Asymmetrical distribution of epithelial membrane antigen on the plasma membranes of human breast cell lines in culture.

A technique for localizing antigens by immunoperoxidase staining on the surfaces of unfixed culture cells is described. The cells can subsequently be studied by light or electron microscopy. These methods have been used to localize epithelial membrane antigen (EMA) on human mammary carcinoma (MCF7) cells in culture. This antigen was expressed on the plasma membrane, being localized on the interface with the culture medium and absent from the other external cell surfaces. This heterogeneous distribution reflects the distribution observed in mammary epithelial cells in vivo.