P1.7 Human vellus hair follicles exhibit quantitative but no qualitative differences in the expression of differentiation markers

R. Dirsch, A. Vogt, S. Hadam, K. Stieler, U. Blume-Peytavi

Center of Experimental and Applied Cutaneous Physiology, Department of Dermatology, Charité - University Medicine Berlin, Germany

Vellus hair follicles (VHF) can be distinguished from terminal hair follicles (THF) by size and morphology of the hair follicles and the hair fibres. To investigate whether these differences reflect hair follicle type-specific characteristics in differentiation and keratinization, immunhistochemical staining with a large panel of antibodies against cytokeratins, hair keratins and the differentiation marker trichohyalin was performed on fresh skin samples from different body sites including scalp, face and trunk. In both, THF and VHF, anti-CK 19 and anti-CK 17 strongly stained the outer root sheath (ORS), while anti-CK 13 and trichohyalin were confirmed as markers of the inner root sheath (IRS). Similarly, the staining pattern of antibodies against the human hair keratins hHa 3-II, hHa4, hHa5 in VHF were comparable with the staining pattern observed in THF indicating that structurally, VHF and THF are closely related. With regard to cytokeratin expression, however, staining in VHF was strong and homogenous while a spotted staining pattern was frequently found in THF.

In culture, the overall expression of hair follicle-associated cytokeratins was higher in VHF-derived passage one keratinocytes than in keratinocytes from THF. Both cell populations inhomogenously expressed ORS and IRS markers indicating that primary keratinocytes in culture loose essential characteristics and that cells cultures in general are of limited value in hair follicle research. Whole organ cultures prepared from THF, in contrast, maintained their cytokeratin expression pattern over several days which are consistent with data recently published by Thibaut et al. These results underline the need of a suitable in vitro model of the VHF to further investigate vellus hair biology. It can be concluded that the differentiation of VHF, in general, is comparable to THF. The factors, which trigger the transformation from one hair follicle type into the other, however, remain to be identified.