Human aminopeptidase N (APN) is involved in the infection by HCoV-229E; 9-O-acetylated sialic acid (9-O-Ac-Sia) receptor for HCoV-OC43 and HCoV-HKU1; angiotensin-converting enzyme 2 (ACE2) for HCoV-NL63, SARS-CoV-1, and SARS-CoV-2; dipeptidyl peptidase 4 (DPP4) for MERS-CoV [23,24]. This evidence concerns the gene DPP4 and infection.