Expression and ultrastructural localization of plasmin(ogen) in the terminally differentiated layers of normal human epidermis

OBJECTIVE: Plasmin, a relatively unspecific trypsin-like serine protease, is involved in many physiological and pathological conditions, particularly in dermatoses with barrier impairment. It is secreted as the inactive zymogen plasminogen and is activated to plasmin by plasminogen activators, such as urokinase. There still exists a paucity of data on the precise localization of epidermal plasmin(ogen) within the epidermis and the stratum corneum. The aim of the present study was to get information about its origin and ultrastructural localization within normal human epidermis. METHOD: We performed immunoelectron transmission electron microscopy immunogold labelling in normal abdominal human skin. RESULT: Plasmin was only observed in the terminally differentiated cell layers of the epidermis and was largely associated with the corneocyte envelopes and to some extent with the intercellular lipid matrix in the stratum corneum. CONCLUSION: Our results indicate that in normal human skin, plasmin(ogen) is synthesized by differentiated epidermal keratinocytes of the stratum granulosum and is not serum-born.