PROS1 and COVID-19: Manifestations in COVID-19 patients mainly involve the respiratory system.29 Nevertheless, researchers also found susceptibility of intestinal tissue to SARS-CoV-2 infection and frequently detected SARS-CoV-2 RNA from stool samples of COVID-19 patients, indicating possible “fecal-oral” transmission of SARS-CoV-2.30 Consistently, we herein found SARS-CoV-2 S protein to exhibit highly fusogenic activity on Calu-3 cells derived from lung tissue and on Caco2 cells derived from intestinal tissue.