Co-culture of human hair follicles and dermal papillae in a collagen matrix.

Human hair follicles, either alone or in combination with dermal papillae, were cultured in a collagen matrix. When plucked hair follicles were cultured alone, spike-like structures composed of outer root sheath cells started growing around the follicle and then radiated into the gel. When isolated dermal papillae were embedded close to the follicles, spikes started growing earlier and grew more rapidly than without the papillae. In cultures of excised follicles from which the dermal papilla had been removed, epithelial cells (possibly hair bulb cells) started growing out from the bulbous portion and then also formed spikes. In the presence of a papilla, the spikes elongated toward the papilla, finally reaching and surrounding it. These findings suggest that dermal papilla cells produce a factor(s) that enhances growth of follicular epithelial cells and also attracts those cells. In cultures of whole excised follicles, two major characteristic patterns of cellular growth were recognized. When the dermal papilla remained inside the bulb in contact with the hair bulb matrix, the hair matrix cells proliferated and differentiated in the normal manner, resulting in elongation of the hair shaft and follicle. But when the papilla was detached from the hair bulb matrix, epithelial cells proliferated from the bulbous portion and finally formed hair follicle-like structures. Thus, attachment of the dermal papilla to the hair bulb matrix in the bulbous portion appears to be necessary for growth of the hair and follicle in the normal manner. Our model may be useful for examining the interaction between follicular epithelial cells and dermal papillae and for studying the growth of hair and follicles in vitro.