The nature and role of epidermal regressive changes in the development of the psoriatic lesion.

Damaged epidermal cells present in psoriatic lesions were investigated using histochemical and histomorphological methods including ultrathick sections. In early lesions these cells were found throughout the epidermis, being particularly numerous in the upper part of the latter and around the adnexa. In a later developmental stage the damage to the keratinocytes in the suprapapillary region was found to precede the damage to the basement membrane. These findings, together with the difference between the damaged keratinocytes lining the ascending side and the venous limb of the papilla respectively with regard to degree of severity of the damage, suggest that blood stasis is the cause of the regressive changes in the suprapapillary epidermis. The enzymatic activity of non-specific esterases and acid phosphatases was increased and that of succindehydrogenases and DPN-diaphorase was decreased in damage keratinocytes. The significance of these findings in relation to the genesis and development of psoriasis is discussed. The view is expressed that there is a causal relationship between damage to the epidermal cells and proliferation of epidermis.