Keratin 14 immunoreactive cells in pleomorphic adenomas and adenoid cysticcarcinomas of salivary glands

Our recent study of developing myoepithelial cells (MECs) in rat salivary g lands demonstrated that developing MECs begin to express alpha-smooth muscl e actin (alpha SMA) First and, thereafter, keratin 14. Therefore, it is unl ikely that duct basal cells expressing keratin 14 alone are immature or und ifferentiated MECs. In this study we carried out immunohistochemistry of pl eomorphic adenomas and adenoid cystic carcinomas including normal salivary glands using monoclonal antibodies to keratin 14, smooth muscle proteins an d keratin 19. The smooth muscle proteins examined included alpha SMA, h-cal desmon and h1-calponin; h1-calponin was observed in keratinocytes: and nerv e fibers, indicating that the protein is not specific to smooth muscle, whe reas alpha SMA and h-caldesmon turned out to be highly specific markers for smooth muscle cells in normal tissues. In normal glands, MECs were positiv e for both keratin 14 and smooth muscle proteins (alpha SMA and h-caldesmon ). Non-MEC cells were essentially devoid of smooth muscle proteins. Non-MEC duct basal cells expressed keratin 14 with or without keratin 19, and lumi nal cells keratin 19 with or without keratin 14. This suggests that the ker atin 14-positive, smooth muscle proteins-negative duct basal cells are lumi nal cell progenitors. Luminal cells in tubular structures of both tumors we re positive for keratin 19 with or without keratin 14. Nonluminal periphera l cells of pleomorphic adenomas were mostly positive for keratin 14, and a small fraction of them expressed smooth muscle proteins. Conversely, periph eral cells of adenoid cystic carcinomas were mostly positive for smooth mus cle proteins, and some of them expressed keratin 14. These results strongly suggest (1) that the luminal cell progenitors transform into major constit uents of pleomorphic adenoma cells with keratin 14 but not smooth muscle pr oteins, and (2) that the peripheral cells of adenoid cystic carcinoma are d erived from undifferentiated MECs. Solid structures of pleomorphic adenomas were formed by proliferation of the peripheral cells. MECs were observed o nly occasionally in the periphery. Solid and cribriform structures of adeno id cystic carcinomas were formed by proliferation of the luminal cells. MEC s were observed in the periphery and around the pseudocyst.