For example, multiple immune and inflammation-related genes, such as C5AR1, CD55, CSF3R, CXCL8, FPR1, TLR1, HIF1A, IFNAR1A, IRF1, and NFKB1A, were significantly upregulated in the blood immune cells of COVID-19 patients (Figs. 5I and S6A, C), which was similar to the lungs (Fig. 3D, E). Here, C5AR1 is linked to COVID-19.