OUTER ROOT SHEATH (ORS) CELLS ORGANIZE INTO EPIDERMOID CYST-LIKE SPHEROIDS WHEN CULTURED INSIDE MATRIGEL - A LIGHT-MICROSCOPIC AND IMMUNOHISTOLOGICAL COMPARISON BETWEEN HUMAN ORS CELLS AND INTERFOLLICULAR KERATINOCYTES

In organotypic cultures, outer root sheath (ORS) cells of the human ha ir follicle develop into a stratified epithelium largely reminiscent o f the epidermis; this apparently reflects their importance during woun d healing. In the present study, ORS cells were grown inside a three-d imensional network of extracellular matrix proteins (Matrigel), togeth er with different mesenchymal cells, in an attempt to mimic their foll icular environment. Thus, inside Matrigel, ORS cells formed spheroids differentiating toward the center and showing all the markers of epide rmal keratinization. Under identical conditions, normal epidermal kera tinocytes developed similar spheroids, but of a significantly smaller size. Human dermal fibroblasts and dermal papilla cells, cocultured in the matrix, had a positive influence on both the proliferation and di fferentiation within bath types of spheroids. Epidermal differentiatio n markers, such as suprabasal keratins, involucrin, filaggrin, gp80 an d pemphigoid antigen, were readily expressed in ORS spheroids, whereas hard (hair) keratins were not detectable by immunostaining. Cells pos itive for an epithelial membrane antigen, strongly expressed in sebace ous glands, were seen in numerous spheroids. In contrast to organotypi c ''surface'' epithelia, the expression and location of different inte grin chains was normalized in ORS spheroids, indicating an enhanced me senchymal influence in this in vitro system.