We have isolated a mouse monoclonal antibody that, upon immunohistochemical localization in frozen sections, displays specificity for human myoepithelial cells in the resting mammary gland, sweat glands, and salivary glands. Furthermore, this antibody was strongly and homogeneously reactive with frozen sections of 3 of 60 breast carcinoma specimens. Using immunolocalization techniques in conjunction with polyacrylamide gel electrophoresis, we have determined that the reactivity of this monoclonal antibody is directed toward a 51,000-dalton keratin polypeptide. The potential uses of this antibody in the prognosis of human mammary carcinoma and in understanding the role of the myoepithelium in development and differentiation are discussed.Myoepithelial cells are derived from ectoderm and are known to exhibit both epithelial and mesenchymal characteristics (1, 2). They are situated between acinar or ductal luminal cells and the basal lamina in a number of secretory glands such as breast, lacrimal, eccrine, and apocrine sweat glands and various salivary glands (3).We report here on a monoclonal antibody directed toward a cytoskeletal keratin that is unique to the myoepithelial or "basal" layer of epithelial cells in human mammary ducts, sweat glands, and salivary glands. Using polyacrylamide gel electrophoresis and immunoblotting, we have found the apparent molecular weight of this basal epithelium-specific keratin to be 51,000 daltons. The antibody is generally nonreactive with luminal epithelium, stroma, muscle, fat, and vasculature. Therefore, it appears to be a useful tool in studying the role of the myoepithelium in the normal development of the breast, during lactation and involution, and in malignancy and metastasis.Recently, considerable advances have been made in tumor diagnosis by immunocytochemical typing of intermediate filaments. For example, carcinomas are characterized by antibodies to cytokeratins; sarcomas of muscle cells, by anti-desmin; nonmuscle sarcomas, by anti-vimentin; and gliomas, by anti-glial fibrillary acidic protein (for review, see ref. 4). The myoepithelium-specific monoclonal antibody described in this report has allowed us to define and characterize subclasses of human mammary carcinomas that would not be possible to distinguish by conventional techniques. The potential application of this antibody in the prognosis of human mammary carcinoma is discussed. MATERIALS AND METHODSImmunization. BALB/c mice raised under pathogen-free conditions were injected via subcutaneous or intravenous routes for 5 weeks at weekly intervals with whole-cell preparations of a secondary culture of an infiltrating ductal breast carcinoma. For each inoculation, 106 cells, which had been cultured as previously described (5), were prepared by scraping the monolayer with a rubber policeman into phosphate-buffered saline. Splenocytes from immunized animals were fused with SP2/0 mouse myeloma cells in the presence of polyethylene glycol (Mr 4000; Merck) by the procedure of Kohler and Milstein (6). Monocl...

The intermediate filaments of most epithelial cells in vivo consist solely of cytokeratins. Using monoclonal antibodies to vimentin or keratin, we have examined the expression of vimentin in homologous specimens of frozen tissue sections and primary cultures of normal human mammary epithelium. In frozen sections, only epithelial cells reacted with the antikeratin antibody, whereas antivimentin reactivity was associated with stromal cells. All epithelial cultures were positive for cytokeratin and in addition coexpressed vimentin as strongly as cultured fibroblasts and as early as the 4th d after initiation of the culture. Two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analysis of cytoskeletal preparations of secondary cultures of normal mammary epithelium have also demonstrated the appearance of a moiety identical to the vimentin found in cultured fibroblasts. Our observations are consistent with the hypothesis that vimentin expression is induced, possibly as a result of changes in cell shape or growth rate, when cells are freed from three-dimensional restrictions imposed by the tissue of origin.