Related glycoproteins from normal secretory and malignant breast cells. Purification and initial comparative...

Monoclonal antibody MA5 recognizes an epitope present on the surface and in the cytoplasm of human breast cancer cells and on the human milk fat globule membrane (MFGM). These immunoreactive determinants are found on tumor-associated glyco-proteins with apparent molecular weights of 280 and 300 kdaltons, whereas the cross-related milk fat globule membrane antigen appears larger (330 kdaltons). Comparative electrophoretic migration analyses following neuraminidase digestion, as well as differential binding to various lectins, established that these molecules are extensively sialylated, and that the tumor antigens were sialylated to a greater extent than normal antigen. Immunoaffinity purification of this class of differentiation antigens from tumor and MFGM demonstrated similar size distributions, lectin affinities and buoyant densities as their respective crude antigens.