Apoptosis in established and healing psoriasis

Previous studies have described apoptosis in the stratum granulosum and in the stratum corneum, but not in the germinative compartment in normal skin. In psoriasis, an increased epidermal apoptosis has been observed in the differentiated compartment, suggesting that apoptosis has a key role in the pathogenesis of psoriasis, as a counteracting factor to the overproduction of cells. Little is known on apoptosis in the germinative compartment.

Apoptosis was studied on biopsies of normal skin, established lesions of psoriasis and PUVA-treated psoriasis using the transferase-mediated uridine nick end labelling method, which detects fragmented DNA, and electron microscopy. Counting of apoptotic cells was restricted to the germinative compartment as defined by Mib1 staining to evaluate the impact of cell loss on cell production and tissue architecture.

The apoptotic index was 0.12% in normal epidermis, 0.035% in established psoriasis and 0.31% in regressive psoriasis.

These results have three implications: (1) they show the physiological presence of apoptosis in the germinative compartment in normal epidermis; (2) they suggest that induction of apoptosis is involved in the regression of psoriatic hyperplasia after PUVA therapy; (3) the decrease of physiological apoptosis in the psoriatic lesion suggests that this phenomenon could play a role in the induction of psoriatic hyperplasia.