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 γ-glutamyl transpeptidase (γ-GTP). However, among the 56 patients whose serum antigen TS135 and γ-GTP levels could be measured simultaneously, 5 were antigen TS135-positive and γ-GTP-negative (8.9%) and 6 were antigen TS135-negative and γ-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 γ-GTP in liver diseases, but that TS135 may also have a unique significance, different from that of γ-GTP, as a liver function test.