Among the 14 mitochondrion-related genes showing upregulation in the blood samples, IFI27 showed significantly upregulated expression in the infiltrating macrophage subsets of patients with COVID-19 (Figures 2C, 5E), suggesting that IFI27 is involved in the blood immune response and in the lung–blood interaction process after viral infection. Here, IFI27 is linked to COVID-19.