Complexity of expression of antigenic determinants, recognized by monoclonal antibodies HMFG-1 and HMFG-2, in normal and malignant human mammary epithelial cells

The monoclonal antibodies HMFG-1 and HMFG-2 super(1) are produced by hybridomas derived by fusing spleen cells of mice immunized with delipidated preparations of the human milk fat globule. Enzyme-linked immunosorbent (ELISA) assays of Western blots prepared from gels separating components of the milk fat globule showed that both antibodies recognize determinants found in high molecular weight components (> 400 K). Lectin-blocking experiments indicated that both antibodies recognize oligosaccharide sequences containing galactose, N-acetyl glucosamine, and, possibly, N-acetyl galactosamine. However, the determinant recognized by HMFG-1 is different from the determinant recognized by HMFG-2, which may contain or be adjacent to a nonterminal sialic acid residue. The expression of these antigenic determinants by normal mammary epithelial cells cultured from milk (HumE) and by a breast cancer cell line (T47D), was studied. The results are consistent with the interpretation that the HMFG-1 determinant is present in large glycoprotein molecules with complex carbohydrate side chains, and the HMFG-2 determinant is more commonly found in smaller molecules where glycosylation may be incomplete and sialic acid residues more exposed. The preferential binding of HMFG-2 to some breast cancers may therefore reflect a changed glycosylation pattern in these cells.