The tumor-associated antigen, RCAS1, can be expressed in immune-mediated diseases as well as in carcinomas of biliary tract

Background/Aims: RCAS1, which is recognized by the specific antibody 22-1-1, was first identified as a tumor-associated antigen in gynecological carcinomas. RCAS1 is the ligand of a putative receptor present on lymphocytes, the expression of which is enhanced by lymphocyte activation. RCAS1 inhibits the growth of receptor-bearing cells and induces apoptotic death. Here we examined RCAS1 expression in biliary diseases. Methods: RCAS1 expression was immunohistochemically examined on tissue samples. Apoptotic death was analyzed by DNA fragmentation detection method. RCAS1 production by cell lines was investigated by flow cytometry, enzyme-linked immunosorbent assay, and reverse transcription–polymerase chain reaction. Results: All cholangiocarcinoma cell lines examined clearly expressed RCAS1 at both the protein and RNA level. Immunohistochemically, RCAS1 was expressed in a high percentage of biliary adenocarcinomas (85.9% of intrahepatic cholangiocarcinomas, 96.4% of extrahepatic cholangiocarcinomas and gallbladder carcinomas). Apoptotic tumor-infiltrating lymphocytes could be found in these specimens. RCAS1 expression was frequently detected also in biliary epithelial cells in cases of immune-mediated cholangitis (74.2% in primary biliary cirrhosis, 66.6% in graft-versus-host disease), although the staining pattern for RCAS1 was different compared with cancer cells. Conclusions: RCAS1 is highly expressed not only in cancer cells but also in non-tumor bile duct cells subjected to immune attack.