ACKR1 and COVID-19: Erythrocyte Duffy antigen, chemokine receptor (DARC), can bind chemokines and play an important role in anti-tumor and inflammatory immunity (21); Red blood cells mediate plasmodium and SARS-CoV-2, norovirus, dengue fever and other viruses through glycoprotein on the surface (22–25); Erythrocyte surface complement receptor 1 (CR1) is also involved in the immune regulation of patients with mycoplasma and COVID-19 (26, 27).