Interferon-producing cells develop from murine CD31^high/Ly6C^- marrow progenitors

In this study, we sorted total bone marrow (BM) into six distinct subsets based on surface expression of CD31 and Ly6C and investigated the capacity of these subsets to acquire characteristics of plasmacytoid dendritic cells (PDCs) after in vitro culture with FMS-like tyrosine kinase 3 ligand (Flt3-L). Cultured CD31^high/Ly6C^- cells were the only subset that consistently developed immunophenotypic, functional, and morphologic characteristics of PDCs. Culture of this subset resulted in expression of CD11c, B220, and the PDC-specific marker 440C and secretion of interferon-α (IFN-α) when stimulated with CPG ODN 2216. Cultured cells displayed the typical plasmacytoid morphology of PDCs with eccentrically located nucleus and mature lymphoid chromatin. Unlike conventional dendritic cells (CDCs) that can be generated from CD31^high/Ly6C^-, CD31⁺/Ly6C⁺, and CD31^-/Ly6C^high BM subpopulations, PDCs can only be derived from the CD31^high/Ly6C^- subset, the subset that reportedly contains the highest frequency of early and late cobblestone area forming cells (CAFC).