To determine whether bilirubin is activating MRGPRA1 to stimulate itch in cholestasis, we induced cholestasis in a mouse that lacks the biosynthetic enzyme for bilirubin, biliverdin reductase (BVR KO) (Kutty and Maines, 1981) (Figure 1E, Figure 5—figure supplement 3A). Here, BLVRA is linked to cholestasis.