Electron microscopic localization of sulfated glycosaminoglycans and proteoglycans in pleomorphic adenomas

Abstract

Although “myoepithelial” cells in pleomorphic adenomas have been implicated by several ultrastructural studies as responsible for the production of myxomatous and chondroid stroma, the cellular source of stromal glycosaminoglycans and proteoglycans has yet to be demonstrated histochemically by electron microscopy.Three major salivary gland pleomorphic adenomas were examined by electron microscopy after fixation in 2.5% glutaraldehyde and in 0.2% ruthenium red-glutaraldehyde. Routine ultrastructural preparations revealed a spectrum of cells with epithelial and mesenchymal features. The mesenchymal cells in the myxoid region displayed intracytoplasmic 70-80Å microfilaments, prominent Golgi complex, RER, and secretory vesicles. The fine structural appearance with ruthenium red stained tissue was similar to that of routine preparations. However, with ruthenium red staining, proteoglycans of the myxoid stroma could be visualized as numerous extracellular 250-500Å polygonal matrix granules with fine projecting filaments (Fig. 1A). Similar positive ruthenium red stained intracellular granules were observed within the cytoplasmic vacuoles of the mesenchymal cells, a feature not present in cells with epithelial differentiation (Fig. 1B).