Infectivity Of Enveloped Viruses Research Articles

The ability of human TIM1 to bind phosphatidylethanolamine enhances viral uptake and efferocytosis compared to rhesus and mouse orthologs.

T-cell immunoglobulin and mucin (TIM) family proteins facilitate the clearance of apoptotic cells, are involved in immune regulation, and promote infection of enveloped viruses. These processes are frequently studied in experimental animals, such as mice or rhesus macaques, but functional differences among the TIM orthologs from these species have not been described. Previously, we reported that while all three human TIM proteins bind phosphatidylserine (PS), only human TIM1 (hTIM1) binds phosphatidylethanolamine (PE), and that this PE-binding ability contributes to both phagocytic clearance of apoptotic cells and viral infection. Here, we show that rhesus macaque TIM1 (rhTIM1) and mouse TIM1 (mTIM1) bind PS but not PE, and that their inability to bind PE makes them less efficient than hTIM1. We also show that alteration of only two residues of mTIM1 or rhTIM1 enables them to bind both PE and PS, and that these PE-binding variants are more efficient at phagocytosis and mediating viral entry. Further, we demonstrate that the mucin domain also contributes to the binding of the virions and apoptotic cells, although it does not directly bind phospholipid. Interestingly, contribution of the hTIM1 mucin domain is more pronounced in the presence of a PE-binding head domain. These results demonstrate that rhTIM1 and mTIM1 are inherently less functional than hTIM1, owing to their inability to bind PE and their less functional mucin domains. They also imply that mouse and macaque models underestimate the activity of hTIM1.IMPORTANCEWe previously reported that human T-cell immunoglobulin and mucin protein 1 (TIM1) binds phosphatidylethanolamine (PE) as well as phosphatidylserine (PS), and that PE is exposed on the apoptotic cells and viral envelopes. Moreover, TIM1 recognition of PE contributes to phagocytic clearance of apoptotic cells and virus uptake. Here, we report that unlike human TIM1, murine and rhesus TIM1 orthologs bind only PS, and as a result, their ability to clear apoptotic cells or promote virus infection is less efficient. These findings are significant because they imply that the activity of TIM1 in humans is greater than what the studies conducted in common animal models would indicate.

The ability of human TIM1 to bind phosphatidylethanolamine enhances viral uptake and efferocytosis compared to rhesus and mouse orthologs.

T-cell Immunoglobulin and Mucin (TIM)-family proteins facilitate the clearance of apoptotic cells, are involved in immune regulation, and promote infection of enveloped viruses. These processes are frequently studied in experimental animals such as mice or rhesus macaques, but functional differences among the TIM orthologs from these species have not been described. Previously, we reported that while all three human TIM proteins bind phosphatidylserine (PS), only human TIM1 (hTIM1) binds phosphatidylethanolamine (PE), and that this PE-binding ability contributes to both phagocytic clearance of apoptotic cells and virus infection. Here we show that rhesus macaque TIM1 (rhTIM1) and mouse TIM1 (mTIM1) bind PS but not PE and that their inability to bind PE makes them less efficient than hTIM1. We also show that alteration of only two residues of mTIM1 or rhTIM1 enables them to bind both PE and PS, and that these PE-binding variants are more efficient at phagocytosis and mediating viral entry. Further, we demonstrate that the mucin domain also contributes to the binding of the virions and apoptotic cells, although it does not directly bind phospholipid. Interestingly, contribution of the hTIM1 mucin domain is more pronounced in the presence of a PE-binding head domain. These results demonstrate that rhTIM1 and mTIM1 are inherently less functional than hTIM1, owing to their inability to bind PE and their less functional mucin domains. They also imply that mouse and macaque models underestimate the activity of hTIM1.

The antimicrobial peptide Sparamosin26–54 exhibits antiviral activity against three aquatic enveloped viruses through lipid-binding-mediated virus lysis

The aquaculture industry is faced with huge economic losses caused by various enveloped virus infections, such as white spot syndrome virus (WSSV), Rana grylio virus (RGV), and Anguillid Herpesvirus 1 (AngHV). The urgent need for readily available broad-spectrum antiviral agents has led to the exploration of antiviral peptides (AVPs), among which antimicrobial peptides (AMPs) with antiviral activity have attracted increasing attention. Sparamosin26–54 (derived from Scylla paramamosain) is a promising antimicrobial agent. In this study, we found that Sparamosin26–54 significantly inhibited WSSV transcription and replication (as indicated by VP28 gene and protein levels), irreversibly inactivated virions, and impeded viral entry before binding to the cell. Transmission electron microscopy observations showed that Sparamosin26–54 had a direct destructive effect on WSSV virions. Lipidomic analysis and ELISA assay highlighted that Sparamosin26–54 had a potent affinity for phosphatidic acid (PA) and phosphatidylserine (PS) of WSSV. Liposome leakage assays further revealed a pronounced effect of Sparamosin26–54 on membrane lipid compositions, emphasizing its efficacy against the other two enveloped viruses (RGV and AngHV), but not against the non-enveloped virus, American eel adomavirus (AEAdov). Notably, in three animal models of viral infection, Sparamosin26–54 reduced viral loads in tissues, increased survival, or decreased infection rates in a concentration-dependent manner. Importantly, Sparamosin26–54 showed no animal toxicity under different modes of administration and could maintain antiviral activity in the complex aquatic environment. Taken together, Sparamosin26–54 was proved to be effective against three enveloped viruses, possibly inducing viral lysis via lipid-binding, providing an alternative approach for combating enveloped virus infections.

Cetylpyridinium chloride and chlorhexidine show antiviral activity against Influenza A virus and Respiratory Syncytial virus in vitro.

The oral cavity is the site of entry and replication for many respiratory viruses. Furthermore, it is the source of droplets and aerosols that facilitate viral transmission. It is thought that appropriate oral hygiene that alters viral infectivity might reduce the spread of respiratory viruses and contribute to infection control. Here, we analyzed the antiviral activity of cetylpyridinium chloride (CPC), chlorhexidine (CHX), and three commercial CPC and CHX-containing mouthwash preparations against the Influenza A virus and the Respiratory syncytial virus. To do so the aforementioned compounds and preparations were incubated with the Influenza A virus or with the Respiratory syncytial virus. Next, we analyzed the viability of the treated viral particles. Our results indicate that CPC and CHX decrease the infectivity of both the Influenza A virus and the Respiratory Syncytial virus in vitro between 90 and 99.9% depending on the concentration. Likewise, CPC and CHX-containing mouthwash preparations were up to 99.99% effective in decreasing the viral viability of both the Influenza A virus and the Respiratory syncytial virus in vitro. The use of a mouthwash containing CPC or CHX alone or in combination might represent a cost-effective measure to limit infection and spread of enveloped respiratory viruses infecting the oral cavity, aiding in reducing viral transmission. Our findings may stimulate future clinical studies to evaluate the effects of CPC and CHX in reducing viral respiratory transmissions.

Human MARCH1, 2, and 8 block Ebola virus envelope glycoprotein cleavage via targeting furin P domain.

Membrane-associated RING-CH (MARCH) family proteins were recently reported to inhibit viral replication through multiple modes. Previous work showed that human MARCH8 blocked Ebola virus (EBOV) glycoprotein (GP) maturation. Our study here demonstrates that human MARCH1 and MARCH2 share a similar pattern to MARCH8 in restricting EBOV GP-pseudotyped viral infection. Human MARCH1 and MARCH2 retain EBOV GP at the trans-Golgi network, reduce its cell surface display, and impair EBOV GP-pseudotyped virions infectivity. Furthermore, we uncover that the host proprotein convertasefurin could interact with human MARCH1/2 and EBOV GP intracellularly. Importantly, the furin P domain is verified to be recognized by MARCH1/2/8, which is critical for their blocking activities. Besides, bovine MARCH2 and murine MARCH1 also impair EBOV GP proteolytic processing. Altogether, our findings confirm that MARCH1/2 proteins of different mammalian origins showed a relatively conserved feature in blocking EBOV GP cleavage, which could provide clues for subsequent MARCHs antiviral studies and may facilitate the development of novel strategies to antagonize enveloped virus infection.

Nanoparticle induced fusion of lipid membranes.

Membrane fusion is crucial for infection of enveloped viruses, cellular transport, and drug delivery via liposomes. Nanoparticles can serve as fusogenic agents facilitating such membrane fusion for direct transmembrane transport. However, the underlying mechanisms of nanoparticle-induced fusion and the ideal properties of such nanoparticles remain largely unknown. Here, we used molecular dynamics simulations to investigate the efficacy of spheroidal nanoparticles with different size, prolateness, and ligand interaction strengths to enhance fusion between vesicles. By systematically varying nanoparticle properties, we identified how each parameter affects the fusion process and determined the optimal parameter range that promotes fusion. These findings provide valuable insights for the design and optimization of fusogenic nanoparticles with potential biotechnological and biomedical applications.

Insights into the function of ESCRT and its role in enveloped virus infection.

The endosomal sorting complex required for transport (ESCRT) is an essential molecular machinery in eukaryotic cells that facilitates the invagination of endosomal membranes, leading to the formation of multivesicular bodies (MVBs). It participates in various cellular processes, including lipid bilayer remodeling, cytoplasmic separation, autophagy, membrane fission and re-modeling, plasma membrane repair, as well as the invasion, budding, and release of certain enveloped viruses. The ESCRT complex consists of five complexes, ESCRT-0 to ESCRT-III and VPS4, along with several accessory proteins. ESCRT-0 to ESCRT-II form soluble complexes that shuttle between the cytoplasm and membranes, mainly responsible for recruiting and transporting membrane proteins and viral particles, as well as recruiting ESCRT-III for membrane neck scission. ESCRT-III, a soluble monomer, directly participates in vesicle scission and release, while VPS4 hydrolyzes ATP to provide energy for ESCRT-III complex disassembly, enabling recycling. Studies have confirmed the hijacking of ESCRT complexes by enveloped viruses to facilitate their entry, replication, and budding. Recent research has focused on the interaction between various components of the ESCRT complex and different viruses. In this review, we discuss how different viruses hijack specific ESCRT regulatory proteins to impact the viral life cycle, aiming to explore commonalities in the interaction between viruses and the ESCRT system.

Design of a bifunctional pan-sarbecovirus entry inhibitor targeting the cell receptor and viral fusion protein.

Development of highly effective antivirals that are robust to viral evolution is a practical strategy for combating the continuously evolved severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Inspired by viral multistep entry process, we here focus on developing a bispecific SARS-CoV-2 entry inhibitor, which acts on the cell receptor angiotensin converting enzyme 2 (ACE2) and viral S2 fusion protein. First, we identified a panel of diverse spike (S) receptor-binding domains (RBDs) and found that the RBD derived from Guangdong pangolin coronavirus (PCoV-GD) possessed the most potent antiviral potency. Next, we created a bispecific inhibitor termed RBD-IPB01 by genetically linking a peptide fusion inhibitor IPB01 to the C-terminal of PCoV-GD RBD, which exhibited greatly increased antiviral potency via cell membrane ACE2 anchoring. Promisingly, RBD-IPB01 had a uniformly bifunctional inhibition on divergent pseudo- and authentic SARS-CoV-2 variants, including multiple Omicron subvariants. RBD-IPB01 also showed consistently cross-inhibition of other sarbecoviruses, including SARS-CoV, PCoV-GD, and Guangxi pangolin coronavirus (PCoV-GX). RBD-IPB01 displayed low cytotoxicity, high trypsin resistance, and favorable metabolic stability. Combined, our studies have provided a tantalizing insight into the design of broad-spectrum and potent antiviral agent. IMPORTANCE Ongoing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) evolution and spillover potential of a wide variety of sarbecovirus lineages indicate the importance of developing highly effective antivirals with broad capability. By directing host angiotensin converting enzyme 2 receptor and viral S2 fusion protein, we have created a dual-targeted virus entry inhibitor with high antiviral potency and breadth. The inhibitor receptor-binding domain (RBD)-IPB01 with the Guangdong pangolin coronavirus (PCoV-GD) spike RBD and a fusion inhibitor IPB01 displays bifunctional cross-inhibitions on pseudo- and authentic SARS-CoV-2 variants including Omicron, as well as on the sarbecoviruses SARS-CoV, PCoV-GD, and Guangxi pangolin coronavirus. RBD-IPB01 also efficiently inhibits diverse SARS-CoV-2 infection of human Calu-3 cells and blocks viral S-mediated cell-cell fusion with a dual function. Thus, the creation of such a bifunctional inhibitor with pan-sarbecovirus neutralizing capability has not only provided a potential weapon to combat future SARS-CoV-2 variants or yet-to-emerge zoonotic sarbecovirus, but also verified a viable strategy for the designing of antivirals against infection of other enveloped viruses.

Exosome-Autophagy Crosstalk in Enveloped Virus Infection.

Exosomes, which are extracellular vesicles (EVs) predominantly present in bodily fluids, participate in various physiological processes. Autophagy, an intracellular degradation mechanism, eliminates proteins and damaged organelles by forming double-membrane autophagosomes. These autophagosomes subsequently merge with lysosomes for target degradation. The interaction between autophagy and endosomal/exosomal pathways can occur at different stages, exerting significant influences on normal physiology and human diseases. The interplay between exosomes and the autophagy pathway is intricate. Exosomes exhibit a cytoprotective role by inducing intracellular autophagy, while autophagy modulates the biogenesis and degradation of exosomes. Research indicates that exosomes and autophagy contribute to the infection process of numerous enveloped viruses. Enveloped viruses, comprising viral nucleic acid, proteins, or virions, can be encapsulated within exosomes and transferred between cells via exosomal transport. Consequently, exosomes play a crucial role in the infection of certain viral diseases. This review presents recent findings on the interplay between exosomes and autophagy, as well as their implications in the infection of enveloped viruses, thereby offering valuable insights into the pathogenesis and vaccine research of enveloped virus infection.

Cetylpyridinium Chloride-Containing Mouthwashes Show Virucidal Activity against Herpes Simplex Virus Type 1.

The oral cavity is particularly susceptible to viral infections that are self-recovering in most cases. However, complications may appear in severe cases and/or immunocompromised subjects. Cetylpyridinium chloride (CPC)-containing mouthwashes are able to decrease the infectivity of the SARS-CoV-2 virus by disrupting the integrity of the viral envelope. Here, we show that CPC, as the active ingredient contained in commercialized, exerts significant antiviral activity against enveloped viruses, such as HSV-1, but not against non-enveloped viruses, such as HPV. CPC-containing mouthwashes have been used as antiseptics for decades, and thus, they can represent a cost-effective measure to limit infection and spread of enveloped viruses infecting the oral cavity, aiding in reducing viral transmission.

Cyclosporines Antagonize the Antiviral Activity of IFITMProteins by Redistributing Them toward the Golgi Apparatus.

Interferon-induced transmembrane proteins (IFITMs) block the fusion of diverse enveloped viruses, likely through increasing the cell membrane's rigidity. Previous studies have reported that the antiviral activity of the IFITM family member, IFITM3, is antagonized by cell pretreatment with rapamycin derivatives and cyclosporines A and H (CsA and CsH) that promote the degradation of IFITM3. Here, we show that CsA and CsH potently enhance virus fusion with IFITM1- and IFITM3-expressing cells by inducing their rapid relocalization from the plasma membrane and endosomes, respectively, towards the Golgi. This relocalization is not associated with a significant degradation of IFITMs. Although prolonged exposure to CsA induces IFITM3 degradation in cells expressing low endogenous levels of this protein, its levels remain largely unchanged in interferon-treated cells or cells ectopically expressing IFITM3. Importantly, the CsA-mediated redistribution of IFITMs to the Golgi occurs on a much shorter time scale than degradation and thus likely represents the primary mechanism of enhancement of virus entry. We further show that rapamycin also induces IFITM relocalization toward the Golgi, albeit less efficiently than cyclosporines. Our findings highlight the importance of regulation of IFITM trafficking for its antiviral activity and reveal a novel mechanism of the cyclosporine-mediated modulation of cell susceptibility to enveloped virus infection.

Antiviral properties of trans-δ-viniferin derivatives against enveloped viruses

Over the last century, the number of epidemics caused by RNA viruses has increased and the current SARS-CoV-2 pandemic has taught us about the compelling need for ready-to-use broad-spectrum antivirals. In this scenario, natural products stand out as a major historical source of drugs. We analyzed the antiviral effect of 4 stilbene dimers [1 (trans-δ-viniferin); 2 (11’,13’-di-O-methyl-trans-δ-viniferin), 3 (11,13-di-O-methyl-trans-δ-viniferin); and 4 (11,13,11’,13’-tetra-O-methyl-trans-δ-viniferin)] obtained from plant substrates using chemoenzymatic synthesis against a panel of enveloped viruses. We report that compounds 2 and 3 display a broad-spectrum antiviral activity, being able to effectively inhibit several strains of Influenza Viruses (IV), SARS-CoV-2 Delta and, to some extent, Herpes Simplex Virus 2 (HSV-2). Interestingly, the mechanism of action differs for each virus. We observed both a direct virucidal and a cell-mediated effect against IV, with a high barrier to antiviral resistance; a restricted cell-mediated mechanism of action against SARS-CoV-2 Delta and a direct virustatic activity against HSV-2. Of note, while the effect was lost against IV in tissue culture models of human airway epithelia, the antiviral activity was confirmed in this relevant model for SARS-CoV-2 Delta. Our results suggest that stilbene dimer derivatives are good candidate models for the treatment of enveloped virus infections.

Human milk inhibits some enveloped virus infections, including SARS-CoV-2, in an intestinal model

Human milk inhibits some enveloped virus infections, including SARS-CoV-2, in an intestinal model

Human milk inhibits some enveloped virus infections, including SARS-CoV-2, in an intestinal model.

Human milk is important for antimicrobial defense in infants and has well demonstrated antiviral activity. We evaluated the protective ability of human milk against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in a human fetal intestinal cell culture model. We found that, in this model, human milk blocks SARS-CoV-2 replication, irrespective of the presence of SARS-CoV-2 spike-specific antibodies. Complete inhibition of both enveloped Middle East respiratory syndrome coronavirus and human respiratory syncytial virus infections was also observed, whereas no inhibition of non-enveloped enterovirus A71 infection was seen. Transcriptome analysis after 24 h of the intestinal monolayers treated with human milk showed large transcriptomic changes from human milk treatment, and subsequent analysis suggested that <i>ATP1A1</i> down-regulation by milk might be of importance. Inhibition of ATP1A1 blocked SARS-CoV-2 infection in our intestinal model, whereas no effect on EV-A71 infection was seen. Our data indicate that human milk has potent antiviral activity against particular (enveloped) viruses by potentially blocking the ATP1A1-mediated endocytic process.

Hydrodynamics of spike proteins dictate a transport-affinity competition for SARS-CoV-2 and other enveloped viruses

Many viruses, such as SARS-CoV-2 or Influenza, possess envelopes decorated with surface proteins (a.k.a. spikes). Depending on the virus type, a large variability is present in the surface-proteins number, morphology and reactivity, which remains generally unexplained. Since viruses’ transmissibility depends on features beyond their genetic sequence, new tools are required to discern the effects of spikes functionality, interaction, and morphology. Here, we postulate the relevance of hydrodynamic interactions in the viral infectivity of enveloped viruses and propose micro-rheological characterization as a platform for virus differentiation. To understand how the spikes affect virion mobility and infectivity, we investigate the diffusivity of spike-decorated structures using mesoscopic-hydrodynamic simulations. Furthermore, we explored the interplay between affinity and passive viral transport. Our results revealed that the diffusional mechanism of SARS-CoV-2 is strongly influenced by the size and distribution of its spikes. We propose and validate a universal mechanism to explain the link between optimal virion structure and maximal infectivity for many virus families.

Axl Mediates Resistance to Respiratory Syncytial Virus Infection Independent of Cell Attachment.

Respiratory syncytial virus (RSV) is a leading cause of severe lower respiratory tract infections in infants and young children. Axl, a TAM family receptor tyrosine kinase, has been demonstrated to be a receptor mediating enveloped virus infection. Here we show that Axl functions as a suppressor of antiviral response during RSV infection. Knockdown of Axl expression in human cells resulted in cell resistance to RSV infection, although the treatment did not significantly affect RSV binding or cell entry. Mice deficient in Axl showed resistance to RSV infection, including reduction in viral load and in pulmonary injury. Although T lymphocyte and macrophage infiltration was reduced, more IFN-γ-producing cells were present in BAL fluid in Axl-/- mice. Fewer alternatively activated alveolar macrophages were found in the lungs of Axl-/- mice. Axl-/- mouse embryonic fibroblasts and siRNA-treated human cells had more robust IFN-β and IFN-stimulated gene induction of antiviral genes. Furthermore, reexpression of Axl using adenovirus-mediated Axl delivery repressed IFN-stimulated gene induction in Axl-null mouse embryonic fibroblasts by RSV infection. The results suggest that Axl, independent of being a virus entry receptor of RSV infection, negatively regulates IFN signaling to modulate host antiviral response against RSV infection.

Sendai virus particles carrying target virus glycoproteins for antibody induction

Induction of antibodies targeting viral glycoproteins is a key for the development of a vaccine against enveloped virus infection. Glycoproteins on the virion exhibiting native multimer structure may be a good immunogen to present antibody epitopes, but it is often difficult to prepare immunogenic inactivated virions. Preparation of soluble glycoprotein multimers has been attempted, while virus-like particles carrying target glycoproteins can be a more immunogenic antigen. In the present study, a target glycoprotein-embedded Sendai virus (SeV) particle was developed for induction of anti-virus antibodies. We constructed a chimeric antigen, HIV-1 EnvF, consisting of HIV-1 Env ectodomain and SeV F transmembrane-cytoplasmic domain, which was shown to be efficiently incorporated into the SeV virion. EnvF was recognized by anti-HIV-1 broadly-neutralizing monoclonal antibodies (bnAbs) including 35O22 that targets an Env trimer-dependent epitope. Analysis revealed that HIV-1AD8 EnvF can mediate viral entry into the cells, which is inhibited by anti-HIV-1 bnAbs and HIV-1 entry inhibitors, suggesting that the EnvF exhibits an HIV-1 Env native-like functional structure to present bnAb epitopes. Immunization of mice with replication-defective SeVs expressing HIV EnvF and non-infectious SeV particles (NVP) carrying HIV EnvF efficiently induced anti-HIV Env antibodies. HTLV-1 EnvF also showed the potential to efficiently induce anti-HTLV-1 Env antibodies. These results indicate that SeV particles carrying EnvF can be a promising vaccine platform for induction of antibodies targeting enveloped virus glycoproteins.

Identification of endoplasmic-reticulum-associated proteins involved in Bombyx mori nucleopolyhedrovirus entry by RNA-seq analysis

Membrane fusion is a key step in enveloped virus infection, releasing the viral genome into the cytoplasm to initiate infection. Bombyx mori nucleopolyhedrovirus (BmNPV) is an enveloped DNA virus that mainly infects silkworms. Information about membrane fusion of BmNPV with host cells is still limited. In this study, BmN cells were pretreated with ??ammonium chloride??, and infection with BmNPV was allowed to occur naturally through endocytosis or artificially through low-pH-induced fusion with the plasma membrane, after which the cells were subjected to RNA-seq. The results indicated that a few endoplasmic reticulum-associated proteins (ERAPs) were among the common upregulated DEGs, including BiP, CRT, and HSP90, and this upregulation was confirmed by q-PCR. Knockdown of BiP, CRT, and HSP90 expression by siRNA resulted in significant inhibition of BmNPV infection. This study suggests that ERAPs may be involved in the BmNPV membrane fusion process during infection.

Echinacea as a Potential Force against Coronavirus Infections? A Mini-Review of Randomized Controlled Trials in Adults and Children.

Echinacea purpurea has been shown to broadly inhibit coronaviruses and SARS-CoV-2 in vitro. This review discusses the available clinical evidence from randomized, blinded and controlled human studies. Two RCTs capturing incidence of viral respiratory tract infections during Echinacea preventative treatment were identified including coronavirus infections. Incidence and/or viral loads were measured by RT-PCR and symptom severity was recorded. In a first study, Jawad et al. collected nasopharyngeal swabs from adults (N = 755) over 4 months of continuous prevention. Overall, 24 and 47 enveloped virus infections occurred, including 21 and 33 coronavirus detections (229E; HKU1; OC43) with Echinaforce® extract (2400 mg daily) and placebo, respectively (p = 0.0114). In a separate study, Ogal et al. administered the same extract (1200 mg) or control for 4 months to children (4–12 years) (N = 203). Echinacea reduced the incidence of enveloped virus infections from 47 to 29 (p = 0.0038) whereas 11 and 13 coronavirus detections (229E, OC43, NL63) were counted (p > 0.05). Respiratory symptoms during coronavirus infections were significantly lower with area-under-curve AUC = 75.8 (+/−50.24) versus 27.1 (+/−21.27) score points (p = 0.0036). Importantly, viral loads in nasal secretions were significantly reduced by 98.5% in the Echinacea group, with Ct-values 31.1 [95% CI 26.3; 35.9] versus 25.0 [95% CI 20.5; 29.5] in the control group (p = 0.0479). Results from clinical studies confirm the antiviral activity found for Echinacea in vitro, embracing enveloped respiratory pathogens and therefore coronaviruses as well. Substantiating results from a new, completed study seem to extrapolate these effects to the prevention of SARS-CoV-2 infections. As hypothesized, the established broad antiviral activity of Echinacea extract appears to be inclusive for SARS-CoV-2.

Phosphatidylserine receptors enhance SARS-CoV-2 infection.

Phosphatidylserine (PS) receptors enhance infection of many enveloped viruses through virion-associated PS binding that is termed apoptotic mimicry. Here we show that this broadly shared uptake mechanism is utilized by SARS-CoV-2 in cells that express low surface levels of ACE2. Expression of members of the TIM (TIM-1 and TIM-4) and TAM (AXL) families of PS receptors enhance SARS-CoV-2 binding to cells, facilitate internalization of fluorescently-labeled virions and increase ACE2-dependent infection of SARS-CoV-2; however, PS receptors alone did not mediate infection. We were unable to detect direct interactions of the PS receptor AXL with purified SARS-CoV-2 spike, contrary to a previous report. Instead, our studies indicate that the PS receptors interact with PS on the surface of SARS-CoV-2 virions. In support of this, we demonstrate that: 1) significant quantities of PS are located on the outer leaflet of SARS-CoV-2 virions, 2) PS liposomes, but not phosphatidylcholine liposomes, reduced entry of VSV/Spike pseudovirions and 3) an established mutant of TIM-1 which does not bind to PS is unable to facilitate entry of SARS-CoV-2. As AXL is an abundant PS receptor on a number of airway lines, we evaluated small molecule inhibitors of AXL signaling such as bemcentinib for their ability to inhibit SARS-CoV-2 infection. Bemcentinib robustly inhibited virus infection of Vero E6 cells as well as multiple human lung cell lines that expressed AXL. This inhibition correlated well with inhibitors that block endosomal acidification and cathepsin activity, consistent with AXL-mediated uptake of SARS-CoV-2 into the endosomal compartment. We extended our observations to the related betacoronavirus mouse hepatitis virus (MHV), showing that inhibition or ablation of AXL reduces MHV infection of murine cells. In total, our findings provide evidence that PS receptors facilitate infection of the pandemic coronavirus SARS-CoV-2 and suggest that inhibition of the PS receptor AXL has therapeutic potential against SARS-CoV-2.