1. In vitro, sheep E cells were cultured with DP fibroblasts or dermal fibroblasts [direct contact between 2 types of cells was prevented]. It was established, that dermal fibroblasts significantly stronger stimulate keratinicytes proliferation, than DP cells.

MOOR G. P. M., DU CROS D. L., ISACS K., PISANSRAKIT P., & WYNN P. C., Hair growth induction: roles of growth factors // 1991 Annals of the New York academy of sciences . vol 642, p227-242

2. In other experiments low-passage DP fibroblasts were the only dermal cells [high-passage DP cells, 3T3 fibroblasts, low- and high-passage dermal fibroblasts were also tested] that at direct contact significantly stimulate adhesion and proliferation of basal keratinocytes. It is strange, but low- and high-passage dermal fibroblasts almost don’t support E cells proliferation.

REYNOLDS A.J., JAHODA C.A., Hair follicle stem cells? A distinct germinative epidermal cells population is activated in vitro by the presence of hair dermal papilla cells. // J. Cell. Sci., vol.99(pt.2)., p.373-385., 1991
JAHODA CA., REYNOLDS AJ ., Dermal- epidermal interaction . Follicle derived cell populations in the study of hair growth mechanism . // J. Invest. Dermatol. 1993 vol. 101 p. 33s-38s .

3. Other research group report that SDS-PAGE analysis for keratinocytes, done after their previous combined cultivation with D fibroblasts in analogous 2-D culture don’t reveal any tricho-specific keratins.

LIMAT A., BREITKREUTZ D., STARK H-J., HUNZINKER T., THIKOETTER G., NOSER F., FUSENIG N.E., Experimental modulation of the differentiated phenotype of keratinocytes from epidermis & hair follicle outer root sheath 7 matrix cells. // 1991 Annals of the New York academy of sciences . vol 642,p.125-147.
MESSENGER A.G., Isolation, culture & in vitro behavior of cells isolated from the papillae of human hair follicles. //In: van neste 1), Lachapelle JM, antoine JL (eds.). Trends in Human Hair Growth & Alopecia Research. Kluwer, London, p.57-66., 1989

4. In 3-D culture [collagen gel] combined cultivation of DP and E cells gave rise to the following structures:
Spheroid bodies with epidermal type of differentiation
Spike-like projectors without no apparent type of terminal differentiation.

JAHODA CA., REYNOLDS AJ ., Dermal- epidermal interaction . Follicle derived cell populations in the study of hair growth mechanism . // J. Invest. Dermatol. 1993 vol. 101 p. 33s-38s .

5. Evidence for the growth stimulatory properties of human keratinocyte-derived conditioned medium on human scalp DP cells and a mouse fibroblast cells was presented. This conditioned medium induced a 2-5-fold increase in mitogenic activity in DP cells relative to sham-conditioned medium as measured by 3H-thymidine incorporation. DP cell growth-stimulating activity of the conditioned medium was sensitive to heat, and from size exclusion the molecular weight was greater than 3000 Da.

WARREN R., WONG T. K., Stimulation of human scalp papilla cells by epitelial cells. // Arch. Dermatol. Res., vol.268(1)., p 1-5., 1994

6. Special interest for us represent a system, where interfollicular epidermis interact not with DP, but with dental papilla [from tooth]. Incisors derived dental papillae of adult rats were transplanted into micro-incision of ear skin. As a result of this giant, highly structured and functionally active HF were formed. But at the base of this HF was a horseshoe-like papilla.

C. A. JAHODA., F. J. REYNOLDS. Inductive properties of hair follicle cells. // 1991 Annals of the New York academy of sciences . vol 642, p227-242
F. J. REYNOLDS., In vivo & in vitro studies of isolating 7 interacting dermal & epidermal components of the integument. // Ph. D. Thesis. University of Dundee, Dundee., Scotland., U.K.
JAHODA CA., R.F. OLIVER., Vibrissa dermal papilla cells in the adult rat., // j. Embriol. Exp. Morphol., vol.79., p.211-224. 1984