[Desmosomal structures in the cytoplasm of normal and abnormal keratinocytes (author's transl)]

The occurrence of intracytoplasmic desmosomes in normal, hyperplastic, and hyperkeratotic epithelia, in carcinoma-in-situ and in invasive carcinoma of the human oral cavity is demonstrated by electron microscopy. The mechanism for formation of these structures by invagination, separation and by intracytoplasmic incorporation of plasma membrane-desmosome-complexes are described in various oral epithelia, and other possible mechanisms are discussed. Intracytoplasmic desmosomes may occur in normal and pathological keratinocytes of all layers of the oral epithelium. Their ultrastructure in the peripheral cytoplasm is similar to that of the regular desmosomes on the cell surface. However, as they migrate centripetally, they show signs of degeneration, suggesting dissolution by lysosomal enzyme systems. Various surface membrane alterations involved in the formation of intracytoplasmic desmosomes may lead to a reduction of plasma membrane material and of desmosome structures and to defective intercellular adhesion. The intracytoplasmic incorporation of desmosome structures is a ubiquitous phenomenon exhibited by epithelial keratinocytes under certain physiological or pathological conditions.