A. Each photo depicts a western blot using the primary antibody indicated below it (2B2, 1A9, 4B12, or 1G10). Empty vector-transfected 293FT cell products are on the lanes labelled as ‘Vec’, while products of 293FT cells expressing full-length SARS-CoV-2 S protein are on the lanes labelled ‘SARS-CoV-2 S’. Primary antibodies were labelled with horseradish peroxidase-conjugated secondary antibodies. A ladder indicative of the molecular weights in kD of the proteins relative to their vertical position on the blots, is indicated on the left of the panel.