We also observed significantly higher TNF-α and IL-6 in the infected KO mice compared to the infected K18 and hSP-A mice (Figures 6H, I); indeed, there was no change in the level of IL-6 in infected 6A2 relative to Sham, supporting the role of elevated IL-6 as a major contributor to severe disease observed in COVID-19 patients (27, 28). Here, TNF is linked to COVID-19.