In Vitro Effects of Ultraviolet B Radiation on Human Langerhans Cell Antigen-Presenting Function

The effects of ultraviolet B radiation (UVB) on the immune function of human epidermal Langerhans cells (LC) were studied by using the mixed epidermal cell-lymphocyte reaction (MELR). Exposure of both enriched LC suspensions (eLC, 8-20% LC) and purified LC suspensions (pLC, 70-90% LC) to increasing doses of UVB radiation (25 to 200 J/m2) decreased the proliferative T cell response in a very similar dose-dependent way, suggesting that keratinocytes did not play a major role in the UVB-induced inhibition of MELR. Supernatants from irradiated cultured eLC or pLC failed to inhibit T cell proliferation induced by untreated pLC. Furthermore, addition of irradiated eLC to untreated pLC did not affect the allogeneic T cell response. Taken together, these results provide evidence that in vitro UVB-induced immunosuppression was not mediated by inhibitory soluble factors that could affect either LC allostimulatory property or T cell proliferative response. UVB irradiation of human LC inhibited the capacity of these cells to induce CD4+ as well as CD8+ T cell proliferation. UVB-irradiated LC also induced a decreased T cell response to recall antigen or mitogen. Moreover, addition of exogeneous cytokines such as IL-1β, IL-1α, or IL-2 did not reverse the defective function of UVB-irradiated LC in MELR. The inhibitory effect of UVB radiation on human LC was not related to a decreased HLA-DR expression. Because cultured LC appeared to be less sensitive than freshly isolated LC to UVB-induced suppressive effects, the deleterious effects of UVB radiation on human LC allostimulatory properties may be associated with an impaired development of LC accessory function.