Impact of Bacterial Toxins in the Lungs.

Bacterial toxins play a key role in the pathogenesis of lung disease. Based on their structural and functional properties, they employ various strategies to modulate lung barrier function and to impair host defense in order to promote infection. Although in general, these toxins target common cellular signaling pathways and host compartments, toxin- and cell-specific effects have also been reported. Toxins can affect resident pulmonary cells involved in alveolar fluid clearance (AFC) and barrier function through impairing vectorial Na+ transport and through cytoskeletal collapse, as such, destroying cell-cell adhesions. The resulting loss of alveolar-capillary barrier integrity and fluid clearance capacity will induce capillary leak and foster edema formation, which will in turn impair gas exchange and endanger the survival of the host. Toxins modulate or neutralize protective host cell mechanisms of both the innate and adaptive immunity response during chronic infection. In particular, toxins can either recruit or kill central players of the lung's innate immune responses to pathogenic attacks, i.e., alveolar macrophages (AMs) and neutrophils. Pulmonary disorders resulting from these toxin actions include, e.g., acute lung injury (ALI), the acute respiratory syndrome (ARDS), and severe pneumonia. When acute infection converts to persistence, i.e., colonization and chronic infection, lung diseases, such as bronchitis, chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF) can arise. The aim of this review is to discuss the impact of bacterial toxins in the lungs and the resulting outcomes for pathogenesis, their roles in promoting bacterial dissemination, and bacterial survival in disease progression.

Expression of Surfactant Protein D Distinguishes Severe Pandemic Influenza A(H1N1) from Coronavirus Disease 2019.

The differentiation between influenza and coronavirus disease 2019 (COVID-19) could constitute a diagnostic challenge during the ongoing winter owing to their clinical similitude. Thus, novel biomarkers are required to enable making this distinction. Here, we evaluated whether the surfactant protein D (SP-D), a collectin produced at the alveolar epithelium with known immune properties, was useful to differentiate pandemic influenza A(H1N1) from COVID-19 in critically ill patients. Our results revealed high serum SP-D levels in patients with severe pandemic influenza but not those with COVID-19. This finding was validated in a separate cohort of mechanically ventilated patients with COVID-19 who also showed low plasma SP-D levels. However, plasma SP-D levels did not distinguish seasonal influenza from COVID-19 in mild-to-moderate disease. Finally, we found that high serum SP-D levels were associated with death and renal failure among severe pandemic influenza cases. Thus, our studies have identified SP-D as a unique biomarker expressed during severe pandemic influenza but not COVID-19.

Bis(monoacylglycero)phosphate, an important actor in the host endocytic machinery hijacked by SARS-CoV-2 and related viruses.

Viruses, including the novel coronavirus SARS-CoV-2, redirect infected cell metabolism to their own purposes. After binding to its receptor angiotensin-converting enzyme 2 (ACE2) on the cell surface, the SARS-CoV-2 is taken up by receptor-mediated endocytosis ending in the acidic endolysosomal compartment. The virus hijacks the endosomal machinery leading to fusion of viral and endosomal membranes and release of the viral RNA into the cytosol. This mini-review specifically highlights the membrane lipid organization of the endosomal system focusing on the unconventional and late endosome/lysosome-specific phospholipid, bis(monoacylglycero)phosphate (BMP). BMP is enriched in alveolar macrophages of lung, one of the target tissue of SARS-CoV-2. This review details the BMP structure, its unsaturated fatty acid composition and fusogenic properties that are essential for the highly dynamic formation of the intraluminal vesicles inside the endosomes. Interestingly, BMP is necessary for infection and replication of enveloped RNA virus such as SARS-CoV-1 and Dengue virus. We also emphasize the role of BMP in lipid sorting and degradation, especially cholesterol transport in cooperation with Niemann Pick type C proteins (NPC 1 and 2) and with some oxysterol-binding protein (OSBP)-related proteins (ORPs) as well as in sphingolipid degradation. Interestingly, numerous virus infection required NPC1 as well as ORPs along the endocytic pathway. Furthermore, BMP content is increased during pathological endosomal lipid accumulation in various lysosomal storage disorders. This is particularly important knowing the high percentage of patients with metabolic disorders among the SARS-CoV-2 infected patients presenting severe forms of COVID-19.

Capillary cell-type specialization in the alveolus.

In the mammalian lung, an apparently homogenous mesh of capillary vessels surrounds each alveolus, forming the vast respiratory surface across which oxygen transfers to the blood1. Here we use single-cell analysis to elucidate the cell types, development, renewal and evolution of the alveolar capillary endothelium. We show that alveolar capillaries are mosaics; similar to the epithelium that lines the alveolus, the alveolar endothelium is made up of two intermingled cell types, with complex 'Swiss-cheese'-like morphologies and distinct functions. The first cell type, which we term the 'aerocyte', is specialized for gas exchange and the trafficking of leukocytes, and is unique to the lung. The other cell type, termed gCap ('general' capillary), is specialized to regulate vasomotor tone, and functions as a stem/progenitor cell in capillary homeostasis and repair. The two cell types develop from bipotent progenitors, mature gradually and are affected differently in disease and during ageing. This cell-type specialization is conserved between mouse and human lungs but is not found in alligator or turtle lungs, suggesting it arose during the evolution of the mammalian lung. The discovery of cell type specialization in alveolar capillaries transforms our understanding of the structure, function, regulation and maintenance of the air-blood barrier and gas exchange in health, disease and evolution.

Postexposure Liponucleotide Prophylaxis and Treatment Attenuates Acute Respiratory Distress Syndrome in Influenza-infected Mice.

There is an urgent need for new drugs for patients with acute respiratory distress syndrome (ARDS), including those with coronavirus disease (COVID-19). ARDS in influenza-infected mice is associated with reduced concentrations of liponucleotides (essential precursors for de novo phospholipid synthesis) in alveolar type II (ATII) epithelial cells. Because surfactant phospholipid synthesis is a primary function of ATII cells, we hypothesized that disrupting this process could contribute significantly to the pathogenesis of influenza-induced ARDS. The goal of this study was to determine whether parenteral liponucleotide supplementation can attenuate ARDS. C57BL/6 mice inoculated intranasally with 10,000 plaque-forming units/mouse of H1N1 influenza A/WSN/33 virus were treated with CDP (cytidine 5'-diphospho)-choline (100 µg/mouse i.p.) ± CDP -diacylglycerol 16:0/16:0 (10 µg/mouse i.p.) once daily from 1 to 5 days after inoculation (to model postexposure influenza prophylaxis) or as a single dose on Day 5 (to model treatment of patients with ongoing influenza-induced ARDS). Daily postexposure prophylaxis with CDP-choline attenuated influenza-induced hypoxemia, pulmonary edema, alterations in lung mechanics, impairment of alveolar fluid clearance, and pulmonary inflammation without altering viral replication. These effects were not recapitulated by the daily administration of CTP (cytidine triphosphate) and/or choline. Daily coadministration of CDP-diacylglycerol significantly enhanced the beneficial effects of CDP-choline and also modified the ATII cell lipidome, reversing the infection-induced decrease in phosphatidylcholine and increasing concentrations of most other lipid classes in ATII cells. Single-dose treatment with both liponucleotides at 5 days after inoculation also attenuated hypoxemia, altered lung mechanics, and inflammation. Overall, our data show that liponucleotides act rapidly to reduce disease severity in mice with severe influenza-induced ARDS.

Is Microthrombosis the Main Pathology in Coronavirus Disease 2019 Severity?-A Systematic Review of the Postmortem Pathologic Findings.

This systematic review attempts to retrieve and report the findings of postmortem studies including the histopathologic data of deceased coronavirus disease 2019 patients and to review the manifestations of coronavirus disease 2019-associated thrombotic pathologies reported in the recent literature. DATA SOURCES: PubMed, Excerpta Medica Database, and Cochrane library between December 1, 2019, and August 26, 2020. STUDY SELECTION: Investigators screened 360 unique references, retrieved published autopsy series, and report on the postmortem histopathologic information on patients who had died of coronavirus disease 2019. DATA EXTRACTION: Investigators independently abstracted all available data including study design, participant demographics, key histopathologic findings, disease severity markers, duration of hospital stay, and cause of death. DATA SYNTHESIS: From the 65 eligible studies, 691 total completed autopsies were included in evidence synthesis. Histopathologic evaluation of the lungs revealed presence of diffuse alveolar damage in 323 of 443 patients and pulmonary microthrombi in 242 of 326 patients. Deep venous thrombosis and pulmonary embolism were found in 41% and ~15%, respectively, of the cadavers examined for thromboembolic events. d-dimer levels were generally higher in patients with severe clinical course of coronavirus disease 2019. Plasma levels of ferritin, lactate dehydrogenase, interleukin-6, and C-reactive protein were higher in nonsurvivors when compared with survivors. Overall, microthrombi and extensive angiogenesis of lung vasculature were the most common pathologic findings in the lungs and microthrombi in most of the assessed organ-tissue. CONCLUSIONS: Diffuse alveolar damage was the most predominant feature in the lungs of coronavirus disease 2019 patients who underwent postmortem assessment. Widespread pulmonary microthrombosis and extensive pulmonary angiogenesis, in addition to frequent pulmonary and extrapulmonary microthrombotic and thromboembolic findings in patients with coronavirus disease 2019, appear to be consistent with the disease-specific hypercoagulability. Further discovery efforts in assessing the link between coronavirus disease 2019, hypercoagulable state, and immunothrombosis are warranted. In the interim, increased attention to anticoagulant treatment approaches in coronavirus disease 2019 patients is needed.

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.

Human-Based Advanced in vitro Approaches to Investigate Lung Fibrosis and Pulmonary Effects of COVID-19.

The coronavirus disease 2019 (COVID-19) pandemic has caused considerable socio-economic burden, which fueled the development of treatment strategies and vaccines at an unprecedented speed. However, our knowledge on disease recovery is sparse and concerns about long-term pulmonary impairments are increasing. Causing a broad spectrum of symptoms, COVID-19 can manifest as acute respiratory distress syndrome (ARDS) in the most severely affected patients. Notably, pulmonary infection with Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2), the causing agent of COVID-19, induces diffuse alveolar damage (DAD) followed by fibrotic remodeling and persistent reduced oxygenation in some patients. It is currently not known whether tissue scaring fully resolves or progresses to interstitial pulmonary fibrosis. The most aggressive form of pulmonary fibrosis is idiopathic pulmonary fibrosis (IPF). IPF is a fatal disease that progressively destroys alveolar architecture by uncontrolled fibroblast proliferation and the deposition of collagen and extracellular matrix (ECM) proteins. It is assumed that micro-injuries to the alveolar epithelium may be induced by inhalation of micro-particles, pathophysiological mechanical stress or viral infections, which can result in abnormal wound healing response. However, the exact underlying causes and molecular mechanisms of lung fibrosis are poorly understood due to the limited availability of clinically relevant models. Recently, the emergence of SARS-CoV-2 with the urgent need to investigate its pathogenesis and address drug options, has led to the broad application of in vivo and in vitro models to study lung diseases. In particular, advanced in vitro models including precision-cut lung slices (PCLS), lung organoids, 3D in vitro tissues and lung-on-chip (LOC) models have been successfully employed for drug screens. In order to gain a deeper understanding of SARS-CoV-2 infection and ultimately alveolar tissue regeneration, it will be crucial to optimize the available models for SARS-CoV-2 infection in multicellular systems that recapitulate tissue regeneration and fibrotic remodeling. Current evidence for SARS-CoV-2 mediated pulmonary fibrosis and a selection of classical and novel lung models will be discussed in this review.

Molecular Mechanisms of Vascular Damage During Lung Injury.

A variety of pulmonary and systemic insults promote an inflammatory response causing increased vascular permeability, leading to the development of acute lung injury (ALI), a condition necessitating hospitalization and intensive care, or the more severe acute respiratory distress syndrome (ARDS), a disease with a high mortality rate. Further, COVID-19 pandemic-associated ARDS is now a major cause of mortality worldwide. The pathogenesis of ALI is explained by injury to both the vascular endothelium and the alveolar epithelium. The disruption of the lung endothelial and epithelial barriers occurs in response to both systemic and local production of pro-inflammatory cytokines. Studies that evaluate the association of genetic polymorphisms with disease risk did not yield many potential therapeutic targets to treat and revert lung injury. This failure is probably due in part to the phenotypic complexity of ALI/ARDS, and genetic predisposition may be obscured by the multiple environmental and behavioral risk factors. In the last decade, new research has uncovered novel epigenetic mechanisms that control ALI/ARDS pathogenesis, including histone modifications and DNA methylation. Enzyme inhibitors such as DNMTi and HDACi may offer new alternative strategies to prevent or reverse the vascular damage that occurs during lung injury. This review will focus on the latest findings on the molecular mechanisms of vascular damage in ALI/ARDS, the genetic factors that might contribute to the susceptibility for developing this disease, and the epigenetic changes observed in humans, as well as in experimental models of ALI/ADRS.

Factors Associated with the Expression of ACE2 in Human Lung Tissue: Pathological Evidence from Patients with Normal FEV1 and FEV1/FVC.

BACKGROUND: Whether COVID-19 comorbidities and risk factors such as old age, male gender, smoking, obesity, eosinophils and blood types have direct contact with expression of ACE2 and pro-inflammation cytokines in human lung tissues were still unclear. PATIENTS AND METHODS: Sixty-four patients with normal FEV1 and FEV1/FVC underwent thoracotomy for pulmonary nodules were included. Blinded histological assessments were performed by two pathologists. Clinical features and results of the immunohistochemical staining of ACE2 were collected and analyzed. RESULTS: ACE2 expressed in alveolar macrophages (most obvious), alveolar epithelia and vascular endothelia, but not in small-airway epithelia. ACE2 expressions are positively related to age (r =0.26, P =0.040), weight (r =0.43, P<0.001), as well as BMI (r = 0.38, P =0.002), and male patients show higher expressions of ACE2 in lungs (P <0.05). ACE2 expressions are negatively related to peripheral eosinophils (r = -0.30, P =0.017). There was no correlation between ABO blood types and ACE2 expression in normal lung tissues (P > 0.05). IL-13 and IL-6R expression in lung tissue increased with age (r =0.26, P <0.05, for both). CONCLUSION: Our pathological evidences showed that the alveolar epithelia, vascular endothelia, and alveolar macrophages are susceptible in human lungs for SARS-CoV-2 infection. The risk factors such as high body weight/BMI, old age, male gender, and eosinopenia may be related to ACE2 expression in human lungs, and associated with more chance to develop the severe cases. IL-6R expression in lung tissue also increased with age. Therefore, weight control and smoking cessation are essential to reduce the susceptibility of SARS-CoV-2 infection, especially in obesity, old or male patients. Peripheral eosinophils monitor is also quite necessary to detect severe tendency in COVID-19 patients.

Plant-derived exosomal microRNAs inhibit lung inflammation induced by exosomes SARS-CoV-2 Nsp12.

Lung inflammation is a hallmark of coronavirus disease 2019 (COVID-19). In this study, we show that mice develop inflamed lung tissue after being administered exosomes released from the lung epithelial cells exposed to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Nsp12 and Nsp13 (exosomesNsp12Nsp13). Mechanistically, we show that exosomesNsp12Nsp13 are taken up by lung macrophages, leading to activation of nuclear factor κB (NF-κB) and the subsequent induction of an array of inflammatory cytokines. Induction of tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-1ß from exosomesNsp12Nsp13-activated lung macrophages contributes to inducing apoptosis in lung epithelial cells. Induction of exosomesNsp12Nsp13-mediated lung inflammation was abolished with ginger exosome-like nanoparticle (GELN) microRNA (miRNA aly-miR396a-5p. The role of GELNs in inhibition of the SARS-CoV-2-induced cytopathic effect (CPE) was further demonstrated via GELN aly-miR396a-5p- and rlcv-miR-rL1-28-3p-mediated inhibition of expression of Nsp12 and spike genes, respectively. Taken together, our results reveal exosomesNsp12Nsp13 as potentially important contributors to the development of lung inflammation, and GELNs are a potential therapeutic agent to treat COVID-19.

Uncoupling of macrophage inflammation from self-renewal modulates host recovery from respiratory viral infection.

Tissue macrophages self-renew during homeostasis and produce inflammatory mediators upon microbial infection. We examined the relationship between proliferative and inflammatory properties of tissue macrophages by defining the impact of the Wnt/ß-catenin pathway, a central regulator of self-renewal, in alveolar macrophages (AMs). Activation of ß-catenin by Wnt ligand inhibited AM proliferation and stemness, but promoted inflammatory activity. In a murine influenza viral pneumonia model, ß-catenin-mediated AM inflammatory activity promoted acute host morbidity; in contrast, AM proliferation enabled repopulation of reparative AMs and tissue recovery following viral clearance. Mechanistically, Wnt treatment promoted ß-catenin-HIF-1α interaction and glycolysis-dependent inflammation while suppressing mitochondrial metabolism and thereby, AM proliferation. Differential HIF-1α activities distinguished proliferative and inflammatory AMs in vivo. This ß-catenin-HIF-1α axis was conserved in human AMs and enhanced HIF-1α expression associated with macrophage inflammation in COVID-19 patients. Thus, inflammatory and reparative activities of lung macrophages are regulated by ß-catenin-HIF-1α signaling, with implications for the treatment of severe respiratory diseases.

Mesenchymal stromal/stem cells (MSCs) and MSC-derived extracellular vesicles in COVID-19-induced ARDS: Mechanisms of action, research progress, challenges, and opportunities.

In late 2019, a novel coronavirus (SARS-CoV-2) emerged in Wuhan city, Hubei province, China. Rapidly escalated into a worldwide pandemic, it has caused an unprecedented and devastating situation on the global public health and society economy. The severity of recent coronavirus disease, abbreviated to COVID-19, seems to be mostly associated with the patients' immune response. In this vein, mesenchymal stromal/stem cells (MSCs) have been suggested as a worth-considering option against COVID-19 as their therapeutic properties are mainly displayed in immunomodulation and anti-inflammatory effects. Indeed, administration of MSCs can attenuate cytokine storm and enhance alveolar fluid clearance, endothelial recovery, and anti-fibrotic regeneration. Despite advantages attributed to MSCs application in lung injuries, there are still several issues __foremost probability of malignant transformation and incidence of MSCs-related coagulopathy__ which should be resolved for the successful application of MSC therapy in COVID-19. In the present study, we review the historical evidence of successful use of MSCs and MSC-derived extracellular vesicles (EVs) in the treatment of acute respiratory distress syndrome (ARDS). We also take a look at MSCs mechanisms of action in the treatment of viral infections, and then through studying both the dark and bright sides of this approach, we provide a thorough discussion if MSC therapy might be a promising therapeutic approach in COVID-19 patients.

A molecular single-cell lung atlas of lethal COVID-19.

Respiratory failure is the leading cause of death in patients with severe SARS-CoV-2 infection1,2, but the host response at the lung tissue level is poorly understood. Here we performed single-nucleus RNA sequencing of about 116,000 nuclei from the lungs of nineteen individuals who died of COVID-19 and underwent rapid autopsy and seven control individuals. Integrated analyses identified substantial alterations in cellular composition, transcriptional cell states, and cell-to-cell interactions, thereby providing insight into the biology of lethal COVID-19. The lungs from individuals with COVID-19 were highly inflamed, with dense infiltration of aberrantly activated monocyte-derived macrophages and alveolar macrophages, but had impaired T cell responses. Monocyte/macrophage-derived interleukin-1ß and epithelial cell-derived interleukin-6 were unique features of SARS-CoV-2 infection compared to other viral and bacterial causes of pneumonia. Alveolar type 2 cells adopted an inflammation-associated transient progenitor cell state and failed to undergo full transition into alveolar type 1 cells, resulting in impaired lung regeneration. Furthermore, we identified expansion of recently described CTHRC1+ pathological fibroblasts3 contributing to rapidly ensuing pulmonary fibrosis in COVID-19. Inference of protein activity and ligand-receptor interactions identified putative drug targets to disrupt deleterious circuits. This atlas enables the dissection of lethal COVID-19, may inform our understanding of long-term complications of COVID-19 survivors, and provides an important resource for therapeutic development.

Effect of ACE1 polymorphism rs1799752 on protein levels of ACE2, the SARS-CoV-2 entry receptor, in alveolar lung epithelium.

Increased protein levels of ACE2 in alveolar epithelium of subjects who are homozygous for the ACE1 insertion of rs1799752 might facilitate host cell entry of #SARSCoV2 and explain the higher prevalence of #COVID19 in certain regions https://bit.ly/3k6aAE8.

COVID-19 and acute respiratory failure treated with CPAP.

Introduction: Patients admitted with COVID-19 often have severe hypoxemic respiratory insufficiency and it can be difficult to maintain adequate oxygenation with oxygen supplementation alone. There is a physiological rationale for the use of Continuous Positive Airway Pressure (CPAP), and CPAP could keep some patients off mechanical ventilation. We aimed to examine the physiological response to CPAP and the outcome of this treatment. Methods: Data from all patients admitted with COVID-19 and treated with CPAP, from March to July 2020 were collected retrospectively. CPAP was initiated on a medical ward when oxygen supplementation exceeded 10 liters/min to maintain oxygen saturation (SpO2) ≥92%. CPAP was administered with full face masks on a continuous basis until stable improvement in oxygenation or until intubation or death. Results: CPAP was initiated in 53 patients (35 men, 18 women) with a median (IQR) age of 68 (57-78) years. Nine patients were not able to tolerate the CPAP treatment. Median duration for the 44 patients receiving CPAP was 3 (2-6) days. The PaO2/FiO2 ratio was severely reduced to an average of 101 mmHg at initiation of treatment. A positive response of CPAP was seen on respiratory rate (p = 0.002) and on oxygenation (p < 0.001). Of the 44 patients receiving CPAP, 12 (27%) avoided intubation,13 (29%) were intubated, and 19 (43%) died. Of the patients with a ceiling of treatment in the ward (26 of 53) only 2 survived. Older age and high initial oxygen demand predicted treatment failure. Discussion: CPAP seems to have positive effect on oxygenation and respiratory rate in most patients with severe respiratory failure caused by COVID-19. Treatment with CPAP to severely hypoxemic patients in a medical ward is possible, but the prognosis for especially elderly patients with high oxygen requirement and with a ceiling of treatment in the ward is poor.

Predictive effects of IgA and IgG combination to assess pulmonary exudation progression in COVID-19 patients.

Our study intended to longitudinally explore the prediction effect of immunoglobulin A (IgA) on pulmonary exudation progression in COVID-19 patients. The serum IgA was tested with chemiluminescence method. Autoregressive moving average model was used to extrapolate the IgA levels before hospital admission. The positive rate of IgA and IgG in our cohort was 97% and 79.0%, respectively. In this study, the IgA levels peaks within 10-15 days after admission, while the IgG levels peaks at admission. We found that the time difference between their peaks was about 10 days. Viral RNA detection results showed that the positive rate in sputum and feces were the highest. Blood gas analysis showed that deterioration of hypoxia with the enlargement of pulmonary exudation area. And alveolar-arterial oxygen difference and oxygenation index were correlated with IgA and IgG. The results of biopsy showed that the epithelium of lung was exfoliated and the mucosa was edematous. In severe COVID-19 patients, the combination of IgA and IgG can predict the progress of pulmonary lesions and is closely related to hypoxemia and both also play an important defense role in invasion and destruction of bronchial and alveolar epithelium by SARS-CoV-2.

The ARREST Pneumonia Clinical Trial. Rationale and Design.

Patients hospitalized for pneumonia are at high risk for mortality. Effective therapies are therefore needed. Recent randomized clinical trials suggest that systemic steroids can reduce the length of hospital stays among patients hospitalized for pneumonia. Furthermore, preliminary findings from a feasibility study demonstrated that early treatment with a combination of an inhaled corticosteroid and a bronchodilator can improve oxygenation and reduce risk of respiratory failure in patients at risk of acute respiratory distress syndrome. Whether such a combination administered early is effective in reducing acute respiratory failure (ARF) among patients hospitalized with pneumonia is unknown. Here we describe the ARREST Pneumonia (Arrest Respiratory Failure due to Pneumonia) trial designed to address this question. ARREST Pneumonia is a two-arm, randomized, double-blinded, placebo-controlled trial designed to test the efficacy of a combination of an inhaled corticosteroid and a ß-agonist compared with placebo for the prevention of ARF in hospitalized participants with severe pneumonia. The primary outcome is ARF within 7 days of randomization, defined as a composite endpoint of intubation and mechanical ventilation; need for high-flow nasal cannula oxygen therapy or noninvasive ventilation for >36 hours (each alone or combined); or death within 36 hours of being placed on respiratory support. The planned enrollment is 600 adult participants at 10 academic medical centers. In addition, we will measure selected plasma biomarkers to better understand mechanisms of action. The trial is funded by the U.S. National Heart Lung and Blood Institute.Clinical trial registered with www.clinicaltrials.gov (NCT04193878).

Distinct uptake, amplification, and release of SARS-CoV-2 by M1 and M2 alveolar macrophages.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) invades the alveoli, where abundant alveolar macrophages (AMs) reside. How AMs respond to SARS-CoV-2 invasion remains elusive. Here, we show that classically activated M1 AMs facilitate viral spread; however, alternatively activated M2 AMs limit the spread. M1 AMs utilize cellular softness to efficiently take up SARS-CoV-2. Subsequently, the invaded viruses take over the endo-lysosomal system to escape. M1 AMs have a lower endosomal pH, favoring membrane fusion and allowing the entry of viral RNA from the endosomes into the cytoplasm, where the virus achieves replication and is packaged to be released. In contrast, M2 AMs have a higher endosomal pH but a lower lysosomal pH, thus delivering the virus to lysosomes for degradation. In hACE2 transgenic mouse model, M1 AMs are found to facilitate SARS-CoV-2 infection of the lungs. These findings provide insights into the complex roles of AMs during SARS-CoV-2 infection, along with potential therapeutic targets.

Secreted Extracellular Cyclophilin A Is a Novel Mediator of Ventilator-induced Lung Injury.

Rationale: Mechanical ventilation is a mainstay of intensive care but contributes to the mortality of patients through ventilator-induced lung injury. eCypA (extracellular CypA [cyclophilin A]) is an emerging inflammatory mediator and metalloproteinase inducer, and the gene responsible for its expression has recently been linked to coronavirus disease (COVID-19). Objectives: To explore the involvement of eCypA in the pathophysiology of ventilator-induced lung injury. Methods: Mice were ventilated with a low or high Vt for up to 3 hours, with or without blockade of eCypA signaling, and lung injury and inflammation were evaluated. Human primary alveolar epithelial cells were exposed to in vitro stretching to explore the cellular source of eCypA, and CypA concentrations were measured in BAL fluid from patients with acute respiratory distress syndrome to evaluate the clinical relevance. Measurements and Main Results: High-Vt ventilation in mice provoked a rapid increase in soluble CypA concentration in the alveolar space but not in plasma. In vivo ventilation and in vitro stretching experiments indicated the alveolar epithelium as the likely major source. In vivo blockade of eCypA signaling substantially attenuated physiological dysfunction, macrophage activation, and MMPs (matrix metalloproteinases). Finally, we found that patients with acute respiratory distress syndrome showed markedly elevated concentrations of eCypA within BAL fluid. Conclusions: CypA is upregulated within the lungs of injuriously ventilated mice (and critically ill patients), where it plays a significant role in lung injury. eCypA represents an exciting novel target for pharmacological intervention.