On the existence of non‐cycling germinative cells in human epidermis in vivo and cell cycle aspects of psoriasis

This report deals with the controversies of whether all germinative epidermal cells in human epidermis are in the cycling state and whether stimulated hyperproliferation of psoriatic epidermis is due to a shortening of the cell cycle time or to a recruitment of non‐cycling germinative epidermal cells. Experiments were performed on human subjects in vivo . Continuous infusion of [ 3 H]thymidine for 8½ days indicated that 40% of germinative epidermal cells reside in the non‐cycling state. Proliferative stimulation by tape stripping indicated recruitment of non‐cycling (G 0 ) germinative epidermal cells in both normal and psoriatic skin, and a prolongation (rather than a shortening) of cell cycle traverse in activated psoriatic epidermal cells.