Antibody to carbonic anhydrase II is present in primary biliary cirrhosis (PBC) irrespective of antimitochondrial antibody status

Antibody to carbonic anhydrase II, an enzyme abundantly present in biliary epithelium, has been proposed as a diagnostic marker for antimitochondrial antibody-negative PBC. In this study we determine its prevalence and clinic al significance in a large series of patients with antimitochondrial antibo dy-positive and -negative PBC. Reactivity to carbonic anhydrase TI was soug ht by Western immunoblotting in sera from 215 consecutive patients with PBC (26 antimitochondrial antibody-negative), 13 with autoimmune hepatitis, 25 with primary Sjogren's syndrome (pSS), 12 with systemic sclerosis, 19 with systemic lupus erythematosus and 73 healthy subjects. The prevalence of an tibody to carbonic anhydrase IT (titre 1:100) in PBC was 8%. No specific re activity to carbonic anhydrase II was found in antimitochondrial antibody-n egative PBC (7% versus 8% in antimitochondrial antibody-positive PBC). Asci tes (P =0.006) and Sjogren's syndrome (SS) (P = 0.022) in PBC were signific antly associated with presence of the antibody. In patients with SS associa ted with PBC, the prevalence (19%) was similar to that observed in pSS (16% ). At a serum dilution of 1:40, the prevalence of positive sera in PBC rose to 27% but disease specificity was reduced. Our findings in a large popula tion of PBC patients rule out a relation between presence of antibody to ca rbonic anhydrase II and lack of antimitochondrial antibody. The higher prev alence of ascites found in positive patients warrants further evaluation.