The ultrastructure of the epidermis in psoriaris vulgaris as revealed by electron microscopy: 7. The stratum corneum in hyperkeratosis

Abstract

The stratum corneum in hyperkeratotic psoriatic epidermis varies in thickness between 15 and 37 layers of cells. The cell height is 0.47–3.52 μ. The dense layer at the cell surfaces is about 100 A in thickness. The intercellular space is fairly narrow and rather constant in width throughout the stratum corneum. Except for the frequently occurring desmosomes this space is for the most part electron optically “empty.” Three sublayers are discerned. The basal layer is 2–14 cells thick. The cytoplasm in these cells is dense. The cells may be mainly filled with closely packed keratin fibrils or the keratin fibrils may be separated by varying amounts of a nonfibrillar material. The fibrils display a keratin pattern of a fairly low contrast; some increase in contrast is obtained by irradiating the embedded tissue with ultraviolet light before staining with uranyl acetate. The filaments are, in the main, longitudinally sectioned and oriented parallel to the skin surface. They seem to be about 50 A in diameter. The intermediate layer forms the main part of the stratum corneum and is 9–17 cells thick. The cytoplasm seems often to be slightly more opaque than in the subjacent cells. This layer is dominated by cells showing opaque areas with fibrils and a nonfibrillar substance, separated by less stained or electron optically “empty” spaces. A varying number of cells smimilar in density to those in the basal layer are also seen. The superficial layer seems to consist of 2–6 cells. The cytoplasm as a whole displays a conspicuous decrease in pacity as compared to that in the cells of the intermediate layer. No keratin pattern is discerned. Nuclei are rather frequently found in the basal and intermediate layers. Mitochondria, polymorphic components, and round or oval granules are observed throughout the stratum corneum.