Lectin binding affinities of human milk fat globule (HMFG) membrane antigens.

Six biotinylated lectins with differing specificities and two monoclonal antibodies (III D 5 and III H 2) were used to characterize the sugar-residues in human milk fat globule (HMFG) membrane antigens. Immunoblotting analysis revealed that most of the antigens contain several sugars. However, the molecules exclusively reacting with anti-HMFG III D 5, a monoclonal antibody previously shown to detect antigen(s) positively correlating with the expression of estrogen receptors in mammary and gynaecological carcinomas, could only be stained with peanut agglutinin and Ricinus communis-lectins. One of these antigens, a 42-57 kDa molecule, was shown to have a complexed quaternary structure with galactose determining the antigenic specificity. It is suggested that the production of this glycoprotein in estrogen sensitive tissues results from activation of galactosyl-transferase-enzyme at the same time as the expression of estrogen receptors.