Studies on the effects of a high dose UVA-1 radiation therapy on surface markers and function of epidermal Langerhans cells

Recently, high-dose UVA-1 therapy (340–400 nm) was introduced as an effective treatment of severe exacerbated atopic dermatitis. Since the target of this type of radiation in the skin is not known we investigated using the mouse model whether surface markers of the antigen-presenting function of epidermal Langerhans cells are affected by UVA-1 radiation. Even repeated high doses of UVA-1 radiation (up to 50 J/cm2) had no detectable effect on surface ATPase activity and Ia antigen expression on Langerhans cells. Also, the contact allergen oxazolone was presented normally in skin treated with UVA-1 radiation. In contrast, if the mice were injected 1 h before irradiation with 8-methoxypsoralen a dramatic reduction in ATPase activity and Ia antigen expression on Langerhans cells was observed and the induction of contact sensitivity was suppressed (PUVA effect). These results show that epidermal Langerhans cells are not impaired either in structure or function and that these cells probably do not represent the primary target of UVA-1 radiation in the skin. No side effects resulting from a diminished Langerhans cell function should result from high-dose UVA-1 therapy.