Human milk bile-salt-stimulated lipase is extremely reactive with the monoclonal antibody 1CF11 which recognizes a human-specific carbohydrate antigen

1CF11 (Kanamaru, Y. et al.; Biochem. Biophys. Res. Commun., 249, 618-623, 1998) is a monoclonal antibody obtained after being raised in a mouse by injection of human milk MUC1 mucin as the antigen. Its reactivity was found to be unique in that it only reacts with a carbohydrate epitope shared by glycoproteins in human secretions, while its chemical nature is still unknown. Since a glycoprotein of Mr 135,000 (135K) in human milk was found to react extremely strongly with this antibody, we intended in this study to isolate the glycoprotein by a combination of various chromatographic techniques and identify it. It is a human milk bile-salt-stimulated lipase. By comparison of its immunoreactivity and glycan structures so far reported with those of lactoferrin from human milk, it is suggested that the epitope recognized by mAb ICF11 could be a human-specific novel glycan.