IMMUNOLOGICAL CHARACTERIZATION OF BLOOD-GROUP-A EPITOPES EXPRESSED ONCELLS AND TISSUES WITH A MONOCLONAL ANTI-CEA ANTIBODY

Background and Methods. Monoclonal antibodies (mAb) specific for the o ligosaccharidic epitopes of glycoproteins or glycolipids, such as bloo d group antigens, are powerful tools for studying the antigenic struct ure of normal and pathological cells and tissues. Anti-A human red blo od cell monoclonal antibodies were produced by immunizing mice with no rmal cells, but only a few fulfilled the conditions necessary for reve aling qualitative differences among A-antigens. Only those produced by hybridomas obtained from mice immunized with human tumor antigens spe cifically recognize A(1) and A(2) blood group antigens. We report here several immunological properties of the A-antigen defined by a mAb ra ised against the tumor-associated carcinoembryonic antigen. Results an d Conclusions. The hybridoma B2C114, obtained as a result of the fusio n of spleen cells from mice immunized with the carcinoembryonic antige n and a murine myeloma cell line, produces a mAb which reacts specific ally against erythrocytes bearing the A blood-group antigen. The monoc lonal antibody showed a high stability and a low dissociation rate fro m the antigen/antibody complex formed with adult A(1), A(2), A(2)B and cord blood samples. The antibody was able not only to discriminate be tween A(1)- and A(2)-RBC but also to detect kinetic differences among A-sites. On the one hand B2C114, reactive with the glycosidic moiety o f the A-antigen, can discern at least two qualitatively different epit opes expressed on the A(1)-RBC surface, with a total number of A sites that is in close agreement with the figures already described for A(1 )-RBC. On the other hand, A(2)-RBC shows a single phenotype that is ki netically similar to A(1)-low affinity binding sites. This antibody al so 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 descr ibed 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 i n vivo cancer diagnosis.