The expression of DPP4 and ACE2 in enterocytes in the intestine is closely related to gut microbiome dysbiosis in COVID-19, but the specific mechanism is still unclear (Vuille-dit-Bille et al., 2015; Olivares et al., 2018; Posadas-Sánchez et al., 2021; Yu et al., 2021). Here, DPP4 is linked to COVID-19.