Ultrastructural documentation of M241 glycoprotein on dendritic and endothelial cells in normal human skin.

M241 is a glycoprotein that recently has been demonstrated to be present in human thymus in a distribution similar to T6. Studies in skin, however, suggest that M241, in contrast to T6, is detected only on a subset of Langerhans cells and on a population of dendritic cells in the superficial dermis. We compared the reactivities of monoclonal antibodies to M241 and T6 with dendritic cells in normal human skin using immunoelectron microscopy. Our findings indicate that M241 is present on a minority of Langerhans cells and on a substantial number of other predominantly dermal dendritic cells with morphologic features of indeterminate cells. Anti-M241 reactivity was generally restricted to the cell membrane, although cytoplasmic reactivity was detected in some Langerhans cells. Dermal endothelial cells, which like dendritic cells are capable of antigen presentation, were also reactive with anti-M241 antibody. M241 is a glycoprotein, different from T6, with a tissue distribution potentially relevant to the understanding of antigen-presenting cells in the skin.