PROS1 and viral infectious disease: For instance, in vitro experiments have shown that the fractions of fucoidans RPI-27 (100 kDa) and RPI-28 (~12 kDa) from the seaweed Saccharina japonica bind specifically and effectively to the SARS-CoV-2 S-protein and, probably, can prevent binding S-protein to heparan sulfate on host cells and thus suppress viral infection [25].