HUMAN LYMPHOID CELLS EXPRESS EPITHELIAL MEMBRANE ANTIGEN

Epithelial membrane antigen (EMA) is generally assumed to be expressed only on epithelial cells. However, EMA was also found on reactive and neoplastic plasma cells, on some non-Hodgkin's lymphomas (particularly cases of T-cell lymphoma and "malignant histiocytosis"), and on Reed-Sternberg cells in cases of lymphocyte-predominant Hodgkin's disease. EMA was also induced on normal blood lymphocytes by exposure to human T-lymphotropic virus type II or phytohaemagglutinin. The specificity of these aberrant reactions was confirmed by the use of three different monoclonal anti-EMA antibodies (E29, HMFG2, and LICR.LON/M8), and by showing that EMA in lymphoid tissue is similar in molecular weight to EMA in human milk. These results indicate that additional anti-epithelial antibodies (eg, anti-cytokeratins) should be used in conjunction with anti-EMA for tumour diagnosis.