Dendritic Cell and NK Cell Reciprocal Cross Talk Promotes Gamma Interferon-Dependent Immunity to Blood-Stage Plasmodium chabaudi AS Infection in Mice

Dendritic cells (DCs) are important accessory cells for promoting NK cell gamma interferon (IFN-γ) production in vitro in response to Plasmodium falciparum-infected red blood cells (iRBC). We investigated the requirements for reciprocal activation of DCs and NK cells leading to Th1-type innate and adaptive immunity to P. chabaudi AS infection. During the first week of infection, the uptake of iRBC by splenic CD11c⁺ DCs in resistant wild-type (WT) C57BL/6 mice was similar to that in interleukin 15^−/− (IL-15^−/−) and IL-12p40^−/− mice, which differ in the severity of P. chabaudi AS infection. DCs from infected IL-15^−/− mice expressed costimulatory molecules, produced IL-12, and promoted IFN-γ secretion by WT NK cells in vitro as efficiently as WT DCs. In contrast, DCs from infected IL-12p40^−/− mice exhibited alterations in maturation and cytokine production and were unable to induce NK cell IFN-γ production. Coculture of DCs and NK cells demonstrated that DC-mediated NK cell activation required IL-12 and, to a lesser extent, IL-2, as well as cell-cell contact. In turn, NK cells from infected WT mice enhanced DC maturation, IL-12 production, and priming of CD4⁺ T-cell proliferation and IFN-γ secretion. Infected WT mice depleted of NK cells, which exhibit increased parasitemia, had impaired DC maturation and DC-induced CD4⁺ Th1 cell priming. These findings indicate that DC-NK cell reciprocal cross talk is critical for control and rapid resolution of P. chabaudi AS infection and provide in vivo evidence for the importance of this interaction in IFN-γ-dependent immunity to malaria.     

Effects of CXCL10 on dendritic cell and CD4+ T-cell functions during Leishmania amazonensis infection

Leishmania amazonensis can cause progressive disease in most inbred strains of mice. We have previously reported that treatment with CXCL10 activates macrophage (MΦ) effector function(s) in parasite killing and significantly delays lesion development in susceptible C57BL/6 mice via enhanced gamma interferon (IFN-γ) and interleukin 12 (IL-12) secretion; however, the mechanism underlying this enhanced immunity against L. amazonensis infection remains largely unresolved. In this study, we utilized stationary promastigotes to infect bone marrow-derived dendritic cells (DCs) of C57BL/6 mice and assessed the activation of DC subsets and the capacity of these DC subsets to prime CD4⁺ T cells in vitro. We found that CXCL10 induced IL-12 p40 production but reduced IL-10 production in uninfected DCs. Yet L. amazonensis-infected DCs produced elevated levels of IL-10 despite CXCL10 treatment. Elimination of endogenous IL-10 led to increased IL-12 p40 production in DCs as well as increased proliferation and IFN-γ production by in vitro-primed CD4⁺ T cells. In addition, CXCL10-treated CD4⁺ T cells became more responsive to IL-12 via increased expression of the IL-12 receptor β₂ chain and produced elevated levels of IFN-γ. This report indicates the utility of CXCL10 in generating a Th1-favored, proinflammatory response, which is a prerequisite for controlling Leishmania infection.     

Interaction between conventional dendritic cells and natural killer cells is integral to the activation of effective antiviral immunity

Dendritic cells (DCs) regulate various aspects of innate immunity, including natural killer (NK) cell function. Here we define the mechanisms involved in DC-NK cell interactions during viral infection. NK cells were efficiently activated by murine cytomegalovirus (MCMV)-infected CD11b(+) DCs. NK cell cytotoxicity required interferon-alpha and interactions between the NKG2D activating receptor and NKG2D ligand, whereas the production of interferon-gamma by NK cells relied mainly on DC-derived interleukin 18. Although Toll-like receptor 9 contributes to antiviral immunity, we found that signaling pathways independent of Toll-like receptor 9 were important in generating immune responses to MCMV, including the production of interferon-alpha and the induction of NK cell cytotoxicity. Notably, adoptive transfer of MCMV-activated CD11b(+) DCs resulted in improved control of MCMV infection, indicating that these cells participate in controlling viral replication in vivo.     

Distinct MAPK pathways are involved in IL-23 production in dendritic cells cocultured with NK cells in the absence or presence of angiotensin II

Accumulated evidence suggests that the crosstalk between dendritic cells (DCs) and natural killer (NK) cells enhances each other's capacity, and results in the production of a variety of soluble factors. However, little is known about the effect of DC-NK crosstalk in interleukin-23 (IL-23) production. In the present study we show that DC-NK coculture caused a high expression of IL-23, angiotensin II (Ang II) alone moderately increased IL-23 production in DCs, but decreased IL-23 secretion in the DC-NK coculture system. We found that Ang II does not influence DC maturation in DC-NK crosstalk. We next investigated the mitogen-activated protein kinase (MAPK) pathway in DCs. We found that Ang II increased IL-23 production through the extracellular signal-related kinase (ERK) pathway. All three MAPK members c-Jun N-terminal kinase (JNK), ERK and p38 were involved in IL-23 production in the DC-NK coculture system. In the presence of Ang II, only the JNK pathway seems to play a role in IL-23 production in DCs cocultured with NK. These data suggest that distinct MAPK pathways are involved in IL-23 production in DCs in response to different stimuli. This work demonstrates for the first time that IL-23 is produced in the DC-NK coculture system, and that Ang II is involved in DC-NK crosstalk. This data will act as a resource that allows further exploitation of role of immune response in atherosclerosis.     

Optimal culture conditions for the generation of natural killer cell-induced dendritic cells for cancer immunotherapy

Dendritic cell (DC)-based vaccines continue to be considered an attractive tool for cancer immunotherapy. DCs require an additional signal from the environment or other immune cells to polarize the development of immune responses toward T helper 1 (Th1) or Th2 responses. DCs play a role in natural killer (NK) cell activation, and NK cells are also able to activate and induce the maturation of DCs. We investigated the types of NK cells that can induce the maturation and enhanced function of DCs and the conditions under which these interactions occur. DCs that were activated by resting NK cells in the presence of inflammatory cytokines exhibited increased expression of several costimulatory molecules and an enhanced ability to produce IL-12p70. NK cell-stimulated DCs potently induced Th1 polarization and exhibited the ability to generate tumor antigen-specific cytotoxic T lymphocyte responses. Our data demonstrate that functional DCs can be generated by coculturing immature DCs with freshly isolated resting NK cells in the presence of Toll-like receptor agonists and proinflammatory cytokines and that the resulting DCs effectively present antigens to induce tumor-specific T-cell responses, which suggests that these cells may be useful for cancer immunotherapy.     

An altered intestinal mucosal microbiome in HIV-1 infection is associated with mucosal and systemic immune activation and endotoxemia

Human immunodeficiency virus-1 (HIV-1) infection disrupts the intestinal immune system, leading to microbial translocation and systemic immune activation. We investigated the impact of HIV-1 infection on the intestinal microbiome and its association with mucosal T-cell and dendritic cell (DC) frequency and activation, as well as with levels of systemic T-cell activation, inflammation, and microbial translocation. Bacterial 16S ribosomal DNA sequencing was performed on colon biopsies and fecal samples from subjects with chronic, untreated HIV-1 infection and uninfected control subjects. Colon biopsies of HIV-1-infected subjects had increased abundances of Proteobacteria and decreased abundances of Firmicutes compared with uninfected donors. Furthermore at the genus level, a significant increase in Prevotella and decrease in Bacteroides was observed in HIV-1-infected subjects, indicating a disruption in the Bacteroidetes bacterial community structure. This HIV-1-associated increase in Prevotella abundance was associated with increased numbers of activated colonic T cells and myeloid DCs. Principal coordinates analysis demonstrated an HIV-1-related change in the microbiome that was associated with increased mucosal cellular immune activation, microbial translocation, and blood T-cell activation. These observations suggest that an important relationship exists between altered mucosal bacterial communities and intestinal inflammation during chronic HIV-1 infection.     

Infection of retinal epithelial cells with L. amazonensis impacts in extracellular matrix proteins

One of the manifestations of leishmaniases is eye injuries which main characteristics are the injury of the anterior chamber of the eye and the resistance to specific treatments. The retinal pigment epithelial (RPE) cells participate in pathogen-induced intraocular inflammatory processes. We investigated Leishmania amazonensis–RPE cells relationship and its impact in laminin and fibronectin production. Using RPE cell (ARPE-19), we demonstrated that L. amazonensis adhere to these cells in the first hour of infection, whereas parasite internalization was only observed after 6 h. Seventy-two hours after infection, vacuoles with parasites debris were observed intracellularly, and no parasite were observed intra- or extracellularly at the 96 h, suggesting that Leishmania can infect ARPE-19 cells although this cells are able to clear the infection. Fibronectin and laminin were associated with L. amazonensis–ARPE-19 interaction. Confocal analysis showed no substantial alterations in fibronectin presence in ARPE-19-infected or ARPE-19-noninfected cells, whereas laminin levels increased three times 10 h after L. amazonensis infection. After this time, laminin levels decreased in infected cells. These results suggest that L. amazonensis–ARPE-19 infection induces increased production of laminin in the beginning of infection which may facilitate parasite–host cell interactions.     

Bidirectional NK/DC interactions promote CD4 expression on NK cells, DC maturation, and HIV infection

Interactions between natural killer (NK) and dendritic cells (DCs) are integral to immune response development, potentially leading to bidirectional NK/DC activation. We demonstrate that autologous NK/DC interactions induce CD4 expression on NK cells, influencing degranulation. Cell contact is required, with high NK:DC ratios and mature DCs most effectively inducing CD4 expression. CD4(+) NK cells, in turn, mediate DC maturation via contact-dependent and independent pathways, more effectively maturing DCs than CD4(-) NK cells. Bidirectional NK/DC interactions also impact HIV infection, as NK-matured DCs effectively deliver infectious HIV to T cells, via trans-infection. DC-induced CD4 expression also renders NK cells susceptible to HIV infection. Focusing on NK/DC interactions, DCs can transfer infectious virus and enhance HIV infection of CD4(+) NK cells, strongly suggesting that these interactions influence HIV pathogenesis. Findings provide new insight regarding NK/DC interactions, defining a mechanism by which cellular interactions in the absence of pathogens promote DC-mediated amplification of HIV infection.     

Dendritic cells,but not macrophages,produce IL-12 immediately following Leishmania donovani infection

Infection with Leishmania, an obligate intracellular parasite of mononuclear phagocytes, stimulates the production of IFN-γ from NK cells, via a pathway which is dependent upon IL-12 and IL-2. IL-12 is also essential for the development of host protective T cell responses to this parasite. However, previous in vitro studies have indicated that macrophages fail to make IL-12 following infection with Leishmania, and that subsequent to infection, macrophages become refractory to normal IL-12-inducing stimuli. We have used an in situ approach to attempt to resolve this apparent paradox, and by immunostaining for IL-12 p40 protein, we now demonstrate for the first time, that dendritic cells (DC) are the critical source of early IL-12 production following Leishmania infection. IL-12 production by DC is transient, peaking at 1 day post infection and returning to the levels seen in uninfected mice by day 3. Although resident tissue macrophages fail to produce IL-12 after Leishmania infection, these cells are not totally refractory to cytokine inducing stimuli, as TNF-α production is induced by day 3 post infection. Not only do these data satisfactorily explain the dfferences between in vivo and in vitro data by identifying the cellular source of IL-12, but they also suggest a novel model for NK cell activation; namely that in response to pathogens which fail to trigger IL-12 production by macrophages, DC-T cell clusters provide the microenvironment for initial NK cell activation.     

Natural killer and dendritic cells collaborate in the immune response induced by the vaccine against uterine cervical cancer

Virus‐like particles (VLPs) of human papillomavirus (HPV) are used as a vaccine against HPV‐induced cancer, and recently we have shown that these VLPs are able to activate natural killer (NK) cells. Since NK cells collaborate with dendritic cells (DCs) to induce an immune response against viral infections and tumors, we studied the impact of this crosstalk in the context of HPV vaccination. NK cells in the presence of HPV‐VLPs enhanced DC‐maturation as shown by an upregulation of CD86 and HLA‐DR and an increased production of IL‐12p70, but not of the immunosuppressive cytokine IL‐10. This activation was bidirectional. Indeed, in the presence of HPV‐VLPs, DCs further activated NK cells by inducing the upregulation of cell surface activation markers (CD69 and HLA‐DR). The function of NK cells was also improved as shown by an increase in IFN‐γ secretion and cytotoxic activity against an HPV⁺ cell line. This crosstalk between NK cells and DCs needed CD40 interaction and IL‐12p70 secretion, whereas NKG2D was not implicated. Our results provide insight into how VLPs interact with innate immune cells and how NK cells and DCs play a role in the immune response induced by this vaccine agent.     

Distinct Roles for MyD88 and Toll-Like Receptor 2 during Leishmania braziliensis Infection in Mice

We have previously reported that Leishmania braziliensis infection can activate murine dendritic cells (DCs) and upregulate signaling pathways that are essential for the initiation of innate immunity. However, it remains unclear whether Toll-like receptors (TLRs) are involved in L. braziliensis-mediated DC activation. To address this issue, we generated bone marrow-derived DCs from MyD88^−/− and TLR2^−/− mice and examined their responsiveness to parasite infection. While wild-type DCs were efficiently activated to produce cytokines and prime naïve CD4⁺ T cells, L. braziliensis-infected MyD88^−/− DCs exhibited less activation and decreased production of interleukin-12 (IL-12) p40. Furthermore, MyD88^−/− mice were more susceptible to infection in that they developed larger and prolonged lesions compared to those in control mice. In sharp contrast, the lack of TLR2 resulted in an enhanced DC activation and increased IL-12 p40 production after infection. As such, L. braziliensis-infected TLR2^−/− DCs were more competent in priming naïve CD4⁺ T cells in vitro than were their controls, findings which correlated with an increased gamma interferon production in vivo and enhanced resistance to infection. Our results suggest that while MyD88 is indispensable for the generation of protective immunity to L. braziliensis, TLR2 seems to have a regulatory role during infection.Leishmaniasis is a vector-borne disease that has a great socioeconomic impact in many tropical and neotropical countries (40). Leishmania parasites multiply as flagellated promastigotes in the midguts of sand flies and are transmitted to the vertebrate host via the bites of parasite-carrying female flies (3, 22). The insult at the bite site initiates a strong neutrophil influx and parasite capture by these cells (38). Interestingly, some of the captured parasites remain viable, and these infected neutrophils actually facilitate the silent entry of parasites into macrophages (Mφs) (29), where parasites survive and replicate as intracellular amastigotes (3). The magnitude and nature of inflammatory responses at the infection site and the profile of subsequent T-cell responses determine the outcome of the infection. In South America, Leishmania braziliensis infection causes cutaneous leishmaniasis in most cases and mucocutanous leishmaniasis in some individuals. The latter is a severe and disfiguring form of the disease. At present, it remains unclear why the infection is controlled in some individuals but progressive in others (40).Dendritic cell (DC)-pathogen interactions are initiated by interaction between receptors on DCs and pathogen-associated molecular patterns, including lipopolysaccharide (LPS), glycolipids, and nucleic acids. Signals through Toll-like receptors (TLRs) can induce DC maturation and the production of proinflammatory cytokines (20, 39), thereby bridging the innate and adaptive immune responses (9). Upon ligand binding, downstream signaling of all TLRs (with the exception of TLR3) uses the adaptor protein MyD88 (32). Gene knockout studies in mice have suggested that TLR signaling is essential for the immune responses against Leishmania parasites (52). For example, MyD88 and TLR4 contribute to the control of Leishmania major infection in C57BL/6 mice (27, 33). TLR9 is involved in NK cell activation in animal models of visceral (Leishmania donovani) and cutaneous (L. major and L. braziliensis) leishmaniasis (30, 45), while TLR2 and TLR3 are required for the intracellular killing of L. donovani in gamma interferon (IFN-γ)-primed Mφs (15). Leishmania lypophosphoglycan (LPG), an abundant molecule in the surfaces of promastigotes, not only is a virulence factor for some Leishmania species (e.g., L. major and L. donovani) (49) but also acts as a ligand for TLR2-mediated signaling (5). However, different species of Leishmania display relatively high variations (biochemical modifications) in LPG molecules (7). In the case of L. braziliensis, the procyclic form of the parasite lacks side chain sugar substitutions on its LPG, whereas the metacyclic form appears to contain decreased amounts of LPG compared to other Leishmania species (47). On the DC surface, TLR2 is present as preexisting heterodimers of TLR2/1 and/or TLR2/6, recognizing triacylated and diacylated lipoproteins, respectively (51). TLR2 has been shown to be important for NK cell activation in vitro by purified L. major LPG (5); however, the functional roles of TLR2 remain largely unclear during both parasite-DC interactions and the course of Leishmania infection in vivo.Most inbred strains of mice are genetically resistant to L. braziliensis infection, due to the capacity of mice to establish a strong Th1 response (43). This self control of infection is accompanied by the selective expansion of IFN-γ-producing CD4⁺ T cells, which induce nitric oxide production in infected Mφs to promote parasite killing (3, 12). We have previously revealed that several key molecules in the innate immunity pathways (e.g., STAT1, STAT3, and ISG15) were upregulated in L. braziliensis-infected DCs and that such DCs were highly efficient in priming CD4⁺ T cells in vitro and in vivo (53). However, it remains unclear whether DC-Leishmania cell interactions in the absence of MyD88 and TLR2 impact T-cell functions and in vivo containment of infection. In the present study, we generated bone marrow-derived DCs (BMDCs) from MyD88^−/− and TLR2^−/− mice and examined their responsiveness to L. braziliensis infection. We found that infected MyD88^−/− DCs showed low levels of cell activation and interleukin-12 (IL-12) p40 production, which correlated with increased susceptibilities of these mice to L. braziliensis infection and decreased expansion of IFN-γ-producing and IL-17-producing CD4⁺ T cells during the course of infection. Given that most TLR pathways share MyD88 and that TLR2 is involved in LPG recognition, we then examined the role of TLR2 in L. braziliensis recognition. Contrary to MyD88^−/− DCs, the lack of TLR2 enhanced DC activation, IL-12 p40 production, and T-cell priming in vitro. Consequently, TLR2^−/− mice were more resistant to infection than were the control mice, a finding that was associated with enhanced IFN-γ production in the draining lymph nodes (dLN). Collectively, our results show that while MyD88 is critical for L. braziliensis recognition in vitro and in vivo, TLR2 appears to have a regulatory role in modulating immune responses to the parasite.     

Modification of anti-tumor immunity by tolerogenic dendritic cells

Immunosuppressive functions of glucocorticoids (GC) can be mediated via various mechanisms, including the modulation of dendritic cells (DC). Our study investigates the effects of tolerogenic GC-treated DCs on NK and T cell anti-tumor responses in OT-1/Rag^?/? mice, expressing a transgenic TCR in CD8⁺ T cells. The effects caused by GC-treated DCs were compared to the responses to immunogenic, CpG-activated DCs. The effects of DCs on anti-tumor immune responses were analyzed using the EG7 tumor model, where the tumor cells express the peptide epitope recognized by OT-1 T cells. We observed that immunization with CpG and peptide-treated DCs protected against tumor growth by activation of NK cell response. Also, immunogenic DCs induced the expansion of cytotoxic CD8⁺OT-1 cells, expressing activation markers CD44 and CD69 and producing IFNγ. In contrast, the peptide and GC-treated DCs in OT-1 mice increased the numbers of immature Mac-1⁺CD27^? NK cells as well as Foxp3⁺ and IL-10 secreting CD8⁺OT-1 cells with suppressive properties. We conclude that the generation of tolerogenic DCs is one of many immunosuppressive mechanisms that can be induced by GC. Our study demonstrated that tolerogenic DCs modify anti-tumor immune response by suppressing NK cell activity and stimulating the formation of IL-10-secreting CD8⁺ Tregs.     

Gut dendritic cell activation links an altered colonic microbiome to mucosal and systemic T-cell activation in untreated HIV-1 infection

HIV-1-associated disruption of intestinal homeostasis is a major factor contributing to chronic immune activation and inflammation. Dendritic cells (DCs) are crucial in maintaining intestinal homeostasis, but the impact of HIV-1 infection on intestinal DC number and function has not been extensively studied. We compared the frequency and activation/maturation status of colonic myeloid DC (mDC) subsets (CD1c⁺ and CD1c^neg) and plasmacytoid DCs in untreated HIV-1-infected subjects with uninfected controls. Colonic mDCs in HIV-1-infected subjects had increased CD40 but decreased CD83 expression, and CD40 expression on CD1c⁺ mDCs positively correlated with mucosal HIV-1 viral load, with mucosal and systemic cytokine production, and with frequencies of activated colon and blood T cells. Percentage of CD83⁺CD1c⁺ mDCs negatively correlated with frequencies of interferon-γ-producing colon CD4⁺ and CD8⁺ T cells. CD40 expression on CD1c⁺ mDCs positively associated with abundance of high prevalence mucosal Prevotella copri and Prevotella stercorea but negatively associated with a number of low prevalence mucosal species, including Rumminococcus bromii. CD1c⁺ mDC cytokine production was greater in response to in vitro stimulation with Prevotella species relative to R. bromii. These findings suggest that, during HIV infection, colonic mDCs become activated upon exposure to mucosal pathobiont bacteria leading to mucosal and systemic immune activation.     

NK cells are primed by ANRS MVAHIV‐infected DCs,via a mechanism involving NKG2D and membrane‐bound IL‐15, to control HIV‐1 infection in CD4+ T cells

Natural killer (NK) cells are the major antiviral effector cell population of the innate immune system. It has been demonstrated that NK‐cell activity can be modulated by the interaction with dendritic cells (DCs). The HIV‐1 vaccine candidate Modified Vaccinia Ankara encoding an HIV polypeptide (MVA_HIV), developed by the French National Agency for Research on AIDS (ANRS), has the ability to prime NK cells to control HIV‐1 infection in DCs. However, whether or not MVA_HIV‐primed NK cells are able to better control HIV‐1 infection in CD4⁺ T cells, and the mechanism underlying the specific priming, remain undetermined. In this study, we show that MVA_HIV‐primed NK cells display a greater capacity to control HIV‐1 infection in autologous CD4⁺ T cells. We also highlight the importance of NKG2D engagement on NK cells and DC‐produced IL‐15 to achieve the anti‐HIV‐1 specific priming, as blockade of either NKG2D or IL‐15 during MVA_HIV‐priming lead to a subsequent decreased control of HIV‐1 infection in autologous CD4⁺ T cells. Furthermore, we show that the decreased control of HIV‐1 infection in CD4⁺ T cells might be due, at least in part, to the decreased expression of membrane‐bound IL‐15 (mbIL‐15) on DCs when NKG2D is blocked during MVA_HIV‐priming of NK cells.     

Immunopathogenesis of non-healing American cutaneous leishmaniasis and progressive visceral leishmaniasis

The outcomes of Leishmania infection are determined by host immune and nutrition status, parasite species, and co-infection with other pathogens. While subclinical infection and self-healing cutaneous leishmaniasis (CL) are common, uncontrolled parasite replication can lead to non-healing local lesions or visceral leishmaniasis (VL). It is known that infection control requires Th1-differentiation cytokines (IL-12, IL-18, and IL-27) and Th1 cell and macrophage activation. However, there is no generalized consensus for the mechanisms of host susceptibility. The recent studies on regulatory T cells and IL-17-producing cells help explain the effector T cell responses that occur independently of the known Th1/Th2 cell signaling pathways. This review focuses on the immunopathogenesis of non-healing American CL and progressive VL. We summarize recent evidence from human and animal studies that reveals the mechanisms of dysregulated, hyper-responses to Leishmania braziliensis, as well as the presence of disease-promoting or the absence of protective responses to Leishmania amazonensis and Leishmania donovani. We highlight immune-mediated parasite growth and immunopathogenesis, with an emphasis on the putative roles of IL-17 and its related cytokines as well as arginase. A better understanding of the quality and regulation of innate immunity and T cell responses triggered by Leishmania will aid in the rational control of pathology and the infection.     

Protective dendritic cell responses against listeriosis induced by the short form of the deubiquitinating enzyme CYLD are inhibited by full‐length CYLD

The deubiquitinating enzyme CYLD is an important tumor suppressor and inhibitor of immune responses. In contrast to full‐length CYLD, the immunological function of the naturally occurring short splice variant of CYLD (sCYLD) is insufficiently described. Previously, we showed that DCs, which lack full‐length CYLD but express sCYLD, exhibit augmented NF‐κB and DC activation. To explore the function of sCYLD in infection, we investigated whether DC‐specific sCYLD regulates the pathogenesis of listeriosis. Upon Listeria monocytogenes infection of CD11c‐Cre Cyld^{ex7/8 fl/fl} mice, infection of CD8α⁺ DCs, which are crucial for the establishment of listeriosis in the spleen, was not affected. However, NF‐κB activity of CD11c‐Cre Cyld^{ex7/8 fl/fl} DCs was increased, while activation of ERK and p38 was normal. In addition, CD11c‐Cre Cyld^{ex7/8 fl/fl} DCs produced more TNF, IL‐10, and IL‐12 upon infection, which led to enhanced stimulation of IFN‐γ‐producing NK cells. In addition CD11c‐Cre Cyld^{ex7/8 fl/fl} DCs presented Listeria Ag more efficiently to CD8⁺ T cells resulting in a stronger pathogen‐specific CD8⁺ T‐cell proliferation and more IFN‐γ production. Collectively, the improved innate and adaptive immunity and survival during listeriosis identify the DC‐specific FL‐CYLD/sCYLD balance as a potential target to modulate NK‐cell and Ag‐specific CD8⁺ T‐cell responses.     

Binding of excreted and/or secreted products of adult hookworms to human NK cells in Necator americanus-infected individuals from Brazil

The impact of the interaction between excreted and/or secreted (ES) Necator americanus products and NK cells from Necator-infected individuals was analyzed. We investigated the binding of ES products to NK cells, the expression of NK cell receptors (CD56, CD159a/NKG2A, CD314/NKG2D, CD335/NKp46, and KLRF1/NKp80), the frequency of gamma interferon (IFN-γ)-producing NK cells after whole-blood in vitro stimulation, and the capacity of N. americanus ES products to induce NK cell chemotaxis. In contrast to those from noninfected individuals, NK cells from Necator-infected individuals demonstrated no binding with N. americanus ES products. This phenomenon was not due to alterations in NK cell receptor expression in infected subjects and could not be reproduced with NK cells from uninfected individuals by incubation with immunoregulatory cytokines (interleukin-10/transforming growth factor β). Further, we found that a significantly greater percentage of NK cells from infected subjects than NK cells from uninfected individuals spontaneously produced IFN-γ upon ex vivo culture. Our findings support a model whereby NK cells from Necator-infected individuals may interact with ES products, making these cells refractory to binding with exogenous ES products. During N. americanus infection, human NK cells are attracted to the site of infection by chemotactic ES products produced by adult Necator worms in the gut mucosa. Binding of ES products causes the NK cells to become activated and secrete IFN-γ locally, thereby contributing to the adult hookworm's ability to evade host immune responses.     

Dendritic cell CD83 homotypic interactions regulate inflammation and promote mucosal homeostasis

Dendritic cells (DCs) form an extensive network in the intestinal lamina propria, which orchestrates the mucosal immune response. Alterations in DC function can predispose to inflammatory bowel disease, although by unknown mechanisms. We show that CD83, a highly regulated DC cell surface protein, modulates the immune response to prevent colitis. Mice with a conditional knockout of CD83 in DCs develop exacerbated colitis following dextran sodium sulfate challenge, whereas mucosal overexpression of CD83 inhibits DC inflammatory response and protects against colitis. These CD83 perturbations can be modeled in vitro where we show that CD83 homotypic interaction occurs via cell–cell contact and inhibits pro-inflammatory responses. CD83 knockdown or cytoplasmic truncation abrogates the effects of homotypic binding. We demonstrate that CD83 homotypic interaction regulates DC activation via the mitogen-activated protein kinase pathway by inhibiting p38α phosphorylation. Our findings indicate that CD83 homotypic interactions regulate DC activation and promote mucosal homeostasis.