Endothelial activation and dysfunction in the pathogenesis of influenza A virus infection

The Role of the Nrf2 Pathway in Airway Tissue Damage Due to Viral Respiratory Infections

Respiratory viruses constitute a significant cause of illness and death worldwide. Respiratory virus-associated injuries include oxidative stress, ferroptosis, inflammation, pyroptosis, apoptosis, fibrosis, autoimmunity, and vascular injury. Several studies have demonstrated the involvement of the nuclear factor erythroid 2-related factor 2 (Nrf2) in the pathophysiology of viral infection and associated complications. It has thus emerged as a pivotal player in cellular defense mechanisms against such damage. Here, we discuss the impact of Nrf2 activation on airway injuries induced by respiratory viruses, including viruses, coronaviruses, rhinoviruses, and respiratory syncytial viruses. The inhibition or deregulation of Nrf2 pathway activation induces airway tissue damage in the presence of viral respiratory infections. In contrast, Nrf2 pathway activation demonstrates protection against tissue and organ injuries. Clinical trials involving Nrf2 agonists are needed to define the effect of Nrf2 therapeutics on airway tissues and organs damaged by viral respiratory infections.

Molecular Basis for Surface-Initiated Non-Thrombin-Generated Clot Formation Following Viral Infection

In this paper, we propose a model that connects two standard inflammatory responses to viral infection, namely, elevation of fibrinogen and the lipid drop shower, to the initiation of non-thrombin-generated clot formation. In order to understand the molecular basis for the formation of non-thrombin-generated clots following viral infection, human epithelial and Madin-Darby Canine Kidney (MDCK, epithelial) cells were infected with H1N1, OC43, and adenovirus, and conditioned media was collected, which was later used to treat human umbilical vein endothelial cells and human lung microvascular endothelial cells. After direct infection or after exposure to conditioned media from infected cells, tissue surfaces of both epithelial and endothelial cells, exposed to 8 mg/mL fibrinogen, were observed to initiate fibrillogenesis in the absence of thrombin. No fibers were observed after direct viral exposure of the endothelium or when the epithelium cells were exposed to SARS-CoV-2 isolated spike proteins. Heating the conditioned media to 60 °C had no effect on fibrillogenesis, indicating that the effect was not enzymatic but rather associated with relatively thermally stable inflammatory factors released soon after viral infection. Spontaneous fibrillogenesis had previously been reported and interpreted as being due to the release of the alpha C domains due to strong interactions of the interior of the fibrinogen molecule in contact with hydrophobic material surfaces rather than cleavage of the fibrinopeptides. Contact angle goniometry and immunohistochemistry were used to demonstrate that the lipids produced within the epithelium and released in the conditioned media, probably after the death of infected epithelial cells, formed a hydrophobic residue responsible for fibrillogenesis. Hence, the standard inflammatory response constitutes the ideal conditions for surface-initiated clot formation.

Vascular endothelial-derived SPARCL1 exacerbates viral pneumonia through pro-inflammatory macrophage activation

Inflammation induced by lung infection is a double-edged sword, moderating both anti-viral and immune pathogenesis effects; the mechanism of the latter is not fully understood. Previous studies suggest the vasculature is involved in tissue injury. Here, we report that expression of Sparcl1, a secreted matricellular protein, is upregulated in pulmonary capillary endothelial cells (EC) during influenza-induced lung injury. Endothelial overexpression of SPARCL1 promotes detrimental lung inflammation, with SPARCL1 inducing 'M1-like' macrophages and related pro-inflammatory cytokines, while SPARCL1 deletion alleviates these effects. Mechanistically, SPARCL1 functions through TLR4 on macrophages in vitro, while TLR4 inhibition in vivo ameliorates excessive inflammation caused by endothelial Sparcl1 overexpression. Finally, SPARCL1 expression is increased in lung ECs from COVID-19 patients when compared with healthy donors, while fatal COVID-19 correlates with higher circulating SPARCL1 protein levels in the plasma. Our results thus implicate SPARCL1 as a potential prognosis biomarker for deadly COVID-19 pneumonia and as a therapeutic target for taming hyperinflammation in pneumonia.

Increase in venous thromboembolism in SARS-CoV-2 infected lung tissue: proteome analysis of lung parenchyma, isolated endothelium, and thrombi

AIMS

COVID-19 pneumonia is characterized by an increased rate of deep venous thrombosis and pulmonary embolism. To better understand the pathophysiology behind thrombosis in COVID-19, we performed proteomics analysis on SARS-CoV-2 infected lung tissue.

METHODS

Liquid chromatography mass spectrometry was performed on SARS-CoV-2 infected postmortem lung tissue samples. Five protein profiling analyses were performed: whole slide lung parenchyma analysis, followed by analysis of isolated thrombi and endothelium, both stratified by disease (COVID-19 versus influenza) and thrombus morphology (embolism versus in situ). Influenza autopsy cases with pulmonary thrombi were used as controls.

RESULTS

Compared to influenza controls, both analyses of COVID-19 whole-tissue and isolated endothelium showed upregulation of proteins and pathways related to liver metabolism including urea cycle activation, with arginase being among the top upregulated proteins in COVID-19 lung tissue. Analysis of isolated COVID-19 thrombi showed significant downregulation of pathways related to platelet activation compared to influenza thrombi. Analysis of isolated thrombi based on histomorphology shows that in situ thrombi have significant upregulation of coronavirus pathogenesis proteins.

CONCLUSIONS

The decrease in platelet activation pathways in severe COVID-19 thrombi suggests a relative increase in venous thromboembolism, as thrombi from venous origin tend to contain fewer platelets than arterial thrombi. Based on histomorphology, in situ thrombi show upregulation of various proteins related to SARS-CoV-2 pathogenesis compared to thromboemboli, which may indicate increased in situ pulmonary thrombosis in COVID-19. Therefore, this study supports the increase of venous thromboembolism without undercutting the involvement of in situ thrombosis in severe COVID-19.

Viral Pneumonia: From Influenza to COVID-19

Respiratory viruses are increasingly recognized as a cause of community-acquired pneumonia (CAP). The implementation of new diagnostic technologies has facilitated their identification, especially in vulnerable population such as immunocompromised and elderly patients and those with severe cases of pneumonia. In terms of severity and outcomes, viral pneumonia caused by influenza viruses appears similar to that caused by non-influenza viruses. Although several respiratory viruses may cause CAP, antiviral therapy is available only in cases of CAP caused by influenza virus or respiratory syncytial virus. Currently, evidence-based supportive care is key to managing severe viral pneumonia. We discuss the evidence surrounding epidemiology, diagnosis, management, treatment, and prevention of viral pneumonia.

Are the integrin binding motifs within SARS CoV-2 spike protein and MHC class II alleles playing the key role in COVID-19?

The previous studies on the RGD motif (aa403-405) within the SARS CoV-2 spike (S) protein receptor binding domain (RBD) suggest that the RGD motif binding integrin(s) may play an important role in infection of the host cells. We also discussed the possible role of two other integrin binding motifs that are present in S protein: LDI (aa585-587) and ECD (661-663), the motifs used by some other viruses in the course of infection. The MultiFOLD models for protein structure analysis have shown that the ECD motif is clearly accessible in the S protein, whereas the RGD and LDI motifs are partially accessible. Furthermore, the amino acids that are present in Epstein-Barr virus protein (EBV) gp42 playing very important role in binding to the HLA-DRB1 molecule and in the subsequent immune response evasion, are also present in the S protein heptad repeat-2. Our MultiFOLD model analyses have shown that these amino acids are clearly accessible on the surface in each S protein chain as monomers and in the homotrimer complex and bind to HLA-DRB1 β chain. Therefore, they may have the identical role in SARS CoV-2 immune evasion as in EBV infection. The prediction analyses of the MHC class II binding peptides within the S protein have shown that the RGD motif is present in the core 9-mer peptide IRGDEVRQI within the two HLA-DRB1*03:01 and HLA-DRB3*01.01 strong binding 15-mer peptides suggesting that RGD motif may be the potential immune epitope. Accordingly, infected HLA-DRB1*03:01 or HLA-DRB3*01.01 positive individuals may develop high affinity anti-RGD motif antibodies that react with the RGD motif in the host proteins, like fibrinogen, thrombin or von Willebrand factor, affecting haemostasis or participating in autoimmune disorders.

Vascular Endothelial-derived SPARCL1 Exacerbates Viral Pneumonia Through Pro-Inflammatory Macrophage Activation

Inflammation upon infectious lung injury is a double-edged sword: while tissue-infiltrating immune cells and cytokines are necessary to control infection, these same factors often aggravate injury. Full appreciation of both the sources and targets of inflammatory mediators is required to facilitate strategies to maintain antimicrobial effects while minimizing off-target epithelial and endothelial damage. Recognizing that the vasculature is centrally involved in tissue responses to injury and infection, we observed that pulmonary capillary endothelial cells (ECs) exhibit dramatic transcriptomic changes upon influenza injury punctuated by profound upregulation of Sparcl1 . Endothelial deletion and overexpression of SPARCL1 implicated this secreted matricellular protein in driving key pathophysiologic symptoms of pneumonia, which we demonstrate result from its effects on macrophage polarization. SPARCL1 induces a shift to a pro-inflammatory "M1-like" phenotype (CD86 + CD206 - ), thereby increasing associated cytokine levels. Mechanistically, SPARCL1 acts directly on macrophages in vitro to induce the pro-inflammatory phenotype via activation of TLR4, and TLR4 inhibition in vivo ameliorates inflammatory exacerbations caused by endothelial Sparcl1 overexpression. Finally, we confirmed significant elevation of SPARCL1 in COVID-19 lung ECs in comparison with those from healthy donors. Survival analysis demonstrated that patients with fatal COVID-19 had higher levels of circulating SPARCL1 protein compared to those who recovered, indicating the potential of SPARCL1 as a biomarker for prognosis of pneumonia and suggesting that personalized medicine approaches might be harnessed to block SPARCL1 and improve outcomes in high-expressing patients.

The Activation of the RIG-I/MDA5 Signaling Pathway upon Influenza D Virus Infection Impairs the Pulmonary Proinflammatory Response Triggered by Mycoplasma bovis Superinfection

Concurrent infections with multiple pathogens are often described in cattle with respiratory illness. However, how the host-pathogen interactions influence the clinical outcome has been only partially explored in this species. Influenza D virus (IDV) was discovered in 2011. Since then, IDV has been detected worldwide in different hosts. A significant association between IDV and bacterial pathogens in sick cattle was shown in epidemiological studies, especially with Mycoplasma bovis. In an experimental challenge, IDV aggravated M. bovis-induced pneumonia. However, the mechanisms through which IDV drives an increased susceptibility to bacterial superinfections remain unknown. Here, we used the organotypic lung model precision-cut lung slices to study the interplay between IDV and M. bovis coinfection. Our results show that a primary IDV infection promotes M. bovis superinfection by increasing the bacterial replication and the ultrastructural damages in lung pneumocytes. In our model, IDV impaired the innate immune response triggered by M. bovis by decreasing the expression of several proinflammatory cytokines and chemokines that are important for immune cell recruitment and the bacterial clearance. Stimulations with agonists of cytosolic helicases and Toll-like receptors (TLRs) revealed that a primary activation of RIG-I/MDA5 desensitizes the TLR2 activation, similar to what was observed with IDV infection. The cross talk between these two pattern recognition receptors leads to a nonadditive response, which alters the TLR2-mediated cascade that controls the bacterial infection. These results highlight innate immune mechanisms that were not described for cattle so far and improve our understanding of the bovine host-microbe interactions and IDV pathogenesis. IMPORTANCE Since the spread of the respiratory influenza D virus (IDV) infection to the cattle population, the question about the impact of this virus on bovine respiratory disease (BRD) remains still unanswered. Animals affected by BRD are often coinfected with multiple pathogens, especially viruses and bacteria. In particular, viruses are suspected to enhance secondary bacterial superinfections. Here, we use an ex vivo model of lung tissue to study the effects of IDV infection on bacterial superinfections. Our results show that IDV increases the susceptibility to the respiratory pathogen Mycoplasma bovis. In particular, IDV seems to activate immune pathways that inhibit the innate immune response against the bacteria. This may allow M. bovis to increase its proliferation and to delay its clearance from lung tissue. These results suggest that IDV could have a negative impact on the respiratory pathology of cattle.

Innate immune responses in pneumonia

The lungs are an immunologically unique environment; they are exposed to innumerable pathogens and particulate matter daily. Appropriate clearance of pathogens and response to pollutants is required to prevent overwhelming infection, while preventing tissue damage and maintaining efficient gas exchange. Broadly, the innate immune system is the collection of immediate, intrinsic immune responses to pathogen or tissue injury. In this review, we will examine the innate immune responses of the lung, with a particular focus on their role in pneumonia. We will discuss the anatomic barriers and antimicrobial proteins of the lung, pathogen and injury recognition, and the role of leukocytes (macrophages, neutrophils, and innate lymphocytes) and lung stromal cells in innate immunity. Throughout the review, we will focus on new findings in innate immunity as well as features that are unique to the lung.

Venous thromboembolism in viral diseases: A comprehensive literature review

Venous thromboembolism (VTE) is known to be a common respiratory and/or cardiovascular complication in hospitalized patients with viral infections. Numerous studies have proven human immunodeficiency virus infection to be a prothrombotic condition. An elevated VTE risk has been observed in critically ill H1N1 influenza patients. VTE risk is remarkably higher in patients infected with the Hepatitis C virus in contrast to uninfected subjects. The elevation of D-dimer levels supported the association between Chikungunya and the Zika virus and the rise of clinical VTE risk. Varicella-zoster virus is a risk factor for both cellulitis and the consequent invasive bacterial disease which may take part in thrombotic initiation. Eventually, hospitalized patients infected with the coronavirus disease of 2019 (COVID-19), the cause of the ongoing worldwide pandemic, could mainly suffer from an anomalous risk of coagulation activation with enhanced venous thrombosis events and poor quality clinical course. Although the risk of VTE in nonhospitalized COVID-19 patients is not known yet, there are a large number of guidelines and studies on thromboprophylaxis administration for COVID-19 cases. This study aims to take a detailed look at the effect of viral diseases on VTE, the epidemiology of VTE in viral diseases, and the diagnosis and treatment of VTE.

Respiratory viruses: their importance and lessons learned from COVID-19

Respiratory virus infection can cause severe illnesses capable of inducing acute respiratory failure that can progress rapidly to acute respiratory distress syndrome (ARDS). ARDS is related to poor outcomes, especially in individuals with a higher risk of infection, such as the elderly and those with comorbidities, i.e. obesity, asthma, diabetes mellitus and chronic respiratory or cardiovascular disease. Despite this, effective antiviral treatments available for severe viral lung infections are scarce. The coronavirus disease 2019 (COVID-19) pandemic demonstrated that there is also a need to understand the role of airborne transmission of respiratory viruses. Robust evidence supporting this exists, but better comprehension could help implement adequate measures to mitigate respiratory viral infections. In severe viral lung infections, early diagnosis, risk stratification and prognosis are essential in managing patients. Biomarkers can provide reliable, timely and accessible information possibly helpful for clinicians in managing severe lung viral infections. Although respiratory viruses highly impact global health, more research is needed to improve care and prognosis of severe lung viral infections. In this review, we discuss the epidemiology, diagnosis, clinical characteristics, management and prognosis of patients with severe infections due to respiratory viruses.

Thromboembolic Events in Patients with Influenza: A Scoping Review

INTRODUCTION

Influenza is an acute respiratory infection that usually causes a short-term and self-limiting illness. However, in high-risk populations, this can lead to several complications, with an increase in mortality. Aside from the well-known extrapulmonary complications, several studies have investigated the relationship between influenza and acute cardio and cerebrovascular events. Reviews of the thromboembolic complications associated with influenza are lacking.

OBJECTIVES

the study aims to conduct a scoping review to analyze the epidemiological and clinical characteristics of patients suffering from influenza and thromboembolic complications.

MATERIALS AND METHODS

A computerized search of historical published cases using PubMed and the terms "influenza" or "flu" and "thrombosis", "embolism", "thromboembolism", "stroke", or "infarct" for the last twenty-five years was conducted. Only articles reporting detailed data on patients with thromboembolic complications of laboratory-confirmed influenza were considered eligible for inclusion in the scoping review.

RESULTS

Fifty-eight cases with laboratory documented influenza A or B and a related intravascular thrombosis were retrieved. Their characteristics were analyzed along with those of a patient who motivated our search. The localizations of thromboembolic events were pulmonary embolism 21/58 (36.2%), DVT 12/58 (20.6%), DVT and pulmonary embolism 3/58 (5.1%), acute ischemic stroke 11/58 (18.9%), arterial thrombosis 4/58 (6.8%), and acute myocardial infarction 5/58 (8.6%).

DISCUSSION

Our findings are important in clarifying which thromboembolic complications are more frequent in adults and children with influenza. Symptoms of pulmonary embolism and influenza can be very similar, so a careful clinical evaluation is required for proper patient management, possible instrumental deepening, and appropriate pharmacological interventions, especially for patients with respiratory failure.

Pathophysiological mechanisms of thrombosis in acute and long COVID-19

COVID-19 patients have a high incidence of thrombosis, and thromboembolic complications are associated with severe COVID-19 and high mortality. COVID-19 disease is associated with a hyper-inflammatory response (cytokine storm) mediated by the immune system. However, the role of the inflammatory response in thrombosis remains incompletely understood. In this review, we investigate the crosstalk between inflammation and thrombosis in the context of COVID-19, focusing on the contributions of inflammation to the pathogenesis of thrombosis, and propose combined use of anti-inflammatory and anticoagulant therapeutics. Under inflammatory conditions, the interactions between neutrophils and platelets, platelet activation, monocyte tissue factor expression, microparticle release, and phosphatidylserine (PS) externalization as well as complement activation are collectively involved in immune-thrombosis. Inflammation results in the activation and apoptosis of blood cells, leading to microparticle release and PS externalization on blood cells and microparticles, which significantly enhances the catalytic efficiency of the tenase and prothrombinase complexes, and promotes thrombin-mediated fibrin generation and local blood clot formation. Given the risk of thrombosis in the COVID-19, the importance of antithrombotic therapies has been generally recognized, but certain deficiencies and treatment gaps in remain. Antiplatelet drugs are not in combination with anticoagulant treatments, thus fail to dampen platelet procoagulant activity. Current treatments also do not propose an optimal time for anticoagulation. The efficacy of anticoagulant treatments depends on the time of therapy initiation. The best time for antithrombotic therapy is as early as possible after diagnosis, ideally in the early stage of the disease. We also elaborate on the possible mechanisms of long COVID thromboembolic complications, including persistent inflammation, endothelial injury and dysfunction, and coagulation abnormalities. The above-mentioned contents provide therapeutic strategies for COVID-19 patients and further improve patient outcomes.

Influenza A(H1N1)pdm09 Virus Alters Expression of Endothelial Factors in Pulmonary Vascular Endothelium in Rats

Influenza virus infection may cause endothelial activation and dysfunction. However, it is still not known to what extent the influenza virus can dysregulate the expression of various endothelial proteins. The aim of the study is to identify the level of expression of endothelial nitric oxide synthase (eNOS), plasminogen activator inhibitor-1 (PAI-1), and tissue plasminogen activator (tPA) in the pulmonary vascular endothelium, as well as the concentration of PAI-1 and tPA in the blood plasma in Wistar rats. Animals were intranasally infected with rat-adapted influenza A(H1N1)pdm09 virus. The expression of eNOS, PAI-1 and tPA in the pulmonary vascular endothelium was determined by immunohistochemistry; the concentration of PAI-1 and tPA was analyzed by ELISA at 24 and 96 h post infection (hpi). Thus, the expression of eNOS in the pulmonary vascular endothelium decreased by 1.9-fold at 24 hpi and increased by 2-fold at 96 hpi. The expression of PAI-1 in the pulmonary vascular endothelium increased by 5.23-fold and 6.54-fold at 24 and 96 hpi, respectively. The concentration of PAI-1 in the blood plasma of the rats decreased by 3.84-fold at 96 hpi, but not at 24 hpi. The expression of tPA in the pulmonary vascular endothelium was increased 2.2-fold at 96 hpi. The obtained data indicate the development of endothelial dysfunction that is characterized by the dysregulation of endothelial protein expression in non-lethal and clinically non-severe experimental influenza virus infection.

Utility of NO and H2S donating platforms in managing COVID-19: Rationale and promise

Viral infections are a continuing global burden on the human population, underscored by the ramifications of the COVID-19 pandemic. Current treatment options and supportive therapies for many viral infections are relatively limited, indicating a need for alternative therapeutic approaches. Virus-induced damage occurs through direct infection of host cells and inflammation-related changes. Severe cases of certain viral infections, including COVID-19, can lead to a hyperinflammatory response termed cytokine storm, resulting in extensive endothelial damage, thrombosis, respiratory failure, and death. Therapies targeting these complications are crucial in addition to antiviral therapies. Nitric oxide and hydrogen sulfide are two endogenous gasotransmitters that have emerged as key signaling molecules with a broad range of antiviral actions in addition to having anti-inflammatory properties and protective functions in the vasculature and respiratory system. The enhancement of endogenous nitric oxide and hydrogen sulfide levels thus holds promise for managing both early-stage and later-stage viral infections, including SARS-CoV-2. Using SARS-CoV-2 as a model for similar viral infections, here we explore the current evidence regarding nitric oxide and hydrogen sulfide's use to limit viral infection, resolve inflammation, and reduce vascular and pulmonary damage.

Proteomic profiling of serum small extracellular vesicles reveals immune signatures of children with pneumonia

BACKGROUND

Pneumonia is the leading cause of death in young children globally. However, the underlying pathological mechanism of pediatric pneumonia remains unclear. In infection disease contexts, small extracellular vesicles (sEVs) have been shown to be a useful source of markers for pathogenesis and immune response. We hypothesized that functional molecules such as protein harbored by sEVs would provide mechanistic insights into the immune response in children with pneumonia.

METHODS

We isolated sEVs from serum collected from children with and without pneumonia, performed proteomic analysis of the sEVs with label-free mass spectrometry, and then conducted functional enrichment analysis of proteomic data.

RESULTS

We identified fifteen differentially expressed proteins and ten unique proteins in children with pneumonia as compared to healthy children. In the pneumonia group, immune-related processes and pathways were positively enriched as upregulated proteins were involved in neutrophil activation, complement regulation, defense against bacteria, humoral immune response and regulation of immune effector processes However, pathways associated with tissue development and extracellular matrix remodeling were negatively enriched, as downregulated proteins were linked to extracellular matrix structure and cell adhesions.

CONCLUSIONS

Our findings provided insights into host responses to pathogen infection, which has contributed to understanding the pathogenesis of children with pneumonia. Furthermore, our studies suggested that serum sEVs proteins could be considered a potential source of biomarkers for diagnosing pediatric pneumonia.

Influenza A Virus Causes Histopathological Changes and Impairment in Functional Activity of Blood Vessels in Different Vascular Beds

It has been established that blood vessels are a target for influenza virus; however, the mechanism by which virus affects the cardiovascular system remains unknown. The aim of the study is the identification of histological changes and changes in the functional activity of the pulmonary and mesenteric blood vessels of Wistar rats. Wistar rats were intranasally infected with the influenza A(H1N1)pdm09 virus. At 24 and 96 h post infection (hpi), histopathological changes were observed in lung tissues with the absence of histological changes in mesenteric tissues. The functional activity of pulmonary and mesenteric arteries was determined using wire myography. In pulmonary arteries, there was a tendency towards an increase in integral response to the vasodilator and a decrease in the integral response to the vasoconstrictor at 24 hpi (compared with control). At 96 hpi, a tendency towards a decrease in the integral response to the vasoconstrictor persisted, while the response to acetylcholine was slightly increased. The functional activity of the mesenteric blood vessels was inverted: a significant decrease in the integral response to the vasodilator and an increase in the response to the vasoconstrictor at 24 hpi were observed; at 96 hpi, the integral response to the vasoconstrictor persisted, while the response to the vasodilator remained significantly reduced. Obtained data indicate the development of endothelial dysfunction in non-lethal and clinically non-severe experimental influenza virus infection.

Fundamentals in Covid-19-Associated Thrombosis: Molecular and Cellular Aspects

The novel coronavirus disease (COVID-19) is associated with a high incidence of coagulopathy and venous thromboembolism that may contribute to the worsening of the clinical outcome in affected patients. Marked increased D-dimer levels are the most common laboratory finding and have been repeatedly reported in critically ill COVID-19 patients. The infection caused by Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) is followed by a massive release of pro-inflammatory cytokines, which mediate the activation of endothelial cells, platelets, monocytes, and neutrophils in the vasculature. In this context, COVID-19-associated thrombosis is a complex process that seems to engage vascular cells along with soluble plasma factors, including the coagulation cascade, and complement system that contribute to the establishment of the prothrombotic state. In this review, we summarize the main findings concerning the cellular mechanisms proposed for the establishment of COVID-19-associated thrombosis.

Viral Endothelial Dysfunction: A Unifying Mechanism for COVID-19

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a highly transmissible virus with significant global impact, morbidity, and mortality. The SARS-CoV-2 virus may result in widespread organ manifestations including acute respiratory distress syndrome, acute renal failure, thromboembolism, and myocarditis. Virus-induced endothelial injury may cause endothelial activation, increased permeability, inflammation, and immune response and cytokine storm. Endothelial dysfunction is a systemic disorder that is a precursor of atherosclerotic vascular disease that is associated with cardiovascular risk factors and is highly prevalent in patients with atherosclerotic cardiovascular and peripheral disease. Several studies have associated various viral infections including SARS-CoV-2 infection with inflammation, endothelial dysfunction, and subsequent innate immune response and cytokine storm. Noninvasive monitoring of endothelial function and identification of high-risk patients who may require specific therapies may have the potential to improve morbidity and mortality associated with subsequent inflammation, cytokine storm, and multiorgan involvement.

Comparative frequency and prognostic impact of myocardial injury in hospitalized patients with COVID-19 and Influenza

AIMS

Myocardial injury (MINJ) in Coronavirus disease 2019 (COVID-19) identifies individuals at high mortality risk but its clinical relevance is less well established for Influenza and no comparative analyses evaluating frequency and clinical implications of MINJ among hospitalized patients with Influenza or COVID-19 are available.

METHODS AND RESULTS

Hospitalized adults with laboratory confirmed Influenza A or B or COVID-19 underwent highly sensitive cardiac T Troponin (hs-cTnT) measurement at admission in four regional hospitals in Canton Ticino, Switzerland. MINJ was defined as hs-cTnT >14 ng/L. Clinical, laboratory and outcome data were retrospectively collected. The primary outcome was mortality up to 28 days. Cox regression models were used to assess correlations between admission diagnosis, MINJ, and mortality. Clinical correlates of MINJ in both viral diseases were also identified. MINJ occurred in 94 (65.5%) out of 145 patients hospitalized for Influenza and 216 (47.8%) out of 452 patients hospitalized for COVID-19. Advanced age and renal impairment were factors associated with MINJ in both diseases. At 28 days, 7 (4.8%) deaths occurred among Influenza and 76 deaths (16.8%) among COVID-19 patients with a hazard ratio (HR) of 3.69 [95% confidence interval (CI) 1.70-8.00]. Adjusted Cox regression models showed admission diagnosis of COVID-19 [HR 6.41 (95% CI 4.05-10.14)] and MINJ [HR 8.01 (95% CI 4.64-13.82)] to be associated with mortality.

CONCLUSIONS

Myocardial injury is frequent among both viral diseases and increases the risk of death in both COVID-19 and Influenza. The absolute risk of death is considerably higher in patients admitted for COVID-19 when compared with Influenza.

Association of Acute Upper Respiratory Tract Infections with Sudden Sensorineural Hearing Loss: A Case-Crossover, Nationwide, Population-Based Cohort Study

The etiology of sudden sensorineural hearing loss (SSNHL) has been unclear until now. Understanding its potential etiology is crucial for the development of preventive medicine. In this study, we investigated the association between acute upper respiratory tract infections (URIs) and SSNHL risk. We conducted a case-crossover study by using the longitudinal health insurance database derived from the National Health Insurance Research Database in Taiwan. Individual acute URI between the case and control periods was reviewed. Multivariable conditional logistic regression models were used to estimate the adjusted odds ratios (aORs) of SSNHL risk associated with acute URIs after adjustments for potential confounders. In total, 1131 patients with SSNHL between 2010 and 2013 fulfilled our inclusion criteria and were included. The aOR (95% confidence interval [CI]) for SSNHL was 1.57 (1.20-2.05) in relation to acute URIs one month before the index date. Moreover, the aORs (95% CIs) of the female and young to middle-aged (≤65 years) populations were 1.63 (1.13-2.36) and 1.76 (1.29-2.40), respectively. In addition, the association between SSNHL and acute URIs was decreased over time. The aOR for SSNHL was 1.25 (1.01-1.56) in relation to acute URIs three months before the index date. Acute URIs increase SSNHL risk and are a potential risk factor for SSNHL. The establishment of a feasible health policy for the prevention of acute URIs is crucial for SSNHL prevention, particularly in female, and young to middle-aged populations.

Acute Neurologic Manifestations of Respiratory Viruses

PURPOSE OF REVIEW

Understanding the pathophysiology of COVID-19 and the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus that causes the disease has demonstrated the complexity of acute respiratory viruses that can cause neurologic manifestations. This article describes the most common respiratory viruses that have neurologic manifestations, with a focus on SARS-CoV-2 and COVID-19.

RECENT FINDINGS

In vitro and in vivo studies have better elucidated the neurotropism of various respiratory viruses. Understanding host cell receptors that mediate viral binding and entry not only demonstrates how viruses enter host cells but also provides possible mechanisms for therapeutic interventions. Elucidation of SARS-CoV-2 binding and fusion with host cells expressing the angiotensin-converting enzyme 2 (ACE2) receptor may also provide greater insights into its systemic and neurologic sequelae. Respiratory virus neurotropism and collateral injury due to concurrent inflammatory cascades result in various neurologic pathologies, including Guillain-Barré syndrome, encephalopathy, encephalitis, ischemic stroke, intracerebral hemorrhage, and seizures.

SUMMARY

Numerous respiratory viruses can infect the cells of the peripheral and central nervous systems, elicit inflammatory cascades, and directly and indirectly cause various neurologic manifestations. Patients with neurologic manifestations from respiratory viruses are often critically ill and require mechanical ventilation. Neurologists and neurointensivists should be familiar with the common neurologic manifestations of respiratory viruses and the unique and still-evolving sequelae associated with COVID-19.

Persistent endotheliopathy in the pathogenesis of long COVID syndrome

BACKGROUND

Persistent symptoms including breathlessness, fatigue, and decreased exercise tolerance have been reported in patients after acute SARS-CoV-2 infection. The biological mechanisms underlying this "long COVID" syndrome remain unknown. However, autopsy studies have highlighted the key roles played by pulmonary endotheliopathy and microvascular immunothrombosis in acute COVID-19.

OBJECTIVES

To assess whether endothelial cell activation may be sustained in convalescent COVID-19 patients and contribute to long COVID pathogenesis.

PATIENTS AND METHODS

Fifty patients were reviewed at a median of 68 days following SARS-CoV-2 infection. In addition to clinical workup, acute phase markers, endothelial cell (EC) activation and NETosis parameters and thrombin generation were assessed.

RESULTS

Thrombin generation assays revealed significantly shorter lag times (p < .0001, 95% CI -2.57 to -1.02 min), increased endogenous thrombin potential (p = .04, 95% CI 15-416 nM/min), and peak thrombin (p < .0001, 95% CI 39-93 nM) in convalescent COVID-19 patients. These prothrombotic changes were independent of ongoing acute phase response or active NETosis. Importantly, EC biomarkers including von Willebrand factor antigen (VWF:Ag), VWF propeptide (VWFpp), and factor VIII were significantly elevated in convalescent COVID-19 compared with controls (p = .004, 95% CI 0.09-0.57 IU/ml; p = .009, 95% CI 0.06-0.5 IU/ml; p = .04, 95% CI 0.03-0.44 IU/ml, respectively). In addition, plasma soluble thrombomodulin levels were significantly elevated in convalescent COVID-19 (p = .02, 95% CI 0.01-2.7 ng/ml). Sustained endotheliopathy was more frequent in older, comorbid patients, and those requiring hospitalization. Finally, both plasma VWF:Ag and VWFpp levels correlated inversely with 6-min walk tests.

CONCLUSIONS

Collectively, our findings demonstrate that sustained endotheliopathy is common in convalescent COVID-19 and raise the intriguing possibility that this may contribute to long COVID pathogenesis.

Nucleic Acid Sensing in the Tumor Vasculature

Endothelial cells form a powerful interface between tissues and immune cells. In fact, one of the underappreciated roles of endothelial cells is to orchestrate immune attention to specific sites. Tumor endothelial cells have a unique ability to dampen immune responses and thereby maintain an immunosuppressive microenvironment. Recent approaches to trigger immune responses in cancers have focused on activating nucleic acid sensors, such as cGAS-STING, in combination with immunotherapies. In this review, we present a case for targeting nucleic acid-sensing pathways within the tumor vasculature to invigorate tumor-immune responses. We introduce two specific nucleic acid sensors-the DNA sensor TREX1 and the RNA sensor RIG-I-and discuss their functional roles in the vasculature. Finally, we present perspectives on how these nucleic acid sensors in the tumor endothelium can be targeted in an antiangiogenic and immune activation context. We believe understanding the role of nucleic acid-sensing in the tumor vasculature can enhance our ability to design more effective therapies targeting the tumor microenvironment by co-opting both vascular and immune cell types.

The cytokine storms of COVID-19, H1N1 influenza, CRS and MAS compared. Can one sized treatment fit all?

An analysis of published data appertaining to the cytokine storms of COVID-19, H1N1 influenza, cytokine release syndrome (CRS), and macrophage activation syndrome (MAS) reveals many common immunological and biochemical abnormalities. These include evidence of a hyperactive coagulation system with elevated D-dimer and ferritin levels, disseminated intravascular coagulopathy (DIC) and microthrombi coupled with an activated and highly permeable vascular endothelium. Common immune abnormalities include progressive hypercytokinemia with elevated levels of TNF-α, interleukin (IL)-6, and IL-1β, proinflammatory chemokines, activated macrophages and increased levels of nuclear factor kappa beta (NFκB). Inflammasome activation and release of damage associated molecular patterns (DAMPs) is common to COVID-19, H1N1, and MAS but does not appear to be a feature of CRS. Elevated levels of IL-18 are detected in patients with COVID-19 and MAS but have not been reported in patients with H1N1 influenza and CRS. Elevated interferon-γ is common to H1N1, MAS, and CRS but levels of this molecule appear to be depressed in patients with COVID-19. CD4+ T, CD8+ and NK lymphocytes are involved in the pathophysiology of CRS, MAS, and possibly H1N1 but are reduced in number and dysfunctional in COVID-19. Additional elements underpinning the pathophysiology of cytokine storms include Inflammasome activity and DAMPs. Treatment with anakinra may theoretically offer an avenue to positively manipulate the range of biochemical and immune abnormalities reported in COVID-19 and thought to underpin the pathophysiology of cytokine storms beyond those manipulated via the use of, canakinumab, Jak inhibitors or tocilizumab. Thus, despite the relative success of tocilizumab in reducing mortality in COVID-19 patients already on dexamethasone and promising results with Baricitinib, the combination of anakinra in combination with dexamethasone offers the theoretical prospect of further improvements in patient survival. However, there is currently an absence of trial of evidence in favour or contravening this proposition. Accordingly, a large well powered blinded prospective randomised controlled trial (RCT) to test this hypothesis is recommended.

The Mechanism behind Influenza Virus Cytokine Storm

Influenza viruses are still a serious threat to human health. Cytokines are essential for cell-to-cell communication and viral clearance in the immune system, but excessive cytokines can cause serious immune pathology. Deaths caused by severe influenza are usually related to cytokine storms. The recent literature has described the mechanism behind the cytokine–storm network and how it can exacerbate host pathological damage. Biological factors such as sex, age, and obesity may cause biological differences between different individuals, which affects cytokine storms induced by the influenza virus. In this review, we summarize the mechanism behind influenza virus cytokine storms and the differences in cytokine storms of different ages and sexes, and in obesity.

Defibrotide: potential for treating endothelial dysfunction related to viral and post-infectious syndromes

INTRODUCTION

Defibrotide (DF) is a polyribonucleotide with antithrombotic, pro-fibrinolytic, and anti-inflammatory effects on endothelium. These effects and the established safety of DF present DF as a strong candidate to treat viral and post-infectious syndromes involving endothelial dysfunction.

AREAS COVERED

We discuss DF and other therapeutic agents that have the potential to target endothelial components of pathogenesis in viral and post-infectious syndromes. We introduce defibrotide (DF), describe its mechanisms of action, and explore its established pleiotropic effects on the endothelium. We describe the established pathophysiology of Coronavirus Disease 2019 (COVID-19) and highlight the processes specific to COVID-19 potentially modulated by DF. We also present influenza A and viral hemorrhagic fevers, especially those caused by hantavirus, Ebola virus, and dengue virus, as viral syndromes in which DF might serve therapeutic benefit. Finally, we offer our opinion on novel treatment strategies targeting endothelial dysfunction in viral infections and their severe manifestations.

EXPERT OPINION

Given the critical role of endothelial dysfunction in numerous infectious syndromes, in particular COVID-19, therapeutic pharmacology for these conditions should increasingly prioritize endothelial stabilization. Several agents with endothelial protective properties should be further studied as treatments for severe viral infections and vasculitides, especially where other therapeutic modalities have failed.

Automated CT Lung Density Analysis of Viral Pneumonia and Healthy Lungs Using Deep Learning-Based Segmentation, Histograms and HU Thresholds

CT patterns of viral pneumonia are usually only qualitatively described in radiology reports. Artificial intelligence enables automated and reliable segmentation of lungs with chest CT. Based on this, the purpose of this study was to derive meaningful imaging biomarkers reflecting CT patterns of viral pneumonia and assess their potential to discriminate between healthy lungs and lungs with viral pneumonia. This study used non-enhanced and CT pulmonary angiograms (CTPAs) of healthy lungs and viral pneumonia (SARS-CoV-2, influenza A/B) identified by radiology reports and RT-PCR results. After deep learning segmentation of the lungs, histogram-based and threshold-based analyses of lung attenuation were performed and compared. The derived imaging biomarkers were correlated with parameters of clinical and biochemical severity (modified WHO severity scale; c-reactive protein). For non-enhanced CTs (n = 526), all imaging biomarkers significantly differed between healthy lungs and lungs with viral pneumonia (all p < 0.001), a finding that was not reproduced for CTPAs (n = 504). Standard deviation (histogram-derived) and relative high attenuation area [600-0 HU] (HU-thresholding) differed most. The strongest correlation with disease severity was found for absolute high attenuation area [600-0 HU] (r = 0.56, 95% CI = 0.46-0.64). Deep-learning segmentation-based histogram and HU threshold analysis could be deployed in chest CT evaluation for the differentiating of healthy lungs from AP lungs.

Serum Levels of Markers of Endothelial Activation Are Not Associated with a Positive Blood Culture in Surinamese Children with Suspected Severe Infection

BACKGROUND

Systemic serum levels of markers of endothelial activation are associated with infection. We hypothesize that levels of markers of endothelial activation are associated with the presence of a positive blood culture as a manifestation of a systemic infection in children with a suspected severe infection in Suriname.

METHODS

In this prospective observational cohort study, children between 1 month and 18 years of age suspected of severe infection as assessed by the threating physician, and in whom laboratory testing and blood culturing was performed before start of intravenous antibiotic treatment, were recruited at the emergency department of the Academic Hospital Paramaribo, Suriname. Serum was collected at blood culturing and after 48-72 h of admission. Serum was stored for measurement of levels of Angiopoietin (Ang)-1, Ang-2, soluble (s)P-selectin, sE-selectin, vascular cell adhesion molecule-1, intercellular adhesion molecule-1 and platelet and endothelial cell adhesion molecule-1.

RESULTS

Fifty-one children were included of whom 10 had a positive blood culture. Baseline characteristics were similar between children with and without a positive blood culture. No significant differences in serum levels of the Angiopoietins or soluble cellular adhesion molecules between groups were observed at start of antibiotic treatment nor after 48-72 h.

CONCLUSIONS

The data from this study indicate that in children with severe infection, serum levels of markers of endothelial cell activation are not associated with a positive blood culture. Thus, having a positive bacterial blood culture may not be the only factor driving endothelial activation in this patient population.

Interactions of Influenza and SARS-CoV-2 with the Lung Endothelium: Similarities, Differences, and Implications for Therapy

Respiratory viruses such as influenza and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are a constant threat to public health given their ability to cause global pandemics. Infection with either virus may lead to aberrant host responses, such as excessive immune cell recruitment and activation, dysregulated inflammation, and coagulopathy. These may contribute to the development of lung edema and respiratory failure. An increasing amount of evidence suggests that lung endothelial cells play a critical role in the pathogenesis of both viruses. In this review, we discuss how infection with influenza or SARS-CoV-2 may induce endothelial dysfunction. We compare the effects of infection of these two viruses, how they may contribute to pathogenesis, and discuss the implications for potential treatment. Understanding the differences between the effects of these two viruses on lung endothelial cells will provide important insight to guide the development of therapeutics.

The Contribution of Endothelial Dysfunction in Systemic Injury Subsequent to SARS-Cov-2 Infection

SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) infection is associated, alongside with lung infection and respiratory disease, to cardiovascular dysfunction that occurs at any stage of the disease. This includes ischemic heart disease, arrhythmias, and cardiomyopathies. The common pathophysiological link between SARS-CoV-2 infection and the cardiovascular events is represented by coagulation abnormalities and disruption of factors released by endothelial cells, which contribute in maintaining the blood vessels into an anti-thrombotic state. Thus, early alteration of the functionality of endothelial cells, which may be found soon after SARS-CoV-2 infection, seems to represent the major target of a SARS CoV-2 disease state and accounts for the systemic vascular dysfunction that leads to a detrimental effect in terms of hospitalization and death accompanying the disease. In particular, the molecular interaction of SARS-CoV-2 with the ACE2 receptor located in the endothelial cell surface, either at the pulmonary and systemic level, leads to early impairment of endothelial function, which, in turn, is followed by vascular inflammation and thrombosis of peripheral blood vessels. This highlights systemic hypoxia and further aggravates the vicious circle that compromises the development of the disease, leading to irreversible tissue damage and death of people with SARS CoV-2 infection. The review aims to assess some recent advances to define the crucial role of endothelial dysfunction in the pathogenesis of vascular complications accompanying SARS-CoV-2 infection. In particular, the molecular mechanisms associated with the interaction of SARS CoV-2 with the ACE2 receptor located on the endothelial cells are highlighted to support its role in compromising endothelial cell functionality. Finally, the consequences of endothelial dysfunction in enhancing pro-inflammatory and pro-thrombotic effects of SARS-CoV-2 infection are assessed in order to identify early therapeutic interventions able to reduce the impact of the disease in high-risk patients.

COVID-19, neutrophil extracellular traps and vascular complications in obstetric practice

An issue of the novel coronavirus infection spreading is currently in the first place among others in the list of the international medical community. Due to lack of information, conflicting research findings, multicomponent effect of the virus on the body host, as well as various consequences that the virus triggers in the body, now every medical specialty does study the viral attack pathogenesis. Recent months showed that vascular complications are the most severe in the Coronavirus Disease 2019 (COVID-19) and are the main cause of death in the patients. The mechanisms of vascular complications are complex and affect both the hemostatic system and immune responses, "inflammatory storm", disorders of the renin-angiotensin-aldosterone system, endotheliopathy, etc. Due to the leading role of vascular complications in the viral infection pathogenesis, several groups of patients are at extra risk, including pregnant women, patients with a burdened obstetric history, with hereditary thrombophilia and antiphospholipid syndrome, and patients after in vitro fertilization (IVF). In this category of pregnant women, use of low-molecular-weight heparins (LMWH) is particularly important for both prevention of vascular and obstetric complications, and for pathogenetic therapy of COVID-19.

Notch1-mediated inflammation is associated with endothelial dysfunction in human brain microvascular endothelial cells upon particulate matter exposure

Exposure to atmospheric particulate matter (PM) is an emerging risk factor for the pathogenesis of several diseases in humans, including cerebrovascular diseases. However, the mechanisms underlying PM-induced endothelial dysfunction are currently unclear. In this study, we examined how PM leads to endothelial dysfunction in human brain microvascular endothelial cells (HBMECs). We demonstrated that PM₁₀ exposure (up to 25 μg/mL) increase Notch1 cleavage, and it regulates endothelial dysfunction through NICD-mediated inflammation and senescence. PM₁₀-induced NICD signaling causes increased expression of interleukin-1 beta (IL-1β) and enhances characteristics of cellular senescence, which leads to increased endothelial permeability in HBMECs. Knockdown of Notch1 by siRNA blocks PM₁₀-induced endothelial dysfunction via the suppression of inflammation and senescence. Furthermore, we found that Notch1-mediated inflammation accelerates endothelial senescence, which eventually leads to endothelial dysfunction. Altogether, our data suggest that Notch1 and NICD are potential target regulators for the prevention of cerebrovascular endothelial dysfunction induced by ambient air pollutants such as PM.

Regeneration of the pulmonary vascular endothelium after viral pneumonia requires COUP-TF2

Acute respiratory distress syndrome is associated with a robust inflammatory response that damages the vascular endothelium, impairing gas exchange. While restoration of microcapillaries is critical to avoid mortality, therapeutic targeting of this process requires a greater understanding of endothelial repair mechanisms. Here, we demonstrate that lung endothelium possesses substantial regenerative capacity and lineage tracing reveals that native endothelium is the source of vascular repair after influenza injury. Ablation of chicken ovalbumin upstream promoter-transcription factor 2 (COUP-TF2) (Nr2f2), a transcription factor implicated in developmental angiogenesis, reduced endothelial proliferation, exacerbating viral lung injury in vivo. In vitro, COUP-TF2 regulates proliferation and migration through activation of cyclin D1 and neuropilin 1. Upon influenza injury, nuclear factor κB suppresses COUP-TF2, but surviving endothelial cells ultimately reestablish vascular homeostasis dependent on restoration of COUP-TF2. Therefore, stabilization of COUP-TF2 may represent a therapeutic strategy to enhance recovery from pathogens, including H1N1 influenza and SARS-CoV-2.

Superior mesenteric vein thrombosis induced by influenza infection: A case report

BACKGROUND

Among the various types and causes of mesenteric ischemia, superior mesenteric vein (SMV) thrombosis is a rare and ambiguous disease. If a patient presents with SMV thrombosis, past medical history should be reviewed, and the patient should be screened for underlying disease. SMV thrombosis may also occur due to systemic infection. In this report, we describe a case of SMV thrombosis complicated by influenza B infection.

CASE SUMMARY

A 64-year-old male visited the hospital with general weakness, muscle aches, fever, and abdominal pain. The patient underwent computed tomography (CT) and was diagnosed with SMV thrombosis. Since the patient’s muscle pain and fever could not be explained by the SMV thrombosis, the clinician performed a test for influenza, which produced a positive result for influenza B. The patient had a thrombus in the SMV only, with no invasion of the portal or splenic veins, and was clinically stable. Anticoagulation treatment was prescribed without surgery or other procedures. The follow-up CT scan showed improvement, and the patient was subsequently discharged with continued oral anticoagulant treatment.

CONCLUSION

This case provides evidence that influenza may be a possible risk factor for SMV thrombosis. If unexplained abdominal pain is accompanied by an influenza infection, examination of an abdominal CT scan may be necessary to screen for possible SMV thrombosis.

Coagulation Abnormalities and Thrombosis in Patients Infected With SARS-CoV-2 and Other Pandemic Viruses

The world is amid a pandemic caused by severe acute respiratory syndrome-coronavirus 2. Severe acute respiratory syndrome-coronavirus causes serious respiratory tract infections that can lead to viral pneumonia, acute respiratory distress syndrome, and death. Some patients with coronavirus disease 2019 (COVID-19) have an activated coagulation system characterized by elevated plasma levels of d-dimer-a biomarker of fibrin degradation. Importantly, high levels of D-dimer on hospital admission are associated with increased risk of mortality. Venous thromboembolism is more common than arterial thromboembolism in hospitalized COVID-19 patients. Pulmonary thrombosis and microvascular thrombosis are observed in autopsy studies, and this may contribute to the severe hypoxia observed in COVID-19 patients. It is likely that multiple systems contribute to thrombosis in COVID-19 patients, such as activation of coagulation, platelet activation, hypofibrinolysis, endothelial cell dysfunction, inflammation, neutrophil extracellular traps, and complement. Targeting these different pathways may reduce thrombosis and improve lung function in COVID-19 patients.

COVID-19: A collision of complement, coagulation and inflammatory pathways

COVID-19 is frequently accompanied by a hypercoagulable inflammatory state with microangiopathic pulmonary changes that can precede the diffuse alveolar damage characteristic of typical acute respiratory distress syndrome (ARDS) seen in other severe pathogenic infections. Parallels with systemic inflammatory disorders such as atypical hemolytic uremic syndrome (aHUS) have implicated the complement pathway in the pathogenesis of COVID-19, and particularly the anaphylatoxins C3a and C5a released from cleavage of C3 and C5, respectively. C5a is a potent cell signalling protein that activates a cytokine storm-a hyper-inflammatory phenomenon-within hours of infection and the innate immune response. However, excess C5a can result in a pro-inflammatory environment orchestrated through a plethora of mechanisms that propagate lung injury, lymphocyte exhaustion, and an immune paresis. Furthermore, disruption of the homeostatic interactions between complement and extrinsic and intrinsic coagulation pathways contributes to a net pro-coagulant state in the microvasculature of critical organs. Fatal COVID-19 has been associated with a systemic inflammatory response accompanied by a pro-coagulant state and organ damage, particularly microvascular thrombi in the lungs and kidneys. Pathologic studies report strong evidence of complement activation. C5 blockade reduces inflammatory cytokines and their manifestations in animal studies, and has shown benefits in patients with aHUS, prompting investigation of this approach in the treatment of COVID-19. This review describes the role of the complement pathway and particularly C5a and its aberrations in highly pathogenic virus infections, and therefore its potential as a therapeutic target in COVID-19.

Extracellular Vesicle-Related Thrombosis in Viral Infection

Although the outcomes of viral infectious diseases are remarkably varied, most infections cause acute diseases after a short period. Novel coronavirus disease 2019, which recently spread worldwide, is no exception. Extracellular vesicles (EVs) are small circulating membrane-enclosed entities shed from the cell surface in response to cell activation or apoptosis. EVs transport various kinds of bioactive molecules between cells, including functional RNAs, such as viral RNAs and proteins. Therefore, when EVs are at high levels, changes in cell activation, inflammation, angioplasty and transportation suggest that EVs are associated with various diseases. Clinical research on EVs includes studies on the coagulatory system. In particular, abnormal enhancement of the coagulatory system through EVs can cause thrombosis. In this review, we address the functions of EVs, thrombosis, and their involvement in viral infection.

Overcoming Barriers: The Endothelium As a Linchpin of Coronavirus Disease 2019 Pathogenesis?

OBJECTIVE

Coronavirus disease 2019 (COVID-19) is a global pandemic involving >5 500 000 cases worldwide as of May 26, 2020. The culprit is the severe acute respiratory syndrome coronavirus-2, which invades cells by binding to ACE2 (angiotensin-converting enzyme 2). While the majority of patients mount an appropriate antiviral response and recover at home, others progress to respiratory distress requiring hospital admission for supplemental oxygen. In severe cases, deterioration to acute respiratory distress syndrome necessitating mechanical ventilation, development of severe thrombotic events, or cardiac injury and dysfunction occurs. In this review, we highlight what is known to date about COVID-19 and cardiovascular risk, focusing in on the putative role of the endothelium in disease susceptibility and pathogenesis. Approach and Results: Cytokine-driven vascular leak in the lung alveolar-endothelial interface facilitates acute lung injury in the setting of viral infection. Given that the virus affects multiple organs, including the heart, it likely gains access into systemic circulation by infecting or passing from the respiratory epithelium to the endothelium for viral dissemination. Indeed, cardiovascular complications of COVID-19 are highly prevalent and include acute cardiac injury, myocarditis, and a hypercoagulable state, all of which may be influenced by altered endothelial function. Notably, the disease course is worse in individuals with preexisting comorbidities that involve endothelial dysfunction and may be linked to elevated ACE2 expression, such as diabetes mellitus, hypertension, and cardiovascular disease.

CONCLUSIONS

Rapidly emerging data on COVID-19, together with results from studies on severe acute respiratory syndrome coronavirus-1, are providing insight into how endothelial dysfunction may contribute to the pandemic that is paralyzing the globe. This may, in turn, inform the design of biomarkers predictive of disease course, as well as therapeutics targeting pathogenic endothelial responses.

Pulmonary endothelium-derived PD-L1 induced by the H9N2 avian influenza virus inhibits the immune response of T cells

BACKGROUND

The PD-1/PD-L1 pathway is an inhibitory signaling pathway that maintains the balance between the immune response and immunotolerance, and its overactivation in cancer and viral infections inhibits T cell function. The target cells of various viruses, microvascular endothelial cells (MECs) have been shown to be key regulatory points in immune regulation and virion diffusion in vivo during infection with multiple influenza virus subtypes. Furthermore, avian influenza virus (AIV) infection can induce immunosuppression by causing imbalances in immune responses and immune organ damage. Thus, the aim of this study was to investigate whether the H9N2 virus inhibited the immune function of T cells that migrated across MECs by upregulating PD-L1 expression on MECs.

METHODS

The susceptibility of rat pulmonary microvascular endothelial cells (RPMECs) to the H9N2 virus was evaluated by a plaque-forming assay and immunofluorescence staining. Then, we quantified the mRNA and protein levels of PD-L1 in RPMECs induced by H9N2 virus infection using quantitative real-time PCR and flow cytometry. The interaction between the activated T cells and RPMECs infected with the H9N2 virus was revealed using a coculture system. The effect of endothelial-derived PD-L1 on T cell function was investigated by using ELISA and flow cytometry with or without a PD-L1-specific antibody.

RESULTS

Surface staining and the plaque-forming assay showed that the H9N2 virus infected and replicated in RPMECs. Both the PD-L1 mRNA level and PD-L1 protein level were upregulated in RPMECs infected with the H9N2 virus. H9N2 virus-induced PD-L1 expression significantly reduced the secretions of IL-2, IFN-γ and granzyme B and perforin expression in T cells. The above data were significantly increased after treatment with an anti-PD-L1 antibody, confirming the above mentioned findings. In addition, the induction of PD-L1 expression decreased the proliferative capacity of the cocultured T cells but did not affect the apoptosis rate of T cells.

CONCLUSIONS

Taken together, the results suggest that the H9N2 virus is able to inhibit the T cell immune response by upregulating PD-L1 expression in pulmonary microvascular endothelial cells.

Risk Assessment of the Tropism and Pathogenesis of the Highly Pathogenic Avian Influenza A/H7N9 Virus Using Ex Vivo and In Vitro Cultures of Human Respiratory Tract

BACKGROUND

Highly pathogenic avian influenza (HPAI)-H7N9 virus arising from low pathogenic avian influenza (LPAI)-H7N9 virus with polybasic amino acid substitutions in the hemagglutinin was detected in 2017.

METHODS

We compared the tropism, replication competence, and cytokine induction of HPAI-H7N9, LPAI-H7N9, and HPAI-H5N1 in ex vivo human respiratory tract explants, in vitro culture of human alveolar epithelial cells (AECs) and pulmonary microvascular endothelial cells (HMVEC-L).

RESULTS

Replication competence of HPAI- and LPAI-H7N9 were comparable in ex vivo cultures of bronchus and lung. HPAI-H7N9 predominantly infected AECs, whereas limited infection was observed in bronchus. The reduced tropism of HPAI-H7N9 in bronchial epithelium may explain the lack of human-to-human transmission despite a number of mammalian adaptation markers. Apical and basolateral release of virus was observed only in HPAI-H7N9- and H5N1-infected AECs regardless of infection route. HPAI-H7N9, but not LPAI-H7N9 efficiently replicated in HMVEC-L.

CONCLUSIONS

Our findings demonstrate that a HPAI-H7N9 virus efficiently replicating in ex vivo cultures of human bronchus and lung. The HPAI-H7N9 was more efficient at replicating in human AECs and HMVEC-L than LPAI-H7N9 implying that endothelial tropism may involve in pathogenesis of HPAI-H7N9 disease.

Cardiovascular complications following pneumonia: focus on pneumococcus and heart failure

PURPOSE OF REVIEW

Pneumonia, an inflammatory disease, is the single largest infectious cause of death. Pneumonia has recently been established as an important contributing factor to major adverse cardiovascular events including heart failure. Developing an intermechanistic understanding of pneumonia and cardiovascular disease is crucial for successful future drug therapy and reducing healthcare expenditure.

RECENT FINDINGS

Up to 30% of patients admitted with pneumonia develop cardiovascular complications such as heart failure within 10 years of hospital discharge. Recent mechanistic studies have identified inflammation, pneumolysin, platelet activation, and thrombus formation at the center of cardiovascular disease progression.

SUMMARY

In this review, we will detail current knowledge of the mechanistic interaction between pneumonia and development of cardiovascular disease as well as discuss the current and potential drug therapy targets.

[COVID-19 - More Lung Pocus and Sparing Use of Stethoscope, Chest X-Ray and Lung CT]

COVID-19 - More Lung Pocus and Sparing Use of Stethoscope, Chest X-Ray and Lung CT Abstract. For an optimal management of COVID-19 (Coronary Virus Disease) we depend on a fast and reliable diagnosis and severity assessment. The gold standard so far is RT-PCR (reverse transcriptase polmerase chain reaction) from the nasopharyngeal smear. Current tests have a sensitivity of 60-90 %. As a consequence, we must expect 10-40 % false negative results. In addition to oxygen saturation for severity classification, stethoscope, chest X-ray and lung computer tomography are routinely used. However, the standard methods stethoscope and chest X-ray are unreliable. Moreover, all three diagnostic examination techniques expose physicians, support staff and subsequent patients to an additional risk of exposure. In view of the contagiousness of SARS-CoV-2 (Severe Acute Respiratory Syndrome Corona Virus), lung point-of-care ultrasound (Lu-PoCUS) is a still underutilized valuable alternative, especially when using pocket devices. In this review the current value and role of stethoscope, pulsoxymetry, chest x ray, lung computer tomography and lung point-of-care ultrasound will be determined based on the available literature.

Neutrophil-endothelial interactions in respiratory syncytial virus bronchiolitis: An understudied aspect with a potential for prediction of severity of disease

Respiratory syncytial virus (RSV) lower respiratory tract infection (LRTI) causes significant morbidity and mortality among young infants worldwide. It is currently widely accepted that neutrophil influx into the airways is a hallmark of the pathophysiology. However, the exact mechanism of neutrophil migration from the vasculature into the alveolar space in RSV LRTI has received little attention. Data shows that endothelial cells become activated upon RSV infection, driving a 'pro-adhesive state' for circulating neutrophils with upregulation of endothelial intercellular adhesion molecule-1 (ICAM-1). During RSV LRTI different subsets of immature and mature neutrophils are present in the bloodstream, that upregulate integrins lymphocyte-function associated antigen (LFA)-1 and macrophage (Mac)-1, serving as ICAM-1 ligands. An alveolar gradient of interleukin-8 may serve as a potent chemoattractant for circulating neutrophils. Neutrophils from lung aspirates of RSV-infected infants show further signs of inflammatory and migratory activation, while soluble endothelial cell adhesion molecules (sCAMs), such as sICAM-1, have become measurable in the systemic circulation. Whether these mechanisms are solely responsible for neutrophil migration into the alveolar space remains under debate. However, data indicate that the currently postulated neutrophil influx into the lungs should rather be regarded as a neutrophil efflux from the vasculature, involving substantial neutrophil-endothelial interactions. Molecular patterns of these interactions may be clinically useful to predict outcomes of RSV LRTI and deserve further study.

HA-Dependent Tropism of H5N1 and H7N9 Influenza Viruses to Human Endothelial Cells Is Determined by Reduced Stability of the HA, Which Allows the Virus To Cope with Inefficient Endosomal Acidification and Constitutively Expressed IFITM3

Previous studies revealed that certain avian influenza A viruses (IAVs), including zoonotic H5N1 and H7N9 IAVs, infect cultured human lung microvascular endothelial cells (HULEC) more efficiently than other IAVs and that tropism to HULEC is determined by viral hemagglutinin (HA). To characterize mechanisms of HA-mediated endotheliotropism, we used 2:6 recombinant IAVs harboring HAs from distinctive avian and human viruses and found that efficient infection of HULEC correlated with low conformational stability of the HA. We next studied effects on viral infectivity of single-point amino acid substitutions in the HA of 2:6 recombinant virus A/Vietnam/1203/2004-PR8 (H5N1). Substitutions H8Q, H103Y, T315I, and K58₂I (K58I in the HA2 subunit), which increased stability of the HA, markedly reduced viral infectivity for HULEC, whereas substitutions K189N and K218Q, which altered typical H5N1 virus-like receptor specificity and reduced binding avidity of the HA, led to only marginal reduction of infectivity. None of these substitutions affected virus infection in MDCK cells. We confirmed the previous observation of elevated basal expression of IFITM3 protein in HULEC and found that endosomal acidification is less efficient in HULEC than in MDCK cells. In accord with these findings, counteraction of IFITM3-mediated restriction by amphotericin B and reduction of endosomal pH by moderate acidification of the extracellular medium enhanced infectivity of viruses with stable HA for HULEC without significant effect on infectivity for MDCK cells. Collectively, our results indicate that relatively high pH optimum of fusion of the HA of zoonotic H5N1 and H7N9 IAVs allows them to overcome antiviral effects of inefficient endosomal acidification and IFITM3 in human endothelial cells.IMPORTANCE Receptor specificity of the HA of IAVs is known to be a critical determinant of viral cell tropism. Here, we show that fusion properties of the HA may also play a key role in the tropism. Thus, we demonstrate that IAVs having a relatively low pH optimum of fusion cannot efficiently infect human endothelial cells owing to their relatively high endosomal pH and increased expression of fusion-inhibiting IFITM3 protein. These restrictions can be overcome by IAVs with elevated pH of fusion, such as zoonotic H5N1 and H7N9. Our results illustrate that the infectivity of IAVs depends on an interplay between HA conformational stability, endosomal acidification and IFITM3 expression in target cells, and the extracellular pH. Given significant variation of levels of HA stability among animal, human, and zoonotic IAVs, our findings prompt further studies on the fusion-dependent tropism of IAVs to different cell types in humans and its role in viral host range and pathogenicity.