SOLUBLE FACTORS FROM HUMAN HAIR PAPILLA CELLS AND DERMAL FIBROBLASTS DRAMATICALLY INCREASE THE CLONAL GROWTH OF OUTER ROOT SHEATH-CELLS

Depending on environmental influences, follicular outer root sheath (O RS) cells in vivo can differentiate either towards interfollicular ker atinocytes or, as demonstrated in the rat vibrissa, hair matrix cells. Crucial regulators of both their proliferation and differentiation ar e the mesenchymal cells of the respective tissues. The interactions of human ORS cells with human hair papilla cells (HPC) or human dermal f ibroblasts (HDF) were studied using a two-chamber model separating the two cell types either by a microporous membrane or additionally by a medium layer. The results of H-3-thymidine incorporation studies indic ated that ORS cell growth was markedly enhanced in co-culture with eit her HPC or HDF, the highest stimulatory effect resulting when ORS cell s were in close association with the mesenchymal cells. No correlation was found between ORS cell proliferation and IL-6 production in the c o-culture system, thus pointing to the secretion by HPC and HDF of gro wth-promoting soluble factors that are different form IL-6 as well as from EGF, bFGF and insulin present in the culture medium.