The innate defense of the skin against microbial threats is influenced by antimicrobial
proteins (
AMP). Staphylococcus aureus often colonizes the skin of patients with
atopic dermatitis (AD). This was explained by diminished expression of
AMP including
cathelicidin/LL-37, human beta-defensins-2 and -3, and
dermcidin. The S100-protein
psoriasin is an additional keratinocyte-derived
AMP that preferentially kills E. coli. As E. coli
infections are not observed in atopic skin we investigated the functional role of
psoriasin in AD patients. Immunohistochemistry demonstrated enhanced epidermal
psoriasin expression in AD. An up to 1500-fold increase in secreted
psoriasin was detected by ELISA in vivo on the surface of AD skin compared to healthy control skin. Surprisingly,
tumor necrosis factor-alpha-enhanced
psoriasin release in primary keratinocytes was inhibited by the Th2-cytokines
IL-4 and -13, whereas
IL-17 and -22 induced
psoriasin. Epidermal barrier disruption significantly enhanced
psoriasin expression as demonstrated by tape stripping in healthy volunteers. The upregulation of
psoriasin in AD maybe induced by the disrupted skin barrier offering a possible explanation why these patients do not suffer from skin
infections with E. coli. This indicates that the antimicrobial response in AD is not generally impaired, but greatly differs according to the type of
AMP produced by the skin.