CELL-CYCLE IN PSORIASIS - REAPPRAISAL

The current belief that the clinical manifestations of psoriasis (excessive scaling) are due to a 12-fold speeding up or shortening of the cell division cycle time of the germinative cells in psoriatic epidermis (from 457 to 37.5 h) was shown to be incorrect. A new concept was introduced: the germinative layer in human epidermis was composed of not 1, but 3 separate and distinct populations of epidermal cells. First, there were cycling cells which were actively moving through the cell cycle. Then there were 2 categories of non-cycling cells (blocked in the G1 [pre-synthetic period] or the G2 [post-synthetic period] periods of the cell cycle) which were 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 release of the 2 categories of non-cycling cells. The idea that germinative epidermal cells were primarily non-cycling, led to the suggestion of focusing attention on non-cycling cells (rather than on cycling cells) for the control and treatment of psoriasis. 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 may be worthwhile.