Monoclonal Antibodies Directed to a Disulfated Glycosphingolipid, S_B1a (GgOse₄Cer-II³IV³-bis-sulfate), Associated with Human Hepatocellular Carcinoma

Abstract

Two murine monoclonal antibodies, 2H6G5 (IgM) and 4A9E10 (IgG₃), were obtained by using either cultured human hepatocellular carcinoma cells (PLC/PRF/5) or the acidic glycolipid mixture prepared from the same cells as immunogens. The antigen in PLC/PRF/5 cell membranes recognized by both antibodies was identified as a disulfated acidic glycolipid, GgOse₄Cer-II³IV³-bis-sulfate (S_B1a). Both antibodies reacted specifically with S_B1a, and no significant reactivity was noted with other sulfated glycolipids or gangliosides except that the antibody 2H6G5 showed a weak cross-reactivity with LacCer-II³-sulfate (S_M3), another sulfated glycolipid which partly shares the same carbohydrate structure as S_B1a. The S_B1a antigen is a relatively minor glycolipid in PLC/PRF/5 cells, but it was strongly expressed at the surface of PLC/PRF/5 cells as ascertained by cytofluorometry using both antibodies. A significant amount of S_B1a antigen was present in 3 of the acidic glycolipid fractions isolated from 15 human hepatocellular carcinoma tissues as well as in the acidic glycolipid fraction prepared from PLC/PRF/5 cells, while all the acidic glycolipid fractions prepared from cirrhotic livers and a normal liver were essentially negative for S_B1a, as ascertained by both solid phase enzyme immunoassay and the thin-layer chromatography-immunostaining method. These results strongly suggest that the S_B1a antigen as defined by these new monoclonal antibodies is associated with human hepatocellular carcinoma.