COMPARATIVE POTENCY OF DIFFERENT UV SOURCES IN REDUCING THE DENSITY AND ANTIGEN-PRESENTING CAPACITY OF LANGERHANS CELLS IN C3H MICE

Abstract Although broadband UV-B irradiation has been shown to induce selective immunosuppression in a variety of experimental systems, the wavelength dependence of the immunomodulation and the initial events in the skin remain unclear. In the present study three UV lamps were used at suberythermal doses on C3H mice: a conventional broadband UV-B source (270–350 nm), a narrowband UV-B source (311–312 nm) and a UV-A source (320400 nm). Their effects on the photoisomerization of the naturally occumng trans- isomer of urocanic acid (UCA) to cis- UCA, on the density of Langerhans cells and on the ability of epidermal cells to stimulate allogeneic lymphocytes in the mixed skin lymphocyte reaction (MSLR) were ascertained. Broadband UV-B irradiation was more efficient than narrowband UV-B at reducing the density and function of Langerhans cells, while UV-A irradiation was least effective. These changes were most pronounced immediately following irradiation, were dose dependent and were only detected in UV-exposed areas of skin. There was a close correlation between the UV-induced reduction in Langerhans cell density and the formation of cis -UCA in the epidermis. This correlation was not detected between the reduction in the MSLR response following UV irradiation in vivo and cis-UCA formation.