Fig. 1

Phenotypic and functional description of dendritic cell types. Dendritic cells (DCs) encompass different cell types, including plasmacytoid dendritic cells (pDCs), CD11c^low (CD11c^low Ly6C^high) and CD11c^high (CD11c^high Ly6C^low) transitional dendritic cells (tDCs) and conventional dendritic cells (cDCs), which are divided into type 1 cDCs (cDC1s) and type 2 cDCs (cDC2s). pDCs are characterized by their capacity to produce large amounts of IFN-I/IIIs upon exposure to a large spectrum of TLR7/9 ligands of viral or synthetic origin (e.g., CpG A and B), while CD11c^low Ly6C^high tDCs are activated mainly by CpG-B. IFN-IIIs can also be produced by cDC1s via a TLR3-TRIF-dependentmechanism. At steady state, cDC2s and CD11c^high Ly6C^low tDCs can present antigens (pale blue) associated with MHC class II (MHC-II) for CD4 T-cell activation, while cDC1s excel in the ability to cross-present cell-associated antigens for CD8 T-cell activation (gray). Upon activation, pDCs also acquire the transcriptional, phenotypic, and functional features of antigen-presenting cells. However, their ability to contribute to the antigen-specific activation of T cells in vivo is controversial. The expression of selected cell surface, cytoplasmic and endosomal molecules, as well as some of the key nuclear transcription factors controlling their development or functions, is shown for each DC type. Molecules exclusively expressed in mice or in humans are depicted in yellow or blue, respectively, while molecules conserved between the two species are in green. The color intensity is proportional to the level of expression