JAG1 and primary biliary cholangitis: Surprisingly, perhaps, NOTCH1 protein expression was totally undetectable in the bile ducts of PBC livers compared to low-level expression in unaffected samples (Nijjar et al., 2001), implying that NOTCH2 is the principal receptor for which expression is altered in PBC, and its cognate ligands are most likely those of the Jagged family (JAG1 and JAG2).