Sialyl Lewis^x expression on human Langerhans cells

Recently, it has been demonstrated that the skin-infiltrating T cells express cutaneous lymphocyte-associated antigen, which is the ligand of E-selectin or endothelial-leukocyte adhesion molecule, suggesting that cutaneous lymphocyte-associated antigen functions as the homing receptor of the skin infiltrating T cells. In contrast, the mechanism for the migration of Langerhans cells from the bone marrow to the skin has not been clarified. Sialyl Lewis^x acts as a ligand for endothelial-leukocyte adhesion molecule and granule membrane protein 140. We examined the expression of sialyl Lewis^x in epidermal dendritic cells in human skin. Two-color immunofluorescence study on an epidermal sheet revealed that human leukocyte antigen DR⁺ or CD1a⁺ epidermal dendritic cells were partially sialyl Lewis^x+, although all of the sialyl Lewis^x+ dendritic cells were human leukocyte antigen DR⁺ and CD1a⁺. Further analysis of these dendritic cells by flow cytometry demonstrated that most of the human leukocyte antigen DR⁺ and CD1a⁺ epidermal cells expressed sialyl Lewis^x, although the magnitude of its expression was more variable than that of CD1a expression, and that some of human leukocyte antigen DR⁺ cells were clearly sialyl Lewis^x. Immunoperoxidase study of normal skin showed the presence of sialyl Lewis^x+ dendritic cells not only in the epidermis but also in the upper dermis. These data demonstrating the heterogeneity of the expression of sialyl Lewis^x by epidermal Langerhans cells suggest their possible relationship to the stage of maturation as well as to the migration of Langerhans cells from the bone marrow to the skin.