Separation of Plasmacytoid Dendritic Cells from B-Cell-Biased Lymphoid Progenitor (BLP) and Pre-Pro B Cells Using PDCA-1

B-cell-biased lymphoid progenitors (BLPs) and Pre-pro B cells lie at a critical juncture between B cell specification and commitment. However, both of these populations are heterogenous, which hampers investigation into the molecular changes that occur as lymphoid progenitors commit to the B cell lineage. Here, we demonstrate that there are PDCA-1+Siglec H+ plasmacytoid dendritic cells (pDCs) that co-purify with BLPs and Pre-pro B cells, which express little or no CD11c or Ly6C. Removal of PDCA-1+ pDCs separates B cell progenitors that express high levels of a Rag1-GFP reporter from Rag1-GFPlow/neg pDCs within the BLP and Pre-pro B populations. Analysis of Flt3-ligand knockout and IL-7Rα knockout mice revealed that there is a block in B cell development at the all-lymphoid progenitor (ALP) stage, as the majority of cells within the BLP or Pre-pro B gates were PDCA-1+ pDCs. Thus, removal of PDCA-1+ pDCs is critical for analysis of BLP and Pre-pro B cell populations. Analysis of B cell potential within the B220+CD19− fraction demonstrated that AA4.1+Ly6D+PDCA-1− Pre-pro B cells gave rise to CD19+ B cells at high frequency, while PDCA-1+ pDCs in this fraction did not. Interestingly, the presence of PDCA-1+ pDCs within CLPs may help to explain the conflicting results regarding the origin of these cells.