Differing cell surface distribution of human leukocyte antigen-DR molecules on epidermal Langerhans cells and eccrine duct cells.

Scanning electron microscopy (SEM) with immunogold labeling was employed to observe the undersurface of the human epidermis after it was split from dermal connective tissue, in an attempt to localize the molecules actually expressed on cell/tissue surfaces. We found that human leukocyte antigen-DR (HLA-DR) molecules were expressed on the surfaces of eccrine duct cells as well as those of epidermal Langerhans cells (LC) in normal skin. HLA-DR molecules, visualized by the deposition of gold particles, were distributed evenly on the LC surface but were present only along the interdigitating borders of the individual duct cells, thus producing a meshwork pattern on the duct surface. Transmission electron microscopy confirmed that the gold particles labeling cell surface HLA-DR molecules were seen only on the portions of duct cell membranes the interdigitated with neighboring duct cells. These findings suggest that the function of HLA-DR molecules may vary with their location and distribution. On the LC surface, the evenly distributed molecules seem to be well suited for promoting "accessory cell" functions. On duct cell surfaces, the HLA-DR molecules present along the intercellular spaces may be involved in trapping various peptide antigens that pass into the sweat gland filtrate and then are reabsorbed by the excretory duct, since these molecules have a highly permissive capacity for binding various peptides.