SARS-CoV-1 and SARS-CoV-2 S Protein Binding Assay

ADCP was measured as previously described^{42 (link)}. Briefly, SARS-CoV-1 and SARS-CoV-2 S proteins were biotinylated according to manufacturer’s instructions (ThermoFisher Scientific), at a biotin to protein ratio of 50, and then incubated with yellow-green streptavidin-fluorescent beads (Molecular Probes) for 2 h at 37 °C. 10 ul of a 100-fold dilution of beads-protein mixture was incubated for 2 h at 37 °C with 100ul of VNAR (1 ug/ml, 0.2 ug/ml, and 0.04 ug/ml), before addition of THP-1 cells (25,000 cells per well; Millipore Sigma, Burlington, MA, USA). After 19 h incubation at 37 °C, the cells were fixed with 4% formaldehyde solution (Tousimis, Rockville, MD, USA) and fluorescence was evaluated on a LSRII (BD Biosciences). The phagocytic score was calculated by multiplying the percentage of bead-positive cells by the geometric mean fluorescence intensity (MFI) of the bead-positive cells and dividing by 10,000.