LONG-TERM ULTRAVIOLET B-INDUCED IMPAIRMENT OF LANGERHANS CELL-FUNCTION - AN IMMUNOELECTRON MICROSCOPIC STUDY

The influence of low-dose, long-term ultraviolet B (UVB) light exposur e on HLA class II-positive human epidermal Langerhans cells (LC) was s tudied using a sensitive immunoelectron microscopic technique for the ultrastructural assessment of HLA class II expression on LC and for qu antification of these cells in situ. Six healthy Caucasian volunteers participated in the experiments and received thrice weekly UVB treatme nts for 4 weeks. The initial dose ranged from 30 to 50 mJ/cm(2) and th e total dose from 600 to 3500 mJ/cm(2), depending on skin type. Suctio n blisters and biopsies were obtained before the start of the UVB prot ocol and 48 h after the last UVB irradiation, and processed for the mi xed epidermal cell-lymphocyte reaction (MECLR) and electronmicroscopy, respectively. The MECLR was used as a measure of the immune response. The distribution of HLA class II molecules on LC was studied by incub ating ultrathin cryosections of human skin tissue with an anti-HLA cla ss II MoAb that was conjugated to 10 nm colloidal gold. Furthermore, t he number of LC was assessed ultrastructurally, when they could be rec ognized by their unique cytoplasmic organelle, the Birbeck granule (BG ). The UVB protocol that was employed caused a marked suppression of t he MECLR responses. This UVB-induced reduction of the immune response was not paralleled by changes in HLA class II expression on LC, nor in the number of epidermal LC. These findings are further support for ou r hypothesis that UVB-induced immune suppression in the skin is not du e to a depletion of local LC.