title: UV-B radiation induces the expression of antimicrobial peptides in human keratinocytes in vitro and in vivo.
abstract: BACKGROUND
  Suppression of the adaptive immune system by UV radiation plays an important role in photocarcinogenesis. Exacerbation of skin infections has been proposed as a further consequence of UV-induced immunosuppression. Clinically bacterial infections are not a problem. For defense against bacteria, the innate immune response including the release of antimicrobial peptides is much more relevant than the adaptive immune response. Keratinocytes have the capacity to release antimicrobial peptides.
  
  
  OBJECTIVE
  We asked whether UV radiation induces antimicrobial peptides in vitro and in vivo.
  
  
  METHODS
  Antimicrobial peptide expression by normal human keratinocytes was measured by real-time PCR and fluorescence-activated cell sorting analysis. Biopsies taken from human volunteers and skin explants were studied with immunohistochemistry.
  
  
  RESULTS
  Real-time PCR of normal human keratinocytes revealed a dose-dependent increase of human beta-defensin-2, -3, ribonuclease 7, and psoriasin (S100A7) after UV radiation. This was confirmed at the protein level by intracellular fluorescence-activated cell sorting and in vitro immunofluorescence analysis. Immunohistochemistry of biopsies taken from healthy volunteers exposed to different UV radiation doses revealed enhanced epidermal expression of antimicrobial peptides after UV exposure. This was also confirmed by exposing human skin explants to UV radiation.
  
  
  CONCLUSIONS
  UV radiation exerts diverse effects on the immune system, suppressing the adaptive but inducing the innate immune response. This may explain why T-cell-mediated immune reactions are suppressed on UV exposure but not host defense reactions against bacterial attacks.
authors.affiliation: Department of Dermatology and Allergology, University Kiel, Kiel, Germany.
authors.forename: Regine
authors.initials: R
authors.lastname: Gläser
authors.forename: Fatemeh
authors.initials: F
authors.lastname: Navid
authors.forename: Winfried
authors.initials: W
authors.lastname: Schuller
authors.forename: Christian
authors.initials: C
authors.lastname: Jantschitsch
authors.forename: Jürgen
authors.initials: J
authors.lastname: Harder
authors.forename: Jens M
authors.initials: JM
authors.lastname: Schröder
authors.forename: Agatha
authors.initials: A
authors.lastname: Schwarz
authors.forename: Thomas
authors.initials: T
authors.lastname: Schwarz