SPP1 and COVID-19: Tsukui et al. (9) identified a subpopulation of pFB characterized by the expression of COL1A1 and COLA31 in IPF samples (two of the genes highly overexpressed in our NanoString analysis in COVID-19 samples) and other ECM genes such as SPP1 (also overexpressed in our COVID-19 samples) or TNC (not included in our panel).