DPP4 and infection: While receptors such as angiotensin-converting enzyme 2 (ACE2; used by severe acute respiratory syndrome coronaviruses SARS-CoV and SARS-CoV-2) and dipeptidyl peptidase-4 (DPP4; used by Middle East Respiratory syndrome coronavirus MERS-CoV) have been extensively studied, the tissue distribution and conservation of APN, a key receptor mediating infections by alphacoronaviruses (α-CoVs) and deltacoronaviruses (δ-CoVs), remain less well-characterized [5, 14].