Impaired cell-cell communication and axon guidance because of pulmonary hypoperfusion during postnatal alveolar development.

BACKGROUND: Pulmonary hypoperfusion is common in children with congenital heart diseases (CHDs) or pulmonary hypertension (PH) and causes adult pulmonary dysplasia. Systematic reviews have shown that some children with CHDs or PH have mitigated clinical outcomes with COVID-19. Understanding the effects of pulmonary hypoperfusion on postnatal alveolar development may aid in the development of methods to improve the pulmonary function of children with CHDs or PH and improve their care during the COVID-19 pandemic, which is characterized by cytokine storm and persistent inflammation. METHODS AND RESULTS: We created a neonatal pulmonary hypoperfusion model through pulmonary artery banding (PAB) surgery at postnatal day 1 (P1). Alveolar dysplasia was confirmed by gross and histological examination at P21. Transcriptomic analysis of pulmonary tissues at P7(alveolar stage 2) and P14(alveolar stage 4) revealed that the postnatal alveolar development track had been changed due to pulmonary hypoperfusion. Under the condition of pulmonary hypoperfusion, the cell-cell communication and axon guidance, which both determine the final number of alveoli, were lost; instead, there was hyperactive cell cycle activity. The transcriptomic results were further confirmed by the examination of axon guidance and cell cycle markers. Because axon guidance controls inflammation and immune cell activation, the loss of axon guidance may explain the lack of severe COVID-19 cases among children with CHDs or PH accompanied by pulmonary hypoperfusion. CONCLUSIONS: This study suggested that promoting cell-cell communication or supplementation with guidance molecules may treat pulmonary hypoperfusion-induced alveolar dysplasia, and that COVID-19 is less likely to cause a cytokine storm in children with CHD or PH accompanied by pulmonary hypoperfusion.

Vasculopathy and Increased Vascular Congestion in Fatal COVID-19 and Acute Respiratory Distress Syndrome.

Rationale: The leading cause of death in coronavirus disease 2019 (COVID-19) is severe pneumonia, with many patients developing acute respiratory distress syndrome (ARDS) and diffuse alveolar damage (DAD). Whether DAD in fatal COVID-19 is distinct from other causes of DAD remains unknown. Objective: To compare lung parenchymal and vascular alterations between patients with fatal COVID-19 pneumonia and other DAD-causing etiologies using a multidimensional approach. Methods: This autopsy cohort consisted of consecutive patients with COVID-19 pneumonia (n = 20) and with respiratory failure and histologic DAD (n = 21; non-COVID-19 viral and nonviral etiologies). Premortem chest computed tomography (CT) scans were evaluated for vascular changes. Postmortem lung tissues were compared using histopathological and computational analyses. Machine-learning-derived morphometric analysis of the microvasculature was performed, with a random forest classifier quantifying vascular congestion (CVasc) in different microscopic compartments. Respiratory mechanics and gas-exchange parameters were evaluated longitudinally in patients with ARDS. Measurements and Main Results: In premortem CT, patients with COVID-19 showed more dilated vasculature when all lung segments were evaluated (P = 0.001) compared with controls with DAD. Histopathology revealed vasculopathic changes, including hemangiomatosis-like changes (P = 0.043), thromboemboli (P = 0.0038), pulmonary infarcts (P = 0.047), and perivascular inflammation (P < 0.001). Generalized estimating equations revealed significant regional differences in the lung microarchitecture among all DAD-causing entities. COVID-19 showed a larger overall CVasc range (P = 0.002). Alveolar-septal congestion was associated with a significantly shorter time to death from symptom onset (P = 0.03), length of hospital stay (P = 0.02), and increased ventilatory ratio [an estimate for pulmonary dead space fraction (Vd); p = 0.043] in all cases of ARDS. Conclusions: Severe COVID-19 pneumonia is characterized by significant vasculopathy and aberrant alveolar-septal congestion. Our findings also highlight the role that vascular alterations may play in Vd and clinical outcomes in ARDS in general.

[Features of the cell composition of inflammatory infiltrate in different phases of diffuse alveolar lung damage with COVID-19]. / Osobennosti kletochnogo sostava vospalitel'nogo infil'trata v raznye fazy diffuznogo al'veolyarnogo povrezhdeniya legkikh pri COVID-19.

BACKGROUND: Acute respiratory distress syndrome (ARDS) with COVID-19 has a worse prognosis than ARDS with other diseases. Mortality from ARDS with COVID-19 is 26.0 - 61.5%, and due to other causes - 35.3-37.2%. OBJECTIVE: To find of the correlation between polymorphonuclear leukocytes (PMNs), lymphocytes, and macrophages in the cellular composition of the inflammatory infiltrate at different stages and phases of diffuse alveolar damage (DAD) with COVID-19, analyzing the autopsy material. MATERIAL AND METHODS: The lung tissue of 25 patients who died from ARDS with COVID-19 without a secondary bacterial or mycotic infection, another thanatologically significant pathology of the lungs, was studied. To study the cellular composition of the inflammatory infiltrate and the dynamics of its changes a double immunohistochemical analysis of the expression of antibodies to CD15, CD3, and CD68 was used. RESULTS: The inflammatory infiltrate and intraalveolar exudate in the exudative phase of DAD was represented by 56.8% of PMNs (CD15-positive cells; hereinafter - the average value of the percentage of positive cells to the total number of cells of the inflammatory infiltrate), 6.9% - lymphocytes (CD3-positive cells) and 19.5% macrophages (CD68-positive cells). In the early stage of the proliferative phase: 14.1% PMNs, 38.7% lymphocytes and 13.5% macrophages. In the late stage of the proliferative phase: 11.3% PMNs, 14.5% lymphocytes and 39.3% macrophages. CONCLUSIONS: In the exudative phase of DAD a statistically significant predominance of PMN was revealed, which could determine the main volume of lung damage and the severity of ARDS with COVID-19. In the early stage of the proliferative phase of DAD, a statistically significant change in the composition of the inflammatory infiltrate was revealed to compare with the exudative phase: a significant decrease in the content of PMNs relative to the total number of cells in the inflammatory infiltrate; an increase in the number of lymphocytes, which is probably associated with the start of organization and repair processes. In the late stage of the proliferative phase of DAD, compared with its early stage, was revealed a statistically significant increase in the number of macrophages in ratio.

Studying the clinical, radiological, histological, microbiological, and immunological evolution during the different COVID-19 disease stages using minimal invasive autopsy.

The WHO defines different COVID-19 disease stages in which the pathophysiological mechanisms differ. We evaluated the characteristics of these COVID-19 disease stages. Forty-four PCR-confirmed COVID-19 patients were included in a prospective minimal invasive autopsy cohort. Patients were classified into mild-moderate (n = 4), severe-critical (n = 32) and post-acute disease (n = 8) and clinical, radiological, histological, microbiological and immunological data were compared. Classified according to Thoracic Society of America, patients with mild-moderate disease had no typical COVID-19 images on CT-Thorax versus 71.9% with typical images in severe-critical disease and 87.5% in post-acute disease (P < 0.001). Diffuse alveolar damage was absent in mild-moderate disease but present in 93.8% and 87.5% of patients with severe-critical and post-acute COVID-19 respectively (P = 0.002). Other organs with COVID-19 related histopathological changes were liver and heart. Interferon-γ levels were significantly higher in patients with severe-critical COVID-19 (P = 0.046). Anti-SARS CoV-2 IgG was positive in 66%, 40.6% and 87.5% of patients with mild-moderate, severe-critical and post-acute COVID-19 respectively (n.s.). Significant differences in histopathological and immunological characteristics between patients with mild-moderate disease compared to patients with severe-critical disease were found, whereas differences between patients with severe-critical disease and post-acute disease were limited. This emphasizes the need for tailored treatment of COVID-19 patients.

Common Laboratory Mice Are Susceptible to Infection with the SARS-CoV-2 Beta Variant.

Small animal models are of crucial importance for assessing COVID-19 countermeasures. Common laboratory mice would be well-suited for this purpose but are not susceptible to infection with wild-type SARS-CoV-2. However, the development of mouse-adapted virus strains has revealed key mutations in the SARS-CoV-2 spike protein that increase infectivity, and interestingly, many of these mutations are also present in naturally occurring SARS-CoV-2 variants of concern. This suggests that these variants might have the ability to infect common laboratory mice. Herein we show that the SARS-CoV-2 beta variant attains infectibility to BALB/c mice and causes pulmonary changes within 2-3 days post infection, consistent with results seen in other murine models of COVID-19, at a reasonable virus dose (2 × 105 PFU). The findings suggest that common laboratory mice can serve as the animal model of choice for testing the effectiveness of antiviral drugs and vaccines against SARS-CoV-2.

COVID-19 Lung Pathogenesis in SARS-CoV-2 Autopsy Cases.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a major public health issue. COVID-19 is considered an airway/multi-systemic disease, and demise has been associated with an uncontrolled immune response and a cytokine storm in response to the virus. However, the lung pathology, immune response, and tissue damage associated with COVID-19 demise are poorly described and understood due to safety concerns. Using post-mortem lung tissues from uninfected and COVID-19 deadly cases as well as an unbiased combined analysis of histology, multi-viral and host markers staining, correlative microscopy, confocal, and image analysis, we identified three distinct phenotypes of COVID-19-induced lung damage. First, a COVID-19-induced hemorrhage characterized by minimal immune infiltration and large thrombus; Second, a COVID-19-induced immune infiltration with excessive immune cell infiltration but no hemorrhagic events. The third phenotype correspond to the combination of the two previous ones. We observed the loss of alveolar wall integrity, detachment of lung tissue pieces, fibroblast proliferation, and extensive fibrosis in all three phenotypes. Although lung tissues studied were from lethal COVID-19, a strong immune response was observed in all cases analyzed with significant B cell and poor T cell infiltrations, suggesting an exhausted or compromised immune cellular response in these patients. Overall, our data show that SARS-CoV-2-induced lung damage is highly heterogeneous. These individual differences need to be considered to understand the acute and long-term COVID-19 consequences.

Identification of Unique Peptides for SARS-CoV-2 Diagnostics and Vaccine Development by an In Silico Proteomics Approach.

Ongoing evolution of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus strains is posing new COVID-19 diagnosis and treatment challenges. To help efforts to meet these challenges we examined data acquired from proteomic analyses of human SARS-CoV-2-infected cell lines and samples from COVID-19 patients. Initially, 129 unique peptides were identified, which were rigorously evaluated for repeats, disorders, polymorphisms, antigenicity, immunogenicity, toxicity, allergens, sequence similarity to human proteins, and contributions from other potential cross-reacting pathogenic species or the human saliva microbiome. We also screened SARS-CoV-2-infected NBHE and A549 cell lines for presence of antigenic peptides, and identified paratope peptides from crystal structures of SARS-CoV-2 antigen-antibody complexes. We then selected four antigen peptides for docking with known viral unbound T-cell receptor (TCR), class I and II peptide major histocompatibility complex (pMHC), and identified paratope sequences. We also tested the paratope binding affinity of SARS-CoV T- and B-cell peptides that had been previously experimentally validated. The resultant antigenic peptides have high potential for generating SARS-CoV-2-specific antibodies, and the paratope peptides can be directly used to develop a COVID-19 diagnostics assay. The presented genomics and proteomics-based in-silico approaches have apparent utility for identifying new diagnostic peptides that could be used to fight SARS-CoV-2.

When Immunity Kills: The Lessons of SARS-CoV-2 Outbreak.

Since its emergence at the end of 2019, SARS-CoV-2 has spread worldwide at a very rapid pace. While most infected individuals have an asymptomatic or mild disease, a minority, mainly the elderly, develop a severe disease that may lead to a fatal acute respiratory distress syndrome (ARDS). ARDS results from a highly inflammatory immunopathology process that includes systemic manifestations and massive alveolar damages that impair gas exchange. The present review summarizes our current knowledge in the rapidly evolving field of SARS-CoV-2 immunopathology, emphasizing the role of specific T cell responses. Indeed, accumulating evidence suggest that while T-cell response directed against SARS-CoV-2 likely plays a crucial role in virus clearance, it may also participate in the immunopathology process that leads to ARDS.

COVID-19 autopsy reports from the Ga-East Municipal and the 37 Military Hospitals in Accra, Ghana.

INTRODUCTION: Since the declaration of COVID-19 by the World Health Organisation (WHO) as a global pandemic on 11th March 2020, the number of deaths continue to increase worldwide. Reports on its pathologic manifestations have been published with very few from the Sub-Saharan African region. This article reports autopsies on COVID-19 patients from the Ga-East and the 37 Military Hospitals to provide pathological evidence for better understanding of COVID-19 in Ghana. METHODS: Under conditions required for carrying out autopsies on bodies infected with category three infectious agents, with few modifications, complete autopsies were performed on twenty patients with ante-mortem and/or postmortem RT -PCR confirmed positive COVID-19 results, between April and June, 2020. RESULTS: There were equal proportion of males and females. Thirteen (65%) of the patients were 55years or older with the same percentage (65%) having Type II diabetes and/or hypertension. The most significant pathological feature found at autopsy was diffuse alveolar damage. Seventy per cent (14/20) had associated thromboemboli in the lungs, kidneys and the heart. Forty per cent (6/15) of the patients that had negative results for COVID-19 by the nasopharyngeal swab test before death had positive results during postmortem using bronchopulmonary specimen. At autopsy all patients were identified to have pre-existing medical conditions. CONCLUSION: Diffuse alveolar damage was a key pathological feature of deaths caused by COVID-19 in all cases studied with hypertension and diabetes mellitus being major risk factors. Individuals without co-morbidities were less likely to die or suffer severe disease from SARS-CoV-2. FUNDING: None declared.

Autopsy-Based Pulmonary and Vascular Pathology: Pulmonary Endotheliitis and Multi-Organ Involvement in COVID-19 Associated Deaths.

BACKGROUND: Findings from autopsies have provided evidence on systemic microvascular damage as one of the underlying mechanisms of Coronavirus disease 2019 (CO-VID-19). The aim of this study was to correlate autopsy-based cause of death in SARS-CoV-2, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) positive patients with chest imaging and severity grade of pulmonary and systemic morphological vascular pathology. METHODS: Fifteen SARS-CoV-2 positive autopsies with clinically distinct presentations (age 22-89 years) were retrospectively analyzed with focus on vascular, thromboembolic, and ischemic changes in pulmonary and in extrapulmonary sites. Eight patients died due to COVID-19 associated respiratory failure with diffuse alveolar damage in various stages and/or multi-organ failure, whereas other reasons such as cardiac decompensation, complication of malignant tumors, or septic shock were the cause of death in 7 further patients. The severity of gross and histopathological changes was semi-quantitatively scored as 0 (absent), 1 (mild), and 3 (severe). Severity scores between the 2 groups were correlated with selected clinical parameters, initial chest imaging, autopsy-based cause of death, and compared using Pearson χ2 and Mann-Whitney U tests. RESULTS: Severe pulmonary endotheliitis (p = 0.031, p = 0.029) and multi-organ involvement (p = 0.026, p = 0.006) correlated significantly with COVID-19 associated death. Pulmonary microthrombi showed limited statistical correlation, while tissue necrosis, gross pulmonary embolism, and bacterial superinfection did not differentiate the 2 study groups. Chest imaging at hospital admission did not differ either. CONCLUSIONS: Extensive pulmonary endotheliitis and multi-organ involvement are characteristic autopsy features in fatal CO-VID-19 associated deaths. Thromboembolic and ischemic events and bacterial superinfections occur frequently in SARS-CoV-2 infection independently of outcome.

Pulmonary post-mortem findings in a series of COVID-19 cases from northern Italy: a two-centre descriptive study.

BACKGROUND: COVID-19 is characterised by respiratory symptoms, which deteriorate into respiratory failure in a substantial proportion of cases, requiring intensive care in up to a third of patients admitted to hospital. Analysis of the pathological features in the lung tissues of patients who have died with COVID-19 could help us to understand the disease pathogenesis and clinical outcomes. METHODS: We systematically analysed lung tissue samples from 38 patients who died from COVID-19 in two hospitals in northern Italy between Feb 29 and March 24, 2020. The most representative areas identified at macroscopic examination were selected, and tissue blocks (median seven, range five to nine) were taken from each lung and fixed in 10% buffered formalin for at least 48 h. Tissues were assessed with use of haematoxylin and eosin staining, immunohistochemical staining for inflammatory infiltrate and cellular components (including staining with antibodies against CD68, CD3, CD45, CD61, TTF1, p40, and Ki-67), and electron microscopy to identify virion localisation. FINDINGS: All cases showed features of the exudative and proliferative phases of diffuse alveolar damage, which included capillary congestion (in all cases), necrosis of pneumocytes (in all cases), hyaline membranes (in 33 cases), interstitial and intra-alveolar oedema (in 37 cases), type 2 pneumocyte hyperplasia (in all cases), squamous metaplasia with atypia (in 21 cases), and platelet-fibrin thrombi (in 33 cases). The inflammatory infiltrate, observed in all cases, was largely composed of macrophages in the alveolar lumina (in 24 cases) and lymphocytes in the interstitium (in 31 cases). Electron microscopy revealed that viral particles were predominantly located in the pneumocytes. INTERPRETATION: The predominant pattern of lung lesions in patients with COVID-19 patients is diffuse alveolar damage, as described in patients infected with severe acute respiratory syndrome and Middle East respiratory syndrome coronaviruses. Hyaline membrane formation and pneumocyte atypical hyperplasia are frequent. Importantly, the presence of platelet-fibrin thrombi in small arterial vessels is consistent with coagulopathy, which appears to be common in patients with COVID-19 and should be one of the main targets of therapy. FUNDING: None.

Identification of key signaling pathways induced by SARS-CoV2 that underlie thrombosis and vascular injury in COVID-19 patients.

The SARS-CoV-2 pandemic has led to hundreds of thousands of deaths and billions of dollars in economic damage. The immune response elicited from this virus is poorly understood. An alarming number of cases have arisen where COVID-19 patients develop complications on top of the symptoms already associated with SARS, such as thrombosis, injuries of vascular system, kidney, and liver, as well as Kawasaki disease. In this review, a bioinformatics approach was used to elucidate the immune response triggered by SARS-CoV-2 infection in primary human lung epithelial and transformed human lung alveolar. Additionally, examined the potential mechanism behind several complications that have been associated with COVID-19 and determined that a specific cytokine storm is leading to excessive neutrophil recruitment. These neutrophils are directly leading to thrombosis, organ damage, and complement activation via neutrophil extracellular trap release.

The Role of Alveolar Edema in COVID-19.

The coronavirus disease 2019 (COVID-19) has spread over the world for more than one year. COVID-19 often develops life-threatening hypoxemia. Endothelial injury caused by the viral infection leads to intravascular coagulation and ventilation-perfusion mismatch. However, besides above pathogenic mechanisms, the role of alveolar edema in the disease progression has not been discussed comprehensively. Since the exudation of pulmonary edema fluid was extremely serious in COVID-19 patients, we bring out a hypothesis that severity of alveolar edema may determine the size of poorly-ventilated area and the blood oxygen content. Treatments to pulmonary edema (conservative fluid management, exogenous surfactant replacements and ethanol-oxygen vapor therapy hypothetically) may be greatly helpful for reducing the occurrences of severe cases. Given that late mechanical ventilation may cause mucus (edema fluid) to be blown deep into the small airways, oxygen therapy should be given at the early stages. The optimal time and blood oxygen saturation (SpO2) threshold for oxygen therapy are also discussed.

Distinctive pseudopalisaded histiocytic hyperplasia characterizes the transition of exudative to proliferative phase of diffuse alveolar damage in patients dying of COVID-19.

Severe COVID-19 results in a glucocorticoid responsive form of acute respiratory distress (ARDS)/diffuse alveolar damage (DAD). Herein we compare the immunopathology of lung tissue procured at autopsy in patients dying of SARS-CoV-2 with those dying of DAD prior to the COVID-19 pandemic. Autopsy gross and microscopic features stratified by duration of illness in twelve patients who tested positive for SARS-CoV-2 viral RNA, as well as seven patients dying of DAD prior to the COVID-19 pandemic were evaluated with multiplex (5-plex: CD4, CD8, CD68, CD20, AE1/AE3) and SARS-CoV immunohistochemistry to characterize the immunopathologic stages of DAD. We observed a distinctive pseudopalisaded histiocytic hyperplasia interposed between the exudative and proliferative phase of COVID-19 associated DAD, which was most pronounced at the fourth week from symptom onset. Pulmonary macrothrombi were seen predominantly in cases with pseudopalisaded histiocytic hyperplasia and/or proliferative phase DAD. Neither pseudopalisaded histiocytic hyperplasia nor pulmonary macrothrombi was seen in non-COVID-19 DAD cases, whereas microthrombi were common in DAD regardless of etiology. The inflammatory pattern of pseudopalisaded histiocytic hyperplasia may represent the distinctive immunopathology associated with the dexamethasone responsive form of DAD seen in severe COVID-19.

Cause of death based on systematic post-mortem studies in patients with positive SARS-CoV-2 tissue PCR during the COVID-19 pandemic.

IMPORTANCE: Assessment of the causative association between the COVID-19 and cause of death has been hampered by limited availability of systematically performed autopsies. We aimed to present autopsy-confirmed causes of death in patients who died with COVID-19 and to assess the association between thrombosis and diffuse alveolar damage consistent with COVID-19 (DAD). METHODS: Consecutive forensic (n = 60) and clinical (n = 42) autopsies with positive post-mortem SARS-CoV-2 PCR in lungs (age 73 ± 14 years, 50% men) were included. The cause of death analysis was based on a review of medical records and histological reports. Thrombotic phenomena in lungs were defined as pulmonary thromboembolism (PE), thrombosis in pulmonary artery branches or microangiopathy in capillary vessels. RESULTS: COVID-19 caused or contributed to death in 71% of clinical and 83% of forensic autopsies, in whom significant DAD was observed. Of the patients with COVID-19 as the primary cause of death, only 19% had no thrombotic phenomena in the lungs, as opposed to 38% amongst those with COVID-19 as a contributing cause of death and 54% amongst patients whose death was not related to COVID-19 (p = 0.002). PE was observed in 5 patients. Two patients fulfilled the criteria for lymphocyte myocarditis. CONCLUSIONS: Vast majority of all PCR-positive fatalities, including out-of-hospital deaths, during the SARS-CoV-2 pandemic were related to DAD caused by COVID-19. Pulmonary artery thrombosis and microangiopathy in pulmonary tissue were common and associated with the presence of DAD, whilst venous PE was rarely observed. Histology-confirmed lymphocyte myocarditis was a rare finding.

Broad Severe Acute Respiratory Syndrome Coronavirus 2 Cell Tropism and Immunopathology in Lung Tissues From Fatal Coronavirus Disease 2019.

BACKGROUND: Coronavirus disease 2019 (COVID-19) patients manifest with pulmonary symptoms reflected by diffuse alveolar damage (DAD), excessive inflammation, and thromboembolism. The mechanisms mediating these processes remain unclear. METHODS: We performed multicolor staining for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) proteins and lineage markers to define viral tropism and lung pathobiology in 5 autopsy cases. RESULTS: Lung parenchyma showed severe DAD with thromboemboli. Viral infection was found in an extensive range of cells including pneumocyte type II, ciliated, goblet, club-like, and endothelial cells. More than 90% of infiltrating immune cells were positive for viral proteins including macrophages, monocytes, neutrophils, natural killer (NK) cells, B cells, and T cells. Most but not all infected cells were angiotensin-converting enzyme 2 (ACE2) positive. The numbers of infected and ACE2-positive cells are associated with extensive tissue damage. Infected tissues exhibited high levels of inflammatory cells including macrophages, monocytes, neutrophils, and NK cells, and low levels of B cells but abundant T cells consisting of mainly T helper cells, few cytotoxic T cells, and no regulatory T cells. Robust interleukin-6 expression was present in most cells, with or without infection. CONCLUSIONS: In fatal COVID-19 lungs, there are broad SARS-CoV-2 cell tropisms, extensive infiltrated innate immune cells, and activation and depletion of adaptive immune cells, contributing to severe tissue damage, thromboemboli, excess inflammation, and compromised immune responses.

COVID-19 Vasculopathy: Mounting Evidence for an Indirect Mechanism of Endothelial Injury.

Patients with coronavirus disease 2019 (COVID-19) who are critically ill develop vascular complications characterized by thrombosis of small, medium, and large vessels. Dysfunction of the vascular endothelium due to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has been implicated in the pathogenesis of the COVID-19 vasculopathy. Although initial reports suggested that endothelial injury was caused directly by the virus, recent studies indicate that endothelial cells do not express angiotensin-converting enzyme 2, the receptor that SARS-CoV-2 uses to gain entry into cells, or express it at low levels and are resistant to the infection. These new findings, together with the observation that COVID-19 triggers a cytokine storm capable of injuring the endothelium and disrupting its antithrombogenic properties, favor an indirect mechanism of endothelial injury mediated locally by an augmented inflammatory reaction to infected nonendothelial cells, such as the bronchial and alveolar epithelium, and systemically by the excessive immune response to infection. Herein we review the vascular pathology of COVID-19 and critically discuss the potential mechanisms of endothelial injury in this disease.

Diffuse interstitial pneumonia-like/macrophage activation syndrome-like changes in patients with COVID-19 correlate with length of illness.

OBJECTIVES: Assess the pathologic changes in the lungs of COVID-19 decedents and correlate these changes with demographic data, clinical course, therapies, and duration of illness. METHODS: Lungs of 12 consecutive COVID-19 decedents consented for autopsy were evaluated for gross and histopathologic abnormalities. A complete Ghon "en block" dissection was performed on all cases; lung weights and gross characteristics recorded. Immunohistochemical studies were performed to characterize lymphocytic infiltrates and to assess SARS-CoV-2 capsid protein. RESULTS: Two distinct patterns of pulmonary involvement were identified. Three of 12 cases demonstrated a predominance of acute alveolar damage (DAD) while 9 of 12 cases demonstrated a marked increase in intra-alveolar macrophages in a fashion resembling desquamative interstitial pneumonia or macrophage activation syndrome (DIP/MAS). Two patterns were correlated solely with a statistically significant difference in the duration of illness. The group exhibiting DAD had duration of illness of 5.7 days while the group with DIP/MAS had duration of illness of 21.5 days (t-test p = 0.014). CONCLUSIONS: The pulmonary pathology of COVID-19 patients demonstrates a biphasic pattern, an acute phase demonstrating DAD changes while the patients with a more prolonged course exhibit a different pattern that resembles DIP/MAS-like pattern. The potential mechanisms and clinical significance are discussed.

Reversed-engineered human alveolar lung-on-a-chip model.

Here, we present a physiologically relevant model of the human pulmonary alveoli. This alveolar lung-on-a-chip platform is composed of a three-dimensional porous hydrogel made of gelatin methacryloyl with an inverse opal structure, bonded to a compartmentalized polydimethylsiloxane chip. The inverse opal hydrogel structure features well-defined, interconnected pores with high similarity to human alveolar sacs. By populating the sacs with primary human alveolar epithelial cells, functional epithelial monolayers are readily formed. Cyclic strain is integrated into the device to allow biomimetic breathing events of the alveolar lung, which, in addition, makes it possible to investigate pathological effects such as those incurred by cigarette smoking and severe acute respiratory syndrome coronavirus 2 pseudoviral infection. Our study demonstrates a unique method for reconstitution of the functional human pulmonary alveoli in vitro, which is anticipated to pave the way for investigating relevant physiological and pathological events in the human distal lung.

COVID-19 tissue atlases reveal SARS-CoV-2 pathology and cellular targets.

COVID-19, which is caused by SARS-CoV-2, can result in acute respiratory distress syndrome and multiple organ failure1-4, but little is known about its pathophysiology. Here we generated single-cell atlases of 24 lung, 16 kidney, 16 liver and 19 heart autopsy tissue samples and spatial atlases of 14 lung samples from donors who died of COVID-19. Integrated computational analysis uncovered substantial remodelling in the lung epithelial, immune and stromal compartments, with evidence of multiple paths of failed tissue regeneration, including defective alveolar type 2 differentiation and expansion of fibroblasts and putative TP63+ intrapulmonary basal-like progenitor cells. Viral RNAs were enriched in mononuclear phagocytic and endothelial lung cells, which induced specific host programs. Spatial analysis in lung distinguished inflammatory host responses in lung regions with and without viral RNA. Analysis of the other tissue atlases showed transcriptional alterations in multiple cell types in heart tissue from donors with COVID-19, and mapped cell types and genes implicated with disease severity based on COVID-19 genome-wide association studies. Our foundational dataset elucidates the biological effect of severe SARS-CoV-2 infection across the body, a key step towards new treatments.