MMP9 and COVID-19: Upregulated DEGs in the severe vs mild sample comparison included CD177, Neutrophil elastase (ELANE), Olfactomedin 4 (OLFM4), Myeloperoxidase (MPO), Resistin (RETN), and matrix metalloproteinases MMP8 and MMP9. Whereas the type I IFN-response genes, such as IFI27 or IFITM3, were not differentially regulated in severe vs mild samples, expression of immunosuppression-associated factor Arginase (ARG1) was more pronounced in severe COVID-19 patients (Fig. 1g, Additional file 3: Table S2).