Epithelial membrane antigen: partial purification, assay and properties.

The Epithelial Membrane Antigen (EMA) has until now only been described in immunological terms and has been shown immunohistochemically to be present on a variety of human non-squamous epithelial surfaces. It is a valuable marker in diagnostic tumour pathology and enables the detection of small deposits of malignant cells in organs such as liver and bone marrow. Its discovery in soluble form in human milk has enabled a purification of the antigen from this source. The antigenic activity in the milk is spread over a wide range of mol. wts and although purification causes a general reduction in size, the antigen remains heterogeneous. Carbohydrate forms the major component of the antigen with galactose and N-acetylglucosamine as the two major sugars. The protein content of EMA is low and shows considerable variation in amino acid composition from one sample to another. A high content of inorganic material has also been found in EMA but is not due to high sulphate or phosphate levels.