Characterization of a human B-lymphocyte carcinoma cross-reacting antigen (BLCa) in B lymphocytes identified by two murine monoclonal antibodies.

The murine monoclonal antibody (MAb) MA6 is selectively reactive against a large variety of human B lymphocytes including those in early stages of B-cell differentiation such as committed progenitors of B lymphocytes, pre-B lymphocytes, Burkitt lymphoma cells, and those at later stages of differentiation such as peripheral blood B lymphocytes and myeloma cells. The major antigen identified by this antibody on such B lymphocytes (BLCa) is a 55-kDa glycoprotein or a group of similar glycoproteins, with the MA6-reactive determinant localized on the carbohydrate moiety. On isoelectric focusing, this antigen exhibits a degree of charge microheterogeneity, migrating as a diffused band with an average isoelectric point at pH 5.7. BLCa was also identified by another murine MAb, MA5. The antigenic determinant recognized by this antibody is also localized on the carbohydrate moiety of the molecule, but, unlike the MA6-reactive determinant, it is shared by other glycoproteins from different types of cells.