Pivotal role of plasmacytoid dendritic cells in inflammation and NK-cell responses after TLR9 triggering in mice

Abstract

The physiologic role played by plasmacytoid dendritic cells (pDCs) in the induction of innate responses and inflammation in response to pathogen signaling is not well understood. Here, we describe a new mouse model lacking pDCs and establish that pDCs are essential for the in vivo induction of NK-cell activity in response to Toll-like receptor 9 (TLR9) triggering. Furthermore, we provide the first evidence that pDCs are critical for the systemic production of a wide variety of chemokines in response to TLR9 activation. Consequently, we observed a profound alteration in monocyte, macrophage, neutrophil, and NK-cell recruitment at the site of inflammation in the absence of pDCs in response to CpG-Dotap and stimulation by microbial pathogens, such as Leishmania major, Escherichia coli, and Mycobacterium bovis. This study, which is based on the development of a constitutively pDC-deficient mouse model, highlights the pivotal role played by pDCs in the induction of innate immune responses and inflammation after TLR9 triggering. (Blood. 2012;120(1): 90-99) IntroductionPlasmacytoid DCs (pDCs) are characterized by their ability to contribute to antiviral innate immunity by producing type I IFNs on stimulation. 1 These cells display a CD11c low B220 ϩ Ly6C ϩ CD45RA ϩ phenotype and also express markers, such as CD317 (BST-2) 2 and SiglecH. 3 Their Toll-like receptor (TLR) expression pattern is limited to TLR7 and TLR9, which recognize viral single-stranded RNA and unmethylated DNA, respectively. The constitutive expression of IFN regulatory factor 7 enables pDCs to rapidly produce high levels of type I IFNs after TLR stimulation. After activation via TLR7 or TLR9 signaling, pDCs produce cytokines, such as IL-12, IL-6, and TNF-␣, and chemokines, including CCL3, CCL4, CCL5, CXCL9, and CXCL10, in addition to type I IFNs. 4 NK cells exhibit potent cytotoxic activity against infected or tumor cells and are efficient producers of several cytokines and chemokines. 5 NK-cell activation is controlled by the recognition of ligands expressed on the surface of target cells. However, NK cells require additional signals for activation, including type I IFNs and IL-12. 6 Because of their ability to produce these cytokines, pDCs may play an important role in stimulating and inducing NK-cell responses. Indeed, pDCs can promote murine cytomegalovirus clearance by NK cells through TLR9 interaction. 7 Furthermore, NK cells express the chemokine receptors CCR5 and CXCR3, which interact with the chemokines produced by activated pDCs, 8 suggesting that pDCs may also influence their recruitment. In addition to NK cells, immature conventional DCs (cDCs), monocytes, macrophages, polymorphonuclear basophiles (PMBs) and eosinophils (PMEs) also respond to type I IFNs 9 and to CCL3, CCL4, and CCL5, 8 suggesting that pDCs participate in the activation and recruitment of inflammatory cells.To directly assess the physiologic role of pDCs in innate immunity, it is crucial to analyze these responses in vivo in the absence of pDCs. pDCs could be immunodeple...

Tumor-Derived TGFβ Alters the Ability of Plasmacytoid Dendritic Cells to Respond to Innate Immune Signaling

“…IFN-α was dosed by ELISA as previously described (6). In some experiments, IFN- and IFN- were determined by the 2-plex Luminex assay (Affymetrix, Thermo Fisher Scientific).…”

“…In addition, upon activation, pDCs secrete a large panel of cytokines, such as TNF-, IL-6 and IL-12 (1)(2)(3)(4), as well as chemokines, including CCL3, CCL4, CCL5, CXCL9 and CXCL10 (5,6). pDCs induce the migration of innate effector cells, such as monocytes and macrophages, cDCs, NK and NKT cells (6)(7)(8)(9), and activate these cells. In addition, activated pDCs can elicit adaptive immune responses through their capacity to present antigen to CD4 + (10) and CD8 + T cells (11,12).…”

Yeast Virus-Derived Stimulator of the Innate Immune System Augments the Efficacy of Virus Vector-Based Immunotherapy

“…Activated pDCs are described to play a pivotal role in the induction of the innate immune response, e.g., by recruitment of NK cells (41). Indeed, we have observed a strong increase of infiltrating NK cells after injection of MVATG9931 and NAB2-Lipofectin 6 times higher than that observed after injection of MVATG9931 or NAB2-Lipofectin alone.…”

“…Indeed, we have observed a strong increase of infiltrating NK cells after injection of MVATG9931 and NAB2-Lipofectin 6 times higher than that observed after injection of MVATG9931 or NAB2-Lipofectin alone. We assume that these NK cells can be activated by IFN-␣ from activated pDCs (41) and, in analogy to the human situation, also from cytokines released from monocytes and dendritic cells activated by NAB2-Lipofectin. NAB2-Lipofectin, when injected several hours after MVATG9931, would also encounter MVA-infected cells expressing MUC1.…”

Dendritic Cell Subtypes from Lymph Nodes and Blood Show Contrasted Gene Expression Programs upon Bluetongue Virus Infection

“…Recently, pDCs were shown to play a pivotal role in the systemic inflammation induced by toll-like receptor 9 (TLR9) triggering or by bacterial infections in vivo in mice (48). We show here that a strong inflammatory gene profile was induced by BTV in blood pDCs in vivo at day 6 postinfection, at the onset of symptoms, with expression of genes encoding cytokines such as CCL2, CCL4, TNF, IL-8, and CXCL10 (see Table S7 in the supplemental material).…”