Immunological activation of dermal Langerhans cells in contact with lymphocytes in a model of human inflamed skin

Langerhans cells play an important role in the skin's immune system. Little is known, however, about the antigen-presenting capacity of Langerhans cel ls in the context of skin inflammation. By immunohistochemistry we investig ated the phenotypic characteristics of epidermal and dermal Langerhans cell s and their spatial relationship with infiltrating lymphocytes, We studied skin flaps autotransplanted to the oral cavity to fill a defect after maxil lofacial cancer surgery. In 15 of 21 cases sampled for the present study, t he skin flaps were severely inflamed by Candida albicans infection. In cont rast to the normal skin, such inflamed skin showed a marked increase in CD1 a(+) dermal Langerhans cells. Double immunohistochemistry revealed that der mal Langerhans cells abundantly expressed B7-2 (CD86), a representative cos timulatory molecule, and CD83, a marker of mature dendritic cells. Furtherm ore, these dermal Langerhans cells were in close contact with CD4(+)/CD45RO (+) lymphocytes, This cell-to-cell contact was further visualized by immuno electron microscopy. Langerhans cells were also observed within lymphatic v essels that mere identified by the expression of vascular endothelial growt h factor receptor-3, Ki-67 labeling indices were 4.2% in CD4(+) T cells and 0.8% in CD8(+) T cells within the dermis, Factor XIIIa(+) dermal dendrocyt es were distributed outside the clusters of lymphocytes and were not in con tact with them. Our observations indicate that dermal Langerhans cells in t he inflamed skin are activated to express common phenotypes to mature dendr itic cells so that they could stimulate neighboring memory CD4+ T cells.