title: Decreased human epidermal antigen-presenting cell activity after ultraviolet A exposure: dose-response effects and protection by sunscreens.
abstract: BACKGROUND
  Ultraviolet (UV) exposure of human skin causes immunosuppression that contributes to the growth of skin cancer. The contribution of UVA in these processes is still a matter of debate.
  
  
  OBJECTIVE
  The purpose of our study was first to find a dose-response effect of UVA exposure on human epidermal antigen-presenting cell (APC) activity and to evaluate the protective capacity of two sunscreen formulations against a high level of acute UVA exposure. We also tried to evaluate the protective capacity afforded by the same sunscreens against UVA-induced clinical changes such as redness and pigmentation.
  
  
  METHODS
  The functional assessment of the alloantigen-presenting capacity of epidermal cells prepared from skin keratotome samples 3 days after UVA exposure was measured with a mixed epidermal cell-lymphocyte reaction (MECLR) in each healthy volunteer (n = 16). Redness and pigmentation were assessed by chromametry 24 h after exposure to a single UVA dose.
  
  
  RESULTS
  In vivo UVA exposure to 15, 30 and 60 J cm(-2) resulted in a dose-dependent decrease in purified allogeneic T cell (CD4+ T cells) proliferation induced by UVA-irradiated epidermal cells. The epidermal APC function was significantly decreased with a suberythemal exposure corresponding to 15 J cm(-2). The decrease, partial and not statistically different between 30 and 60 J cm(-2), exhibits a plateau-response effect. There was no correlation between the decrease of the epidermal APC function and the intensity of erythema and persistent pigment darkening. Both sunscreen formulations strongly inhibited the UVA-induced reduction of MECLR at 90 J cm(-2).
  
  
  CONCLUSIONS
  Our results clearly demonstrate that UVA impairs the APC activity of the epidermal cells and thus may contribute to UV-induced immunosuppression in humans. They also indicate that erythema and immunosuppression have different dose-response curves in the UVA range. The two sunscreen formulations afforded a significant protection against the decrease in epidermal APC activity induced by exposure to a high UVA dose (90 J cm(-2)).
authors.affiliation: Service de Dermatologie, CHU Caremeau, Place du Pr. Debre, 30029 Nîmes cedex 09, France.
authors.forename: P E
authors.initials: PE
authors.lastname: Stoebner
authors.forename: R
authors.initials: R
authors.lastname: Poosti
authors.forename: K
authors.initials: K
authors.lastname: Djoukelfit
authors.forename: J
authors.initials: J
authors.lastname: Martinez
authors.forename: L
authors.initials: L
authors.lastname: Meunier
mesh_terms: D000328:Adult; D000938:Antigen-Presenting Cells / Q000528:radiation effects*; D015496:CD4-Positive T-Lymphocytes / Q000528:radiation effects; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D007111:Immunity, Cellular / Q000528:radiation effects; D007519:Isoantigens / Q000528:radiation effects; D008297:Male; D012880:Skin Pigmentation / Q000528:radiation effects*; D013473:Sunscreening Agents / Q000008:administration & dosage*; D014466:Ultraviolet Rays / Q000009:adverse effects*
chemical_list: D007519:Isoantigens; D013473:Sunscreening Agents