In vivo UVA-1 and UVB irradiation differentially perturbs the antigen-presenting function of human epidermal Langerhans cells

Ultraviolet B (UVB, 290-320 nm) radiation is known to suppress the immune f unction of epidermal Langerhans cells. We have recently described that in v itro UVB irradiation perturbs the antigen-presenting cell function of Lange rhans cells by inhibiting their expression of functional B7 costimulatory m olecules (B7-1, B7-2), The aim of this study was to determine wavelength-sp ecific UV effects on Langerhans cells function in vivo, specifically UVB an d UVA-1, To address this issue, volunteers were irradiated on the sunprotec ted volar aspects of their forearms with 3 X minimal erythema dose of UVB ( Philips TL-12) and UVA-1 (UVASUN 5000 Mutzhaas), Langerhans cells were isol ated from suction blister roofs immediately following irradiation. Langerha ns cells isolated from UVB- but not from UVA-l-irradiated skin failed to ac tivate naive resting allogeneic T cells (mixed epidermal cell leukocyte rea ction) or primed tetanus toroid reactive autologous T cells. Langerhans cel ls isolated from sham-irradiated or UVA-l-irradiated skin strongly upregula ted B7-2 molecules during shortterm tissue culture. By contrast, Langerhans cells from UVB-irradiated skin did not upregulate B7-2 molecules. Furtherm ore, exogenous stimulation of the B7 pathway by anti-CD28 stimulatory monoc lonal antibodies restored the capacity of UVB-irradiated Langerhans cells t o activate both alloreactive and tetanus toroid-reactive T cells, implying suppressed antigen-presenting cell activities and perturbed B7 expression o f Langerhans cells isolated from UVB-irradiated skill are related. Those st udies demonstrate that in vivo UVB, but not UVA-1, interferes with the acti vation-dependent upregulation of B7 molecules on Langerhans cells, which in turn is of functional relevance for the perturbed antigen-presenting cell function of Langerhans cells within UVB- but not UVA-1-irradiated skin.