Transient production of stem cell factor in dermal cells but increasing expression of Kit receptor in mast cells during normal wound healing.

Mast cells are involved in inflammatory skin disorders and wound healing processes, but the mechanism behind mast cell activation is obscure. In this study, we stained the stem cell factor (SCF) and the Kit receptor in tryptase-positive mast cells, since these molecules are essential for mast cell survival, growth, migration and activation. For this purpose, biopsies were taken from the edge of normally healing wounds of 12 patients undergoing skin transplantation on days 0, 1, 3, 7 and 14, and from chronic leg ulcers and psoriatic skin for comparison. In healing wounds, SCF-positive cells rapidly increased in number in the dermis peaking on day 1, but declined thereafter to their baseline values. The percentage of Kit-positive mast cells increased slowly but steadily reaching a maximum (73+/-22%, P=0.02) on day 14. In chronic ulcers, most of the mast cells were Kit-positive both in the wound bed and in the perilesional skin (87+/-9% and 86+/-13%, respectively). The number of SCF-positive cells was higher in the wound bed than in the dermis of perilesional skin. In the psoriatic skin of ten patients, lesional specimens showed significantly higher numbers of SCF-positive dermal cells as well as a higher percentage (88+/-12% vs 46+/-26%, P=0.004) of Kit-positive mast cells than nonlesional skin. In conclusion, our findings show that the expression of SCF increases rapidly in the early stages of wound healing but declines thereafter, whereas the expression of Kit in mast cells is induced slowly in healing wounds. In chronic wounds as well as in psoriatic lesions, both SCF and Kit are intensely expressed. Thus, it seems possible that SCF and Kit receptor interact, and this could lead to persistent mast cell activation and growth in chronic wounds and psoriasis, whereas only temporary mast cell activation is apparently needed in healing wounds.