C. Each photo depicts an immunofluorescence assay using either no primary antibody, or the primary antibody indicated below it (Myc, 2B2, 1A9, 4B12, or 1G10). Immunofluorescence analysis was performed on empty vector-transfected COS-7 cells (top photos) and cells expressing full-length SARS-CoV-2 S protein (bottom photos). The indicated primary antibodies were used followed by Alexa Fluor 488-conjugated secondary antibody (green). Cell nuclei were counterstained with DAPI (blue). Scale bar = 50 µm.