The Role of Antimicrobial Peptides in Human Skin and in Skin Infectious Diseases

Antimicrobial peptides or proteins (AMPs) represent an ancient and efficient innate defense mechanism which protects interfaces from infection with pathogenic microorganisms. In human skin AMPs are produced mainly by keratinocytes, neutrophils, sebocytes or sweat glands and are either expressed constitutively or after an inflammatory stimulus. In several human skin diseases there is an inverse correlation between severity of the disease and the level of AMP production. Skin lesions of patients with atopic dermatitis show a diminished expression of the beta-defensins and the cathelicidin LL-37. Furthermore, these patients have a reduced amount of the AMP dermcidin in their sweat which correlates with an impaired innate defense of human skin in vivo. In addition, decreased levels of AMPs are associated with burns and chronic wounds. In contrast, overexpression of AMPs can lead to increased protection against skin infections as seen in patients with psoriasis and rosacea, inflammatory skin-diseases which rarely result in superinfection. In other skin diseases, e.g. in patients with acne vulgaris, increased levels of AMPs are often found in inflamed or infected skin areas indicating a role of these peptides in the protection from infection. These data indicate that AMPs have a therapeutical potential as topical anti-infectives in several skin diseases. The broad spectrum of antimicrobial activity, the low incidence of bacterial resistance and their function as immunomodulatory agents are attractive features of AMPs for their clinical use.