Anti‐phosphoenolpyruvate carboxykinase 2 antibody in patients with autoimmune hepatitis

Aim To identify a novel autoantibody specific to autoimmune hepatitis ( AIH ) and to evaluate its clinical significance. Methods Non‐nuclear component protein extracted from normal human liver cell C yroh NH pes cultures that reacted with sera from AIH patients on a western blot was identified as an antigenic protein and subjected to N ‐terminal amino acid analysis to identify phosphoenolpyruvate carboxykinase 2 ( PCK 2). Enzyme‐linked immunoassay ( ELISA ) for anti‐ PCK 2 antibody was conducted on sera samples from patients with AIH ( n  = 42), primary biliary cirrhosis ( PBC ; n  = 48), non‐alcoholic steatohepatitis ( NASH , n  = 41), chronic hepatitis C ( CHC , n  = 20), drug‐induced liver injury ( DILI , n  = 10), systemic lupus erythematosus ( SLE , n  = 16) and on sera samples from healthy volunteers ( n  = 30). Clinical findings were compared for AIH patients testing positive and negative for anti‐ PCK 2 antibody. Results ELISA findings showed that mean anti‐ PCK 2 antibody titer in sera from AIH patients was significantly higher than in PBC , NASH , CHC , DILI and SLE patients, as well as in healthy volunteers. Anti‐ PCK 2 antibody was present in 50.0% (21/42) of AIH , 14.6% (7/48) of PBC , 4.9% (2/41) of NASH , and 10.0% (2/20) of CHC patients, 0% (0/10) of DILI , 12.5% (2/16) of SLE and in 3.3% (1/30) of healthy volunteers. The sensitivity, specificity and accuracy of using the detection of anti‐ PCK 2 antibody in diagnosing AIH were 50.0%, 91.5% and 83.1%, respectively. None of the AIH patients positive for anti‐ PCK 2 antibody showed characteristic clinical features. Conclusion Although further investigations into the clinical usefulness are necessary, anti‐ PCK 2 may have potential as a diagnostic marker for AIH .