ISG15 and viral infectious disease: Recently, several studies have indicated that virus infection, especially PEDV infection, in epithelial cells stimulates the secretion of IFN, which triggered high levels of interferon-stimulated genes (ISGs), mainly OAS1 (encoding 2′-5’-Oligoadenylate Synthetase 1) and ISG15 (encoding interferon-stimulated gene 15) (Palma-Ocampo et al., 2015; Li et al., 2017, 2021).