Topographic relation between skin-derived antileukoproteinase (SKALP) and leukocyte elastase in a case of annular pustular psoriasis.

We have assessed the distribution pattern of a new epidermal elastase inhibitor, skin-derived antileukoproteinase (SKALP) and polymorphonuclear leukocytes (PMN) in a patient with annular pustular psoriasis, using immunohistochemical methods. In clinically uninvolved skin SKALP was not expressed and only occasionally a few PMN could be identified. In the erythematous distal margin of the lesion, expression of SKALP was shown in suprabasal keratinocytes. Although PMN were present in the dermis, no transepidermal PMN migration had occurred at this stage. In the pustular region a dense SKALP-positive zone was demonstrated in the suprabasal compartment. In the centrally healed area neither SKALP expression nor PMN accumulation was shown. The present case report suggests that the induction of SKALP expression does not result from the passage of PMN through the epidermis. The offswitch of SKALP expression coincides with the disappearance of the PMN infiltration and not with the resolution of the mononuclear infiltrate.