The biochemistry of skin disease

The morphological details of globular keratohyalin granules

In quickly dividing epithelia such as that of the tongue, keratohyalin formation takes place in globular keratohyalin granules (KHG). This is in contrast with the irregular KHG as seen in normal, slowly dividing epidermis. The morphogenesis of the globular KHG is explained in this study. In small KHG, dense aggregates of ribosomes can be seen at the site of blebs. It is suggested that these blebs framed with ribosomes are internalized giving rise to "dense homogeneous deposits" or "single granules". Lipid droplets occur in the upper spinous and horny layer. Globular KHG also contain variable amounts of lipids, and the lipid content seems to be inversely related to the protein content, dependent on the degree of cell differentiation or on the rate of cell turnover. It is suggested that in epithelia with a high cell turnover few rigid keratohyalin components are dispersed in lipids, which maintain a globular shape due to the surface tension.

Abnormal keratohyalin-like forms in leukoedema

Electron microscopic, histochemical and light-microscopic studies were carried out on biopsy specimens of 12 cases of leukoedema and on the desquamated epithelial cells of a further 50 examples. For comparison, similar observations were made of 4 examples of healthy cheek mucosa and 29 cases of a variety of pathological conditions of the oral mucosa. Only in leukoedema were a series of structures encountered which consisted of an aggregation of ribosomes and electron dense masses, or a network of electron-dense material, or an electron-dense network with a central dense core or a solid body with a few central cavities. Histochemical stains and RNA extraction studies showed that they are probably abnormal forms of keratohyalin granules and that ribosomes is an important component of their composition.

Cytoplasmic granules in exfoliated buccal epithelial cells

The cytoplasmic granules in exfoliated epithelial cells of healthy cheek mucosae of seven subjects were studied by means of phase-contrast microscopy, electron microscopy and histochemistry. An electron microscopic technique was used to study specific granules which had been identified with the light microscope. Phase-contrast microscopy revealed that the cytoplasmic granules are present in unfixed material. Ultrastructurally they consist mostly of discrete, dense granular bodies. Also seen were collections of electron-dense masses, collections of organelles and organelles mixed with granular bodies and electron-dense masses. Histochemically they stain like keratohyalin. No lipids were detected. We propose that the discrete bodies are normal keratohyalin granules and the electron-dense masses are granules in stages of disintegration. When the granules break down they become mixed with organelles. The keratohyalin granules are the darkly-stained granules seen microscopically, and the disintegrating granules and collections of organelles the weakly-stained, indistinct cytoplasmic granules.