Ly6D+ Siglec-H+ precursors contribute to conventional dendritic cells via a Zbtb46+ Ly6D+ intermediary stage

Plasmacytoid and conventional dendritic cells (pDC and cDC) are generated from progenitor cells in the bone marrow and it was shown that commitment to pDCs or cDC subtypes may occur in earlier and later progenitor stages. Cells within the CD11c+ MHCII-/lo Siglec-H+ CCR9lo DC precursor fraction of the mouse bone marrow were shown to generate both pDCs and cDCs. Here we investigate the heterogeneity and commitment of subsets in this compartment by single-cell transcriptomics and high-dimensional flow cytometry combined with cell fate analysis: Within the CD11c+ MHCII-/lo Siglec-H+ CCR9lo DC precursor pool cells expressing high levels of Ly6D and lacking expression of transcription factor Zbtb46 contain CCR9lo B220hi immediate pDC precursors and CCR9lo B220lo (lo-lo) cells which still generate pDCs and cDCs in vitro and in vivo under steady state conditions. cDC-primed cells within the Ly6Dhi Zbtb46– lo-lo precursors rapidly upregulate Zbtb46 and pass through a Zbtb46+ Ly6D+ intermediate stage before acquiring cDC phenotype after cell division. Type I IFN stimulation limits cDC and promotes pDC output from this precursor fraction by arresting cDC-primed cells in the Zbtb46+ Ly6D+ stage preventing their expansion and differentiation into cDCs. Modulation of pDC versus cDC output from precursors by external factors may allow for adaptation of DC subset composition at later differentiation stages.