ISG15 and Abnormal intestine morphology: Mechanistically, HDCA has dual protective effects: (1) it activates the TGR5-cAMP axis, leading to the induction of IFN-β and subsequent upregulation of the potent antiviral effector ISG15, thereby directly inhibiting viral replication; (2) it suppresses NF-κB-mediated inflammatory signalling, mitigating PEDV-induced enteropathy (Figure 9a).