MS-1 sinusoidal endothelial antigen is expressed by factor XIIIa+, HLA-DR+ dermal perivascular dendritic cells

We have recently described a monoclonal antibody, termed MS-1, which reacts with sinusoidal endothelium as well as interstitial cells in a variety of nonlymphoid organs. In this report, we characterize the phenotypes of MS-1-positive cells in normal human skin. Double immunohistochemical and immunofluorescence labeling techniques demonstrate that MS-1 antibody identifies two cell types in human dermis: the first represented by weakly reactive lymphatic endothelial cells; and the second comprised of strongly reactive, highly dendritic perivascular cells which constitutively express both HLA-DR and factor XIIIa. These MS-1-positive dendritic interstitial cells are ultrastructurally distinctive, separate from mast cells, phagocytic macrophages, pericytes, blood vascular endothelial cells, and fibroblasts. MS-1-positive cells express this protein in discrete cytoplasmic compartments, and possibly as small plasma membrane-associated regions. The phenotype, dendritic morphology, and perivascular localization of MS-1-positive cells suggest that MS-1 antibody recognizes an epitope expressed by cells previously referred to as dermal perivascular dendritic cells or dermal dendrocytes. We have proposed that MS-1 protein may serve as an anchoring molecule for endothelial cells in sinusoidal spaces in the absence of well-formed basement membranes. MS-1 may similarly function to maintain the spatial relationship of dermal perivascular dendritic cells with the microvasculature.