Kallikrein Protease Involvement in Skin Pathologies Supports a New View of the Origin of Inflamed Itchy Skin

Abstract

Skin barrier defects in common dermatological diseases, such as atopic dermatitis and psoriasis, are mostly attributed to anomalies in T-cell immunity. A new viewpoint of inflammatory dermatoses onset was recently suggested, in which barrier defects trigger secretion of pro-inflammatory mediators by stressed keratinocyte cells, which activate the T-cell immune system and further deteriorate the barrier. Herein, we review epidermal keratinocytes as active immune cells. In particular, we focus on recent groundbreaking evidence on the role of keratinocyte-secreted kallikreins as inflammation and allergy mediators. Kallikreins are skin surface proteases known for their role in digesting adhesion proteins and maintaining barrier integrity and function. Kallikrein hyperactivity in skin pathologies was recently shown to mediate inflammation secondary to inherited and acquired barrier defects, in support of the epidermal roots of inflamed and itchy skin. Hence, future therapy design should be directed toward ameliorating keratinocyte-induced barrier defects and inflammation, alone or in combination with dampening T-cell immune responses.