The cell cycle in psoriasis: a reappraisal.

The current belief that the clinical manifestations of psoriasis (excessive scaling) are due to a twelve-fold speeding up or shortening of the cell division cycle time of the germinative cells in psoriatic epidermis (from 457 to 37-5 h) is shown to be incorrect. A new concept is introduced--that the germinative layer in human epidermis is composed of not one, but three separate and distinct populations of epidermal cells. First, there are cycling cells which are actively moving through the cell cycle. Then there are two categories of non-cycling cells (blocked in the G1 or the G2 periods of the cell cycle) which are capable of moving into the proliferative pool upon specific stimulation. Thus, increased epidermal cell proliferation in active lesions of psoriasis would be brought about mainly by a recruitment or a relase of the two categories of non-cycling cells. The idea that germinative epidermal cells are primarily non-cycling, leads to the suggestion of focusing attention on non-cycling cells (rather than on cycling cells) for the control and treatment of psoriasis. It might be worthwhile considering treating psoriatic patients during periods of clinical remission--with factors to keep the germinative cells in the non-cycling state--rather than during psoriatic flare up--with cancer chemotherapy drugs.