Naveen et al. predicted the molecular model of SARS-Cov-2 and found that the S1 domain of SARS-Cov-2 spike glycoprotein might interact with DPP4 of host cells directly, which implies the effects of DPP4 in COVID-19 (Vankadari and Wilce, 2020). Here, DPP4 is linked to COVID-19.