Single-cell omics reveal human mononuclear phagocyte heterogeneity and inflammatory DC in health and disease

Human mononuclear phagocytes comprise phenotypically and functionally overlapping subsets of dendritic cells (DC) and monocytes, but their identification remains elusive. By integrating high-dimensional single-cell protein and RNA expression data, we clearly delineated monocytes from conventional DC2 (cDC2), identifying new markers including CD88/CD89 for monocytes and HLA-DQ/FcRI for cDC2, allowing their unambiguous characterization in blood and tissues. We also show that cDC2 can be subdivided into phenotypically and functionally distinct subsets based on CD5, CD163 and CD14 expression, including a unique subset of circulating inflammatory CD5-CD163+CD14+ cells related to previously defined DC3. These inflammatory DC3 were expanded in systemic lupus erythematosus patients, correlating with disease activity. Unravelling the heterogeneity of DC sub-populations in health and disease paves the way for specific DC subset-targeting therapies.