Sialyl LewisX 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 LewisX acts as a ligand for endothelial-leukocyte adhesion molecule and granule membrane protein 140. We examined the expression of sialyl LewisX 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 LewisX+, although all of the sialyl LewisX+ 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 LewisX, 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 LewisX-. Immunoperoxidase study of normal skin showed the presence of sialyl LewisX+ dendritic cells not only in the epidermis but also in the upper dermis. These data demonstrating the heterogeneity of the expression of sialyl LewisX 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.