Further studies showed that Paneth cell-specific ablation (Defa6-Cre) of Xbp1 led to a similar phenotype of spontaneous enteritis as that observed in mice with total IEC deletion (Villin-Cre) of Xbp1, implying that Paneth cell-specific UPR plays an essential role in mucosal homeostasis in murine ileum [26]. Here, XBP1 is linked to enteritis.