PCSK5 and viral infectious disease: In order to reach the full potential of those mAb that target HA cleavage site, one may need an inhibition on those membrane bound proteases, like furin, proprotein convertase 5/6, or type II transmembrane serine proteases, like TMPRSS2, 4, HAT [8,9], so that these mAb can recognize its intact uncut epitope and prevent subsequent viral infection.