Immunocytochemistry of Intermediate Filament Proteins Present in Pleomorphic Adenomas of the Human Parotid Gland: Characterization of Different Cell Types in the Same Tumor

Abstract

Frozen sections through human pleomorphic adenomas of the parotid gland have been examined by immunofluorescence microscopy using antibodies to subunit proteins of different types of intermediate-sized filaments. These tumors are characterized by a highly complex histologic appearance. The following cell types commonly occurring in pleomorphic adenomas have been distinguished: (1) ‘Duct-lining type cells’ (DLT-cells) are typical epithelial cells lining duct-like structures. (2) ‘Ductal epidermoid foci’ (DBF-cells) are cell aggregates with epidermoid differentiation. (3) ‘Ductal isolated epithelial cells’ (DIE-cells) are cuboidal cells morphologically similar to DLT-cells but are not lining duct-like structures. (4) ‘Duct-associated small myoepithelioid cells’ (DSM-cells) are darkly staining cells resembling myoepithelial cells in their position. (5) ‘Indifferent pleomorphic tumor cells’ (IPT-cells) are highly variable in shape and position and generally smaller than DIE cells. (6) ‘Fibrovascular stroma cells’ (FVS-cells) are non-neoplastic, mesenchymally derived cells. The first five cell types, which are the adenoma cells proper, are stained with various antibodies to cytokeratins, in agreement with their putative origin from ductal cells of the parotid gland. Of these the cells of the epidermoid foci (DEF-cells) are the only cells stained with antibodies to human epidermal keratins. Tumor-associated mesenchymally derived cells such as fibroblasts and vascular cells are not stained with cytokeratin antibodies but are strongly decorated by vimentin antibodies. The first three types of tumor cells are characterized by epithelial cell morphology and are not stained by vimentin antibodies as commonly found for epithelia-derived tumor cells. However, the less-differentiated (‘indifferent’) pleomorphic cells (DSM- and IPT-cells) have been stained with both cytokeratin and vimentin antibodies. The reaction of vimentin antibodies with these cells is greatly diminished after absorption on purified vimentin but not after absorption with purified epidermal prekeratin. Our observations show that the different types of cells present in pleomorphic adenomas can be distinguished by their specific reactions with antibodies to intermediate filament proteins. The unusual finding of specific reaction of certain cell types, the DSM-cells and IPT-cells, with both antibodies to cytokeratin and vimentin is discussed in relation to current views of the origin of these tumor cells.