Ultraviolet AI exposure of human skin results in Langerhans cell depletionand reduction of epidermal antigen-presenting cell function: partial protection by a broad-spectrum sunscreen

Background Ultraviolet (UV) B-induced effects on the skin immune system hav e been extensively investigated, but little is known regarding the immunolo gical changes induced by UVA exposure of human skin. Recent data assessing the protection afforded by sunscreens against photoimmunosuppression stress the need for broad-spectrum sunscreens with an adequate UVA protection. Objectives The purpose of this study was first to determine the changes obs erved in epidermal Langerhans cells (ELC) density and epidermal antigen-pre senting cell (APC) activity after exposure of human skin to UVAI (340-400 n m) radiation, and secondly to assess the immune protection afforded in vivo by a sunscreen formulation containing a long wavelength UVA filter with a low UVA protection factor (UVA-PF = 3). Methods Epidermal cell (EC) suspensions were prepared from skin biopsies 3 days after exposure to a single dose of UVAI (either 30 or 60 J cm(-2)). Results Flow-cytometric analysis of EC suspensions revealed that exposure t o 60 J cm(-2) UVAI resulted in a decreased number of ELC without infiltrati on of CD36+ DR+ CD1a- antigen-presenting macrophages into the epidermis, an d a significant reduction of HLA-DR expression on viable ELC. In vivo expos ure to both 30 and 60 J cm(-2) resulted in a decreased allogeneic CD4+ T-ce ll proliferation induced by UVAI-irradiated ECs. The sunscreen application partially prevented (57 +/- 9%) the decrease in epidermal allogeneic APC ac tivity induced by 60 J cm(-2) UVAI. Conclusions In vivo UVAI exposure of human skin results in a decreased numb er of ELC and in a downregulation of epidermal APC activity. This last effe ct is partially prevented by prior application of a sunscreen with a low UV AI-PF value. These results indicate that increasing the absorption of UV fi lters for long UVA wavelengths may lead to an improved immune protection.