Preferential Expression of a MT 155,000 Milk-Fat-Globule Membrane Glycoprotein on Luminal Epithelium of Lobules in Human Breast1

An integral membrane glycoprotein with an apparent molecular weight of 155,000 and isoelectric points ranging from 7.2 to 7.6 has been found to be predominantly expressed on the apical plasma membrane of luminal epithelial cell lining the lobules and terminal ducts in breast. The glyco protein was purified to homogeneity from human milk-fat-globule mem brane and was termed MFGM-gp 155. Polyclonal antibodies were raised which specifically reacted to a single component that electrophoretically comigrated with this glycoprotein in immunoblotting experiments. These antibodies appear to recognize epitopes which are expressed on the protein segment of the glycoprotein. Using an indirect immunohistological method, the glycoprotein was localized predominantly on the apical plasma membrane of luminal epithelial cells lining the alveoli of normal breasts. The expression of the antigen was maintained in both morpho logically welland poorly differentiated lobular carcinoma cells. The antigen was weakly detectable on normal epithelial cells lining the terminal ducts and malignant cells of infiltrating ductal and medullary carcinomas. Expression of the glycoprotein is not organ specific as it is detectable in normal epithelial cells of kidney, pancreas, salivary gland, and stomach and in malignant cells of colon and stomach. The antibodies did not react with large ductal, myoepithelial, stromal, endothelial, epi dermal squamous epithelial cells, melanocytes, eccrine sweat glands and ducts, sebaceous glands, erythrocytes, and lymphocytes in breast and skin tissues. Thus, antibodies to this glycoprotein appear to be useful pin-nul)pr markers to study differentiation of mammary epithelial cells and the pathogenesis of different histolÃ3gica!types of mammary carci nomas, including Paget's disease and signet-ring cell carcinoma of mam