Of the tested 51 plasma proteins, the levels of 25 proteins: CCL2/18/19/20, CD163, C5a, CXCL10, G-CSF, GM-CSF, IL-6/8/10/15/23, LCN2, M-CSF, MPO, β-NGF, S100A9, SCGF, TF, TFPI, TGF-α, TNF and TREM-1, were significantly elevated in the plasma from patients with COVID-19 compared with that from healthy donors (Fig. 1). Here, MPO is linked to COVID-19.