CSF1 and COVID-19: Although above in vitro result suggested an inconsistence between pGM-CSF mRNA and protein level in PRRSV infected PAMs, it is necessary to figure out if PRRSV infection induced pGM-CSF in vivo whereas previous reports strongly suggested that pGM-CSF demonstrated dual roles in virus-induced pneumonia as observed in influenza A virus infection and COVID-19 patients (39, 42, 43).