Differences between connective tissue-epithelial junctions in human skin and the anagen hair follicle.

Although the ultrastructure of the dermal-epidermal junction has been well characterized, little is known about the junctions between the dermal papilla and the surrounding epithelial cells of the hair bulb, or between the connective tissues and the epithelial cells on the outside of the hair follicle. Because the dermal papilla plays a major role in controlling the hair follicle, we also examined the ultrastructure of the potentially important dermal papilla-epithelial junction in normal scalp anagen follicles. The dermal-epidermal junction in skin was a trilaminar basement membrane characterized by the anchoring points of hemidesmosomes and tonofilaments in keratinocytes. In the hair follicle, the junction that separated the dermal papilla and epithelial cells was a trilaminar basement membrane, but relatively few putative anchoring points were seen. These were similar to modified dermal-melanocyte junctions, in which the intercellular cytoplasmic filaments do not come together at an attachment plaque, the laminar components tend to be thinner, and the anchoring fibrils beneath the lamina densa are fewer. A trilaminar membrane also was interposed between the connective and epithelial tissues on the outside of the follicle, but nothing that resembled a hemidesmosome or any other type of anchoring structure was seen. The difference in structure of the junctional complex between skin and hair follicles probably reflects the relatively permanent state of the epidermis, compared to the dynamic processes involved during the anagen phase of the hair follicle.