Dermal microvascular endothelial cells express the 180-kDa macrophage mannose receptor in situ and in vitro

Expression of the 180-kDa mannose receptor (MR) is mainly found on cells of the macrophage lineage. MR mediates the uptake of micro-organisms and host -derived glycoproteins. We demonstrate that endothelium of the human skin i n situ and dermal microvascular endothelial cells (DMEC) in vitro expressed MR at both the protein and mRNA levels, In contrast, HUVEC were consistent ly negative for MR expression, DMEC internalized dextran as well as Escheri chia coli by the may of MR into acidic phagosomes, only a few of which fuse d with CD63- and lysosomal-associated membrane glycoprotein-2-positive lyso somes, This contrasts with the situation in monocyte-derived dendritic cell s, where almost all of the MR-Ag complexes reached CD63- and lysosomal-asso ciated membrane glycoprotein-2-positive compartments, indicating difference s in the phagolysosomal fusion rate between DMEC and dendritic cells. In co nclusion, DMEC express functional MR, a finding that corroborates a role of skin endothelium in Ag capture/clearing.