The lipid envelope of SARS-CoV2 is an essential component of the virus, however its molecular composition is unknown. Addressing this knowledge gap could support the design of anti-viral agents, and further understanding of viral interaction with extracellular host proteins, infectivity, pathogenicity, and innate immune system clearance. Lipidomics analysis of SARS-CoV2 particles generated from Vero or A549 cells revealed that the virus envelope comprised mainly of phospholipids (PL), primarily phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylinositol (PI), with very little cholesterol, sphingolipids or other lipids, indicating significant differences from host membranes. Unlike healthy cellular membranes, procoagulant aminoPL (aPL), specifically PE and phosphatidylserine (PS), were present on the external side at levels far exceeding those seen on activated platelets. As a result, purified virions directly promoted coagulation. To investigate whether these differences enabled the viral envelope to be selectively targeted at relevant sites in vivo, we tested whether non-toxic oral rinses containing lipid disrupting chemicals could reduce viral infectivity. Products containing PL-disrupting surfactant solutions (cetylpyridinium chloride (CPC) or ethyl lauroyl arginate) met EN14476 virucidal standards in vitro, however products containing essential oils, PVP-I, or Chlorhexidine did not, nor did rinses containing components that altered the critical micelle concentration of CPC. This result was recapitulated in vivo, where a 30-second oral rinse with CPC-mouthwash eliminated live virus in the oral cavity of COVID19 patients for at least 1hr, while PVP-Iodine and saline mouthwashes were ineffective. Thus, the SARS-CoV2 lipid envelope is distinct from the host plasma membrane which may enable design of selective anti-viral approaches, it exposes PE and PS which may influence thrombosis, pathogenicity, and inflammation, and can be selectively targeted in vivo by specific oral rinses.
Subject(s)Inflammation , Thrombosis , COVID-19
Cell autonomous antiviral defenses can inhibit the replication of viruses and reduce transmission and disease severity. To better understand the antiviral response to SARS-CoV-2, we used interferon-stimulated gene (ISG) expression screening to reveal that OAS1, through RNase L, potently inhibits SARS-CoV-2. We show that while some people can express a prenylated OAS1 variant, that is membrane-associated and blocks SARS-CoV-2 infection, other people express a cytosolic, nonprenylated OAS1 variant which does not detect SARS-CoV-2 (determined by the splice-acceptor SNP Rs10774671). Alleles encoding nonprenylated OAS1 predominate except in people of African descent. Importantly, in hospitalized patients, expression of prenylated OAS1 was associated with protection from severe COVID-19, suggesting this antiviral defense is a major component of a protective antiviral response. Remarkably, approximately 55 million years ago, retrotransposition ablated the OAS1 prenylation signal in horseshoe bats (the presumed source of SARS-CoV-2). Thus, SARS-CoV-2 never had to adapt to evade this defense. As prenylated OAS1 is widespread in animals, the billions of people that lack a prenylated OAS1 could make humans particularly vulnerable to the spillover of coronaviruses from horseshoe bats.
The outcome of infection is dependent on the ability of viruses to manipulate the infected cell to evade immunity, and the ability of the immune response to overcome this evasion. Understanding this process is key to understanding pathogenesis, genetic risk factors, and both natural and vaccine-induced immunity. SARS-CoV-2 antagonises the innate interferon response, but whether it manipulates innate cellular immunity is unclear. An unbiased proteomic analysis determined how cell surface protein expression is altered on SARS-CoV-2-infected lung epithelial cells, showing downregulation of activating NK ligands B7-H6, MICA, ULBP2, and Nectin1, with minimal effects on MHC-I. This correlated with a reduction in NK cell activation, identifying a novel mechanism by which SARS-CoV2 antagonises innate immunity. Later in the disease process, strong antibody-dependent NK cell activation (ADNKA) developed. These responses were sustained for at least 6 months in most patients, and led to high levels of pro-inflammatory cytokine production. Depletion of spike-specific antibodies confirmed their dominant role in neutralisation, but these antibodies played only a minor role in ADNKA compared to antibodies to other proteins, including ORF3a, Membrane, and Nucleocapsid. In contrast, ADNKA induced following vaccination was focussed solely on spike, was weaker than ADNKA following natural infection, and was not boosted by the second dose. These insights have important implications for understanding disease progression, vaccine efficacy, and vaccine design.
The ability of widely-available mouthwashes to inactivate SARS-CoV-2 in vitro was tested using a protocol capable of detecting a 5-log10 reduction in infectivity, under conditions mimicking the naso/oropharynx. During a 30 second exposure, two rinses containing cetylpyridinium chloride and a third with ethanol/ethyl lauroyl arginate eliminated live virus to EN14476 standards (>4-log10 reduction), while others with ethanol/essential oils and povidone-iodine (PVP-I) eliminated virus by 2-3-log10. Chlorhexidine or ethanol alone had little or no ability to inactivate virus in this assay. Studies are warranted to determine whether these formulations can inactivate virus in the human oropharynx in vivo, and whether this might impact transmission.