Interestingly, 11 proteins were altered between the mild and severe COVID-19 patients (Fig. 1, A and C): hepatocyte growth factor, pleiotrophin, the chemokines CXC chemokine ligand 12, CXC chemokine ligand 13, and chemokine ligand 23 (also known as macrophage inflammatory protein 3), monocyte chemotactic protein 3 (also known as chemokine ligand 7), IL-12, tumor necrosis factor–like weak inducer of apoptosis, vascular endothelial growth factor A, angiopoietin 2, and Fas ligand (adjusted p < 0.05). Here, FASLG is linked to COVID-19.