patients with fatal disease. The amount of plasma Myl9 in COVID-19 was correlated with the clinical severity, and measuring plasma Myl9 together with other markers allowed us to predict the severity of the disease more accurately. This study provides detailed insight into the pathogenesis of vasculitis and immunothrombosis, which may lead to optimal medical treatment for COVID-19.

SARS-CoV-2 Omicron Induces Enhanced Mucosal Interferon Response Compared to other Variants of Concern, Associated with Restricted Replication in Human Lung Tissues.

SARS-CoV-2 Omicron variant has been characterized by decreased clinical severity, raising the question of whether early variant-specific interactions within the mucosal surfaces of the respiratory tract could mediate its attenuated pathogenicity. Here, we employed ex vivo infection of native human nasal and lung tissues to investigate the local-mucosal susceptibility and innate immune response to Omicron compared to Delta and earlier SARS-CoV-2 variants of concern (VOC). We show that the replication of Omicron in lung tissues is highly restricted compared to other VOC, whereas it remains relatively unchanged in nasal tissues. Mechanistically, Omicron induced a much stronger antiviral interferon response in infected tissues compared to Delta and earlier VOC-a difference, which was most striking in the lung tissues, where the innate immune response to all other SARS-CoV-2 VOC was blunted. Notably, blocking the innate immune signaling restored Omicron replication in the lung tissues. Our data provide new insights to the reduced lung involvement and clinical severity of Omicron.

DNA Based Vaccine Expressing SARS-CoV-2 Spike-CD40L Fusion Protein Confers Protection Against Challenge in a Syrian Hamster Model.

SARS-CoV-2 infections present a tremendous threat to public health. Safe and efficacious vaccines are the most effective means in preventing the infections. A variety of vaccines have demonstrated excellent efficacy and safety around the globe. Yet, development of alternative forms of vaccines remains beneficial, particularly those with simpler production processes, less stringent storage conditions, and the capability of being used in heterologous prime/boost regimens which have shown improved efficacy against many diseases. Here we reported a novel DNA vaccine comprised of the SARS-CoV-2 spike protein fused with CD40 ligand (CD40L) serving as both a targeting ligand and molecular adjuvant. A single intramuscular injection in Syrian hamsters induced significant neutralizing antibodies 3-weeks after vaccination, with a boost substantially improving immune responses. Moreover, the vaccine also reduced weight loss and suppressed viral replication in the lungs and nasal turbinates of challenged animals. Finally, the incorporation of CD40L into the DNA vaccine was shown to reduce lung pathology more effectively than the DNA vaccine devoid of CD40L. These results collectively indicate that this DNA vaccine candidate could be further explored because of its efficacy and known safety profile.

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

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.

Human NLRP1 is a sensor of pathogenic coronavirus 3CL proteases in lung epithelial cells.

Inflammation observed in SARS-CoV-2-infected patients suggests that inflammasomes, proinflammatory intracellular complexes, regulate various steps of infection. Lung epithelial cells express inflammasome-forming sensors and constitute the primary entry door of SARS-CoV-2. Here, we describe that the NLRP1 inflammasome detects SARS-CoV-2 infection in human lung epithelial cells. Specifically, human NLRP1 is cleaved at the Q333 site by multiple coronavirus 3CL proteases, which triggers inflammasome assembly and cell death and limits the production of infectious viral particles. Analysis of NLRP1-associated pathways unveils that 3CL proteases also inactivate the pyroptosis executioner Gasdermin D (GSDMD). Subsequently, caspase-3 and GSDME promote alternative cell pyroptosis. Finally, analysis of pyroptosis markers in plasma from COVID-19 patients with characterized severe pneumonia due to autoantibodies against, or inborn errors of, type I interferons (IFNs) highlights GSDME/caspase-3 as potential markers of disease severity. Overall, our findings identify NLRP1 as a sensor of SARS-CoV-2 infection in lung epithelia.

SARS-CoV-2 Variants of Concern Hijack IFITM2 for Efficient Replication in Human Lung Cells.

It has recently been shown that an early SARS-CoV-2 isolate (NL-02-2020) hijacks interferon-induced transmembrane proteins (IFITMs) for efficient replication in human lung cells, cardiomyocytes, and gut organoids. To date, several "variants of concern" (VOCs) showing increased infectivity and resistance to neutralization have emerged and globally replaced the early viral strains. Here, we determined whether the five current SARS-CoV-2 VOCs (Alpha, Beta, Gamma, Delta, and Omicron) maintained the dependency on IFITM proteins for efficient replication. We found that depletion of IFITM2 strongly reduces viral RNA production by all VOCs in the human epithelial lung cancer cell line Calu-3. Silencing of IFITM1 had modest effects, while knockdown of IFITM3 resulted in an intermediate phenotype. Strikingly, depletion of IFITM2 generally reduced infectious virus production by more than 4 orders of magnitude. In addition, an antibody directed against the N terminus of IFITM2 inhibited SARS-CoV-2 VOC replication in induced pluripotent stem cell (iPSC)-derived alveolar epithelial type II cells, thought to represent major viral target cells in the lung. In conclusion, endogenously expressed IFITM proteins (especially IFITM2) are critical cofactors for efficient replication of genuine SARS-CoV-2 VOCs, including the currently dominant Omicron variant. IMPORTANCE Recent data indicate that SARS-CoV-2 requires endogenously expressed IFITM proteins for efficient infection. However, the results were obtained with an early SARS-CoV-2 isolate. Thus, it remained to be determined whether IFITMs are also important cofactors for infection of emerging SARS-CoV-2 VOCs that outcompeted the original strains in the meantime. This includes the Omicron VOC, which currently dominates the pandemic. Here, we show that depletion of endogenous IFITM2 expression almost entirely prevents productive infection of Alpha, Beta, Gamma, Delta, and Omicron SARS-CoV-2 VOCs in human lung cells. In addition, an antibody targeting the N terminus of IFITM2 inhibited SARS-CoV-2 VOC replication in iPSC-derived alveolar epithelial type II cells. Our results show that SARS-CoV-2 VOCs, including the currently dominant Omicron variant, are strongly dependent on IFITM2 for efficient replication, suggesting a key proviral role of IFITMs in viral transmission and pathogenicity.

Inflammasome activation in infected macrophages drives COVID-19 pathology.

Severe COVID-19 is characterized by persistent lung inflammation, inflammatory cytokine production, viral RNA and a sustained interferon (IFN) response, all of which are recapitulated and required for pathology in the SARS-CoV-2-infected MISTRG6-hACE2 humanized mouse model of COVID-19, which has a human immune system1-20. Blocking either viral replication with remdesivir21-23 or the downstream IFN-stimulated cascade with anti-IFNAR2 antibodies in vivo in the chronic stages of disease attenuates the overactive immune inflammatory response, especially inflammatory macrophages. Here we show that SARS-CoV-2 infection and replication in lung-resident human macrophages is a critical driver of disease. In response to infection mediated by CD16 and ACE2 receptors, human macrophages activate inflammasomes, release interleukin 1 (IL-1) and IL-18, and undergo pyroptosis, thereby contributing to the hyperinflammatory state of the lungs. Inflammasome activation and the accompanying inflammatory response are necessary for lung inflammation, as inhibition of the NLRP3 inflammasome pathway reverses chronic lung pathology. Notably, this blockade of inflammasome activation leads to the release of infectious virus by the infected macrophages. Thus, inflammasomes oppose host infection by SARS-CoV-2 through the production of inflammatory cytokines and suicide by pyroptosis to prevent a productive viral cycle.

SARS-CoV-2 infection of human-induced pluripotent stem cells-derived lung lineage cells evokes inflammatory and chemosensory responses by targeting mitochondrial pathways.

The COVID-19 disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) primarily affects the lung, particularly the proximal airway and distal alveolar cells. NKX2.1+ primordial lung progenitors of the foregut (anterior) endoderm are the developmental precursors to all adult lung epithelial lineages and are postulated to play an important role in viral tropism. Here, we show that SARS-CoV-2 readily infected and replicated in human-induced pluripotent stem cell-derived proximal airway cells, distal alveolar cells, and lung progenitors. In addition to the upregulation of antiviral defense and immune responses, transcriptomics data uncovered a robust epithelial cell-specific response, including perturbation of metabolic processes and disruption in the alveolar maturation program. We also identified spatiotemporal dysregulation of mitochondrial heme oxygenase 1 (HMOX1), which is associated with defense against antioxidant-induced lung injury. Cytokines, such as TNF-α, INF-γ, IL-6, and IL-13, were upregulated in infected cells sparking mitochondrial ROS production and change in electron transport chain complexes. Increased mitochondrial ROS then activated additional proinflammatory cytokines leading to an aberrant cell cycle resulting in apoptosis. Notably, we are the first to report a chemosensory response resulting from SARS-CoV-2 infection similar to that seen in COVID-19 patients. Some of our key findings were validated using COVID-19-affected postmortem lung tissue sections. These results suggest that our in vitro system could serve as a suitable model to investigate the pathogenetic mechanisms of SARS-CoV-2 infection and to discover and test therapeutic drugs against COVID-19 or its consequences.

A Novel Soluble ACE2 Protein Provides Lung and Kidney Protection in Mice Susceptible to Lethal SARS-CoV-2 Infection.

BACKGROUND: Severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) uses full-length angiotensin converting enzyme 2 (ACE2) as a main receptor to enter target cells. The goal of this study was to demonstrate the preclinical efficacy of a novel soluble ACE2 protein with increased duration of action and binding capacity in a lethal mouse model of COVID-19. METHODS: A human soluble ACE2 variant fused with an albumin binding domain (ABD) was linked via a dimerization motif hinge-like 4-cysteine dodecapeptide (DDC) to improve binding capacity to SARS-CoV-2. This novel soluble ACE2 protein (ACE2-1-618-DDC-ABD) was then administered intranasally and intraperitoneally to mice before intranasal inoculation of SARS-CoV-2 and then for two additional days post viral inoculation. RESULTS: Untreated animals became severely ill, and all had to be humanely euthanized by day 6 or 7 and had pulmonary alveolar hemorrhage with mononuclear infiltrates. In contrast, all but one mouse infected with a lethal dose of SARS-CoV-2 that received ACE2-1-618-DDC-ABD survived. In the animals inoculated with SARS-CoV-2 that were untreated, viral titers were high in the lungs and brain, but viral titers were absent in the kidneys. Some untreated animals, however, had variable degrees of kidney proximal tubular injury as shown by attenuation of the proximal tubular brush border and increased NGAL and TUNEL staining. Viral titers in the lung and brain were reduced or nondetectable in mice that received ACE2-1-618-DDC-ABD, and the animals developed only moderate disease as assessed by a near-normal clinical score, minimal weight loss, and improved lung and kidney injury. CONCLUSIONS: This study demonstrates the preclinical efficacy of a novel soluble ACE2 protein, termed ACE2-1-618-DDC-ABD, in a lethal mouse model of SARS-CoV-2 infection that develops severe lung injury and variable degrees of moderate kidney proximal tubular injury.

Single-Cell Landscape of Lungs Reveals Key Role of Neutrophil-Mediated Immunopathology during Lethal SARS-CoV-2 Infection.

Due to the limitation of human studies with respect to individual difference or the accessibility of fresh tissue samples, how severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection results in pathological complications in lung, the main site of infection, is still incompletely understood. Therefore, physiologically relevant animal models under realistic SARS-CoV-2 infection conditions would be helpful to our understanding of dysregulated inflammation response in lung in the context of targeted therapeutics. Here, we characterized the single-cell landscape in lung and spleen upon SARS-CoV-2 infection in an acute severe disease mouse model that replicates human symptoms, including severe lung pathology and lymphopenia. We showed a reduction of lymphocyte populations and an increase of neutrophils in lung and then demonstrated the key role of neutrophil-mediated lung immunopathology in both mice and humans. Under severe conditions, neutrophils recruited by a chemokine-driven positive feedback produced elevated "fatal signature" proinflammatory genes and pathways related to neutrophil activation or releasing of granular content. In addition, we identified a new Cd177high cluster that is undergoing respiratory burst and Stfahigh cluster cells that may dampen antigen presentation upon infection. We also revealed the devastating effect of overactivated neutrophil by showing the highly enriched neutrophil extracellular traps in lung and a dampened B-cell function in either lung or spleen that may be attributed to arginine consumption by neutrophil. The current study helped our understanding of SARS-CoV-2-induced pneumonia and warranted the concept of neutrophil-targeting therapeutics in COVID-19 treatment. IMPORTANCE We demonstrated the single-cell landscape in lung and spleen upon SARS-CoV-2 infection in an acute severe disease mouse model that replicated human symptoms, including severe lung pathology and lymphopenia. Our comprehensive study revealed the key role of neutrophil-mediated lung immunopathology in SARS-CoV-2-induced severe pneumonia, which not only helped our understanding of COVID-19 but also warranted the concept of neutrophil targeting therapeutics in COVID-19 treatment.

A proposed lung ultrasound and phenotypic algorithm for the care of COVID-19 patients with acute respiratory failure.

Pulmonary complications are the most common clinical manifestations of coronavirus disease (COVID-19). From recent clinical observation, two phenotypes have emerged: a low elastance or L-type and a high elastance or H-type. Clinical presentation, pathophysiology, pulmonary mechanics, radiological and ultrasound findings of these two phenotypes are different. Consequently, the therapeutic approach also varies between the two. We propose a management algorithm that combines the respiratory rate and oxygenation index with bedside lung ultrasound examination and monitoring that could help determine earlier the requirement for intubation and other surveillance of COVID-19 patients with respiratory failure.

RéSUMé: Les complications pulmonaires du coronavirus (COVID-19) constituent ses manifestations cliniques les plus fréquentes. De récentes observations cliniques ont fait émerger deux phénotypes : le phénotype à élastance faible ou type L (low), et le phénotype à élastance élevée, ou type H (high). La présentation clinique, la physiopathologie, les mécanismes pulmonaires, ainsi que les observations radiologiques et échographiques de ces deux différents phénotypes sont différents. L'approche thérapeutique variera par conséquent selon le phénotype des patients atteints de COVID-19 souffrant d'insuffisance respiratoire.

Altered TMPRSS2 usage by SARS-CoV-2 Omicron impacts infectivity and fusogenicity.

The SARS-CoV-2 Omicron BA.1 variant emerged in 20211 and has multiple mutations in its spike protein2. Here we show that the spike protein of Omicron has a higher affinity for ACE2 compared with Delta, and a marked change in its antigenicity increases Omicron's evasion of therapeutic monoclonal and vaccine-elicited polyclonal neutralizing antibodies after two doses. mRNA vaccination as a third vaccine dose rescues and broadens neutralization. Importantly, the antiviral drugs remdesivir and molnupiravir retain efficacy against Omicron BA.1. Replication was similar for Omicron and Delta virus isolates in human nasal epithelial cultures. However, in lung cells and gut cells, Omicron demonstrated lower replication. Omicron spike protein was less efficiently cleaved compared with Delta. The differences in replication were mapped to the entry efficiency of the virus on the basis of spike-pseudotyped virus assays. The defect in entry of Omicron pseudotyped virus to specific cell types effectively correlated with higher cellular RNA expression of TMPRSS2, and deletion of TMPRSS2 affected Delta entry to a greater extent than Omicron. Furthermore, drug inhibitors targeting specific entry pathways3 demonstrated that the Omicron spike inefficiently uses the cellular protease TMPRSS2, which promotes cell entry through plasma membrane fusion, with greater dependency on cell entry through the endocytic pathway. Consistent with suboptimal S1/S2 cleavage and inability to use TMPRSS2, syncytium formation by the Omicron spike was substantially impaired compared with the Delta spike. The less efficient spike cleavage of Omicron at S1/S2 is associated with a shift in cellular tropism away from TMPRSS2-expressing cells, with implications for altered pathogenesis.