Morphological characteristics of epithelial and fibroblastic cells growing out from biopsies of human skin.

Skin biopsies are routinely used to establish fibroblast cultures in vitro, but the ultrastructural properties of the cells during this outgrowth have not received much attention. In the present study, the rate and the nature of the outgrowth of skin biopsy explants were examined in a quantitative and qualitative fashion. Attention was particularly focused on the morphogenetic properties of the various cell types present in the initial outgrowth. The rate of success in obtaining an outgrowth from the explants was slightly dependent on the composition of the medium or the serum. In more than 95% of the cases an initial epithelial outgrowth was obtained. At a later stage the outgrowth became fibroblastic. Remarkable differences in the behavior and ultrastructural properties of epithelial and fibroblastic cells were observed. Incorporation of 3H-thymidine occurred almost simultaneously with the epithelial outgrowth but preceded the migration of the fibroblasts. Under scanning and transmission electron microscopy, the cells of the outermost layers of the epithelium remained flat and polygonal and were covered with small villi during migration. The cells were closely apposed. The germinative cells had a spiky surface and were separated by large intercellular spaces. No basal lamina was formed by the migrating cells. The fibroblasts maintained their shape and smooth surface and reached the substratum under the epithelial outgrowth. They accumulated microfilaments and microtubules in their cytoplasm and were characterized by surface-associated extracellular material. On the substratum, the fibroblasts spreadout. The behavior and ultrastructural properties of these fibroblasts resemble closely those observed on fibroblasts growing-out from aggregates.