Dendritic cells: transcriptional control of plasmacytoid dendritic cell development by E2-2

TRAF5 promotes plasmacytoid dendritic cell development from bone marrow progenitors

The conventional dendritic cells (cDCs) and plasmacytoid DCs (pDCs) originate from the same common dendritic cell precursor cells in the bone marrow. The pDCs produce large amounts of type 1 interferon in response to foreign nucleic acid and crucially contribute to host defense against viral infection. Tumor necrosis factor (TNF) receptor-associated factor 5 (TRAF5) is a pivotal component of various TNF receptor signaling pathways in the immune system. Although the functions of TRAF5 in T and B lymphocytes have been well studied, its roles in pDCs remains to be fully elucidated. In this study, we show that the expression of TRAF5 supports the generation of pDCs in the bone marrow and also critically contributes to the homeostasis of the pDC subset in the periphery in a cell-intrinsic manner. Furthermore, we provide evidence that TRAF5 promotes the commitment of DC precursor cells toward pDC versus cDC subsets, which is regulated by the balance of transcription factors TCF4 and ID2. Together our findings reveal that TRAF5 acts as a positive regulator of pDC differentiation from bone marrow progenitors.

Dendritic Cell Subsets in Asthma: Impaired Tolerance or Exaggerated Inflammation?

Asthma is a prevalent chronic heterogeneous inflammatory disease of the airways, leading to reversible airway obstruction, in which various inflammatory responses can be observed. Mild to moderate asthma patients often present with a Th2-mediated eosinophilic inflammation whereas in severe asthma patients, a Th17-associated neutrophilic or combined Th2 and Th17-mediated eosinophilic/neutrophilic inflammation is observed. The differentiation of these effector Th2 and Th17-cells is induced by allergen-exposed dendritic cells (DCs) that migrate toward the lung draining lymph node. The DC lineage comprises conventional DCs (cDCs) and plasmacytoid DCs (pDCs), of which the cDC lineage consists of type 1 cDCs (cDC1s) and cDC2s. During inflammation, also monocytes can differentiate into so-called monocyte-derived DCs (moDCs). These DC subsets differ both in ontogeny, localization, and in their functional properties. New identification tools and the availability of transgenic mice targeting specific DC subsets enable the investigation of how these different DC subsets contribute to or suppress asthma pathogenesis. In this review, we will discuss mechanisms used by different DC subsets to elicit or hamper the pathogenesis of both Th2-mediated eosinophilic asthma and more severe Th17-mediated neutrophilic inflammation.

Galectin-9 signaling prolongs survival in murine lung-cancer by inducing macrophages to differentiate into plasmacytoid dendritic cell-like macrophages

Galectin-9 (Gal-9) expanded plasmacytoid dendritic cell-like macrophages (pDC-Mϕs) in lung cancer-bearing mice and prolonged the survival. Gal-9 increased the frequency of CD11c(high) cells in M-CSF- but not GM-CSF-induced Mϕs in vitro in a Tim-3 independent manner. CD11c(high) cells differentiated with M-CSF+Gal-9 expressed pDC-Mϕ markers, such as PDCA-1 and F4/80. These cells expressed high TLR7, TLR8 and TLR9, although they exhibited decreased IFN-α mRNA levels. LPS or LLC stimulation further elevated pDC-Mϕ markers, indicating that M-CSF+Gal-9-induced Mϕs were pDC-Mϕ precursors. Moreover, LPS stimulation resulted in the increased IRF7 and E2-2 levels, suggesting that the pDC-Mϕ precursors matured into pDC-Mϕs. These matured pDC-Mϕs augmented NK cell-mediated cytotoxicity though they did not produce IFN-α upon TLR7 or TLR9 stimulation. The present results suggest that Gal-9 induces Mϕs to differentiate to pDC-Mϕs, and that this switch in differentiation favors the activation of NK cells that are able to prolong the survival of tumor-bearing mice.