Psoriasis as a barrier disease

Skin is equipped with a barrier function, in particular, to prevent invasion of pathogens. Skin barrier is composed of a mechanical barrier, a permeability barrier, and innate and adaptive immunity barriers. Psoriasis is an inflammatory skin disease, which develops through the interaction of epidermal keratinocytes and immune cells, although its pathoetiology has not been fully understood. Recent studies revealed that defects in epidermal barrier-related genes were associated with a risk of psoriasis. Indeed, psoriasis is characterized by compromised barrier function, similar to atopic dermatitis (AD), in which mutations of the filaggrin gene play a role. However, it remains to be determined whether epidermal barrier disruption leads to an altered inflammatory/immunological response in psoriasis. In this review, I demonstrate evidence, in human psoriasis as well as mouse models, showing that barrier insult contributes to psoriasis development through alteration of the innate and adaptive immunity.