NK cell activation in visceral leishmaniasis requires TLR9, myeloid DCs, and IL-12, but is independent of plasmacytoid DCs

Institute of Medical Microbiology and Hygiene, University of Freiburg, D-79104 Freiburg, Germany.
Journal of Experimental Medicine (Impact Factor: 12.52). 05/2007; 204(4):893-906. DOI: 10.1084/jem.20061293
Source: PubMed

ABSTRACT Natural killer (NK) cells are sentinel components of the innate response to pathogens, but the cell types, pathogen recognition receptors, and cytokines required for their activation in vivo are poorly defined. Here, we investigated the role of plasmacytoid dendritic cells (pDCs), myeloid DCs (mDCs), Toll-like receptors (TLRs), and of NK cell stimulatory cytokines for the induction of an NK cell response to the protozoan parasite Leishmania infantum. In vitro, pDCs did not endocytose Leishmania promastigotes but nevertheless released interferon (IFN)-alpha/beta and interleukin (IL)-12 in a TLR9-dependent manner. mDCs rapidly internalized Leishmania and, in the presence of TLR9, produced IL-12, but not IFN-alpha/beta. Depletion of pDCs did not impair the activation of NK cells in L. infantum-infected mice. In contrast, L. infantum-induced NK cell cytotoxicity and IFN-gamma production were abolished in mDC-depleted mice. The same phenotype was observed in TLR9(-/-) mice, which lacked IL-12 expression by mDCs, and in IL-12(-/-) mice, whereas IFN-alpha/beta receptor(-/-) mice showed only a minor reduction of NK cell IFN-gamma expression. This study provides the first direct evidence that mDCs are essential for eliciting NK cell cytotoxicity and IFN-gamma release in vivo and demonstrates that TLR9, mDCs, and IL-12 are functionally linked to the activation of NK cells in visceral leishmaniasis.

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    • "Upregulation of TLRs in canine macrophages obtained from the LP of jejunum and colon could be explained either by recruitment of inflammatory cells expressing TLRs or by proliferation of resident macrophages induced by Leishmania antigens. Leishmania reaches intestinal LP via blood or lymphatic vessels, and TLR2 and TLR9 on the macrophage surface can interact with Leishmania[40,41]. de Veer et al. [11] showed that TLR2 activates NF-κB mediated by LPG. "
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    ABSTRACT: Background Infection with parasite protozoa is a long-term health issue in tropical and subtropical regions throughout the world. The Toll-like receptor (TLR) signaling pathway is one of the first-responding defense systems against Leishmania. The aim of this study was to investigate the expression of TLR2 and TLR9 in jejunum and colon and its correlation with CD11c, CD11b, and CD14 receptors used as markers for dendritic cells and macrophages. Methods Twenty four dogs infected with Leishmania infantum were used in this study. Cytometry was carried out in lamina propria cells from jejunum and colon using markers for TLR2, TLR9, CD11b, CD11c and CD14. Results Cellular inflammatory exudate was diffuse in the mucosa and submucosa, predominately comprising mononuclear cells: plasma cells, macrophages, and lymphocytes. Despite the parasite load, microscopy showed no erosion was evident in the epithelial mucosa layers. The colon harbored more parasites than the jejunum. Flow cytometry revealed higher frequency of TLR2+ and CD11c+ dendritic cells in the colon than in the jejunum. Conversely, TLR9-expressing cells were more frequent in jejunum. Moreover, frequency of macrophages (CD11b+ and CD14+) expressing simultaneity TLR9 were lower in the colon than in jejunum, while CD11c+ cells predominated in the colon. Despite of the negative ELISA serum results, IL-10 and TNF-α were higher in jejunum than colon of infected animals. However, IL-4 was higher in colon than jejunum of infected animals. A higher expression these cytokines were demonstrated in infected dogs compared to uninfected dogs. Conclusions There was no correlation between clinical signs and pathological changes and immunological and parasitological findings in the gastrointestinal tract in canine visceral leishmaniasis. However, jejunum showed a lower parasite load with increased frequency and expression of CD11b, TLR9, CD14/CD11b/TLR9 receptors and IL-10 and TNF-α cytokines. Conversely, the colon showed a higher parasite load along with increased frequency and expression of TLR2, CD11c receptors, and IL-4 cytokine. Thus, Leishmania infantum is able to interfere in jejunum increased expression of TLR2, TLR9, CD11b, CD14, CD14/CD11b/TLR9 receptors, IL-10, and TNF-α; and in colon increased expression of CD11c, TLR2, TLR9, CD11b, CD14 e, CD14/CD11b/TLR9 receptors, IL-10, and TNF-α.
    BMC Immunology 05/2013; 14(1):22. DOI:10.1186/1471-2172-14-22 · 2.48 Impact Factor
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    • "Although a variety of cell types are capable of acting as accessory cells for NK cell activation in vitro, many in vivo studies have focused on the role of DCs, leaving the in vivo role of macrophages and monocytes relatively under explored (Andrews et al., 2003; Fernandez et al., 1999; Hou et al., 2011; Kassim et al., 2006; Lucas et al., 2007; Pribul et al., 2008; Schleicher et al., 2007). It is likely that the relative contributions of DCs, macrophages and monocytes in vivo will vary with the route and type of infection. "
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    ABSTRACT: Infection leads to heightened activation of natural killer (NK) cells, a process that likely involves direct cell-to-cell contact, but how this occurs in vivo is poorly understood. We have used two-photon laser-scanning microscopy in conjunction with Toxoplasma gondii mouse infection models to address this question. We found that after infection, NK cells accumulated in the subcapsular region of the lymph node, where they formed low-motility contacts with collagen fibers and CD169(+) macrophages. We provide evidence that interactions with collagen regulate NK cell migration, whereas CD169(+) macrophages increase the activation state of NK cells. Interestingly, a subset of CD169(+) macrophages that coexpress the inflammatory monocyte marker Ly6C had the most potent ability to activate NK cells. Our data reveal pathways through which NK cell migration and function are regulated after infection and identify an important accessory cell population for activation of NK cell responses in lymph nodes.
    Cell Reports 07/2012; 2(1):124-35. DOI:10.1016/j.celrep.2012.06.001 · 8.36 Impact Factor
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    • "Macrophages can either kill or host intracellular amastigote forms of Leishmania depending on the balance of two inducible enzymes, nitric oxide synthase 2 (NOS2/iNOS; Wei et al., 1995) and arginase-1 (Kropf et al., 2005) which share the same substrate, l-arginine and are controlled by the environmental balance of Th1/pro-inflammatory (e.g., IFNγ, TNFα) and Th2/anti-inflammatory (e.g., IL-4, IL-10, IL-13, IL-21) cytokines (Figure 5A). Increased arginase is associated with resistance to worm infections, allergic conditions such as asthma and Th2 induced pathologies (Tominaga, 1989; Kropf et al., 2004; Schleicher et al., 2007; Whitaker et al., 2008). Th1 cytokines induce classical activation of macrophages (CAMΦ), upregulating iNOS which catabolizes l-arginine into the Leishmania-toxic metabolite nitric oxide (NO). "
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    ABSTRACT: Leishmania are transmitted by the bite of their sand fly vector and this has a significant influence on the virulence of the resulting infection. From our studies into the interaction between parasite, vector, and host we have uncovered an important missing ingredient during Leishmania transmission. Leishmania actively adapt their sand fly hosts into efficient vectors by secreting Promastigote Secretory Gel (PSG), a proteophosphoglycan (PPG)-rich, mucin-like gel which accumulates in sand fly gut and mouthparts. This has the effect of blocking the fly, such that during bloodfeeding both parasites and gel are co-transmitted in an act of regurgitation. We are discovering that this has further implications for the mammalian infection, again, in favor of the parasite. Experimentally, PSG exacerbates cutaneous and visceral leishmaniasis and can promote the chronicity of Leishmania infection, even in mouse strains normally capable of controlling leishmaniasis. The underlying mechanism of PSG's action is a major focus of our ongoing work. This review aims to synthesize what is known about the role and action of PSG and its constituent proteophosphoglycans, for parasite colonization of the sand fly, transmission, and mammalian infection. Lastly, we discuss potential exploitation of this important vector-transmitted product and future avenues of research.
    Frontiers in Microbiology 06/2012; 3:223. DOI:10.3389/fmicb.2012.00223 · 3.99 Impact Factor
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