Hepatocyte surface molecule involved in the adhesion of TA3 mammary carcinoma cells to rat hepatocyte cultures.

To identify adhesion molecules involved in the formation of liver metastases, we prepared monoclonal antibodies against rat liver plasma membranes, that inhibited the adhesion of mouse metastatic TA3 mammary carcinoma cells to rat hepatocytes in vitro. Two such antibodies (designated OPAR-1 and OPAR-2) were obtained, that inhibited by over 70%. As assessed with gel electrophoresis and immunoblotting, these antibodies bound predominantly to plasma membrane proteins with molecular weights of 125,000 and 100,000. Using immunoelectron microscopy, the OPAR antigen was found to be abundantly present on the sinusoidal surface of hepatocytes, and in addition on contiguous hepatocyte surfaces and Kupffer cells, but was absent from sinusoidal endothelial cells. The tissue distribution and molecular weight indicate that the OPAR antigen is different from other hepatic adhesion molecules. Adhesion of MB6A lymphosarcoma cells was not inhibited by OPAR antibodies, indicating that these cells adhere to hepatocytes via a different surface molecule.