Plasminogen activation in bullous pemphigoid immunohistology reveals urokinase type plasminogen activator, its receptor and plasminogen activator inhibitor type-2 in lesional epidermis

Keratinocytes synthesize urokinase-type plasminogen activator (uPA) and a specific cell surface receptor for uPA (uPA-R, CD 87). Plasminogen is present in plasma and interstitial fluids from where it is bound to cell surfaces via plasmin(ogen) binding sites, uPA binds to the uPA-R in an autocrine manner and activates cell-bound plasminogen: a mechanism, which provides plasmin for pericellular proteolysis. Cell-bound uPA is regulated by plasminogen activator inhibitor type-1 (PAI-1) or type-2 (PAI-2). Bullous pemphigoid is an autoimmune inflammatory skin disease characterized by subepidermal blisters. Although circumstantial evidence suggested plasminogen activation in lesional epidermis of bullous pemphigoid, immunohistological data on the type of plasminogen activators, on the uPA-receptor or the type of plasminogen activator inhibitors in the lesions of bullous pemphigoid are lacking so far. To obtain this information we have performed the present immunohistological study, The presence of uPA and its receptor as well as PAI-2 was disclosed in epidermal keratinocytes in the roof of the subepidermal blisters. Moreover, keratinocytes at the bottom of the blister, which most likely represent keratinocytes during reepithelialization were stained. Co-localization was found for uPA and its receptor, uPA and plasmin(ogen) as well as for uPA and PAI-2. In non-lesional epidermis of bullous pemphigoid only PAI-2 was found. We propose that the expression of uPA and uPA-R, as well as the upregulation of PAI-2 in keratinocytes of lesional epidermis is part of the repair and reepithelialization process following lesion formation, i.e. epidermo-dermal dyshesion, in bullous pemphigoid.