We thank Dr. J. Bara (INSERM, Villejuif, France) for providing the anti-H and anti-A mAbs and Dr. A. Blancher for helpful discussions.

Conflict of interest statement
None declared. Abbreviations
ACE2 angiotensin-converting enzyme 2
CHO chinese hamster ovary
CoV coronavirus
EGFP enhanced green fluorescent protein
HBGA histo-blood group antigen; mAb, monoclonal antibody
PBS phosphate buffered saline
RBD receptor binding domain
RBM receptor binding motif
S protein spike protein
SARS-CoV severe acute respiratory syndrome coronavirus
S-EGFP S protein-EGFP fusion construction