Perivascular dendritic macrophages as immunobiological constituents of the human dermal microvascular unit.

We have recently observed a previously uncharacterized population of class II (Ia) antigen-positive dendritic cells that is intimately associated with the dermal microvessels of normal human adult and newborn skin. Immunofluorescence and immunoelectron microscopy studies have indicated that this cell is a perivascular macrophage. This dermal perivascular dendritic macrophage was seen in greatest density in the superficial vascular plexus and appears to constitute a large percentage of the total dermal macrophage population. Because tissue macrophages do not always share the same immunologic repertoire as circulating monocytes/macrophages, we became interested in examining the functional immunologic capabilities of this dermal dendritic macrophage. A procedure was developed to isolate and partially purify these cells from normal human newborn foreskin. Preliminary findings are compatible with the possibility that these cells possess the capacity to present alloantigens to CD4+ T cells. The potential immunologic function of this dermal perivascular macrophage is discussed in the context of its possible interactions with the other cellular components of the dermal microvascular unit (i.e., microvascular endothelial cells, perivascular T cells, and mast cells).