The cell cycle time in psoriasis

In the uninvolved epidermis of psoriasis and other conditions where an increased labelling index has been shown, the assumption is often made that this indicates a shortened cell cycle time producing accelerated cell replication. These studies on the uninvolved epidermis of six patients with psoriasis shows that this assumption may not always be correct. Employing the PLM curve method the mean S Phase duration (T_S) was found to be 11·4 h, similar to previous estimates of T_S in involved psoriatic epidermis, but too short to explain the wide ratio between labelled cells and mitoses (200:1) found in uninvolved psoriatic epidermis. The results imply that first, not all labelled cells are cycling S phase, cells and secondly if T_S is similar to that found in involved epidermis it does little to support the concept of a long cell cycle time in uninvolved epidermis. It is suggested that the increase in dividing cells and expansion of the epidermal compartment so characteristic of psoriasis may reflect alterations in growth fraction and not rapid cell replication.