In vitro effect of UV radiation on immune function and membrane markers of human Langerhans cells.

Human Langerhans cells (LC) are located in the epidermal tissue which is naturally accessible to UV irradiation. They may be the first immunocompetent cells exposed to its effect. In the present study, the epidermal tissue was dissociated with trypsin, and epidermal cell (EC) suspensions, which contain keratinocytes, melanocytes, and LC were irradiated with UVB (10 or 20 mJ/cm2). After irradiation LC retained their surface determinants: T-6 and HLA-Dr. In addition, their number did not decrease during 3 days of culture following UVB exposure as compared with nonirradiated EC cultured in parallel. On the contrary, UV irradiation of EC resulted in decreased lymphocyte-stimulating ability in a mixed skin cell-lymphocyte culture reaction (MSLR). EC used directly after irradiation in MSLR induced about half the lymphocyte response compared to nonirradiated EC. After 24-h culture, the irradiated EC did not produce any lymphocyte response, whereas the 48-h cultures showed a slight lymphocyte stimulation. At 72 h the cultures from irradiated and nonirradiated EC showed similar responses in MSLR. The doses of UV radiation which decreased MSLR responses did not affect EC viability and did not significantly reduce their DNA content. It is suggested that under the experimental conditions used in this study the defect induced by UV irradiation was essentially functional and was the result of the transient inhibition of the antigen processing function of LC rather than of an alteration in membrane antigen expression (T-6 and HLA-Dr).