ABSTRACT
Different serological assays were rapidly generated to study humoral responses against the SARS-CoV-2 Spike glycoprotein. Due to the intrinsic difficulty of working with SARS-CoV-2 authentic virus, most serological assays use recombinant forms of the Spike glycoprotein or its receptor binding domain (RBD). Cell-based assays expressing different forms of the Spike, as well as pseudoviral assays, are also widely used. To evaluate whether these assays recapitulate findings generated when the Spike is expressed in its physiological context (at the surface of the infected primary cells), we developed an intracellular staining against the SARS-CoV-2 nucleocapsid (N) to distinguish infected from uninfected cells. Human airway epithelial cells (pAECs) were infected with authentic SARS-CoV-2 D614G or Alpha variants. We observed robust cell-surface expression of the SARS-CoV-2 Spike at the surface of the infected pAECs using the conformational-independent anti-S2 CV3-25 antibody. The infected cells were also readily recognized by plasma from convalescent and vaccinated individuals and correlated with several serological assays. This suggests that the antigenicity of the Spike present at the surface of the infected primary cells is maintained in serological assays involving expression of the native full-length Spike.
Subject(s)
Cell Membrane/metabolism , Epithelial Cells/metabolism , Spike Glycoprotein, Coronavirus/metabolism , Antibodies, Viral/immunology , Antibody-Dependent Cell Cytotoxicity , Bronchioles/cytology , Cells, Cultured , Coronavirus Nucleocapsid Proteins/metabolism , Epithelial Cells/virology , HEK293 Cells , Humans , Neutralization Tests , Phosphoproteins/metabolism , SARS-CoV-2/immunology , SARS-CoV-2/metabolism , Spike Glycoprotein, Coronavirus/genetics , Spike Glycoprotein, Coronavirus/immunologySubject(s)
Anti-Inflammatory Agents/pharmacology , Azithromycin/pharmacology , Coronavirus Infections/drug therapy , Interleukin-1beta/metabolism , Membrane Proteins/metabolism , Nasal Mucosa/drug effects , Pneumonia, Viral/drug therapy , Serine Endopeptidases/metabolism , Serine Proteases/metabolism , Betacoronavirus/pathogenicity , COVID-19 , Cells, Cultured , Chronic Disease , Coronavirus Infections/immunology , Coronavirus Infections/metabolism , Coronavirus Infections/virology , Down-Regulation , Host-Pathogen Interactions , Humans , Interleukin-1beta/genetics , Male , Membrane Proteins/genetics , Nasal Mucosa/immunology , Nasal Mucosa/metabolism , Pandemics , Pilot Projects , Pneumonia, Viral/immunology , Pneumonia, Viral/metabolism , Pneumonia, Viral/virology , Rhinitis/drug therapy , Rhinitis/immunology , Rhinitis/metabolism , SARS-CoV-2 , Serine Endopeptidases/genetics , Serine Proteases/genetics , Signal Transduction , Sinusitis/drug therapy , Sinusitis/immunology , Sinusitis/metabolism , COVID-19 Drug TreatmentABSTRACT
The seasonal nature of outbreaks of respiratory viral infections with increased transmission during low temperatures has been well established. Accordingly, temperature has been suggested to play a role on the viability and transmissibility of SARS-CoV-2, the virus responsible for the COVID-19 pandemic. The receptor-binding domain (RBD) of the Spike glycoprotein is known to bind to its host receptor angiotensin-converting enzyme 2 (ACE2) to initiate viral fusion. Using biochemical, biophysical, and functional assays to dissect the effect of temperature on the receptor-Spike interaction, we observed a significant and stepwise increase in RBD-ACE2 affinity at low temperatures, resulting in slower dissociation kinetics. This translated into enhanced interaction of the full Spike glycoprotein with the ACE2 receptor and higher viral attachment at low temperatures. Interestingly, the RBD N501Y mutation, present in emerging variants of concern (VOCs) that are fueling the pandemic worldwide (including the B.1.1.7 (α) lineage), bypassed this requirement. This data suggests that the acquisition of N501Y reflects an adaptation to warmer climates, a hypothesis that remains to be tested.