Are antibodies to carbonic anhydrase II specific for anti-mitochondrial antibody-negative primary biliary cirrhosis?

Antibodies to carbonic anhydrase II (CAII) have been reported to be specific to anti-mitochondrial antibody (AMA)-negative primary biliary cirrhosis (PBC). We examined whether antibodies to CAII are specific for AMA-negative PBC or a nonspecific response in autoimmune liver disease. Antibody assays to CAII, by western immunoblot (dilution 1:200), were performed on sera from 16 AMA-negative PBC patients, 21 AMA-positive PBC patients, 21 autoimmune hepatitis type 1 (AIH) patients, and 18 alcoholic liver disease (ALD) patients. CAII antibody activity was found in 8 of 16 (50%) of the AMA-negative PBC patients, 9 of 21 (43%) of the AMA-positive PBC group, 10 of 21 (48%) of the AIH group, and in 3 of 18 (17%) of the ALD control group. There was no difference in the prevalence of CAII antibody reactivity between the AMA-negative PBC, AMA-positive PBC, and AIH groups. In conclusion, we determined that CAII antibodies are detected with equal frequency in AMA-positive PBC and AIH. Given that CAII antibodies have been reported in other nonhepatic autoimmune diseases, we conclude that CAII antibodies are likely a nonspecific marker of autoimmunity rather than specific for AMA-negative PBC.