A macrophage phenotype for a constitutive, class II antigen-expressing, human dermal perivascular dendritic cell.

A previously uncharacterized population of class II antigen-bearing dendritic cells that are intimately associated with the dermal microvasculature was identified in normal human skin using a double-label, indirect immunofluorescence technique. The only other major HLA-DR positive dermal cell type noted in these studies, the dermal microvascular endothelial cell (DMVEC), appeared to express lesser amounts of HLA-DR region gene product than did this dermal perivascular dendritic cell (DPDC). These DPDC were particularly common around small vessels in the superficial vascular plexus of the papillary dermis and were distinct from the mast cell, another cell type normally seen in a similar location. Phenotypic and ultrastructural studies have determined that the DPDC is more closely related to the monocyte/macrophage lineage than the dendritic cell lineage. The perivascular location and phenotype of this cell distinguishes it from other previously described constitutive dermal cell types such as the classic "histiocyte," veiled cell, and dendrocyte. The relatively rich expression of all three major HLA-D region gene products by this dermal perivascular dendritic macrophage would suggest that it could play a significant role in the immunobiology of the dermal microvascular unit.