CDKN1A and primary biliary cholangitis: In addition, the up‐regulation of WAF1 and p53 related to biliary apoptosis is found in cholangiocytes of PBC,4 and significantly greater apoptosis has been demonstrated in cholangiocytes of PBC patients than of other chronic cholestatic diseases, even when controlling to similar degrees of inflammation.4, 20 Enhanced apoptosis has been implicated in several autoimmune diseases.