Surface LSP1 is a phenotypic marker distinguishing human classical versus monocyte-derived dendritic cells

Human mononuclear phagocytes comprise several subsets of dendritic cells (DCs), monocytes and macrophages. Distinguishing one population from another is challenging, especially in inflammed tissues, due to the promiscuous expression of phenotypic markers. Using a synthetic library of humanized llama single domain antibodies, we identified a novel surface marker for human naturally-occuring monocyte-derived DCs. Our antibody targets an extra-cellular domain of LSP-1, specifically on monocyte-derived DCs, but not on monocytes, macrophages or classical DCs. Using this antibody, we provide evidence that the recently described blood DC3 population does not correspond to circulating monocyte-derived DCs. Our findings will pave the way for a better characterization of human mononuclear phagocytes in pathological settings.