Immunological characterization of blood group A epitopes expressed on cells and tissues with a monoclonal anti-CEA...

Monoclonal antibodies (mAb) specific for the oligosaccharide epitopes of glycoproteins or glycolipids, such as blood group antigens, are powerful tools for studying the antigenic structure of normal and pathological cells and tissues. Anti-A human red blood cell monoclonal antibodies were produced by immunizing mice with normal cells, but only a few fulfilled the conditions necessary for revealing qualitative differences among A-antigens. Only those produced by hybridomas obtained from mice immunized with human tumor antigens specifically recognize A1 and A2 blood group antigens. We report here several immunological properties of the A-antigen defined by a mAb raised against the tumor-associated carcinoembryonic antigen.

The hybridoma B2C114, obtained as a result of the fusion of spleen cells from mice immunized with the carcinoembryonic antigen and a murine myeloma cell line, produces a mAb which reacts specifically against erythrocytes bearing the A blood-group antigen. The monoclonal antibody showed a high stability and a low dissociation rate from the antigen/antibody complex formed with adult A1, A2, A2B and cord blood samples. The antibody was able not only to discriminate between A1- and A2-RBC but also to detect kinetic differences among A-sites. On the one hand B2C114, reactive with the glycosidic moiety of the A-antigen, can discern at least two qualitatively different epitopes expressed on the A1-RBC surface, with a total number of A sites that is in close agreement with the figures already described for A1-RBC. On the other hand, A2-RBC shows a single phenotype that is kinetically similar to A1-low affinity binding sites. This antibody also labelled spontaneous and chemically-induced murine tumors as well as human tumors. Its reactivity with colon carcinoma frozen specimens obtained from O- and B-blood group patients indicated expression of an incompatible A-antigen. The immunochemical properties of B2C114 described here give support to our purpose of employing this mAb as a blood group reagent as well as a histopathological probe for in vitro and in vivo cancer diagnosis.