Stratum corneum chymotryptic enzyme in psoriasis.

Stratum corneum chymotryptic enzyme (SCCE) is a serine protease which may function in the turnover of the stratum corneum by means of degradation of intercellular adhesive structures between corneocytes. It is also potentially an epidermal activating enzyme for cytokines such as interleukin-1beta. The aim of this work was to study the expression of SCCE in psoriatic epidermis by means of immunohistochemistry, and to elucidate the nature of the SCCE present in psoriatic scales by means of biochemical analyses. In comparison to normal skin the number of cell layers expressing SCCE in psoriatic lesions was consistently increased. In nonlesional psoriatic skin the pattern of SCCE expression varied. It was similar to the pattern in normal skin in some biopsies, whereas in other biopsies evidence of an increased expression of SCCE was found. By means of zymography and immunoblotting, extracts of psoriatic scales were found to contain active SCCE as well as enzymatically inactive SCCE precursor. Also the effects of inhibitors on the activity towards a chromogenic protease substrate in the extracts after partial purification by gel exclusion chromatography were compatible with the presence of enzymatically active SCCE. We conclude that the expression of SCCE in psoriasis may be upregulated, and that the conversion of inactive SCCE-precursor to active SCCE occurs in the psoriatic lesion. The possible role of SCCE in the pathophysiology of psoriasis remains to be elucidated, but should be considered in future studies.