The role of GM-CSF during DC subset development. DCs are derived from HSCs through gradually restricted precursors. DC subsets can be classified into 3 main categories: migratory DCs, lymphoid-resident DCs, and plasmacytoid DCs. Supplemental Tables 1 and 2 show the phenotype and assigned classification of different DC populations that have been identified in distinct tissues in vivo or can be generated through specific culture methods. GM-CSF supports development of the common DC progenitor (CDP) and of the granulocyte/macrophage progenitor (G/M). Commitment of the CDP toward the plasmacytoid DC lineage is inhibited by GM-CSF, but terminal differentiation of committed plasmacytoid DC precursors (interferon-producing cells [IPCs]) is probably supported by GM-CSF. In contrast to lymphoid-resident DCs, whose development is hardly influenced by GM-CSF, migratory DC development requires GM-CSF. CLP indicates common lymphoid progenitor; lin⁻Flt3⁺, lineage⁻Flt3⁺ hematopoietic progenitor; CMP, common myeloid progenitor; MDP, macrophage and DC progenitor; CDP, common DC progenitor; pre-DC, precursor DC; mono, monocytes; pDC, plasmacytoid DC; cDC, conventional DC; intDC, interstitial DC; LC, Langerhans cell; and TIP-DC, TNF-α and inducible nitric-oxide synthase-producing DC.