MMP9 and COVID-19: Furthermore, 15 genes (IL1B, CCR3, CXCL8, IL12B, TNF, CYSLTR2, FGF1, IL6, BMP7, MMP9, MUC5B, SFTPC, MECP2, TGFA, HMOX1) were up-regulated in the “lung fibrosis” pathways in the low viral load compared to the high viral load COVID-19 samples (Table 4 and Figure S8A).