Immunoperoxidase localization of a glycoprotein on plasma membrane of secretory epithelium from human breast.

A glycoprotein component of human milk-fat globule membrane, which is said to derive form apical plasma membrane of mammary secretory epithelium, has been purified. The purified glycoprotein yields a single band under reduced condition and has an estimated molecular weight of 70,000 daltons on sodium dodecyl sulfate polyacrylamide gel electrophoresis. The glycoprotein was termed "secretory epithelial membrane antigen" (SEMA-70) to indicate its origin and molecular size. Specific antisera to SEMA-70 were raised. Using the peroxidase-antiperoxidase method of staining, the presence of SEMA-70 was demonstrated on the apical plasma membrane of the mammary epithelial cells lining the ducts of both normal and lactating breast. No significant staining of cytoplasm was observed. these observations add further evidence as to the origin of milk-fat globule membrane. Although the antigen continues to be expressed on breast adenocarcinoma cells, its cellular distribution appears to be different. The potential usefulness of specific antisera to SEMA-70 is suggested to identify rearrangements in cellular architecture due to pathological changes.