The role of C5a in acute lung injury induced by highly pathogenic viral infections

Neutrophil Extracellular Traps: An Emerging Therapeutic Target to Improve Infectious Disease Outcomes

Neutrophils possess a diverse repertoire of pathogen clearance mechanisms, one of which is the formation of neutrophil extracellular traps (NETs). NETs are complexes of histone proteins and DNA coated with proteolytic enzymes that are released extracellularly to entrap pathogens and aid in their clearance, in a process known as NETosis. Intravascular NETosis may drive a massive inflammatory response that has been shown to contribute to morbidity and mortality in many infectious diseases, including malaria, dengue fever, influenza, bacterial sepsis, and severe acute respiratory syndrome coronavirus 2 infection. In this review we seek to (1) summarize the current understanding of NETs, (2) discuss infectious diseases in which NET formation contributes to morbidity and mortality, and (3) explore potential adjunctive therapeutics that may be considered for future study in treating severe infections driven by NET pathophysiology. This includes drugs specifically targeting NET inhibition and US Food and Drug Administration-approved drugs that may be repurposed as NET inhibitors.

Flavonoid substituted polysaccharides from Tamarix chinensis Lour. alleviate H1N1-induced acute lung injury via inhibiting complement system

ETHNOPHARMACOLOGICAL RELEVANCE

Viral pneumonia is a highly pathogenic respiratory infectious disease associated with excessive activation of the complement system. Our previous studies found that the anticomplement polysaccharides from some medicinal plants could significantly alleviate H1N1-induced acute lung injury (H1N1-ALI). The leaves and twigs of Tamarix chinensis Lour. are traditionally used as a Chinese medicine Xiheliu for treating inflammatory disorders. Interestingly, its crude polysaccharides (MBAP90) showed potent anticomplement activity in vitro.

AIM OF THE STUDY

To evaluate the therapeutic effects and possible mechanism of MBAP90 on viral pneumonia and further isolate and characterize the key active substance of MBAP90.

MATERIALS AND METHODS

The protective effects of MBAP90 were evaluated by survival tests and pharmacodynamic experiments on H1N1-ALI mice. Histopathological changes, viral load, inflammatory markers, and complement deposition in lungs were analyzed by H&E staining, enzyme-linked immunosorbent assay (ELISA), and immunohistochemistry (IHC), respectively. An anticomplement homogenous polysaccharide (MBAP-3) was obtained from MBAP90 by bio-guided separation, and its structure was further characterized by methylation analysis and NMR spectroscopy.

RESULTS

Oral administration of MBAP90 at a dose of 400 mg/kg significantly increased the survival rate of mice infected with the lethal H1N1 virus. In H1N1-induced ALI, mice treated with MBAP90 (200 and 400 mg/kg) could decrease the lung index, lung pathological injury, the levels of excessive proinflammatory cytokines (IL-6, TNF-α, MCP-1, IL-18, and IL-1β), and complement levels (C3c and C5b-9). In addition, MBAP-3 was characterized as a novel homogenous polysaccharide with potent in vitro anticomplement activity (CH50: 0.126 ± 0.002 mg/mL), containing 10.51% uronic acids and 9.67% flavonoids, which were similar to the composition of MBAP90. The backbone of MBAP-3 consisted of →4)-α-D-Glcp-(1→, →3,4,6)-α-D-Glcp-(1→, and →3,4)-α-D-Glcp-(1→, with branches comprising α-L-Araf-(1→, α-D-GlcpA-(1→, →4,6)-α-D-Manp-(1→ and →4)-β-D-Galp-(1 → . Particularly, O-6 of →4)-β-D-Galp-(1→ was conjugated with a flavonoid, myricetin.

CONCLUSIONS

MBAP90 could ameliorate H1N1-ALI by inhibiting inflammation and over-activation of the complement system. These polysaccharides (MBAP90 and MBAP-3) with relative high contents of uronic acid and flavonoid substituent might be vital components of T. chinensis for treating viral pneumonia.

Intravenous ravulizumab in mechanically ventilated patients hospitalised with severe COVID-19: a phase 3, multicentre, open-label, randomised controlled trial

BACKGROUND

The complement pathway is a potential target for the treatment of severe COVID-19. We evaluated the safety and efficacy of ravulizumab, a terminal complement C5 inhibitor, in patients hospitalised with severe COVID-19 requiring invasive or non-invasive mechanical ventilation.

METHODS

This phase 3, multicentre, open-label, randomised controlled trial (ALXN1210-COV-305) enrolled adult patients (aged ≥18 years) from 31 hospitals in France, Japan, Spain, the UK, and the USA. Eligible patients had a confirmed diagnosis of SARS-CoV-2 that required hospitalisation and either invasive or non-invasive mechanical ventilation, with severe pneumonia, acute lung injury, or acute respiratory distress syndrome confirmed by CT scan or x-ray. We randomly assigned participants (2:1) to receive intravenous ravulizumab plus best supportive care (BSC) or BSC alone using a web-based interactive response system. Randomisation was in permuted blocks of six with stratification by intubation status. Bodyweight-based intravenous doses of ravulizumab were administered on days 1, 5, 10, and 15. The primary efficacy endpoint was survival based on all-cause mortality at day 29 in the intention-to-treat (ITT) population. Safety endpoints were analysed in all randomly assigned patients in the ravulizumab plus BSC group who received at least one dose of ravulizumab, and in all randomly assigned patients in the BSC group. The trial is registered with ClinicalTrials.gov, NCT04369469, and was terminated at interim analysis due to futility.

FINDINGS

Between May 10, 2020, and Jan 13, 2021, 202 patients were enrolled in the study and randomly assigned to ravulizumab plus BSC or BSC. 201 patients were included in the ITT population (135 in the ravulizumab plus BSC group and 66 in the BSC group). The ravulizumab plus BSC group comprised 96 (71%) men and 39 (29%) women with a mean age of 63·2 years (SD 13·23); the BSC group comprised 43 (65%) men and 23 (35%) women with a mean age of 63·5 years (12·40). Most patients (113 [84%] of 135 in the ravulizumab plus BSC group and 53 [80%] of 66 in the BSC group) were on invasive mechanical ventilation at baseline. Overall survival estimates based on multiple imputation were 58% for patients receiving ravulizumab plus BSC and 60% for patients receiving BSC (Mantel-Haenszel analysis: risk difference -0·0205; 95% CI -0·1703 to 0·1293; one-sided p=0·61). In the safety population, 113 (89%) of 127 patients in the ravulizumab plus BSC group and 56 (84%) of 67 in the BSC group had a treatment-emergent adverse event. Of these events, infections and infestations (73 [57%] vs 24 [36%] patients) and vascular disorders (39 [31%] vs 12 [18%]) were observed more frequently in the ravulizumab plus BSC group than in the BSC group. Five patients had serious adverse events considered to be related to ravulizumab. These events were bacteraemia, thrombocytopenia, oesophageal haemorrhage, cryptococcal pneumonia, and pyrexia (in one patient each).

INTERPRETATION

Addition of ravulizumab to BSC did not improve survival or other secondary outcomes. Safety findings were consistent with the known safety profile of ravulizumab in its approved indications. Despite the lack of efficacy, the study adds value for future research into complement therapeutics in critical illnesses by showing that C5 inhibition can be accomplished in severely ill patients.

FUNDING

Alexion, AstraZeneca Rare Disease.

Multifaceted Tissue-Protective Functions of Polyvalent Immunoglobulin Preparations in Severe Infections-Interactions with Neutrophils, Complement, and Coagulation Pathways

Severe infections induce immune defense mechanisms and initial tissue damage, which produce an inflammatory neutrophil response. Upon dysregulation of these responses, inflammation, further tissue damage, and systemic spread of the pathogen may occur. Subsequent vascular inflammation and activation of coagulation processes may cause microvascular obstruction at sites distal to the primary site of infection. Low immunoglobulin (Ig) M and IgG levels have been detected in patients with severe infections like sCAP and sepsis, associated with increased severity and mortality. Based on Ig's modes of action, supplementation with polyvalent intravenous Ig preparations (standard IVIg or IgM/IgA-enriched Ig preparations) has long been discussed as a treatment option for severe infections. A prerequisite seems to be the timely administration of Ig preparations before excessive tissue damage has occurred and coagulopathy has developed. This review focuses on nonclinical and clinical studies that evaluated tissue-protective activities resulting from interactions of Igs with neutrophils, complement, and the coagulation system. The data indicate that coagulopathy, organ failure, and even death of patients can possibly be prevented by the timely combined interactions of (natural) IgM, IgA, and IgG with neutrophils and complement.

The occurrence and development of vertebral osteoporosis regulated by IL-8

Vertebral osteoporotic fracture is a common type of fracture, and the incidence is higher in the elderly. However, the relationship between vertebral osteoporotic fractures and interleukin-8 (IL-8) remains unclear. A total of 163 patients with osteoporotic vertebral fractures were recruited. Clinical and follow-up data were recorded, and the expression levels of IL1, MMP9, IL-8, and C-reactive protein in blood were measured. Pearson Chi-square test and Spearman correlation coefficient were used to analyze the relationship between vertebral osteoporotic fractures and related parameters. Univariate and multivariate logistic regression and univariate and multivariate Cox proportional hazards regression were used for further analysis. Pearson chi-square test, Spearman correlation coefficient and Logistic regression analysis showed that IL1 and IL-8 were significantly associated with vertebral osteoporotic fractures. Univariate Cox regression analysis showed that age and IL-8 expression level were significantly associated with maintenance time from recovery to recurrence of vertebral osteoporotic fractures. Multivariate Cox regression analysis showed that IL-8 expression level was significantly associated with maintenance time from recovery to recurrence of vertebral osteoporotic fractures. The higher the expression level of IL-8, the more likely it is to develop vertebral osteoporotic fracture, and the more likely it is to relapse in a short time.

Clinically Evaluated COVID-19 Drugs with Therapeutic Potential for Biological Warfare Agents

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreak resulted in hundreds of millions of coronavirus cases, as well as millions of deaths worldwide. Coronavirus Disease 2019 (COVID-19), the disease resulting from exposure to this pathogen, is characterized, among other features, by a pulmonary pathology, which can progress to "cytokine storm", acute respiratory distress syndrome (ARDS), respiratory failure and death. Vaccines are the unsurpassed strategy for prevention and protection against the SARS-CoV-2 infection. However, there is still an extremely high number of severely ill people from at-risk populations. This may be attributed to waning immune response, variant-induced breakthrough infections, unvaccinated population, etc. It is therefore of high importance to utilize pharmacological-based treatments, despite the progression of the global vaccination campaign. Until the approval of Paxlovid, an efficient and highly selective anti-SARS-CoV-2 drug, and the broad-spectrum antiviral agent Lagevrio, many pharmacological-based countermeasures were, and still are, being evaluated in clinical trials. Some of these are host-directed therapies (HDTs), which modulate the endogenic response against the virus, and therefore may confer efficient protection against a wide array of pathogens. These could potentially include Biological Warfare Agents (BWAs), exposure to which may lead to mass casualties due to disease severity and a possible lack of efficient treatment. In this review, we assessed the recent literature on drugs under advanced clinical evaluation for COVID-19 with broad spectrum activity, including antiviral agents and HDTs, which may be relevant for future coping with BWAs, as well as with other agents, in particular respiratory infections.

The association between serum complement C3a and severity in patients with community-acquired pneumonia

Background

A few studies found that the complement system may be involved in the onset and progression of community-acquired pneumonia (CAP). However, the role of the complement system in CAP was obscure. The goal of this study was to analyze the association of serum complement C3a with CAP severity scores based on a cross-sectional study.

Methods

All 190 CAP patients and 95 control subjects were enrolled. Demographic information and clinical data were extracted. Peripheral blood samples were collected on admission.

Results

Serum complement C3a on admission was elevated in CAP patients compared with healthy subjects. The level of complement C3a was gradually elevated in parallel with CAP severity scores (CURB-65, CRB-65, PSI, SMART-COP, and CURXO). Complement C3a was positively correlated with blood routine parameters, renal function markers, and inflammatory cytokines in CAP patients. Furthermore, multivariate linear and logistic regression models found that serum complement C3a on admission was positively associated with CAP severity scores. Mechanistic research suggested that complement system inhibition alleviated Streptococcus pneumoniae-induced upregulation of IL-1β, TNF-α, IL-6, and CRP in MLE-12 cells.

Conclusions

Serum complement C3a on admission is positively associated with the severity of CAP patients. Inhibiting complement system attenuates S. pneumoniae-elevated secretion of inflammatory cytokines in pulmonary epithelial cells, indicating that complement C3a is involved in the pathophysiology of CAP. Serum complement C3a may serve as an earlier diagnostic biomarker for CAP.

Complement activation in COVID-19 and targeted therapeutic options: A scoping review

Increasing evidence suggests that activation of the complement system plays a key role in the pathogenesis and disease severity of Coronavirus disease 2019 (COVID-19). We used a systematic approach to create an overview of complement activation in COVID-19 based on histopathological, preclinical, multiomics, observational and clinical interventional studies. A total of 1801 articles from PubMed, EMBASE and Cochrane was screened of which 157 articles were included in this scoping review. Histopathological, preclinical, multiomics and observational studies showed apparent complement activation through all three complement pathways and a correlation with disease severity and mortality. The complement system was targeted at different levels in COVID-19, of which C5 and C5a inhibition seem most promising. Adequately powered, double blind RCTs are necessary in order to further investigate the effect of targeting the complement system in COVID-19.

Complement activation predicts negative outcomes in COVID-19: The experience from Northen Italian patients

Coronavirus disease 19 (COVID-19) may present as a multi-organ disease with a hyperinflammatory and prothrombotic response (immunothrombosis) in addition to upper and lower airway involvement. Previous data showed that complement activation plays a role in immunothrombosis mainly in severe forms. The study aimed to investigate whether complement involvement is present in the early phases of the disease and can be predictive of a negative outcome. We enrolled 97 symptomatic patients with a positive RT-PCR for SARS-CoV-2 presenting to the emergency room. The patients with mild symptoms/lung involvement at CT-scan were discharged and the remaining were hospitalized. All the patients were evaluated after a 4-week follow-up and classified as mild (n. 54), moderate (n. 17) or severe COVID-19 (n. 26). Blood samples collected before starting any anti-inflammatory/immunosuppressive therapy were assessed for soluble C5b-9 (sC5b-9) and C5a plasma levels by ELISA, and for the following serum mediators by ELLA: IL-1β, IL-6, IL-8, TNFα, IL-4, IL-10, IL-12p70, IFNγ, IFNα, VEGF-A, VEGF-B, GM-CSF, IL-2, IL-17A, VEGFR2, BLyS. Additional routine laboratory parameters were measured (fibrin fragment D-dimer, C-reactive protein, ferritin, white blood cells, neutrophils, lymphocytes, monocytes, platelets, prothrombin time, activated partial thromboplastin time, and fibrinogen). Fifty age and sex-matched healthy controls were also evaluated. SC5b-9 and C5a plasma levels were significantly increased in the hospitalized patients (moderate and severe) in comparison with the non-hospitalized mild group. SC5b9 and C5a plasma levels were predictive of the disease severity evaluated one month later. IL-6, IL-8, TNFα, IL-10 and complement split products were higher in moderate/severe versus non-hospitalized mild COVID-19 patients and healthy controls but with a huge heterogeneity. SC5b-9 and C5a plasma levels correlated positively with CRP, ferritin values and the neutrophil/lymphocyte ratio. Complement can be activated in the very early phases of the disease, even in mild non-hospitalized patients. Complement activation can be observed even when pro-inflammatory cytokines are not increased, and predicts a negative outcome.

COVID-19 and Acute Kidney Injury - Direct and Indirect Pathophysiological Mechanisms Underlying Lesion Development

COVID-19 is a pandemic disease caused by the SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) responsible for millions of deaths worldwide. Although the respiratory system is the main target of COVID-19, the disease can affect other organs, including the kidneys. Acute Kidney Injury (AKI), commonly seen in patients infected with COVID-19, has a multifactorial cause. Several studies associate this injury with the direct involvement of the virus in renal cells and the indirect damage stimulated by the infection. The direct cytopathic effects of SARS-CoV-2 are due to the entry and replication of the virus in renal cells, changing several regulatory pathways, especially the renin-angiotensin-aldosterone system (RAAS), with repercussions on the kallikrein-kinin system (KKS). Furthermore, the virus can deregulate the immune system, leading to an exaggerated response of inflammatory cells, characterizing the state of hypercytokinemia. The such exaggerated inflammatory response is commonly associated with hemodynamic changes, reduced renal perfusion, tissue hypoxia, generation of reactive oxygen species (ROS), endothelial damage, and coagulopathies, which can result in severe damage to the renal parenchyma. Thereby, understanding the molecular mechanisms and pathophysiology of kidney injuries induced by SARS-COV-2 is of fundamental importance to obtaining new therapeutic insights for the prevention and management of AKI.

Therapeutic Potential of 2-Methylquinazolin-4(3H)-one as an Antiviral Agent against Influenza A Virus-Induced Acute Lung Injury in Mice

Qingdai-Mabo (QM), a traditional Chinese herbal formula composed of medicinal herb and fungus, has been used for treatment of cough and viral pneumonia. However, the underlying mechanism and bioactive components against anti-influenza A virus remain unclear. In the present study, ethyl acetate (EA) extract of QM decoctions was tested for its biological activity against acute lung injury (ALI) and its main components were identified using UPLC-MS/MS. In total, 18 bioactive components were identified, including 2-Methylquinaozlin-4(3H)-one (C1), which showed significant antiviral activity in vitro with an IC₅₀ of 23.8 μg/mL. Furthermore, we validated the efficacy of C1 in ameliorating ALI lesions and inflammation in influenza A virus-infected mice. The results showed that C1 significantly reduced the lung index, downregulated neuraminidase (NA) and nucleoprotein (NP), and decreased the expression of pro-inflammatory molecules IFN-α, TNF-α, MCP-1, IL-6, and IL-8; however, they enhanced levels of IL-10 and IFN-γ in lung homogenate from mice infected by influenza A virus. In addition, C1 inhibited the recruitment of macrophages. These in vitro and in vivo studies suggested that the significant anti-influenza A virus activity contributed to its curative effect on lesions and inflammation of viral pneumonia in mice. Given its potential antiviral activity against influenza A virus, C1 is determined to be a main active component in the EA extract of QM. Taken together, the antiviral activity of C1 suggests its potential as an effective treatment against viral pneumonia via the inhibition of virus replication, but the mechanism C1 on antiviral research needs to be explored further.

Targeting thromboinflammation in COVID-19 - A narrative review of the potential of C1 inhibitor to prevent disease progression

Coronavirus disease 2019 (COVID-19) caused by SARS-CoV-2 is associated with a clinical spectrum ranging from asymptomatic carriers to critically ill patients with complications including thromboembolic events, myocardial injury, multisystemic inflammatory syndromes and death. Since the beginning of the pandemic several therapeutic options emerged, with a multitude of randomized trials, changing the medical landscape of COVID-19. The effect of various monoclonal antibodies, antiviral, anti-inflammatory and anticoagulation drugs have been studied, and to some extent, implemented into clinical practice. In addition, a multitude of trials improved the understanding of the disease and emerging evidence points towards a significant role of the complement system, kallikrein-kinin, and contact activation system as drivers of disease in severe COVID-19. Despite their involvement in COVID-19, treatments targeting these plasmatic cascades have neither been systematically studied nor introduced into clinical practice, and randomized studies with regards to these treatments are scarce. Given the multiple-action, multiple-target nature of C1 inhibitor (C1-INH), the natural inhibitor of these cascades, this drug may be an interesting candidate to prevent disease progression and combat thromboinflammation in COVID-19. This narrative review will discuss the current evidence with regards to the involvement of these plasmatic cascades as well as endothelial cells in COVID-19. Furthermore, we summarize the evidence of C1-INH in COVID-19 and potential benefits and pitfalls of C1-INH treatment in COVID-19.

A disturbed balance between blood complement protective factors (FH, ApoE) and common pathway effectors (C5a, TCC) in acute COVID-19 and during convalesce

A complement effect on homeostasis during infection is determined by both cytotoxic (activate complement component 5 (C5a) terminal cytotoxic complex (TCC)), and cytoprotective elements (complement factor H (FH), as well as apolipoprotein E (ApoE)). Here, we investigated the gap in knowledge in their blood milieu during SARS-CoV-2 infection with respect to the viral burden, level of tissue necrosis, and immunological response. 101 patients hospitalized with a PCR-confirmed diagnosis of COVID-19 had blood collected at H1 (48 h), H2 (3-4 Days), H3 (5-7 days), H4 (more than 7 days up to 93 days). Pre-existing conditions, treatment, the incidence of cerebrovascular events (CVA), a history of deep venous thrombosis (DVT) and pulmonary embolism (PE), and mortality was collected using electronic medical records. Plasma C5a, TCC, FH, and ApoE were considered as a complement milieu. Tissue necrosis (HMGB1, RAGE), non-specific inflammatory responses (IL-6, C-reactive protein), overall viral burden (SARS-CoV-2 spike protein), and specific immune responses (IgG, IgA, IgM directed αS- & N-proteins) were assessed simultaneously. C5a remained elevated across all time points, with the peak at 5-7 days. Studied elements of complement coalesced around three clusters: #0 (↑↑↑C5a, ↑↑TCC, ↓↓ApoE), #1 ↑C5a, ↑TCC, ↑↑↑FH); #2 (↑C5a, ↑TCC, ↑FH, ↑↑↑ApoE). The decline in FH and ApoE was a predictor of death, while TCC and C5a correlated with patient length of stay, APACHE, and CRP. Increased levels of C5a (Δ = 122.64; p = 0.0294; data not shown) and diminished levels of FH (Δ = 836,969; p = 0.0285; data not shown) co-existed with CVA incidence. C5a correlated storngly with blood RAGE and HMGB1, but not with viral load and immunological responsiveness. Remdesivir positively affected FH preservation, while convalescent plasma treatment elevated C5a levels. Three clusters of complement activation demonstrated a various milieu of ApoE & FH vs C5a & TCC in COVID-19 patients. Complement activation is linked to increased necrosis markers but not to viral burden or immune system response.

Complement-mediated microvascular injury and thrombosis in the pathogenesis of severe COVID-19: A review

Coronavirus disease 2019 (COVID-19) causes acute microvascular thrombosis in both venous and arterial structures which is highly associated with increased mortality. The mechanisms leading to thromboembolism are still under investigation. Current evidence suggests that excessive complement activation with severe amplification of the inflammatory response (cytokine storm) hastens disease progression and initiates complement-dependent cytotoxic tissue damage with resultant prothrombotic complications. The concept of thromboinflammation, involving overt inflammation and activation of the coagulation cascade causing thrombotic microangiopathy and end-organ damage, has emerged as one of the core components of COVID-19 pathogenesis. The complement system is a major mediator of the innate immune response and inflammation and thus an appealing treatment target. In this review, we discuss the role of complement in the development of thrombotic microangiopathy and summarize the current data on complement inhibitors as COVID-19 therapeutics.

Favipiravir therapy for Covid-19 infection and tacrolimus toxicity in a kidney transplant patient on chronic eculizumab therapy

Although the latest data show that complement activation has an essential role in the pathogenesis and severity of Covid-19, the data on the prognosis of patients using complement inhibitors during Covid-19 infection are scarce. There is no specific treatment for Covid-19 yet. The introduction of novel agents such as favipiravir may affect metabolism of immunosuppressive drugs. We report the clinical course of Covid-19 in a kidney transplant patient with atypical haemolytic uraemic syndrome on chronic eculizumab therapy. The patient had mild Covid-19 but had severe tacrolimus toxicity, which may be associated with favipiravir and eculizumab. The mild course of Covid-19 in our patient is encouraging for eculizumab use; on the other hand, unusually high levels of tacrolimus that we observed underlines the importance of frequent drug level monitoring in transplanted patients who are receiving new drugs.

Integrated Pharmacology Reveals the Molecular Mechanism of Gegen Qinlian Decoction Against Lipopolysaccharide-induced Acute Lung Injury

ALI is a severe inflammatory disease of the lungs. In previous studies, we found that GQD was effective against ALI, but specific molecular mechanism is still unclear. Therefore, this study was to examine effect of GQD on LPS-induced ALI rats and underlying mechanisms using multi-omics and molecular methods. The results showed that GQD significantly improved lung tissue damage, reduced pulmonary edema, inhibited MPO activity, and improved respiratory function in ALI rat. Additionally, GQD significantly reduced the levels of TNF-α, IL-1β, and IL-6 in serum and BALF. Furthermore, metabolomic analysis showed that GQD reduced pulmonary inflammation by improving metabolic remodeling. Moreover, transcriptomic analysis showed that GQD inhibited the activation of complement pathway and regulated Th17 and Treg cells balance. Additionally, GQD inhibited the expression of C3, C5a, and IL-17, and promoted the expression of TGF-β and CYP1A1 at the mRNA and protein levels. Gut microbial assay showed that GQD treatment increased the relative abundance of Firmicutes and their genera in intestinal microbiota, and increased short-chain fatty acids concentration. Overall, GQD treated ALI by improving metabolic remodeling, affecting immune-related pathways and regulating intestinal microbiota. This study provides a solid scientific basis for promoting the clinical use of GQD in treating ALI.

Exploring Relevant mRNAs and miRNAs in Injured Urethral Tissues of Rats with High-Throughput Sequencing

Acute urethral injuries caused by urethral endoscopy and other mechanical injuries are the main reasons for secondary infection and late urethral stricture. However, there are no studies to explore the transcriptomic changes in urethral injury and the molecular mechanism of urethral injury, which is important for the treatment and cure of urethral injury. Therefore, we used RNA-seq and sRNA-seq profiles from normal and injured urethral tissues to identify and characterize differentially expressed mRNAs and miRNAs. In total, we found 166 differentially expressed mRNAs, of which 69 were upregulated, and 97 were downregulated in injured urethral tissues. The differentially expressed mRNAs were mainly involved in the positive regulation of epithelial cell differentiation, focal adhesion, cell adhesion molecules, protein activation cascade, complement activation, complement and coagulation cascades, and chemokine-mediated signaling pathway. Additionally, we found six upregulated and four downregulated miRNAs, respectively, in the injured urethral tissues. Notably, their target genes were involved in the vascular endothelial growth factor receptor 2 binding, PI3k-Akt signaling pathway, and Notch signaling pathway. In summary, our results suggest that the cell damage response induced by mechanical injury activates the pathological immune response in a variety of ways in injured urethral tissues.

Antibody-Dependent Complement Responses toward SARS-CoV-2 Receptor-Binding Domain Immobilized on "Pseudovirus-like" Nanoparticles

Many aspects of innate immune responses to SARS viruses remain unclear. Of particular interest is the role of emerging neutralizing antibodies against the receptor-binding domain (RBD) of SARS-CoV-2 in complement activation and opsonization. To overcome challenges with purified virions, here we introduce "pseudovirus-like" nanoparticles with ∼70 copies of functional recombinant RBD to map complement responses. Nanoparticles fix complement in an RBD-dependent manner in sera of all vaccinated, convalescent, and naı̈ve donors, but vaccinated and convalescent donors with the highest levels of anti-RBD antibodies show significantly higher IgG binding and higher deposition of the third complement protein (C3). The opsonization via anti-RBD antibodies is not an efficient process: on average, each bound antibody promotes binding of less than one C3 molecule. C3 deposition is exclusively through the alternative pathway. C3 molecules bind to protein deposits, but not IgG, on the nanoparticle surface. Lastly, "pseudovirus-like" nanoparticles promote complement-dependent uptake by granulocytes and monocytes in the blood of vaccinated donors with high anti-RBD titers. Using nanoparticles displaying SARS-CoV-2 proteins, we demonstrate subject-dependent differences in complement opsonization and immune recognition.

How the Innate Immune System of the Blood Contributes to Systemic Pathology in COVID-19-Induced ARDS and Provides Potential Targets for Treatment

Most SARS-CoV-2 infected patients experience influenza-like symptoms of low or moderate severity. But, already in 2020 early during the pandemic it became obvious that many patients had a high incidence of thrombotic complications, which prompted treatment with high doses of low-molecular-weight heparin (LMWH; typically 150-300IU/kg) to prevent thrombosis. In some patients, the disease aggravated after approximately 10 days and turned into a full-blown acute respiratory distress syndrome (ARDS)-like pulmonary inflammation with endothelialitis, thrombosis and vascular angiogenesis, which often lead to intensive care treatment with ventilator support. This stage of the disease is characterized by dysregulation of cytokines and chemokines, in particular with high IL-6 levels, and also by reduced oxygen saturation, high risk of thrombosis, and signs of severe pulmonary damage with ground glass opacities. The direct link between SARS-CoV-2 and the COVID-19-associated lung injury is not clear. Indirect evidence speaks in favor of a thromboinflammatory reaction, which may be initiated by the virus itself and by infected damaged and/or apoptotic cells. We and others have demonstrated that life-threatening COVID-19 ARDS is associated with a strong activation of the intravascular innate immune system (IIIS). In support of this notion is that activation of the complement and kallikrein/kinin (KK) systems predict survival, the necessity for usage of mechanical ventilation, acute kidney injury and, in the case of MBL, also coagulation system activation with thromboembolism. The general properties of the IIIS can easily be translated into mechanisms of COVID-19 pathophysiology. The prognostic value of complement and KKsystem biomarkers demonstrate that pharmaceuticals, which are licensed or have passed the phase I trial stage are promising candidate drugs for treatment of COVID-19. Examples of such compounds include complement inhibitors AMY-101 and eculizumab (targeting C3 and C5, respectively) as well as kallikrein inhibitors ecallantide and lanadelumab and the bradykinin receptor (BKR) 2 antagonist icatibant. In this conceptual review we discuss the activation, crosstalk and the therapeutic options that are available for regulation of the IIIS.

A combination of two human neutralizing antibodies prevents SARS-CoV-2 infection in cynomolgus macaques

BACKGROUND

Human monoclonal antibody (mAb) treatments are promising for COVID-19 prevention or therapy. The pre-exposure prophylactic efficacy of neutralizing antibodies that are engineered with mutations to extend their persistence in human serum and the neutralizing antibody titer in serum required for protection against SARS-CoV-2 infection remain poorly characterized.

METHODS

The Fc region of two neutralizing mAbs (COV2-2130 and COV2-2381) targeting non-overlapping epitopes on the receptor binding domain of SARS-CoV-2 spike protein was engineered to extend their persistence in humans and reduce interactions with Fc gamma receptors. We assessed protection by individual antibodies or a combination of the two antibodies (designated ADM03820) given prophylactically by an intravenous or intramuscular route in a non-human primate (NHP) model of SARS-CoV-2 infection.

FINDINGS

Passive transfer of individual mAbs or ADM03820 conferred virological protection in the NHP respiratory tract in a dose-dependent manner, and ADM03820 potently neutralized SARS-CoV-2 variants of concern in vitro. We defined a protective serum-neutralizing antibody titer and concentration in NHPs for passively transferred human antibodies that acted by direct viral neutralization.

CONCLUSIONS

In summary, we demonstrate that neutralizing antibodies with extended half-life and lacking Fc-mediated effector functions are efficient for pre-exposure prophylaxis of SARS-CoV-2 infection in NHPs. These results support clinical development of ADM03820 for COVID-19 prevention.

FUNDING

This research was supported by a contract from the JPEO-CBRND (W911QY-20-9-003, 20-05); the Joint Sciences and Technology Office and Joint Program Executive Office (MCDC-16-01-002 JSTO, JPEO); a DARPA grant (HR0011-18-2-0001); an NIH grant (R01 AI157155); and the 2019 Future Insight Prize from Merck KGaA.

Pharmacogenetics and Precision Medicine Approaches for the Improvement of COVID-19 Therapies

Many drugs are being administered to tackle coronavirus disease 2019 (COVID-19) pandemic situations without establishing clinical effectiveness or tailoring safety. A repurposing strategy might be more effective and successful if pharmacogenetic interventions are being considered in future clinical studies/trials. Although it is very unlikely that there are almost no pharmacogenetic data for COVID-19 drugs, however, from inferring the pharmacokinetic (PK)/pharmacodynamic(PD) properties and some pharmacogenetic evidence in other diseases/clinical conditions, it is highly likely that pharmacogenetic associations are also feasible in at least some COVID-19 drugs. We strongly mandate to undertake a pharmacogenetic assessment for at least these drug-gene pairs (atazanavir-UGT1A1, ABCB1, SLCO1B1, APOA5; efavirenz-CYP2B6; nevirapine-HLA, CYP2B6, ABCB1; lopinavir-SLCO1B3, ABCC2; ribavirin-SLC28A2; tocilizumab-FCGR3A; ivermectin-ABCB1; oseltamivir-CES1, ABCB1; clopidogrel-CYP2C19, ABCB1, warfarin-CYP2C9, VKORC1; non-steroidal anti-inflammatory drugs (NSAIDs)-CYP2C9) in COVID-19 patients for advancing precision medicine. Molecular docking and computational studies are promising to achieve new therapeutics against SARS-CoV-2 infection. The current situation in the discovery of anti-SARS-CoV-2 agents at four important targets from in silico studies has been described and summarized in this review. Although natural occurring compounds from different herbs against SARS-CoV-2 infection are favorable, however, accurate experimental investigation of these compounds is warranted to provide insightful information. Moreover, clinical considerations of drug-drug interactions (DDIs) and drug-herb interactions (DHIs) of the existing repurposed drugs along with pharmacogenetic (e.g., efavirenz and CYP2B6) and herbogenetic (e.g., andrographolide and CYP2C9) interventions, collectively called multifactorial drug-gene interactions (DGIs), may further accelerate the development of precision COVID-19 therapies in the real-world clinical settings.

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

Complement plays an important role in the direct defense to pathogens, but can also activate immune cells and the release of pro-inflammatory cytokines. However, in critically ill patients with COVID-19 the immune system is inadequately activated leading to severe acute respiratory syndrome (SARS) and acute kidney injury, which is associated with higher mortality. Therefore, we characterized local complement deposition as a sign of activation in both lungs and kidneys from patients with severe COVID-19. Using immunohistochemistry we investigated deposition of complement factors C1q, MASP-2, factor D (CFD), C3c, C3d and C5b-9 as well as myeloperoxidase (MPO) positive neutrophils and SARS-CoV-2 virus particles in lungs and kidneys from 38 patients who died from COVID-19. In addition, tissue damage was analyzed using semi-quantitative scores followed by correlation with complement deposition. Autopsy material from non-COVID patients who died from cardiovascular causes, cerebral hemorrhage and pulmonary embolism served as control (n=8). Lung injury in samples from COVID-19 patients was significantly more pronounced compared to controls with formation of hyaline membranes, thrombi and edema. In addition, in the kidney tubular injury was higher in these patients and correlated with lung injury (r=0.361*). In autopsy samples SARS-CoV-2 spike protein was detected in 22% of the lungs of COVID-19 patients but was lacking in kidneys. Complement activation was significantly stronger in lung samples from patients with COVID-19 via the lectin and alternative pathway as indicated by deposition of MASP-2, CFD, C3d and C5b9. Deposits in the lung were predominantly detected along the alveolar septa, the hyaline membranes and in the alveolar lumina. In the kidney, complement was significantly more deposited in patients with COVID-19 in peritubular capillaries and tubular basement membranes. Renal COVID-19-induced complement activation occurred via the lectin pathway, while activation of the alternative pathway was similar in both groups. Furthermore, MPO-positive neutrophils were found in significantly higher numbers in lungs and kidneys of COVID-19 patients and correlated with local MASP-2 deposition. In conclusion, in patients who died from SARS-CoV-2 infection complement was activated in both lungs and kidneys indicating that complement might be involved in systemic worsening of the inflammatory response. Complement inhibition might thus be a promising treatment option to prevent deregulated activation and subsequent collateral tissue injury in COVID-19.

Uncommon pathogens in an immunocompetent host: respiratory isolation of Cunninghamella bertholletiae, Aspergillus niger, Staphylococcus pseudintermedius and adenovirus in a patient with necrotising pneumonia

We present the unusual case of a 60-year-old immunocompetent woman with chronic obstructive pulmonary disease who developed a necrotising pneumonia with isolation of Cunninghamella bertholletiae, Aspergillus niger, Staphylococcus pseudintermedius and adenovirus. The patient recovered with antimicrobial therapy and supportive care in the intensive care unit. The current literature on diagnosis and treatment of these pathogens is reviewed.

Eculizumab in patients with severe coronavirus disease 2019 (COVID-19) requiring continuous positive airway pressure ventilator support: Retrospective cohort study

Background

Complement activation contributes to lung dysfunction in coronavirus disease 2019 (COVID-19). We assessed whether C5 blockade with eculizumab could improve disease outcome.

Methods

In this single-centre, academic, unblinded study two 900 mg eculizumab doses were added-on standard therapy in ten COVID-19 patients admitted from February 2020 to April 2020 and receiving Continuous-Positive-Airway-Pressure (CPAP) ventilator support from ≤24 hours. We compared their outcomes with those of 65 contemporary similar controls. Primary outcome was respiratory rate at one week of ventilator support. Secondary outcomes included the combined endpoint of mortality and discharge with chronic complications.

Results

Baseline characteristics of eculizumab-treated patients and controls were similar. At baseline, sC5b-9 levels, ex vivo C5b-9 and thrombi deposition were increased. Ex vivo tests normalised in eculizumab-treated patients, but not in controls. In eculizumab-treated patients respiratory rate decreased from 26.8±7.3 breaths/min at baseline to 20.3±3.8 and 18.0±4.8 breaths/min at one and two weeks, respectively (p<0.05 for both), but did not change in controls. Between-group changes differed significantly at both time-points (p<0.01). Changes in respiratory rate correlated with concomitant changes in ex vivo C5b-9 deposits at one (rs = 0.706, p = 0.010) and two (rs = 0.751, p = 0.032) weeks. Over a median (IQR) period of 47.0 (14.0–121.0) days, four eculizumab-treated patients died or had chronic complications versus 52 controls [HR_Crude (95% CI): 0.26 (0.09–0.72), p = 0.010]. Between-group difference was significant even after adjustment for age, sex and baseline serum creatinine [HR_Adjusted (95% CI): 0.30 (0.10–0.84), p = 0.023]. Six patients and 13 controls were discharged without complications [HR_Crude (95% CI): 2.88 (1.08–7.70), p = 0.035]. Eculizumab was tolerated well. The main study limitations were the relatively small sample size and the non-randomised design.

Conclusions

In patients with severe COVID-19, eculizumab safely improved respiratory dysfunction and decreased the combined endpoint of mortality and discharge with chronic complications. Findings need confirmation in randomised controlled trials.

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.

Persistence of High Levels of Serum Complement C5a in Severe COVID-19 Cases After Hospital Discharge

Evidence supports a role of complement anaphylatoxin C5a in the pathophysiology of COVID-19. However, information about the evolution and impact of C5a levels after hospital discharge is lacking. We analyzed the association between circulating C5a levels and the clinical evolution of hospitalized patients infected with SARS-CoV-2. Serum C5a levels were determined in 32 hospitalized and 17 non-hospitalized patients from Clinica Universidad de Navarra. One hundred and eighty eight serial samples were collected during the hospitalization stay and up to three months during the follow-up. Median C5a levels were 27.71 ng/ml (25th to 75th percentile: 19.35-34.96) for samples collected during hospitalization, versus 16.76 ng/ml (12.90-25.08) for samples collected during the follow-up (p<0.001). There was a negative correlation between serum C5a levels and the number of days from symptom onset (p<0.001). C5a levels also correlated with a previously validated clinical risk score (p<0.001), and was associated with the severity of the disease (p<0.001). An overall reduction of C5a levels was observed after hospital discharge. However, elevated C5a levels persisted in those patients with high COVID-19 severity (i.e. those with a longest stay in the hospital), even after months from hospital discharge (p=0.020). Moreover, high C5a levels appeared to be associated with the presence of long-term respiratory symptoms (p=0.004). In conclusion, serum C5a levels remain high in severe cases of COVID-19, and are associated with the presence of respiratory symptoms after hospital discharge. These results may suggest a role for C5a in the long-term effects of COVID-19 infection.

Complement inhibition: A possible therapeutic approach in the fight against Covid-19

The complement system, as a vital part of innate immunity, has an important role in the clearance of pathogens; however, unregulated activation of this system probably has a key role in the pathogenesis of acute lung injury, which is induced by highly pathogenic viruses (i.e. influenza A viruses and severe acute respiratory syndrome [SARS] coronavirus). The novel coronavirus SARS-CoV-2, which is the causal agent for the ongoing global pandemic of the coronavirus disease 2019 (Covid-19), has recently been spread to almost all countries around the world. Although most people are immunocompetent to SARS-CoV-2, a small group develops hyper-inflammation that leads to complications like acute respiratory distress syndrome, disseminated intravascular coagulation, and multi-organ failure. Emerging evidence demonstrates that the complement system exerts a crucial role in this inflammatory reaction. Additionally, patients with the severe form of Covid-19 show over-activation of the complement in their skin, sera, and lungs. This study aims to summarise current knowledge concerning the interaction of SARS-CoV-2 with the complement system and to critically appraise complement inhibition as a potential new approach for Covid-19 treatment.

Systemic Inflammation and Complement Activation Parameters Predict Clinical Outcome of Severe SARS-CoV-2 Infections

Overactivation of the complement system has been characterized in severe COVID-19 cases. Complement components are known to trigger NETosis via the coagulation cascade and have also been reported in human tracheobronchial epithelial cells. In this longitudinal study, we investigated systemic and local complement activation and NETosis in COVID-19 patients that underwent mechanical ventilation. Results confirmed significantly higher baseline levels of serum C5a (24.5 ± 39.0 ng/mL) and TCC (11.03 ± 8.52 µg/mL) in patients compared to healthy controls (p < 0.01 and p < 0.0001, respectively). Furthermore, systemic NETosis was significantly augmented in patients (5.87 (±3.71) × 106 neutrophils/mL) compared to healthy controls (0.82 (±0.74) × 106 neutrophils/mL) (p < 0.0001). In tracheal fluid, baseline TCC levels but not C5a and NETosis, were significantly higher in patients. Kinetic studies of systemic complement activation revealed markedly higher levels of TCC and CRP in nonsurvivors compared to survivors. In contrast, kinetic studies showed decreased local NETosis in tracheal fluid but comparable local complement activation in nonsurvivors compared to survivors. Systemic TCC and NETosis were significantly correlated with inflammation and coagulation markers. We propose that a ratio comprising systemic inflammation, complement activation, and chest X-ray score could be rendered as a predictive parameter of patient outcome in severe SARS-CoV-2 infections.

SARS-CoV-2 Antibodies Mediate Complement and Cellular Driven Inflammation

The ongoing pandemic of coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to constitute a serious public health threat worldwide. Protective antibody-mediated viral neutralization in response to SARS-CoV-2 infection has been firmly characterized. Where the effects of the antibody response are generally considered to be beneficial, an important biological question regarding potential negative outcomes of a SARS-CoV-2 antibody response has yet to be answered. We determined the distribution of IgG subclasses and complement activation levels in plasma from convalescent individuals using in-house developed ELISAs. The IgG response towards SARS-CoV-2 receptor-binding domain (RBD) after natural infection appeared to be mainly driven by IgG1 and IgG3 subclasses, which are the main ligands for C1q mediated classical complement pathway activation. The deposition of the complement components C4b, C3bc, and TCC as a consequence of SARS-CoV-2 specific antibodies were depending primarily on the SARS-CoV-2 RBD and significantly correlated with both IgG levels and disease severity, indicating that individuals with high levels of IgG and/or severe disease, might have a more prominent complement activation during viral infection. Finally, freshly isolated monocytes and a monocyte cell line (THP-1) were used to address the cellular mediated inflammatory response as a consequence of Fc-gamma receptor engagement by SARS-CoV-2 specific antibodies. Monocytic Fc gamma receptor charging resulted in a significant rise in the secretion of the pro-inflammatory cytokine TNF-α. Our results indicate that SARS-CoV-2 antibodies might drive significant inflammatory responses through the classical complement pathway and via cellular immune-complex activation that could have negative consequences during COVID-19 disease. We found that increased classical complement activation was highly associated to COVID-19 disease severity. The combination of antibody-mediated complement activation and subsequent cellular priming could constitute a significant risk of exacerbating COVID-19 severity.

Crosstalk between the renin-angiotensin, complement and kallikrein-kinin systems in inflammation

During severe inflammatory and infectious diseases, various mediators modulate the equilibrium of vascular tone, inflammation, coagulation and thrombosis. This Review describes the interactive roles of the renin–angiotensin system, the complement system, and the closely linked kallikrein–kinin and contact systems in cell biological functions such as vascular tone and leakage, inflammation, chemotaxis, thrombosis and cell proliferation. Specific attention is given to the role of these systems in systemic inflammation in the vasculature and tissues during hereditary angioedema, cardiovascular and renal glomerular disease, vasculitides and COVID-19. Moreover, we discuss the therapeutic implications of these complex interactions, given that modulation of one system may affect the other systems, with beneficial or deleterious consequences.

The renin–angiotensin, complement and kallikrein–kinin systems comprise a multitude of mediators that modulate physiological responses during inflammatory and infectious diseases. This Review investigates the complex interactions between these systems and how these are dysregulated in various conditions, including cardiovascular diseases and COVID-19, as well as their therapeutic implications.

Is It All About Endothelial Dysfunction and Thrombosis Formation? The Secret of COVID-19

The world is in a hard battle against COVID-19. Endothelial cells are among the most critical targets of SARS-CoV-2. Dysfunction of endothelium leads to vascular injury following by coagulopathies and thrombotic conditions in the vital organs increasing the risk of life-threatening events. Growing evidences revealed that endothelial dysfunction and consequent thrombotic conditions are associated with the severity of outcomes. It is not yet fully clear that these devastating sequels originate directly from the virus or a side effect of virus-induced cytokine storm. Due to endothelial dysfunction, plasma levels of some biomarkers are changed and relevant clinical manifestations appear as well. Stabilization of endothelial integrity and supporting its function are among the promising therapeutic strategies. Other than respiratory, COVID-19 could be called a systemic vascular disease and this aspect should be scrutinized in more detail in order to reduce related mortality. In the present investigation, the effects of COVID-19 on endothelial function and thrombosis formation are discussed. In this regard, critical players, laboratory findings, clinical manifestation, and suggestive therapies are presented.

Pulmonary vascular system: A vulnerable target for COVID-19

The number of coronavirus disease 2019 (COVID‐19) cases has been increasing significantly, and the disease has evolved into a global pandemic, posing an unprecedented challenge to the healthcare community. Angiotensin‐converting enzyme 2, the binding and entry receptor of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) in hosts, is also expressed on pulmonary vascular endothelium; thus, pulmonary vasculature is a potential target in COVID‐19. Indeed, pulmonary vascular thickening is observed by early clinical imaging, implying a tropism of SARS‐CoV‐2 for pulmonary vasculature. Recent studies reported that COVID‐19 is associated with vascular endothelial damage and dysfunction along with inflammation, coagulopathy, and microthrombosis; all of these pathologic changes are the hallmarks of pulmonary vascular diseases. Notwithstanding the not fully elucidated effects of COVID‐19 on pulmonary vasculature, the vascular endotheliopathy that occurs after infection is attributed to direct infection and indirect damage mainly caused by renin‐angiotensin‐aldosterone system imbalance, coagulation cascade, oxidative stress, immune dysregulation, and intussusceptive angiogenesis. Degradation of endothelial glycocalyx exposes endothelial cell (EC) surface receptors to the vascular lumen, which renders pulmonary ECs more susceptible to SARS‐CoV‐2 infection. The present article reviews the potential pulmonary vascular pathophysiology and clinical presentations in COVID‐19 to provide a basis for clinicians and scientists, providing insights into the development of therapeutic strategies targeting pulmonary vasculature.

High-dose intravenous immunoglobulins might modulate inflammation in COVID-19 patients

The use of high-dose of intravenous immunoglobulins (IVIGs) as immunomodulators for the treatment of COVID-19-affected individuals has shown promising results. IVIG reduced inflammation in these patients, who progressively restored respiratory function. However, little is known about how they may modulate immune responses in COVID-19 individuals. Here, we have analyzed the levels of 41 inflammatory biomarkers in plasma samples obtained at day 0 (pretreatment initiation), 3, 7, and 14 from five hospitalized COVID-19 patients treated with a 5-d course of 400 mg/kg/d of IVIG. The plasmatic levels of several cytokines (Tumor Necrosis Factor, IL-10, IL-5, and IL-7), chemokines (macrophage inflammatory protein-1α), growth/tissue repairing factors (hepatic growth factor), complement activation (C5a), and intestinal damage such as Fatty acid-binding protein 2 and LPS-binding protein showed a progressive decreasing trend during the next 2 wk after treatment initiation. This trend was not observed in IVIG-untreated COVID-19 patients. Thus, the administration of high-dose IVIG to hospitalized COVID-19 patients may improve their clinical evolution by modulating their hyperinflammatory and immunosuppressive status.

Status of mannose-binding lectin (MBL) and complement system in COVID-19 patients and therapeutic applications of antiviral plant MBLs

Coronavirus disease 2019 (COVID-19) is an infectious disease caused by a virus called "Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)." In the majority of patients, infection with COVID-19 may be asymptomatic or may cause only mild symptoms. However, in some patients, there can also be immunological problems, such as macrophage activation syndrome (CSS) that results in cytokine storm syndrome (CSS) and acute respiratory distress syndrome (ARDS). Comprehension of host-microbe communications is the critical aspect in the advancement of new therapeutics against infectious illnesses. Endogenous animal lectins, a class of proteins, may perceive non-self glycans found on microorganisms. Serum mannose-binding lectin (sMBL), as a part of the innate immune framework, recognizes a wide range of microbial microorganisms and activates complement cascade via an antibody-independent pathway. Although the molecular basis for the intensity of SARS-CoV-2 infection is not generally understood, scientific literature indicates that COVID-19 is correlated with unregulated activation of the complement in terms of disease severity. Disseminated intravascular coagulation (DIC), inflammation, and immune paralysis contribute to unregulated complement activation. Pre-existing genetic defects in MBL and their association with complement play a major role in immune response dysregulation caused by SARS-CoV-2. In order to generate anti-complement-based therapies in Covid-19, an understanding of sMBL in immune response to SARS-CoV-2 and complement is therefore essential. This review highlights the role of endogenous sMBL and complement activation during SARS-CoV-2 infection and their therapeutic management by various agents, mainly plant lectins, since antiviral mannose-binding plant lectins (pMBLs) offer potential applications in the prevention and control of viral infections.

Natural products provide a new perspective for anti-complement treatment of severe COVID-19: a review

Exaggerated immune response and cytokine storm are accounted for the severity of COVID-19, including organ dysfunction, especially progressive respiratory failure and generalized coagulopathy. Uncontrolled activation of complement contributes to acute and chronic inflammation, the generation of cytokine storm, intravascular coagulation and cell/tissue damage, which may be a favorable target for the treatment of multiple organ failure and reduction of mortality in critically ill patients with COVID-19. Cytokine storm suppression therapy can alleviate the symptoms of critically ill patients to some extent, but as a remedial etiological measure, its long-term efficacy is still questionable. Anti-complement therapy has undoubtedly become an important hotspot in the upstream regulation of cytokine storm. However, chemosynthetic complement inhibitors are expensive, and their drug resistance and long-term side effects require further investigation. New complement inhibitors with high efficiency and low toxicity can be obtained from natural products at low development cost. This paper puts forward some insights of the development of natural anti-complement products in traditional Chinese medicine, that may provide a bright perspective for suppressing cytokine storm in critically ill patients with COVID-19.

Complement Inhibition and COVID-19: The Story so Far

Acute respiratory distress syndrome (ARDS) is the most severe complication of COVID-19, a disease caused by severe acute respiratory syndrome coronavirus (SARS CoV) 2. The mechanisms underlying the progression from asymptomatic disease to pneumonia and ARDS are complex and by far unelucidated. As for bacterial sepsis, the release of damage associated molecular patterns and pathogen associated molecular patterns triggers activation of the complement cascade. Subsequently, overexpressed anaphylatoxins recruit inflammatory cells in the lung and other organs and contribute initiating and amplifying a vicious circle of thromboinflammation causing organs damage and eventually death. Preclinical and observational studies in patients with COVID-19 provided evidence that complement inhibition effectively may attenuate lung and systemic inflammation, restore the coagulation/fibrinolysis balance, improve organs function and eventually may save life. Ongoing Phase 2/3 trials should elucidate the benefit to risk profile of complement inhibitors and may clarify the optimal targets in the complement cascade.

Elevated Expression Levels of Lung Complement Anaphylatoxin, Neutrophil Chemoattractant Chemokine IL-8, and RANTES in MERS-CoV-Infected Patients: Predictive Biomarkers for Disease Severity and Mortality

The complement system, a network of highly-regulated proteins, represents a vital part of the innate immune response. Over-activation of the complement system plays an important role in inflammation, tissue damage, and infectious disease severity. The prevalence of MERS-CoV in Saudi Arabia remains significant and cases are still being reported. The role of complement in Middle East Respiratory Syndrome coronavirus (MERS-CoV) pathogenesis and complement-modulating treatment strategies has received limited attention, and studies involving MERS-CoV-infected patients have not been reported. This study offers the first insight into the pulmonary expression profile including seven complement proteins, complement regulatory factors, IL-8, and RANTES in MERS-CoV infected patients without underlying chronic medical conditions. Our results significantly indicate high expression levels of complement anaphylatoxins (C3a and C5a), IL-8, and RANTES in the lungs of MERS-CoV-infected patients. The upregulation of lung complement anaphylatoxins, C5a, and C3a was positively correlated with IL-8, RANTES, and the fatality rate. Our results also showed upregulation of the positive regulatory complement factor P, suggesting positive regulation of the complement during MERS-CoV infection. High levels of lung C5a, C3a, factor P, IL-8, and RANTES may contribute to the immunopathology, disease severity, ARDS development, and a higher fatality rate in MERS-CoV-infected patients. These findings highlight the potential prognostic utility of C5a, C3a, IL-8, and RANTES as biomarkers for MERS-CoV disease severity and mortality. To further explore the prediction of functional partners (proteins) of highly expressed proteins (C5a, C3a, factor P, IL-8, and RANTES), the computational protein–protein interaction (PPI) network was constructed, and six proteins (hub nodes) were identified.

Complement Decay-Accelerating Factor is a modulator of influenza A virus lung immunopathology

Clearance of viral infections, such as SARS-CoV-2 and influenza A virus (IAV), must be fine-tuned to eliminate the pathogen without causing immunopathology. As such, an aggressive initial innate immune response favors the host in contrast to a detrimental prolonged inflammation. The complement pathway bridges innate and adaptive immune system and contributes to the response by directly clearing pathogens or infected cells, as well as recruiting proinflammatory immune cells and regulating inflammation. However, the impact of modulating complement activation in viral infections is still unclear. In this work, we targeted the complement decay-accelerating factor (DAF/CD55), a surface protein that protects cells from non-specific complement attack, and analyzed its role in IAV infections. We found that DAF modulates IAV infection in vivo, via an interplay with the antigenic viral proteins hemagglutinin (HA) and neuraminidase (NA), in a strain specific manner. Our results reveal that, contrary to what could be expected, DAF potentiates complement activation, increasing the recruitment of neutrophils, monocytes and T cells. We also show that viral NA acts on the heavily sialylated DAF and propose that the NA-dependent DAF removal of sialic acids exacerbates complement activation, leading to lung immunopathology. Remarkably, this mechanism has no impact on viral loads, but rather on the host resilience to infection, and may have direct implications in zoonotic influenza transmissions.

Exacerbated complement activation and immune deregulation are at the basis of several pathologies induced by respiratory viruses. Here, we report that complement decay-accelerating factor (DAF), which inhibits complement activation in healthy cells, increases disease severity upon influenza A virus (IAV) infection. Remarkably, DAF interaction with IAV proteins, hemagglutinin (HA) and neuraminidase (NA), resulted in excessive complement activation and recruitment of innate and adaptive immune cells, without affecting viral loads. Furthermore, we observed that viral NA directly cleaves DAF and promotes complement activation, providing a possible link between IAV-DAF interaction and pathology. Therefore, our results unveil a novel pathway that could modulate disease severity, which may help to understand the increased pathogenicity of zoonotic and pandemic IAV infections.

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

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

Immunological and physiopathological approach of COVID-19 in pregnancy

Coronavirus disease-2019 (COVID-19) related to Coronavirus-2 (SARS-CoV-2) is a worldwide health concern. Despite the majority of patients will evolve asymptomatic or mild-moderate upper respiratory tract infections, 20% will develop severe disease. Based on current pathogenetic knowledge, a severe COVID-19 form is mainly a hyperinflammatory, immune-mediated disorder, triggered by a viral infection. Due to their particular immunological features, pregnant women are supposed to be particularly susceptible to complicate by intracellular infections as well as immunological disturbances. As an example, immune-thrombosis has been identified as a common immune-mediated and pathogenic phenomenon both in COVID-19, in obstetric diseases and in COVID-19 pregnant women. According to extensive published clinical data, is rationale to expect an interference with the normal development of pregnancy in selected SARS-CoV-2-infected cases, mainly during third trimester.This manuscript provides insights of research to elucidate the potential harmful responses to SARS-CoV-2 and /or other coronavirus infections, as well as bidirectional interactions between COVID-19 and pregnancy to improve their respective management.

Is the mechanism of COVID-19 coagulopathy still a rabbit's hole?

The pathophysiology of COVID-19 is an enigma with its severity often determined by the extent of coagulopathy. Several regulatory pathways targeted by the SARS-CoV-2 include the renin-angiotensin system, von Willebrand Factor, and most importantly, the complement pathway. This article discusses these pathways to help design potential future therapies.

The role of the lectin pathway of the complement system in SARS-CoV-2 lung injury

Although some evidence showed the activation of complement systems in COVID-19 patients, proinflammatory status and lectin pathway remain unclear. Thus, the present study aimed to demonstrate the role of MBL and ficolin-3 in the complement system activation and compared to pandemic Influenza A virus H1N1 subtype infection (H1N1pdm09) and control patients. A total of 27 lungs formalin-fixed paraffin-embedded samples (10 from H1N1 group, 6 from the COVID-19 group, and 11 from the control group) were analyzed by immunohistochemistry using anti-IL-6, TNF-alfa, CD163, MBL e FCN3 antibodies. Genotyping of target polymorphisms in the MBL2 gene was performed by real-time PCR. Proinflammatory cytokines such as IL-6 and TNF-alpha presented higher tissue expression in the COVID-19 group compared to H1N1 and control groups. The same results were observed for ICAM-1 tissue expression. Increased expression of the FCN3 was observed in the COVID-19 group and H1N1 group compared to the control group. The MBL tissue expression was higher in the COVID-19 group compared to H1N1 and control groups. The genotypes AA for rs180040 (G/A), GG for rs1800451 (G/A) and CC for rs5030737 (T/C) showed a higher prevalence in the COVID-19 group. The intense activation of the lectin pathway, with particular emphasis on the MBL pathway, together with endothelial dysfunction and a massive proinflammatory cytokines production, possibly lead to a worse outcome in patients infected with SARS-Cov-2. Moreover, 3 SNPs of our study presented genotypes that might be correlated with high MBL tissue expression in the COVID-19 pulmonary samples.

Therapeutic Targeting of the Complement System: From Rare Diseases to Pandemics

The complement system was discovered at the end of the 19th century as a heat-labile plasma component that "complemented" the antibodies in killing microbes, hence the name "complement." Complement is also part of the innate immune system, protecting the host by recognition of pathogen-associated molecular patterns. However, complement is multifunctional far beyond infectious defense. It contributes to organ development, such as sculpting neuron synapses, promoting tissue regeneration and repair, and rapidly engaging and synergizing with a number of processes, including hemostasis leading to thromboinflammation. Complement is a double-edged sword. Although it usually protects the host, it may cause tissue damage when dysregulated or overactivated, such as in the systemic inflammatory reaction seen in trauma and sepsis and severe coronavirus disease 2019 (COVID-19). Damage-associated molecular patterns generated during ischemia-reperfusion injuries (myocardial infarction, stroke, and transplant dysfunction) and in chronic neurologic and rheumatic disease activate complement, thereby increasing damaging inflammation. Despite the long list of diseases with potential for ameliorating complement modulation, only a few rare diseases are approved for clinical treatment targeting complement. Those currently being efficiently treated include paroxysmal nocturnal hemoglobinuria, atypical hemolytic-uremic syndrome, myasthenia gravis, and neuromyelitis optica spectrum disorders. Rare diseases, unfortunately, preclude robust clinical trials. The increasing evidence for complement as a pathogenetic driver in many more common diseases suggests an opportunity for future complement therapy, which, however, requires robust clinical trials; one ongoing example is COVID-19 disease. The current review aims to discuss complement in disease pathogenesis and discuss future pharmacological strategies to treat these diseases with complement-targeted therapies. SIGNIFICANCE STATEMENT: The complement system is the host's defense friend by protecting it from invading pathogens, promoting tissue repair, and maintaining homeostasis. Complement is a double-edged sword, since when dysregulated or overactivated it becomes the host's enemy, leading to tissue damage, organ failure, and, in worst case, death. A number of acute and chronic diseases are candidates for pharmacological treatment to avoid complement-dependent damage, ranging from the well established treatment for rare diseases to possible future treatment of large patient groups like the pandemic coronavirus disease 2019.

Mechanisms of SARS-CoV-2-induced lung vascular disease: potential role of complement

The outbreak of COVID-19 disease, caused by SARS-CoV-2 beta-coronovirus, urges a focused search for the underlying mechanisms and treatment options. The lung is the major target organ of COVID-19, wherein the primary cause of mortality is hypoxic respiratory failure, resulting from acute respiratory distress syndrome, with severe hypoxemia, often requiring assisted ventilation. While similar in some ways to acute respiratory distress syndrome secondary to other causes, lungs of some patients dying with COVID-19 exhibit distinct features of vascular involvement, including severe endothelial injury and cell death via apoptosis and/or pyroptosis, widespread capillary inflammation, and thrombosis. Furthermore, the pulmonary pathology of COVID-19 is characterized by focal inflammatory cell infiltration, impeding alveolar gas exchange resulting in areas of local tissue hypoxia, consistent with potential amplification of COVID-19 pathogenicity by hypoxia. Vascular endothelial cells play essential roles in both innate and adaptive immune responses, and are considered to be "conditional innate immune cells" centrally participating in various inflammatory, immune pathologies. Activated endothelial cells produce cytokines/chemokines, dynamically recruit and activate inflammatory cells and platelets, and centrally participate in pro-thrombotic processes (thrombotic microangiopathies). Initial reports presented pathological findings of localized direct infection of vascular endothelial cells with SARS-CoV-2, yet emerging evidence does not support direct infection of endothelial or other vascular wall cell and thus widespread endothelial cell dysfunction and inflammation may be better explained as secondary responses to epithelial cell infection and inflammation. Endothelial cells are also actively engaged in a cross-talk with the complement system, the essential arm of innate immunity. Recent reports present evidence for complement deposition in SARS-CoV-2-damaged lung microcirculation, further strengthening the idea that, in severe cases of COVID-19, complement activation is an essential player, generating destructive hemorrhagic, capillaritis-like tissue damage, clotting, and hyperinflammation. Thus, complement-targeted therapies are actively in development. This review is intended to explore in detail these ideas.

Neutrophils in COVID-19

Strong evidence has been accumulated since the beginning of the COVID-19 pandemic that neutrophils play an important role in the pathophysiology, particularly in those with severe disease courses. While originally considered to be a rather homogeneous cell type, recent attention to neutrophils has uncovered their fascinating transcriptional and functional diversity as well as their developmental trajectories. These new findings are important to better understand the many facets of neutrophil involvement not only in COVID-19 but also many other acute or chronic inflammatory diseases, both communicable and non-communicable. Here, we highlight the observed immune deviation of neutrophils in COVID-19 and summarize several promising therapeutic attempts to precisely target neutrophils and their reactivity in patients with COVID-19.

How Do Inflammatory Mediators, Immune Response and Air Pollution Contribute to COVID-19 Disease Severity? A Lesson to Learn

Inflammatory and immune processes are defensive mechanisms that aim to remove harmful agents. As a response to infections, inflammation and immune response contribute to the pathophysiological mechanisms of diseases. Coronavirus disease 2019 (COVID-19), whose underlying mechanisms remain not fully elucidated, has posed new challenges for the knowledge of pathophysiology. Chiefly, the inflammatory process and immune response appear to be unique features of COVID-19 that result in developing a hyper-inflammatory syndrome, and air pollution, the world's largest health risk factor, may partly explain the behaviour and fate of COVID-19. Understanding the mechanisms involved in the progression of COVID-19 is of fundamental importance in order to avoid the late stage of the disease, associated with a poor prognosis. Here, the role of the inflammatory and immune mediators in COVID-19 pathophysiology is discussed.

Complement Activation in the Disease Course of Coronavirus Disease 2019 and Its Effects on Clinical Outcomes

BACKGROUND

Excessive activation of immune responses in coronavirus disease 2019 (COVID-19) is considered to be related to disease severity, complications, and mortality rate. The complement system is an important component of innate immunity and can stimulate inflammation, but its role in COVID-19 is unknown.

METHODS

A prospective, longitudinal, single center study was performed in hospitalized patients with COVID-19. Plasma concentrations of complement factors C3a, C3c, and terminal complement complex (TCC) were assessed at baseline and during hospital admission. In parallel, routine laboratory and clinical parameters were collected from medical files and analyzed.

RESULTS

Complement factors C3a, C3c, and TCC were significantly increased in plasma of patients with COVID-19 compared with healthy controls (P < .05). These complement factors were especially elevated in intensive care unit patients during the entire disease course (P < .005 for C3a and TCC). More intense complement activation was observed in patients who died and in those with thromboembolic events.

CONCLUSIONS

Patients with COVID-19 demonstrate activation of the complement system, which is related to disease severity. This pathway may be involved in the dysregulated proinflammatory response associated with increased mortality rate and thromboembolic complications. Components of the complement system might have potential as prognostic markers for disease severity and as therapeutic targets in COVID-19.

Targeting the Complement Serine Protease MASP-2 as a Therapeutic Strategy for Coronavirus Infections

MASP-2, mannose-binding protein-associated serine protease 2, is a key enzyme in the lectin pathway of complement activation. Hyperactivation of this protein by human coronaviruses SARS-CoV, MERS-CoV and SARS-CoV-2 has been found to contribute to aberrant complement activation in patients, leading to aggravated lung injury with potentially fatal consequences. This hyperactivation is triggered in the lungs through a conserved, direct interaction between MASP-2 and coronavirus nucleocapsid (N) proteins. Blocking this interaction with monoclonal antibodies and interfering directly with the catalytic activity of MASP-2, have been found to alleviate coronavirus-induced lung injury both in vitro and in vivo. In this study, a virtual library of 8736 licensed drugs and clinical agents has been screened in silico according to two parallel strategies. The first strategy aims at identifying direct inhibitors of MASP-2 catalytic activity, while the second strategy focusses on finding protein-protein interaction inhibitors (PPIs) of MASP-2 and coronaviral N proteins. Such agents could represent promising support treatment options to prevent lung injury and reduce mortality rates of infections caused by both present and future-emerging coronaviruses. Forty-six drug repurposing candidates were purchased and, for the ones selected as potential direct inhibitors of MASP-2, a preliminary in vitro assay was conducted to assess their interference with the lectin pathway of complement activation. Some of the tested agents displayed a dose-response inhibitory activity of the lectin pathway, potentially providing the basis for a viable support strategy to prevent the severe complications of coronavirus infections.

Interleukin-33 Amplifies Human Mast Cell Activities Induced by Complement Anaphylatoxins

Both, aberrant mast cell responses and complement activation contribute to allergic diseases. Since mast cells are highly responsive to C3a and C5a, while Interleukin-33 (IL-33) is a potent mast cell activator, we hypothesized that IL-33 critically regulates mast cell responses to complement anaphylatoxins. We sought to understand whether C3a and C5a differentially activate primary human mast cells, and probe whether IL-33 regulates C3a/C5a-induced mast cell activities. Primary human mast cells were generated from peripheral blood precursors or isolated from healthy human lung tissue, and mast cell complement receptor expression, degranulation, mediator release, phosphorylation patterns, and calcium flux were assessed. Human mast cells of distinct origin express constitutively higher levels of C3aR1 than C5aR1, and both receptors are downregulated by anaphylatoxins. While C3a is a potent mast cell degranulation inducer, C5a is a weaker secretagogue with more delayed effects. Importantly, IL-33 potently enhances the human mast cell reactivity to C3a and C5a (degranulation, cytokine and chemokine release), independent of changes in C3a or C5a receptor expression or the level of Ca²⁺ influx. Instead, this reflects differential dynamics of intracellular signaling such as ERK1/2 phosphorylation. Since primary human mast cells respond differentially to anaphylatoxin stimulation, and that IL-33 is a key regulator of mast cell responses to complement anaphylatoxins, this is likely to aggravate Th2 immune responses. This newly identified cross-regulation may be important for controlling exacerbated complement- and mast cell-dependent Th2 responses and thus provides an additional rationale for targeting anti-IL33 therapeutically in allergic diseases.