In vivo expression of antimicrobial peptides in atopic dermatitis

The aim of this review is to present findings on expression of antimicrobial peptides (AMPs) in atopic dermatitis (AD) skin, focusing only on in vivo studies, and to discuss differences in results obtained using various skin sampling techniques and different methodology for analysis of AMPs. The review also includes a discussion of the effect of frequently used treatments on AMP expression. Many studies have shown a reduced level of AMPs in lesional AD skin when compared to psoriatic skin, explaining the high frequency of AD‐related infections. Interestingly, however, non‐lesional AD skin has shown the same upregulation of AMPs after barrier disruption as non‐lesional psoriatic skin. Various methods have been used to analyse AMP expression in the skin, and when comparing these methods, differences are revealed in AMP expression depending on the method used for sampling and analysis. Comparisons indicate that analyses of mRNA levels of AMPs may find greater differences in expression than analyses of protein levels. Few studies evaluate the effect of topical treatments on the expression of AMPs, and these indicate an inhibition of AMP expression, particularly after use of corticosteroids. AMPs are important components of the skin as a defense against infections, and despite much research, the clinical importance of the effect of common treatments, including systemic treatments for AD and the interplay between AMPs and the skin microbiome, is still largely unknown.