Measurement of circulating biliary glycoprotein (CD66a) in liver diseases.
PURPOSE: Biliary glycoprotein (BGP), a member of the carcinoembryonic antigen (CEA) gene family, is produced by hepatocytes, and is suggested to function as a cell adhesion molecule, mouse hepatitis virus receptor, and tumor suppressor. Our aim was to establish an enzyme immunoassay for circulating BGP and to study its significance in liver diseases. METHODS: For enzyme immunoassay, a monoclonal antibody (mAb), TS135, which recognizes BGP was used as a catcher, and biotin-labeled polyclonal anti-CEA antibodies were used as a tracer. Seventy-six serum specimens obtained from patients with various liver diseases were submitted to the assay. RESULTS: The incidence of positivity for antigen TS135 in the serum samples of the 76 patients was 57.9%. The most significant correlation among conventional liver function tests was found between antigen TS135 and gamma-glutamyl transpeptidase (gamma-GTP). However, among the 56 patients whose serum antigen TS135 and gamma-GTP levels could be measured simultaneously, 5 were antigen TS135-positive and gamma-GTP-negative (8.9%) and 6 were antigen TS135-negative and gamma-GTP-positive (10.7%). The increased serum level of antigen TS135 in 6 cholangiocellular carcinoma (CCC) patients led us to the immunohistochemical study of CCC, in which 8 of the 8 tissue specimens tested were positive for mAb TS135, indicating the production of the antigen from CCCs. CONCLUSIONS: This preliminary study suggests that the circulating antigen TS135 level correlates with gamma-GTP in liver diseases, but that TS135 may also have a unique significance, different from that of gamma-GTP, as a liver function test.