Lung pathology of severe acute respiratory syndrome (SARS): a study of 8 autopsy cases from Singapore

Pathogenesis and virulence of coronavirus disease: Comparative pathology of animal models for COVID-19

Animal models that can replicate clinical and pathologic features of severe human coronavirus infections have been instrumental in the development of novel vaccines and therapeutics. The goal of this review is to summarize our current understanding of the pathogenesis of coronavirus disease 2019 (COVID-19) and the pathologic features that can be observed in several currently available animal models. Knowledge gained from studying these animal models of SARS-CoV-2 infection can help inform appropriate model selection for disease modelling as well as for vaccine and therapeutic developments.

A spatially resolved single-cell lung atlas integrated with clinical and blood signatures distinguishes COVID-19 disease trajectories

COVID-19 is characterized by a broad range of symptoms and disease trajectories. Understanding the correlation between clinical biomarkers and lung pathology during acute COVID-19 is necessary to understand its diverse pathogenesis and inform more effective treatments. Here, we present an integrated analysis of longitudinal clinical parameters, peripheral blood markers, and lung pathology in 142 Brazilian patients hospitalized with COVID-19. We identified core clinical and peripheral blood signatures differentiating disease progression between patients who recovered from severe disease compared with those who succumbed to the disease. Signatures were heterogeneous among fatal cases yet clustered into two patient groups: "early death" (<15 days until death) and "late death" (>15 days). Progression to early death was characterized systemically and in lung histopathological samples by rapid endothelial and myeloid activation and the presence of thrombi associated with SARS-CoV-2+ macrophages. In contrast, progression to late death was associated with fibrosis, apoptosis, and SARS-CoV-2+ epithelial cells in postmortem lung tissue. In late death cases, cytotoxicity, interferon, and T helper 17 (TH17) signatures were only detectable in the peripheral blood after 2 weeks of hospitalization. Progression to recovery was associated with higher lymphocyte counts, TH2 responses, and anti-inflammatory-mediated responses. By integrating antemortem longitudinal blood signatures and spatial single-cell lung signatures from postmortem lung samples, we defined clinical parameters that could be used to help predict COVID-19 outcomes.

Mechanism of Lian Hua Qing Wen capsules regulates the inflammatory response caused by M1 macrophage based on cellular experiments and computer simulations

PURPOSE

The polarization of macrophages with the resulting inflammatory response play a crucial part in tissue and organ damage due to inflammatory. Study has proved Lian Hua Qing Wen capsules (LHQW) can reduce activation of inflammatory response and damage of tissue derived from the inflammatory reactions. However, the mechanism of LHQW regulates the macrophage-induced inflammatory response is unclear. Therefore, we investigated the mechanism of LHQW regulated the inflammatory response of M1 macrophages by cellular experiments and computer simulations.

METHODS

This study has analysed the targets and mechanisms of macrophage regulating inflammatory response at gene and protein levels through bioinformatics. The monomeric components of LHQW were analyzed by High Performance Liquid Chromatography (HPLC). We established the in vitro cell model by M1 macrophages (Induction of THP-1 cells into M1 macrophages). RT-qPCR and immunofluorescence were used to detect changes in gene and protein levels of key targets after LHQW treatment. Computer simulations were utilized to verify the binding stability of monomeric components and protein targets.

RESULTS

Macrophages had 140,690 gene targets, inflammatory response had 12,192 gene targets, intersection gene targets were 11,772. Key monomeric components (including: Pinocembrin, Fargesone-A, Nodakenin and Bowdichione) of LHQW were screened by HPLC. The results of cellular experiments indicated that LHQW could significantly reduce the mRNA expression of CCR5, CSF2, IFNG and TNF, thereby alleviating the inflammatory response caused by M1 macrophage. The computer simulations further validated the binding stability and conformation of key monomeric components and key protein targets, and IFNG/Nodakenin was able to form the most stable binding conformation for its action.

CONCLUSION

In this study, the mechanism of LHQW inhibits the polarization of macrophages and the resulting inflammatory response was investigated by computer simulations and cellular experiments. We found that LHQW may not only reduce cell damage and death by acting on TNF and CCR5, but also inhibit the immune recognition process and inflammatory response by regulating CSF2 and IFNG to prevent polarization of macrophages. Therefore, these results suggested that LHQW may act through multiple targets to inhibit the polarization of macrophages and the resulting inflammatory response.

Radiology of fibrosis. Part I: Thoracic organs

Sustained injury from factors such as hypoxia, infection, or physical damage may provoke improper tissue repair and the anomalous deposition of connective tissue that causes fibrosis. This phenomenon may take place in any organ, ultimately leading to their dysfunction and eventual failure. Tissue fibrosis has also been found to be central in both the process of carcinogenesis and cancer progression. Thus, its prompt diagnosis and regular monitoring is necessary for implementing effective disease-modifying interventions aiming to reduce mortality and improve overall quality of life. While significant research has been conducted on these subjects, a comprehensive understanding of how their relationship manifests through modern imaging techniques remains to be established. This work intends to provide a comprehensive overview of imaging technologies relevant to the detection of fibrosis affecting thoracic organs as well as to explore potential future advancements in this field.

Differential TLR-ERK1/2 activity promotes viral ssRNA and dsRNA mimic-induced dysregulated immunity in macrophages

RNA virus induced excessive inflammation and impaired antiviral interferon (IFN-I) responses are associated with severe disease. This innate immune response, also referred to as 'dysregulated immunity,' is caused by viral single-stranded RNA (ssRNA) and double-stranded-RNA (dsRNA) mediated exuberant inflammation and viral protein-induced IFN antagonism. However, key host factors and the underlying mechanism driving viral RNA-mediated dysregulated immunity are poorly defined. Here, using viral ssRNA and dsRNA mimics, which activate toll-like receptor 7 (TLR7) and TLR3, respectively, we evaluated the role of viral RNAs in causing dysregulated immunity. We show that murine bone marrow-derived macrophages (BMDMs) stimulated with TLR3 and TLR7 agonists induce differential inflammatory and antiviral cytokine response. TLR7 activation triggered a robust inflammatory cytokine/chemokine induction compared to TLR3 activation, whereas TLR3 stimulation induced significantly increased IFN/IFN stimulated gene (ISG) response relative to TLR7 activation. To define the mechanistic basis for dysregulated immunity, we examined cell-surface and endosomal TLR levels and downstream mitogen-activated protein kinase (MAPK) and nuclear factor kappa B (NF-kB) activation. We identified a significantly higher cell-surface and endosomal TLR7 expression compared to TLR3, which further correlated with early and robust MAPK (pERK1/2 and p-P38) and NF-kB activation in TLR7-stimulated macrophages. Furthermore, blocking EKR1/2, p38, and NF-kB activity reduced TLR3/7-induced inflammatory cytokine/chemokine levels, whereas only ERK1/2 inhibition enhanced viral RNA-mimic-induced IFN/ISG responses. Collectively, our results illustrate that high cell surface and endosomal TLR7 expression and robust ERK1/2 activation drive viral ssRNA mimic-induced excessive inflammatory and reduced IFN/ISG responses, and blocking ERK1/2 activity would mitigate viral-RNA/TLR-induced dysregulated immunity.

Virus-Induced Cell Fusion and Syncytia Formation

Most enveloped viruses encode viral fusion proteins to penetrate host cell by membrane fusion. Interestingly, many enveloped viruses can also use viral fusion proteins to induce cell-cell fusion, both in vitro and in vivo, leading to the formation of syncytia or multinucleated giant cells (MGCs). In addition, some non-enveloped viruses encode specialized viral proteins that induce cell-cell fusion to facilitate viral spread. Overall, viruses that can induce cell-cell fusion are nearly ubiquitous in mammals. Virus cell-to-cell spread by inducing cell-cell fusion may overcome entry and post-entry blocks in target cells and allow evasion of neutralizing antibodies. However, molecular mechanisms of virus-induced cell-cell fusion remain largely unknown. Here, I summarize the current understanding of virus-induced cell fusion and syncytia formation.

Differences in syncytia formation by SARS-CoV-2 variants modify host chromatin accessibility and cellular senescence via TP53

Coronavirus disease 2019 (COVID-19) remains a significant public health threat due to the ability of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants to evade the immune system and cause breakthrough infections. Although pathogenic coronaviruses such as SARS-CoV-2 and Middle East respiratory syndrome (MERS)-CoV lead to severe respiratory infections, how these viruses affect the chromatin proteomic composition upon infection remains largely uncharacterized. Here, we use our recently developed integrative DNA And Protein Tagging methodology to identify changes in host chromatin accessibility states and chromatin proteomic composition upon infection with pathogenic coronaviruses. SARS-CoV-2 infection induces TP53 stabilization on chromatin, which contributes to its host cytopathic effect. We mapped this TP53 stabilization to the SARS-CoV-2 spike and its propensity to form syncytia, a consequence of cell-cell fusion. Differences in SARS-CoV-2 spike variant-induced syncytia formation modify chromatin accessibility, cellular senescence, and inflammatory cytokine release via TP53. Our findings suggest that differences in syncytia formation alter senescence-associated inflammation, which varies among SARS-CoV-2 variants.

Differential effects of microRNAs miR-21, miR-99 and miR-145 on lung regeneration and inflammation during recovery from influenza pneumonia

In a mouse model of influenza pneumonia, we previously documented that proliferating alveolar type II (AT2) cells are the major stem cells involved in early lung recovery. Profiling of microRNAs revealed significant dysregulation of specific ones, including miR-21 and miR-99a. Moreover, miR-145 is known to exhibit antagonism to miR-21. This follow-up study investigated the roles of microRNAs miR-21, miR-99a, and miR-145 in the murine pulmonary regenerative process and inflammation during influenza pneumonia. Inhibition of miR-21 resulted in severe morbidity, and in significantly decreased proliferating AT2 cells due to impaired transition from innate to adaptive immune responses. Knockdown of miR-99a culminated in moderate morbidity, with a significant increase in proliferating AT2 cells that may be linked to PTEN downregulation. In contrast, miR-145 antagonism did not impact morbidity nor the proliferating AT2 cell population, and was associated with downregulation of TNF-alpha, IL1-beta, YM1, and LY6G. Hence, a complex interplay exists between expression of specific miRNAs, lung regeneration, and inflammation during recovery from influenza pneumonia. Inhibition of miR-21 and miR-99a (but not miR-145) can lead to deleterious cellular and molecular effects on pulmonary repair and inflammatory processes during influenza pneumonia.

Alveolar Type 2 Epithelial Cell Organoids: Focus on Culture Methods

Lung diseases rank third in terms of mortality and represent a significant economic burden globally. Scientists have been conducting research to better understand respiratory diseases and find treatments for them. An ideal in vitro model must mimic the in vivo organ structure, physiology, and pathology. Organoids are self-organizing, three-dimensional (3D) structures originating from adult stem cells, embryonic lung bud progenitors, embryonic stem cells (ESCs), and induced pluripotent stem cells (iPSCs). These 3D organoid cultures may provide a platform for exploring tissue development, the regulatory mechanisms related to the repair of lung epithelia, pathophysiological and immunomodulatory responses to different respiratory conditions, and screening compounds for new drugs. To create 3D lung organoids in vitro, both co-culture and feeder-free methods have been used. However, there exists substantial heterogeneity in the organoid culture methods, including the sources of AT2 cells, media composition, and feeder cell origins. This article highlights the currently available methods for growing AT2 organoids and prospective improvements to improve the available culture techniques/conditions. Further, we discuss various applications, particularly those aimed at modeling human distal lung diseases and cell therapy.

Deficiency in the production of antibodies to lipids correlates with increased lipid metabolism in severe COVID-19 patients

Background

Antibodies to lipids are part of the first line of defense against microorganisms and regulate the pro/anti-inflammatory balance. Viruses modulate cellular lipid metabolism to enhance their replication, and some of these metabolites are proinflammatory. We hypothesized that antibodies to lipids would play a main role of in the defense against SARS-CoV-2 and thus, they would also avoid the hyperinflammation, a main problem in severe condition patients.

Methods

Serum samples from COVID-19 patients with mild and severe course, and control group were included. IgG and IgM to different glycerophospholipids and sphingolipids were analyzed using a high-sensitive ELISA developed in our laboratory. A lipidomic approach for studying lipid metabolism was performed using ultra-high performance liquid chromatography coupled to electrospray ionization and quadrupole time-of-flight mass spectrometry (UHPLC-ESI-QTOF-MS).

Results

Mild and severe COVID-19 patients had higher levels of IgM to glycerophosphocholines than control group. Mild COVID-19 patients showed higher levels of IgM to glycerophosphoinositol, glycerophosphoserine and sulfatides than control group and mild cases. 82.5% of mild COVID-19 patients showed IgM to glycerophosphoinositol or glycerophosphocholines plus sulfatides or glycerophosphoserines. Only 35% of severe cases and 27.5% of control group were positive for IgM to these lipids. Lipidomic analysis identify a total of 196 lipids, including 172 glycerophospholipids and 24 sphingomyelins. Increased levels of lipid subclasses belonging to lysoglycerophospholipids, ether and/or vinyl-ether-linked glycerophospholipids, and sphingomyelins were observed in severe COVID-19 patients, when compared with those of mild cases and control group.

Conclusion

Antibodies to lipids are essential for defense against SARS-CoV-2. Patients with low levels of anti-lipid antibodies have an elevated inflammatory response mediated by lysoglycerophospholipids. These findings provide novel prognostic biomarkers and therapeutic targets.

Ultrastructural study confirms the formation of single and heterotypic syncytial cells in bronchoalveolar fluids of COVID-19 patients

BACKGROUND

SARS-CoV-2 was reported to induce cell fusions to form multinuclear syncytia that might facilitate viral replication, dissemination, immune evasion, and inflammatory responses. In this study, we have reported the types of cells involved in syncytia formation at different stages of COVID-19 disease through electron microscopy.

METHODS

Bronchoalveolar fluids from the mild (n = 8, SpO2 > 95%, no hypoxia, within 2-8 days of infection), moderate (n = 8, SpO2 90% to ≤ 93% on room air, respiratory rate ≥ 24/min, breathlessness, within 9-16 days of infection), and severe (n = 8, SpO2 < 90%, respiratory rate > 30/min, external oxygen support, after 17th days of infection) COVID-19 patients were examined by PAP (cell type identification), immunofluorescence (for the level of viral infection), scanning (SEM), and transmission (TEM) electron microscopy to identify the syncytia.

RESULTS

Immunofluorescence studies (S protein-specific antibodies) from each syncytium indicate a very high infection level. We could not find any syncytial cells in mildly infected patients. However, identical (neutrophils or type 2 pneumocytes) and heterotypic (neutrophils-monocytes) plasma membrane initial fusion (indicating initiation of fusion) was observed under TEM in moderately infected patients. Fully matured large-size (20-100 μm) syncytial cells were found in severe acute respiratory distress syndrome (ARDS-like) patients of neutrophils, monocytes, and macrophage origin under SEM.

CONCLUSIONS

This ultrastructural study on the syncytial cells from COVID-19 patients sheds light on the disease's stages and types of cells involved in the syncytia formations. Syncytia formation was first induced in type II pneumocytes by homotypic fusion and later with haematopoetic cells (monocyte and neutrophils) by heterotypic fusion in the moderate stage (9-16 days) of the disease. Matured syncytia were reported in the late phase of the disease and formed large giant cells of 20 to 100 μm.

Morphological prediction of lethal outcomes in the evaluation of lung tissue structural changes in patients on respiratory support with СOVID-19: Ukrainian experience

The impact of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on lung tissue in patients on respiratory support is of significant scientific interest in predicting mortality. This study aimed to analyze post-mortem histological changes in the lung tissue of COVID-19 patients on respiratory support using vital radiology semiotics. A total of 41 autopsies were performed on patients who died of SARS-CoV-2 and had confirmed COVID-19 by polymerase chain reaction (PCR) and radiological evidence of lung tissue consolidation and ground glass opacity. The results showed that the duration of COVID-19 in patients on respiratory support was significantly associated with the development of all stages of diffuse alveolar damage, acute fibrous organizing pneumonia, pulmonary capillary congestion, fibrin thrombi, perivascular inflammation, alveolar hemorrhage, proliferating interstitial fibroblasts, and pulmonary embolism. The prediction model for lethal outcomes based on the duration of total respiratory support had a sensitivity of 68.3% and a specificity of 87.5%. In conclusion, for COVID-19 patients on long-term respiratory support with radiological signs of ground glass opacity and lung consolidation, post-mortem morphological features included various stages of diffuse alveolar lung damage, pulmonary capillary congestion, fibrin clots, and perivascular inflammation.

Lung Expression of Macrophage Markers CD68 and CD163, Angiotensin Converting Enzyme 2 (ACE2), and Caspase-3 in COVID-19

Background and Objectives: The coronavirus (SARS-CoV-2) damages all systems and organs. Yet, to a greater extent, the lungs are particularly involved, due to the formation of diffuse exudative inflammation in the form of acute respiratory distress syndrome (ARDS) with next progression to pulmonary fibrosis. SARS-associated lung damage is accompanied by the pronounced activation of mononuclear cells, damage of the alveoli and microvessels, and the development of organized pneumonia. To study the expression of macrophage markers (CD68 and CD163), angiotensin-converting enzyme-2 (ACE2), and caspase-3 on the results of two fatal clinical observations of COVID-19. Materials and Methods: In both clinical cases, the female patients died from complications of confirmed COVID-19. Conventional morphological and immunohistochemical methods were used. Results: There was an acute exudative hemorrhagic pneumonia with the formation of hyaline membranes, focal organization of fibrin, stromal sclerosis, stasis, and thrombus formation in the lung vessels. Signs such as the formation of hyaline membranes, organization, and fibrosis were more pronounced in severe disease activity. The activation of CD68+/CD163+ macrophages could cause cell damage at an early stage of pneumonia development, and subsequently cause fibrotic changes in lung tissue. ACE2 expression in lung tissue was not detected in severe pneumonia, while in moderate pneumonia, weak expression was noted in individual cells of the alveolar epithelium and vascular endothelium. Conclusions: This finding could show the dependence of ACE2 expression on the severity of the inflammatory process in the lungs. The expression of caspase-3 was more pronounced in severe pneumonia.

Computational framework to understand the clinical stages of COVID-19 and visualization of time course for various treatment strategies

Coronavirus disease 2019 is known to be regulated by multiple factors such as delayed immune response, impaired T cell activation, and elevated levels of proinflammatory cytokines. Clinical management of the disease remains challenging due to interplay of various factors as drug candidates may elicit different responses depending on the staging of the disease. In this context, we propose a computational framework which provides insights into the interaction between viral infection and immune response in lung epithelial cells, with an aim of predicting optimal treatment strategies based on infection severity. First, we formulate the model for visualizing the nonlinear dynamics during the disease progression considering the role of T cells, macrophages and proinflammatory cytokines. Here, we show that the model is capable of emulating the dynamic and static data trends of viral load, T cell, macrophage levels, interleukin (IL)-6 and TNF-α levels. Second, we demonstrate the ability of the framework to capture the dynamics corresponding to mild, moderate, severe, and critical condition. Our result shows that, at late phase (>15 days), severity of disease is directly proportional to pro-inflammatory cytokine IL6 and tumor necrosis factor (TNF)-α levels and inversely proportional to the number of T cells. Finally, the simulation framework was used to assess the effect of drug administration time as well as efficacy of single or multiple drugs on patients. The major contribution of the proposed framework is to utilize the infection progression model for clinical management and administration of drugs inhibiting virus replication and cytokine levels as well as immunosuppressant drugs at various stages of the disease.

Spatial transcriptomic characterization of COVID-19 pneumonitis identifies immune circuits related to tissue injury

Severe lung damage resulting from COVID-19 involves complex interactions between diverse populations of immune and stromal cells. In this study, we used a spatial transcriptomics approach to delineate the cells, pathways, and genes present across the spectrum of histopathological damage in COVID-19-affected lung tissue. We applied correlation network-based approaches to deconvolve gene expression data from 46 areas of interest covering more than 62,000 cells within well-preserved lung samples from 3 patients. Despite substantial interpatient heterogeneity, we discovered evidence for a common immune-cell signaling circuit in areas of severe tissue that involves crosstalk between cytotoxic lymphocytes and pro-inflammatory macrophages. Expression of IFNG by cytotoxic lymphocytes was associated with induction of chemokines, including CXCL9, CXCL10, and CXCL11, which are known to promote the recruitment of CXCR3+ immune cells. The TNF superfamily members BAFF (TNFSF13B) and TRAIL (TNFSF10) were consistently upregulated in the areas with severe tissue damage. We used published spatial and single-cell SARS-CoV-2 data sets to validate our findings in the lung tissue from additional cohorts of patients with COVID-19. The resulting model of severe COVID-19 immune-mediated tissue pathology may inform future therapeutic strategies.

Safety and efficacy of pulmonary physiotherapy in hospitalized patients with severe COVID-19 pneumonia (PPTCOVID study): A prospective, randomised, single-blind, controlled trial

BACKGROUND

Pulmonary physiotherapy (PPT) is an important treatment in the management of patients with different types of pulmonary disorders. We aimed to evaluate safety and efficacy of PPT in hospitalized patients with severe COVID-19 pneumonia.

METHODS

In this randomised, single-blind, controlled trial, we enrolled hospitalized, non-intubated patients (18 to 75 years with oxygen saturation (Spo2) in free-air breathing ≤90%) with COVID-19 pneumonia at a referral hospital. Participants were randomly assigned (1:1) to receive PPT (six sessions PPT with breathing exercises and airway clearance techniques) or basic care. The primary outcomes were venous blood O2 (pO2) and CO2 (pCO2) pressures, Spo2, and three-minute walking test (3MWT) that were assessed before and end of sixth session. Secondary outcomes included level of dyspnea, venous blood PH, one-month mortality, three-month mortality and short form-36 (SF-36) after one and three months. The assessor was blinded to the assignment. This trial is registered with ClinicalTrials.gov (NCT04357340).

FINDINGS

In April-May 2020, 40 participants were randomly assigned to PPT or basic care groups. While at the end of intervention, pO2 (adjusted mean difference to baseline measure (AMD) 6.43 mmHg [95%CI 2.8, 10.07], P<0.01), Spo2 (AMD 4.43% [95%CI 2.04, 6.83], P = 0.0011), and 3MTW (AMD 91.44 m [95%CI 68.88, 113.99], P<0.01) were higher in PPT group and basic care group, pCO2 was not improved (AMD -2.1 mmHg [95%CI-6.36, 2.21], P = 0.33). Based on the logistic model adjusted to baseline Spo2, the risks of mortality were reduced 81% ([95%CI: 97% reduction to 30% increase], P = .09) and 84% ([95%CI 74% reduction to 5% increase], P = .06) at one-month and three-month, respectively. There were no significant differences in most SF-36 domains scores after one and three months. No serious adverse event was observed during PPT sessions.

CONCLUSION

Early PPT can be considered a safe and relatively effective therapeutic choice for patients with severe COVID-19.

Role of CCL2/CCR2 axis in the pathogenesis of COVID-19 and possible Treatments: All options on the Table

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is cause of the novel coronavirus disease (COVID-19). In the last two years, SARS-CoV-2 has infected millions of people worldwide with different waves, resulting in the death of many individuals. The evidence disclosed that the host immune responses to SARS-CoV-2 play a pivotal role in COVID-19 pathogenesis and clinical manifestations. In addition to inducing antiviral immune responses, SARS-CoV-2 can also cause dysregulated inflammatory responses characterized by the noticeable release of proinflammatory mediators in COVID-19 patients. Among these proinflammatory mediators, chemokines are considered a subset of cytokines that participate in the chemotaxis process to recruit immune and non-immune cells to the site of inflammation and infection. Researchers have demonstrated that monocyte chemoattractant protein-1 (MCP-1/CCL2) and its receptor (CCR2) are involved in the recruitment of monocytes and infiltration of these cells into the lungs of patients suffering from COVID-19. Moreover, elevated levels of CCL2 have been reported in the bronchoalveolar lavage fluid (BALF) obtained from patients with severe COVID-19, initiating cytokine storm and promoting CD163+ myeloid cells infiltration in the airways and further alveolar damage. Therefore, CCL2/CCR axis plays a key role in the immunopathogenesis of COVID-19 and targeted therapy of involved molecules in this axis can be a potential therapeutic approach for these patients. This review discusses the biology of the CCL2/CCR2 axis as well as the role of this axis in COVID-19 immunopathogenesis, along with therapeutic options aimed at inhibiting CCL2/CCR2 and modulating dysregulated inflammatory responses in patients with severe SARS-CoV-2 infection.

Alveolar cell fate selection and lifelong maintenance of AT2 cells by FGF signaling

The lung's gas exchange surface is comprised of alveolar AT1 and AT2 cells that are corrupted in several common and deadly diseases. They arise from a bipotent progenitor whose differentiation is thought to be dictated by differential mechanical forces. Here we show the critical determinant is FGF signaling. Fgfr2 is expressed in the developing progenitors in mouse then restricts to nascent AT2 cells and remains on throughout life. Its ligands are expressed in surrounding mesenchyme and can, in the absence of exogenous mechanical cues, induce progenitors to form alveolospheres with intermingled AT2 and AT1 cells. FGF signaling directly and cell autonomously specifies AT2 fate; progenitors lacking Fgfr2 in vitro and in vivo exclusively acquire AT1 fate. Fgfr2 loss in AT2 cells perinatally results in reprogramming to AT1 identity, whereas loss or inhibition later in life triggers AT2 apoptosis and compensatory regeneration. We propose that Fgfr2 signaling selects AT2 fate during development, induces a cell non-autonomous AT1 differentiation signal, then continuously maintains AT2 identity and survival throughout life.

Astersaponin I from Aster koraiensis is a natural viral fusion blocker that inhibits the infection of SARS-CoV-2 variants and syncytium formation

The continuous emergence of SARS-CoV-2 variants prolongs COVID-19 pandemic. Although SARS-CoV-2 vaccines and therapeutics are currently available, there is still a need for development of safe and effective drugs against SARS-CoV-2 and also for preparedness for the next pandemic. Here, we discover that astersaponin I (AI), a triterpenoid saponin in Aster koraiensis inhibits SARS-CoV-2 entry pathways at the plasma membrane and within the endosomal compartments mainly by increasing cholesterol content in the plasma membrane and interfering with the fusion of SARS-CoV-2 envelope with the host cell membrane. Moreover, we find that this functional property of AI as a fusion blocker enables it to inhibit the infection with SARS-CoV-2 variants including the Alpha, Beta, Delta, and Omicron with a similar efficacy, and the formation of syncytium, a multinucleated cells driven by SARS-CoV-2 spike protein-mediated cell-to-cell fusion. Finally, we claim that the triterpene backbone as well as the attached hydrophilic sugar moieties of AI are structurally important for its inhibitory activity against the membrane fusion event. Overall, this study demonstrates that AI is a natural viral fusion inhibitor and proposes that it can be a broad-spectrum antiviral agent against current COVID-19 pandemic and future outbreaks of novel viral pathogens.

Goblet Cell Hyperplasia Increases SARS-CoV-2 Infection in Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is one of the underlying conditions in adults of any age that place them at risk for developing severe illnesses associated with COVID-19. To determine whether SARS-CoV-2's cellular tropism plays a critical role in severe pathophysiology in the lung, we investigated its host cell entry receptor distribution in the bronchial airway epithelium of healthy adults and high-risk adults (those with COPD). We found that SARS-CoV-2 preferentially infects goblet cells in the bronchial airway epithelium, as mostly goblet cells harbor the entry receptor angiotensin-converting enzyme 2 (ACE2) and its cofactor transmembrane serine protease 2 (TMPRSS2). We also found that SARS-CoV-2 replication was substantially increased in the COPD bronchial airway epithelium, likely due to COPD-associated goblet cell hyperplasia. Likewise, SARS-CoV and Middle East respiratory syndrome (MERS-CoV) infection increased disease pathophysiology (e.g., syncytium formation) in the COPD bronchial airway epithelium. Our results reveal that goblet cells play a critical role in SARS-CoV-2-induced pathophysiology in the lung. IMPORTANCE SARS-CoV-2 or COVID-19's first case was discovered in December 2019 in Wuhan, China, and by March 2020 it was declared a pandemic by the WHO. It has been shown that various underlying conditions can increase the chance of having severe COVID-19. COPD, which is the third leading cause of death worldwide, is one of the conditions listed by the CDC which can increase the chance of severe COVID-19. The present study uses a healthy and COPD-derived bronchial airway epithelial model to study the COVID-19 and host factors which could explain the reason for COPD patients developing severe infection due to COVID-19.

Alveolar macrophages protect mice from MERS-CoV-induced pneumonia and severe disease

Emerging and re-emerging human coronaviruses (hCoVs) cause severe respiratory illness in humans, but the basis for lethal pneumonia in these diseases is not well understood. Alveolar macrophages (AMs) are key orchestrators of host antiviral defense and tissue tolerance during a variety of respiratory infections, and AM dysfunction is associated with severe COVID-19. In this study, using a mouse model of Middle East respiratory syndrome coronavirus (MERS-CoV) infection, we examined the role of AMs in MERS pathogenesis. Our results show that depletion of AMs using clodronate (CL) liposomes significantly increased morbidity and mortality in human dipeptidyl peptidase 4 knock-in (hDPP4-KI) mice. Detailed examination of control and AM-depleted lungs at different days postinfection revealed increased neutrophil activity but a significantly reduced MERS-CoV-specific CD4 T-cell response in AM-deficient lungs during later stages of infection. Furthermore, enhanced MERS severity in AM-depleted mice correlated with lung inflammation and lesions. Collectively, these data demonstrate that AMs are critical for the development of an optimal virus-specific T-cell response and controlling excessive inflammation during MERS-CoV infection.

Cytopathological Findings in Bronchoalveolar Lavage from Patients with COVID-19

Information on cellular analysis of bronchoalveolar lavage (BAL) in patients with COVID-19 is limited. Some studies have described an increase in lymphocyte percentage or exuberant plasmacytosis. Some reports addressed the importance of molecular testing on BAL samples to confirm COVID-19 pneumonia, in clinically highly suspected patients with consecutive negative nasopharyngeal swab results. In addition to atypical lymphocytes in the peripheral blood, morphologic findings of atypical lymphocytes in BAL were also reported in a few patients. The objective of this study was to describe the cytopathic characteristics identified, any data presented here are descriptives and intended to trigger further research. Three general aspects have been evaluated in each sample: reactive changes, virus-related pathological changes, and differential leukocyte count. Seventeen samples were collected. All samples were negative for malignancy, with an inflammatory background, predominantly lymphohistiocytic in 5 samples, histiocytic in 9, and 3 with predominantly neutrophilic. Hemosiderin-laden macrophages were observed in 12/17. Nonspecific reactive cell changes were identified in 4 samples, including bronchial, alveolar, and reserve cell hyperplasia. Virus-related pathological changes were observed in 14 samples, such as loss of nuclear chromatin pattern, lymphocytes with atypical nuclei, nuclear and cytoplasmic inclusions, multinucleations in bronchial cells and macrophages, or multinucleated giant cells. The identification of multinucleated giant cells could represent a cytopathic effect induced by the virus, at the same time the nuclear clearance of pneumocytes as a possible direct effect. BAL is a procedure aimed at obtaining cells from the respiratory tract that can provide valuable and rapid information. It is important to collect and describe as many cytopathological findings as possible, which can provide relevant information for future studies.

Therapy Targets SARS-CoV-2 Infection-Induced Cell Death

Coronavirus Disease 2019 (COVID-19) caused by SARS-CoV-2 has become a global health issue. The clinical presentation of COVID-19 is highly variable, ranging from asymptomatic and mild disease to severe. However, the mechanisms for the high mortality induced by SARS-CoV-2 infection are still not well understood. Recent studies have indicated that the cytokine storm might play an essential role in the disease progression in patients with COVID-19, which is characterized by the uncontrolled release of cytokines and chemokines leading to acute respiratory distress syndrome (ARDS), multi-organ failure, and even death. Cell death, especially, inflammatory cell death, might be the initiation of a cytokine storm caused by SARS-CoV-2 infection. This review summarizes the forms of cell death caused by SARS-CoV-2 in vivo or in vitro and elaborates on the dedication of apoptosis, necroptosis, NETosis, pyroptosis of syncytia, and even SARS-CoV-2 E proteins forming channel induced cell death, providing insights into targets on the cell death pathway for the treatment of COVID-19.

Histopathological Findings in COVID-19 Cases: A Systematic Review

The ongoing coronavirus disease 2019 (COVID-19) pandemic has turned into one of the most serious public health crises of the last few decades. Although the disease can result in diverse and multiorgan pathologies, very few studies have addressed the postmortem pathological findings of COVID-19 cases. Active autopsy findings amid this pandemic could be an essential tool for diagnosis, surveillance, and research. We aimed to provide a comprehensive picture of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) histopathological features of different body organs through a systematic review of the published literature. A systematic search of electronic databases (PubMed, ScienceDirect, Google Scholar, medRxiv, and bioRxiv) for journal articles of different study designs reporting postmortem pathological findings in COVID-19 cases was performed. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were used for conducting the review. A total of 50 articles reporting 430 cases were included in our analysis. Postmortem pathological findings were reported for different body organs: pulmonary system (42 articles), cardiovascular system (23 articles), hepatobiliary system (22 articles), kidney (16 articles), spleen and lymph nodes (12 articles), and central nervous system (seven articles). In lung samples, diffuse alveolar damage (DAD) was the most commonly reported finding in 239 cases (84.4%). Myocardial hypertrophy (87 cases, 51.2%), arteriosclerosis (121 cases, 62%), and steatosis (118 cases, 59.3%) were the most commonly reported pathological findings in the heart, kidney, and the hepatobiliary system respectively. Autopsy examination as an investigation tool could lead to a better understanding of SARS-CoV-2 pathophysiology, diagnosis, and management, subsequently improving patient care.

Neutrophil subsets and their differential roles in viral respiratory diseases

Neutrophils play significant roles in immune homeostasis and as neutralizers of microbial infections. Recent evidence further suggests heterogeneity of neutrophil developmental and activation states that exert specialized effector functions during inflammatory disease conditions. Neutrophils can play multiple roles during viral infections, secreting inflammatory mediators and cytokines that contribute significantly to host defense and pathogenicity. However, their roles in viral immunity are not well understood. In this review, we present an overview of neutrophil heterogeneity and its impact on the course and severity of viral respiratory infectious diseases. We focus on the evidence demonstrating the crucial roles neutrophils play in the immune response toward respiratory infections, using influenza as a model. We further extend the understanding of neutrophil function with the studies pertaining to COVID-19 disease and its neutrophil-associated pathologies. Finally, we discuss the relevance of these results for future therapeutic options through targeting and regulating neutrophil-specific responses.

Potential intestinal infection and faecal-oral transmission of human coronaviruses

Human coronaviruses (HCoVs) were first described in 1960s for patients experiencing common cold. Since then, increasing number of HCoVs have been discovered, including those causing severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), and the circulating coronavirus disease 2019 (COVID‐19), which can cause fatal respiratory disease in humans on infection. HCoVs are believed to spread mainly through respiratory droplets and close contact. However, studies have shown that a large proportion of patients with HCoV infection develop gastrointestinal (GI) symptoms, and many patients with confirmed HCoV infection have shown detectable viral RNA in their faecal samples. Furthermore, multiple in vitro and in vivo animal studies have provided direct evidence of intestinal HCoV infection. These data highlight the nature of HCoV GI infection and its potential faecal‐oral transmission. Here, we summarise the current findings on GI manifestations of HCoVs. We also discuss how HCoV GI infection might occur and the current evidence to establish the occurrence of faecal‐oral transmission.

Inactivation of SARS-CoV-2 by a chitosan/α-Ag2WO4 composite generated by femtosecond laser irradiation

In the current COVID-19 pandemic, the next generation of innovative materials with enhanced anti-SARS-CoV-2 activity is urgently needed to prevent the spread of this virus within the community. Herein, we report the synthesis of chitosan/α-Ag₂WO₄ composites synthetized by femtosecond laser irradiation. The antimicrobial activity against Escherichia coli, Methicilin-susceptible Staphylococcus aureus (MSSA), and Candida albicans was determined by estimating the minimum inhibitory concentration (MIC) and minimal bactericidal/fungicidal concentration (MBC/MFC). To assess the biocompatibility of chitosan/α-Ag₂WO₄ composites in a range involving MIC and MBC/MFC on keratinocytes cells (NOK-si), an alamarBlue™ assay and an MTT assay were carried out. The SARS-CoV-2 virucidal effects was analyzed in Vero E6 cells through viral titer quantified in cell culture supernatant by PFU/mL assay. Our results showed a very similar antimicrobial activity of chitosan/α-Ag₂WO₄ 3.3 and 6.6, with the last one demonstrating a slightly better action against MSSA. The chitosan/α-Ag₂WO₄ 9.9 showed a wide range of antimicrobial activity (0.49-31.25 µg/mL). The cytotoxicity outcomes by alamarBlue™ revealed that the concentrations of interest (MIC and MBC/MFC) were considered non-cytotoxic to all composites after 72 h of exposure. The Chitosan/α-Ag₂WO₄ (CS6.6/α-Ag₂WO₄) composite reduced the SARS-CoV-2 viral titer quantification up to 80% of the controls. Then, our results suggest that these composites are highly efficient materials to kill bacteria (Escherichia coli, Methicillin-susceptible Staphylococcus aureus, and the yeast strain Candida albicans), in addition to inactivating SARS-CoV-2 by contact, through ROS production.

The Mechanism and Consequences of SARS-CoV-2 Spike-Mediated Fusion and Syncytia Formation

Syncytia are formed when individual cells fuse. SARS-CoV-2 induces syncytia when the viral spike (S) protein on the surface of an infected cell interacts with receptors on neighboring cells. Syncytia may potentially contribute to pathology by facilitating viral dissemination, cytopathicity, immune evasion, and inflammatory response. SARS-CoV-2 variants of concern possess several mutations within the S protein that enhance receptor interaction, fusogenicity and antibody binding. In this review, we discuss the molecular determinants of S mediated fusion and the antiviral innate immunity components that counteract syncytia formation. Several interferon-stimulated genes, including IFITMs and LY6E act as barriers to S protein-mediated fusion by altering the composition or biophysical properties of the target membrane. We also summarize the effect that the mutations associated with the variants of concern have on S protein fusogenicity. Altogether, this review contextualizes the current understanding of Spike fusogenicity and the role of syncytia during SARS-CoV-2 infection and pathology.

What Is COVID 19 Teaching Us about Pulmonary Ultrasound?

In lung ultrasound (LUS), the interactions between the acoustic pulse and the lung surface (including the pleura and a small subpleural layer of tissue) are crucial. Variations of the peripheral lung density and the subpleural alveolar shape and its configuration are typically connected to the presence of ultrasound artifacts and consolidations. COVID-19 pneumonia can give rise to a variety of pathological pulmonary changes ranging from mild diffuse alveolar damage (DAD) to severe acute respiratory distress syndrome (ARDS), characterized by peripheral bilateral patchy lung involvement. These findings are well described in CT imaging and in anatomopathological cases. Ultrasound artifacts and consolidations are therefore expected signs in COVID-19 pneumonia because edema, DAD, lung hemorrhage, interstitial thickening, hyaline membranes, and infiltrative lung diseases when they arise in a subpleural position, generate ultrasound findings. This review analyzes the structure of the ultrasound images in the normal and pathological lung given our current knowledge, and the role of LUS in the diagnosis and monitoring of patients with COVID-19 lung involvement.

Development of flow cytometry-based assays to assess the ability of antibodies to bind to SARS-CoV-2-infected and Spike-transfected cells and mediate NK cell degranulation

Since the beginning of the SARS-CoV-2 pandemic, antibody responses and antibody effector functions targeting SARS-CoV-2-infected cells have been understudied. Consequently, the role of these types of antibodies in SARS-CoV-2 disease (COVID-19) and immunity is still undetermined. To provide tools to study these responses, we used plasma from SARS-CoV-2-infected individuals (n=50) and SARS-CoV-2 naive healthy controls (n=20) to develop four specific and reproducible flow cytometry-based assays: (i) two assessing antibody binding to, and antibody-mediated NK cell degranulation against, SARS-CoV-2-infected cells and (ii) two assessing antibody binding to, and antibody-mediated NK cell degranulation against, SARS-CoV-2 Spike-transfected cells. All four assays demonstrated the ability to detect the presence of these functional antibody responses in a specific and reproducible manner. Interestingly, we found weak to moderate correlations between the four assays (Spearman rho ranged from 0.50-0.74), suggesting limited overlap in the responses captured by the individual assays. Lastly, while we initially developed each assay with multiple dilutions in an effort to capture the full relationship between antibody titers and assay outcome, we explored the relationship between fewer antibody dilutions and the full dilution series for each assay to reduce assay costs and improve assay efficiency. We found high correlations between the full dilution series and fewer or single dilutions of plasma. Use of single or fewer sample dilutions to accurately determine the response rates and magnitudes of the responses allows for high-throughput use of these assays platforms to facilitate assessment of antibody responses elicited by SARS-CoV-2 infection and vaccination in large clinical studies. This article is protected by copyright. All rights reserved.

Causes of Hypoxemia in COVID-19

The global pandemic of a new coronavirus disease (COVID-19) has posed challenges to public health specialists around the world associated with diagnosis, intensive study of epidemiological and clinical features of the coronavirus infection, development of preventive approaches, therapeutic strategies and rehabilitation measures. However, despite the successes achieved in the study of COVID-19 pathogenesis, many aspects that aggravate the severity of the disease and cause high mortality of patients remain unclear. The main clinical manifestation of the new variant of SARS-CoV-2 virus infection is pneumonia with massive parenchymal lesions of lung tissue, diffuse alveolar damage, thrombotic manifestations, disruption of ventilation-perfusion relationships, etc. However, symptoms in patients hospitalized with COVID pneumonia show a broad diversity: the majority has minimal manifestations, others develop severe respiratory failure complicated by acute respiratory distress syndrome (ARDS) with rapidly progressing hypoxemia that leads to high mortality. Numerous clinical data publications report that some COVID pneumonia patients without subjective signs of severe respiratory failure (dyspnea, “air hunger”) have an extremely low saturation level. As a result, there arises a paradoxical condition (called “silent hypoxia” or even “happy hypoxia”) contradicting the very basics of physiology, as it essentially represents a severe life-incompatible hypoxemia which lacks respiratory discomfort. All this raises numerous questions among professionals and has already ignited a discussion in scientific publications concerned with the pathogenesis of COVID-19. Respiratory failure is a complex clinical problem, many aspects of which remain controversial. However, according to the majority of authors, one of the first objective indicators of the clinical sign of respiratory failure are hypoxemia-associated changes in external respiration. This review addresses some possible causes of hypoxemia in COVID-19.

Activation of Complement Components on Circulating Blood Monocytes From COVID-19 Patients

The coronavirus disease-2019 (COVID-19) caused by the SARS-CoV-2 virus may vary from asymptomatic to severe infection with multi-organ failure and death. Increased levels of circulating complement biomarkers have been implicated in COVID-19-related hyperinflammation and coagulopathy. We characterized systemic complement activation at a cellular level in 49-patients with COVID-19. We found increases of the classical complement sentinel C1q and the downstream C3 component on circulating blood monocytes from COVID-19 patients when compared to healthy controls (HCs). Interestingly, the cell surface-bound complement inhibitor CD55 was also upregulated in COVID-19 patient monocytes in comparison with HC cells. Monocyte membrane-bound C1q, C3 and CD55 levels were associated with plasma inflammatory markers such as CRP and serum amyloid A during acute infection. Membrane-bounds C1q and C3 remained elevated even after a short recovery period. These results highlight systemic monocyte-associated complement activation over a broad range of COVID-19 disease severities, with a compensatory upregulation of CD55. Further evaluation of complement and its interaction with myeloid cells at the membrane level could improve understanding of its role in COVID-19 pathogenesis.

Coagulation Disorders and Thrombosis in COVID-19 Patients and a Possible Mechanism Involving Endothelial Cells: A Review

Coronavirus disease 2019 (COVID-19) is still an ongoing pandemic worldwide. COVID-19 is an age-related disease with a higher risk of organ dysfunction and mortality in older adults. Coagulation disorders and thrombosis are important pathophysiological changes in COVID-19 infection. Up to 95% of COVID-19 patients have coagulation disorders characterized by an elevated D-dimer, a prolonged prothrombin time, a low platelet count and other laboratory abnormalities. Thrombosis is found in critical cases with an increased risk of death. Endothelial cells are prone to be affected by the novel SARS-CoV-2 and express angiotensin-converting enzyme 2. The evidence, such as the presence of the virus, has been identified, leading to the inflammation and dysfunction. Endothelial cell activation and dysfunction play a pivotal role in the hypercoagulation status in COVID-19 patients. In addition to the direct exposure of subendothelial tissue to blood, Weibel-Palade bodies within the endothelium containing coagulants can be released into the circulation. Endothelial nitric oxide synthase may be impaired, thus facilitating platelet adhesion. Moreover, anti-β2-glycoprotein I antibodies may also contribute to the coagulopathy in COVID-19 by inducing the upregulation of proinflammatory mediators and adhesion molecules. To conclude, coagulation disorders and thrombosis are vital and predict a poor outcome in COVID-19 patients, especially in severe cases. Endothelial cell activation and dysfunction may play an important role in causing clot formation. More basic and clinical research is warranted to further our understanding of the role of coagulopathy and their possible mechanism in COVID-19 patients.

Persistent Oxidative Stress and Inflammasome Activation in CD14highCD16- Monocytes From COVID-19 Patients

The poor outcome of the coronavirus disease-2019 (COVID-19), caused by SARS-CoV-2, is associated with systemic hyperinflammatory response and immunopathology. Although inflammasome and oxidative stress have independently been implicated in COVID-19, it is poorly understood whether these two pathways cooperatively contribute to disease severity. Herein, we found an enrichment of CD14highCD16- monocytes displaying inflammasome activation evidenced by caspase-1/ASC-speck formation in severe COVID-19 patients when compared to mild ones and healthy controls, respectively. Those cells also showed aberrant levels of mitochondrial superoxide and lipid peroxidation, both hallmarks of the oxidative stress response, which strongly correlated with caspase-1 activity. In addition, we found that NLRP3 inflammasome-derived IL-1β secretion by SARS-CoV-2-exposed monocytes in vitro was partially dependent on lipid peroxidation. Importantly, altered inflammasome and stress responses persisted after short-term patient recovery. Collectively, our findings suggest oxidative stress/NLRP3 signaling pathway as a potential target for host-directed therapy to mitigate early COVID-19 hyperinflammation and also its long-term outcomes.

Histologic pulmonary lesions of SARS-CoV-2 in 4 nonhuman primate species: An institutional comparative review

Coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is an emergent, amphixenotic infection that resulted in a pandemic declaration in March 2020. A rapid search for appropriate animal models of this newly emergent viral respiratory disease focused initially on traditional nonhuman primate research species. Nonhuman primate models have previously been shown to be valuable in evaluation of emerging respiratory coronaviruses with pandemic potential (ie, SARS-CoV and Middle East respiratory syndrome coronavirus). In this article, we review the pulmonary histopathologic characteristics and immunohistochemical evaluation of experimental SARS-CoV-2 infection in the rhesus macaque, pigtail macaque, African green monkey, and squirrel monkey. Our results indicate that all evaluated nonhuman primate species developed variably severe histopathologic changes typical of coronavirus respiratory disease characterized by interstitial pneumonia with or without syncytial cell formation, alveolar fibrin, and pulmonary edema that progressed to type II pneumocyte hyperplasia. Lesion distribution was multifocal, frequently subpleural, and often more severe in lower lung lobes. However, squirrel monkeys showed the least severe and least consistent lesions of the evaluated nonhuman primates. Additionally, our results highlight the disparate physical relationship between viral antigen and foci of pulmonary lesions. While classic respiratory coronaviral lesions were observed in the lungs of all nonhuman primates evaluated, none of the primates exhibited severe lesions or evidence of diffuse alveolar damage and therefore are unlikely to represent the severe form of SARS-CoV-2 infection observed in fatal human cases.

Nebulization of glutathione and N-Acetylcysteine as an adjuvant therapy for COVID-19 onset

Ever since its emergence, the highly transmissible and debilitating coronavirus disease spread at an incredibly fast rate, causing global devastation in a matter of months. SARS-CoV-2, the novel coronavirus responsible for COVID-19, infects hosts after binding to ACE2 receptors present on cells from many structures pertaining to the respiratory, cardiac, hematological, neurological, renal and gastrointestinal systems. COVID-19, however, appears to trigger a severe cytokine storm syndrome in pulmonary structures, resulting in oxidative stress, exacerbated inflammation and alveolar injury. Due to the recent nature of this disease no treatments have shown complete efficacy and safety. More recently, however, researchers have begun to direct some attention towards GSH and NAC. These natural antioxidants play an essential role in several biological processes in the body, especially the maintenance of the redox equilibrium. In fact, many diseases appear to be strongly related to severe oxidative stress and deficiency of endogenous GSH. The high ratios of ROS over GSH, in particular, appear to reflect severity of symptoms and prolonged hospitalization of COVID-19 patients. This imbalance interferes with the body's ability to detoxify the cellular microenvironment, fold proteins, replenish antioxidant levels, maintain healthy immune responses and even modulate apoptotic events. Oral administration of GSH and NAC is convenient and safe, but they are susceptible to degradation in the digestive tract. Considering this drawback, nebulization of GSH and NAC as an adjuvant therapy may therefore be a viable alternative for the management of the early stages of COVID-19.

Temporal Patterns of COVID-19-Associated Pulmonary Pathology: An Autopsy Study

Introduction

The novel coronavirus variant - severe acute respiratory distress syndrome coronavirus 2 (SARS-CoV-2) and the disease it causes clinically (novel coronavirus disease 2019 or COVID-19) have placed medical science into a frenzy due to the significant morbidity and mortality, as well as the myriad of clinical complications developing as a direct result of infection. The most notable and one of the most severe changes in COVID-19 develops in the lungs.

Materials and methods

All cases of real-time polymerase chain reaction (rtPCR)-proved COVID-19 subjected to autopsy were withdrawn from the central histopathology archive of a single tertiary medical institution - St. Marina University Hospital - Varna, Varna, Bulgaria. Pulmonary gross and histopathology changes observed on light microscopy with hematoxylin and eosin as well with other histochemical and immunohistochemical stains were compared with the time from patient-reported symptom onset to expiration, to compare the extent and type of changes based on disease duration.

Results

A total of 27 autopsy cases fit the established criteria. All cases clinically manifested with severe COVID-19. From the selected 27 cases, n=14 were male and n=13 were female. The mean age in the cohort was 67.44 years (range 18-91 years), with the mean age for males being 68.29 (range 38-80 years) and the mean age for females being 66.54 (range 18-91 years). Gross changes in patients who expired in the first 10 days after disease onset showed a significantly increased mean weight - 1050g, compared to a relatively lower weight in patients expiring more than 10 days after symptom onset - 940g. Histopathology changes were identified as intermittent (developing independent from symptom onset and persisting) - diffuse alveolar damage with hyaline membranes - acute respiratory distress syndrome, endothelitis with vascular degeneration and fibrin thrombi; early (developing within the first week, but persisting) - type II pneumocyte hyperplasia, alveolar cell multinucleation and scant interstitial mononuclear inflammation; intermediate (developing within the late first and second weeks) - Clara cell hyperplasia and late (developing after the second week of symptom onset) - respiratory tract and alveolar squamous cell metaplasia and fibrosis.

Conclusion

COVID-19-associated pulmonary pathology, both gross and histopathology, show a time-related dynamic with persistent early and a myriad of later developing dynamic changes in patients with severe disease. These changes underline both the severity of the condition, as well as the mechanisms and the probability of long-lasting severe complications in patients with post-COVID syndrome.

The journey of SARS-CoV-2 in human hosts: a review of immune responses, immunosuppression, and their consequences

Coronavirus disease 2019 (COVID-19) is a highly infectious viral disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Laboratory findings from a significant number of patients with COVID-19 indicate the occurrence of leukocytopenia, specifically lymphocytopenia. Moreover, infected patients can experience contrasting outcomes depending on lymphocytopenia status. Patients with resolved lymphocytopenia are more likely to recover, whereas critically ill patients with signs of unresolved lymphocytopenia develop severe complications, sometimes culminating in death. Why immunodepression manifests in patients with COVID-19 remains unclear. Therefore, the evaluation of clinical symptoms and laboratory findings from infected patients is critical for understanding the disease course and its consequences. In this review, we take a logical approach to unravel the reasons for immunodepression in patients with COVID-19. Following the footprints of the virus within host tissues, from entry to exit, we extrapolate the mechanisms underlying the phenomenon of immunodepression.

SARS-CoV-2 Exacerbates COVID-19 Pathology Through Activation of the Complement and Kinin Systems

Infection with SARS-CoV-2 triggers the simultaneous activation of innate inflammatory pathways including the complement system and the kallikrein-kinin system (KKS) generating in the process potent vasoactive peptides that contribute to severe acute respiratory syndrome (SARS) and multi-organ failure. The genome of SARS-CoV-2 encodes four major structural proteins - the spike (S) protein, nucleocapsid (N) protein, membrane (M) protein, and the envelope (E) protein. However, the role of these proteins in either binding to or activation of the complement system and/or the KKS is still incompletely understood. In these studies, we used: solid phase ELISA, hemolytic assay and surface plasmon resonance (SPR) techniques to examine if recombinant proteins corresponding to S1, N, M and E: (a) bind to C1q, gC1qR, FXII and high molecular weight kininogen (HK), and (b) activate complement and/or the KKS. Our data show that the viral proteins: (a) bind C1q and activate the classical pathway of complement, (b) bind FXII and HK, and activate the KKS in normal human plasma to generate bradykinin and (c) bind to gC1qR, the receptor for the globular heads of C1q (gC1q) which in turn could serve as a platform for the activation of both the complement system and KKS. Collectively, our data indicate that the SARS-CoV-2 viral particle can independently activate major innate inflammatory pathways for maximal damage and efficiency. Therefore, if efficient therapeutic modalities for the treatment of COVID-19 are to be designed, a strategy that includes blockade of the four major structural proteins may provide the best option.

Tissue factor expression, extracellular vesicles, and thrombosis after infection with the respiratory viruses influenza A virus and coronavirus

Tissue factor (TF) is induced in a variety of cell types during viral infection, which likely contributes to disseminated intravascular coagulation and thrombosis. TF-expressing cells also release TF-positive extracellular vesicles (EVs) into the circulation that can be measured using an EVTF activity assay. This review summarizes studies that analyze TF expression, TF-positive EVs, activation of coagulation, and thrombosis after infection with influenza A virus (IAV) and coronaviruses (CoVs), including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), SARS-CoV, and Middle East respiratory syndrome CoV (MERS-CoV). The current pandemic of coronavirus disease 2019 (COVID-19) is caused by infection with SARS-CoV-2. Infection of mice with IAV increased TF expression in lung epithelial cells as well as increased EVTF activity and activation of coagulation in the bronchoalveolar lavage fluid (BALF). Infection of mice with MERS-CoV, SARS-CoV, and SARS-CoV-2 also increased lung TF expression. Single-cell RNA sequencing analysis on the BALF from severe COVID-19 patients revealed increased TF mRNA expression in epithelial cells. TF expression was observed in peripheral blood mononuclear cells infected with SARS-CoV. TF was also expressed by peripheral blood mononuclear cells, monocytes in platelet-monocyte aggregates, and neutrophils isolated from COVID-19 patients. Elevated circulating EVTF activity was observed in severe IAV and COVID-19 patients. Importantly, EVTF activity was associated with mortality in severe IAV patients and with plasma D-dimer, severity, thrombosis, and mortality in COVID-19 patients. These studies strongly suggest that increased TF expression in patients infected with IAV and pathogenic CoVs contributes to thrombosis.

Abnormal Airway Mucus Secretion Induced by Virus Infection

The airway mucus barrier is a primary defensive layer at the airway surface. Mucins are the major structural components of airway mucus that protect the respiratory tract. Respiratory viruses invade human airways and often induce abnormal mucin overproduction and airway mucus secretion, leading to airway obstruction and disease. The mechanism underlying the virus-induced abnormal airway mucus secretion has not been fully studied so far. Understanding the mechanisms by which viruses induce airway mucus hypersecretion may open new avenues to treatment. In this article, we elaborate the clinical and experimental evidence that respiratory viruses cause abnormal airway mucus secretion, review the underlying mechanisms, and also discuss the current research advance as well as potential strategies to treat the abnormal airway mucus secretion caused by SARS-CoV-2.

SARS-CoV-2 Alpha, Beta, and Delta variants display enhanced Spike-mediated syncytia formation

Severe COVID‐19 is characterized by lung abnormalities, including the presence of syncytial pneumocytes. Syncytia form when SARS‐CoV‐2 spike protein expressed on the surface of infected cells interacts with the ACE2 receptor on neighboring cells. The syncytia forming potential of spike variant proteins remain poorly characterized. Here, we first assessed Alpha (B.1.1.7) and Beta (B.1.351) spread and fusion in cell cultures, compared with the ancestral D614G strain. Alpha and Beta replicated similarly to D614G strain in Vero, Caco‐2, Calu‐3, and primary airway cells. However, Alpha and Beta formed larger and more numerous syncytia. Variant spike proteins displayed higher ACE2 affinity compared with D614G. Alpha, Beta, and D614G fusion was similarly inhibited by interferon‐induced transmembrane proteins (IFITMs). Individual mutations present in Alpha and Beta spikes modified fusogenicity, binding to ACE2 or recognition by monoclonal antibodies. We further show that Delta spike also triggers faster fusion relative to D614G. Thus, SARS‐CoV‐2 emerging variants display enhanced syncytia formation.

Histopathological findings and clinicopathologic correlation in COVID-19: a systematic review

The severe acute respiratory syndrome Coronavirus-2 (SARS-CoV-2) pandemic has had devastating effects on global health and worldwide economy. Despite an initial reluctance to perform autopsies due to concerns for aerosolization of viral particles, a large number of autopsy studies published since May 2020 have shed light on the pathophysiology of Coronavirus disease 2019 (COVID-19). This review summarizes the histopathologic findings and clinicopathologic correlations from autopsies and biopsies performed in patients with COVID-19. PubMed and Medline (EBSCO and Ovid) were queried from June 4, 2020 to September 30, 2020 and histopathologic data from autopsy and biopsy studies were collected based on 2009 Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A total of 58 studies reporting 662 patients were included. Demographic data, comorbidities at presentation, histopathologic findings, and virus detection strategies by organ system were collected. Diffuse alveolar damage, thromboembolism, and nonspecific shock injury in multiple organs were the main findings in this review. The pathologic findings emerging from autopsy and biopsy studies reviewed herein suggest that in addition to a direct viral effect in some organs, a unifying pathogenic mechanism for COVID-19 is ARDS with its known and characteristic inflammatory response, cytokine release, fever, inflammation, and generalized endothelial disturbance. This study supports the notion that autopsy studies are of utmost importance to our understanding of disease features and treatment effect to increase our knowledge of COVID-19 pathophysiology and contribute to more effective treatment strategies.

Cytokine storm and histopathological findings in 60 cases of COVID-19-related death: from viral load research to immunohistochemical quantification of major players IL-1β, IL-6, IL-15 and TNF-α

This study involves the histological analysis of samples taken during autopsies in cases of COVID-19 related death to evaluate the inflammatory cytokine response and the tissue localization of the virus in various organs. In all the selected cases, SARS-CoV-2 RT-PCR on swabs collected from the upper (nasopharynx and oropharynx) and/or the lower respiratory (trachea and primary bronchi) tracts were positive. Tissue localization of SARS-CoV-2 was detected using antibodies against the nucleoprotein and the spike protein. Overall, we tested the hypothesis that the overexpression of proinflammatory cytokines plays an important role in the development of COVID-19-associated pneumonia by estimating the expression of multiple cytokines (IL-1β, IL-6, IL-10, IL-15, TNF-α, and MCP-1), inflammatory cells (CD4, CD8, CD20, and CD45), and fibrinogen. Immunohistochemical staining showed that endothelial cells expressed IL-1β in lung samples obtained from the COVID-19 group (p < 0.001). Similarly, alveolar capillary endothelial cells showed strong and diffuse immunoreactivity for IL-6 and IL-15 in the COVID-19 group (p < 0.001). TNF-α showed a higher immunoreactivity in the COVID-19 group than in the control group (p < 0.001). CD8 + T cells where more numerous in the lung samples obtained from the COVID-19 group (p < 0.001). Current evidence suggests that a cytokine storm is the major cause of acute respiratory distress syndrome (ARDS) and multiple organ failure and is consistently linked with fatal outcomes.

COVID-19: a Disease with a Potpourri of Histopathologic Findings-a Literature Review and Comparison to the Closely Related SARS and MERS

Since the coronavirus disease 2019 (COVID-19) pandemic has hit the entire world, there is ample knowledge regarding its clinical course and prognostic biomarkers. Still, the pathophysiology of COVID-19 is poorly understood. Since the first guidelines published in February 2020 for autopsy of both confirmed and suspected COVID-19 cases, there has been an increasing number of autopsies and literature reporting histopathological findings. However, our knowledge about the immunological response of various organ systems to the virus, as well as response patterns, is inadequate but is essential to understand and initiate timely and targeted antiviral, anti-inflammatory, or anticoagulative therapy. Although severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is primarily considered a respiratory virus, current evidence shows that it causes life-threatening complications in almost all organ systems including the heart, brain, kidney, spleen, liver, and eyes. Hence, in this article, we reviewed the published case reports and case series in order to increase our understanding of COVID-19 pathophysiology. The main histopathological findings of the lungs include diffuse alveolar damage with activated type II pneumocytes, fibroblasts, protein-rich exudate, and hyaline membranes. Other significant histopathological findings include cardiomegaly, right ventricular dilation, splenic pulp atrophy, kidneys with severe podocytopathy, and collapsing glomerulopathy, and the brain showed hypoxic changes in the cerebellum and cerebrum. Furthermore, in this review, we also explained different pathological findings of SARS-CoV and MERS and compared them to SARS-CoV-2. This comprehensive review will improve our understanding of COVID-19 pathophysiology and various disease stages, hence promoting the application of targeted therapy.

A cohort autopsy study defines COVID-19 systemic pathogenesis

Severe COVID-19 disease caused by SARS-CoV-2 is frequently accompanied by dysfunction of the lungs and extrapulmonary organs. However, the organotropism of SARS-CoV-2 and the port of virus entry for systemic dissemination remain largely unknown. We profiled 26 COVID-19 autopsy cases from four cohorts in Wuhan, China, and determined the systemic distribution of SARS-CoV-2. SARS-CoV-2 was detected in the lungs and multiple extrapulmonary organs of critically ill COVID-19 patients up to 67 days after symptom onset. Based on organotropism and pathological features of the patients, COVID-19 was divided into viral intrapulmonary and systemic subtypes. In patients with systemic viral distribution, SARS-CoV-2 was detected in monocytes, macrophages, and vascular endothelia at blood-air barrier, blood-testis barrier, and filtration barrier. Critically ill patients with long disease duration showed decreased pulmonary cell proliferation, reduced viral RNA, and marked fibrosis in the lungs. Permanent SARS-CoV-2 presence and tissue injuries in the lungs and extrapulmonary organs suggest direct viral invasion as a mechanism of pathogenicity in critically ill patients. SARS-CoV-2 may hijack monocytes, macrophages, and vascular endothelia at physiological barriers as the ports of entry for systemic dissemination. Our study thus delineates systemic pathological features of SARS-CoV-2 infection, which sheds light on the development of novel COVID-19 treatment.

Human Coronaviruses: Counteracting the Damage by Storm

Over the past 18 years, three highly pathogenic human (h) coronaviruses (CoVs) have caused severe outbreaks, the most recent causative agent, SARS-CoV-2, being the first to cause a pandemic. Although much progress has been made since the COVID-19 pandemic started, much about SARS-CoV-2 and its disease, COVID-19, is still poorly understood. The highly pathogenic hCoVs differ in some respects, but also share some similarities in clinical presentation, the risk factors associated with severe disease, and the characteristic immunopathology associated with the progression to severe disease. This review aims to highlight these overlapping aspects of the highly pathogenic hCoVs-SARS-CoV, MERS-CoV, and SARS-CoV-2-briefly discussing the importance of an appropriately regulated immune response; how the immune response to these highly pathogenic hCoVs might be dysregulated through interferon (IFN) inhibition, antibody-dependent enhancement (ADE), and long non-coding RNA (lncRNA); and how these could link to the ensuing cytokine storm. The treatment approaches to highly pathogenic hCoV infections are discussed and it is suggested that a greater focus be placed on T-cell vaccines that elicit a cell-mediated immune response, using rapamycin as a potential agent to improve vaccine responses in the elderly and obese, and the potential of stapled peptides as antiviral agents.

Complement Anaphylatoxins and Inflammatory Cytokines as Prognostic Markers for COVID-19 Severity and In-Hospital Mortality

COVID-19 severity due to innate immunity dysregulation accounts for prolonged hospitalization, critical complications, and mortality. Severe SARS-CoV-2 infections involve the complement pathway activation for cytokine storm development. Nevertheless, the role of complement in COVID-19 immunopathology, complement-modulating treatment strategies against COVID-19, and the complement and SARS-CoV-2 interaction with clinical disease outcomes remain elusive. This study investigated the potential changes in complement signaling, and the associated inflammatory mediators, in mild-to-critical COVID-19 patients and their clinical outcomes. A total of 53 patients infected with SARS-CoV-2 were enrolled in the study (26 critical and 27 mild cases), and additional 18 healthy control patients were also included. Complement proteins and inflammatory cytokines and chemokines were measured in the sera of patients with COVID-19 as well as healthy controls by specific enzyme-linked immunosorbent assay. C3a, C5a, and factor P (properdin), as well as interleukin (IL)-1β, IL-6, IL-8, tumor necrosis factor (TNF)-α, and IgM antibody levels, were higher in critical COVID-19 patients compared to mild COVID-19 patients. Additionally, compared to the mild COVID-19 patients, factor I and C4-BP levels were significantly decreased in the critical COVID-19 patients. Meanwhile, RANTES levels were significantly higher in the mild patients compared to critical patients. Furthermore, the critical COVID-19 intra-group analysis showed significantly higher C5a, C3a, and factor P levels in the critical COVID-19 non-survival group than in the survival group. Additionally, IL-1β, IL-6, and IL-8 were significantly upregulated in the critical COVID-19 non-survival group compared to the survival group. Finally, C5a, C3a, factor P, and serum IL-1β, IL-6, and IL-8 levels positively correlated with critical COVID-19 in-hospital deaths. These findings highlight the potential prognostic utility of the complement system for predicting COVID-19 severity and mortality while suggesting that complement anaphylatoxins and inflammatory cytokines are potential treatment targets against COVID-19.