Signaling through Notch receptors and their transcriptional effector RBP-J is essential for lymphocyte development and function, whereas its role in other immune cell types is unclear. We tested the function of the canonical Notch–RBP-J pathway in dendritic cell (DC) development and maintenance in vivo. Genetic inactivation of RBP-J in the bone marrow did not preclude DC lineage commitment but caused the reduction of splenic DC fraction. The inactivation of RBP-J in DCs using a novel DC-specific deleter strain caused selective loss of the splenic CD8− DC subset and reduced the frequency of cytokine-secreting CD8− DCs after challenge with Toll-like receptor ligands. In contrast, other splenic DC subsets and DCs in the lymph nodes and tissues were unaffected. The RBP-J–deficient splenic CD8− DCs were depleted at the postprogenitor stage, exhibited increased apoptosis, and lost the expression of the Notch target gene Deltex1. In the spleen, CD8− DCs were found adjacent to cells expressing the Notch ligand Delta-like 1 in the marginal zone (MZ). Thus, canonical Notch–RBP-J signaling controls the maintenance of CD8− DCs in the splenic MZ, revealing an unexpected role of the Notch pathway in the innate immune system.

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CD103(+)CD11b(+) dendritic cells (DCs) represent the major migratory DC population within the small intestinal lamina propria (SI-LP), but their in vivo function remains unclear. Here we demonstrate that intestinal CD103(+)CD11b(+) DC survival was dependent on interferon regulatory factor 4 (IRF4). Mice with a DC deletion in Irf4 displayed reduced numbers of intestinal interleukin 17 (IL-17)-secreting helper T 17 (Th17) cells and failed to support Th17 cell differentiation in draining mesenteric lymph nodes (MLN) following immunization. The latter was associated with a selective reduction in CD103(+)CD11b(+) MLN DCs and DC derived IL-6. Immunized Il6(-/-) mice failed to support Th17 cell differentiation in MLN in vivo and CD103(+)CD11b(+) MLN DCs supported IL-6-dependent Th17 cell differentiation in vitro. Together, our results suggest a central role for IRF4-dependent, IL-6 producing CD103(+)CD11b(+) DCs in intestinal Th17 cell differentiation.

Summary Plasmacytoid dendritic cells (PDC) represent a unique immune cell type specialized in type I interferon (IFN) secretion in response to viral nucleic acids. The molecular control of PDC lineage specification has been poorly understood. We report that basic helix-loop-helix transcription factor (E protein) E2-2/Tcf4 is preferentially expressed in murine and human PDC. Constitutive or inducible deletion of murine E2-2 blocked the development of PDC but not of other lineages, and abolished IFN response to unmethylated DNA. Moreover, E2-2 haploinsufficiency in mice and in human Pitt-Hopkins syndrome patients was associated with aberrant expression profile and impaired IFN response of the PDC. E2-2 directly activated multiple PDC-enriched genes, including transcription factors involved in PDC development (SpiB, Irf8) and function (Irf7). These results identify E2-2 as a specific transcriptional regulator of the PDC lineage in mice and humans, and reveal a key function of E proteins in the innate immune system.

Summary Dendritic cells (DCs) in tissues and lymphoid organs comprise distinct functional subsets that differentiate in situ from circulating progenitors. Tissue-specific signals that regulate DC subset differentiation are poorly understood. We report that DC-specific deletion of the Notch2 receptor caused a reduction of DC populations in the spleen. Within the splenic CD11b+ DC subset, Notch signaling blockade ablated a distinct population marked by high expression of the adhesion molecule Esam. The Notch-dependent Esamhi DC subset required lymphotoxin beta receptor signaling, proliferated in situ and facilitated CD4+ T cell priming. The Notch-independent Esamlo DCs expressed monocyte-related genes and showed superior cytokine responses. In addition, Notch2 deletion led to the loss of CD11b+ CD103+ DCs in the intestinal lamina propria and to a corresponding decrease of IL-17-producing CD4+ T cells in the intestine. Thus, Notch2 is a common differentiation signal for T cell-priming CD11b+ DC subsets in the spleen and intestine.