High-voltage electron microscopy and three-dimensional graphic study of R and T cells in head and neck carcinomas

Individual head and neck carcinomas show extreme regional cellular differentiation. Some cells are rich in keratin filaments (T cells) and some have little keratin and a high density of free ribosomes (R or RT cells). We attempted to isolate these two cell types in order to test their relative invasiveness in an in vitro model. The high frequency of mitosis of hyperkeratinized cells showed that there was no constraint on the motility of cell division. High-voltage electron microscopy of serial thick sections and three-dimensional graphic reconstruction demonstrated that keratin cytoskeleton filaments were cross-linked into short, thick bundles. However, the keratin cytoskeleton was absent from some portions of the cytoplasm. In normal differentiated keratinized cells, a more uniform spanning of the whole cell by thin keratin intermediate-filament bundles was evident. The cytoplasm may be more mobile in the keratinized tumor cells. Even heavily keratinized T cells, like the less keratinized cell types, may have invasive motility.