Human Dermal CD14+ Cells Are a Transient Population of Monocyte-Derived Macrophages

Dendritic cells (DCs), monocytes, and macrophages are leukocytes with critical roles in immunity and tolerance. The DC network is evolutionarily conserved; the homologs of human tissue CD141(hi) XCR1(+)CLEC9A(+) DCs and CD1c(+) DCs are murine CD103(+) DCs and CD64(-)CD11b(+) DCs. In addition, human tissues also contain CD14(+) cells, currently designated as DCs, with an as-yet unknown murine counterpart. Here we have demonstrated that human dermal CD14(+) cells are a tissue-resident population of monocyte-derived macrophages with a short half-life of <6 days. The decline and reconstitution kinetics of human blood CD14(+) monocytes and dermal CD14(+) cells in vivo supported their precursor-progeny relationship. The murine homologs of human dermal CD14(+) cells are CD11b(+) CD64(+) monocyte-derived macrophages. Human and mouse monocytes and macrophages were defined by highly conserved gene transcripts, which were distinct from DCs. The demonstration of monocyte-derived macrophages in the steady state in human tissue supports a conserved organization of human and mouse mononuclear phagocyte system.