Up-regulation of elafin/SKALP gene expression in psoriatic epidermis.

The expression of mRNA for elafin/SKALP, an inhibitor of leukocyte elastase and proteinase 3, in human normal and psoriatic epidermis was examined by in situ hybridization. In normal epidermis, elafin/SKALP mRNA was detected in the granular layer, but not in the spinous or basal layers. In fully developed psoriatic lesions, elafin/SKALP mRNA was found in the suprabasal layers of the ridges, and in the upper two thirds of the stratum malpighii at the elongated rete ridges. Intense staining was noted near the subcorneal microabscess in psoriasis vulgaris and under the subcorneal pustule in localized pustular psoriasis. In the marginal psoriatic epidermis, elafin/SKALP mRNA was expressed from the middle or upper spinous layer to the subcorneal layer, and the cells expressing elafin/SKALP mRNA increased especially under the parakeratotic corneal layer intermingled with pyknotic nuclei of neutrophils. These findings suggest that the induction of elafin/SKALP gene expression is related closely to the infiltration of neutrophils into the epidermis in psoriasis and plays an important role in protecting the skin components against the tissue damage caused by the infiltrated leukocytes.