Localization of proteolytic activity in psoriatic skin.

Incubation of unfixed slices of skin for 1 hat 37° C in Hanks' medium allowed the expression of proteolytic activity in the upper keratinocyte layers in psoriatic lesions and, in some cases, in uninvolved skin of psoriatics, but never in normal skin. This proteolysis was inhibited by DFP and TLCK, known inhibitors of the neutral proteinase previously described as increased in psoriatic lesions. The topographical analysis of this proteolytic activity suggests that a disturbance of the protease‐antiprotease equilibrium in human epidermis may be implicated in the appearance of psoriatic lesions.