Two distinct mechanisms for induction of dendritic cell apoptosis in response to intact Streptococcus pneumoniae

Apoptotic dendritic cells (DCs) are ineffective at inducing immunity. Thus, parameters that regulate DC viability during a primary infection will help to determine the outcome of the subsequent immune response. In this regard, pathogens have developed strategies to promote DC apoptosis to counterbalance the nascent primary immune response. We demonstrate, using cultured bone marrow-derived DCs, that Streptococcus pneumoniae can induce DC apoptosis through two distinct mechanisms: 1) a rapid, caspase-independent mechanism of apoptosis induction, critically dependent on bacterial expression of pneumolysin, and 2) a delayed-onset, caspase-dependent mechanism of apoptosis induction associated with terminal DC maturation. Delayed-onset apoptosis does not require bacterial internalization, but rather is triggered by the interaction of bacterial subcapsular components and bone marrow-derived DC (likely Toll-like) receptors acting in a myeloid differentiation factor 88-dependent manner. In this regard, heavy polysaccharide encapsulation interferes with both DC maturation and apoptosis induction. In contrast, neither CD95/CD95 ligand interactions nor TNF-alpha appear to play a role in the delayed onset of apoptosis. These data are the first to define two mechanistically distinct pathways of DC apoptosis induction in response to an extracellular bacterium that likely have important consequences for the establishment of antibacterial immunity.     

Cross-talk in the innate immune system: neutrophils instruct recruitment and activation of dendritic cells during microbial infection

Type I inflammatory cytokines are essential for immunity to many microbial pathogens, including Toxoplasma gondii. Dendritic cells (DC) are key to initiating type 1 immunity, but neutrophils are also a source of chemokines and cytokines involved in Th1 response ignition. We found that T. gondii triggered neutrophil synthesis of CC chemokine ligand (CCL)3, CCL4, CCL5, and CCL20, chemokines that were strongly chemotactic for immature DC. Moreover, supernatants obtained from parasite-stimulated polymorphonuclear leukocytes induced DC IL-12(p40) and TNF-alpha production. Parasite-triggered neutrophils also released factors that induced DC CD40 and CD86 up-regulation, and this response was dependent upon parasite-triggered neutrophil TNF-alpha production. In vivo evidence that polymorphonuclear leukocytes exert an important influence on DC activation was obtained by examining splenic DC cytokine production following infection of neutrophil-depleted mice. These animals displayed severely curtailed splenic DC IL-12 and TNF-alpha production, as revealed by ex vivo flow cytometric analysis and in vitro culture assay. Our results reveal a previously unrecognized regulatory role for neutrophils in DC function during microbial infection, and suggest that cross-talk between these cell populations is an important component of the innate immune response to infection.     

NK cells promote type 1 T cell immunity through modulating the function of dendritic cells during intracellular bacterial infection

Dendritic cells (DC) play a key role in establishing protective adaptive immunity in intracellular bacterial infections, but the cells influencing DC function in vivo remain unclear. In this study, we investigated the role of NK cells in modulating the function of DC using a murine Chlamydia infection model. We found that the NK cell-depleted mice showed exacerbated disease after respiratory tract Chlamydia muridarum infection, which was correlated with altered T cell cytokine profile. Furthermore, DC from C. muridarum-infected NK-depleted mice (NK(-)DC) exhibited a less mature phenotype compared with that of DC from the infected mice without NK depletion (NK(+)DC). NK(-)DC produced significantly lower levels of both IL-12 and IL-10 than those of NK(+)DC. Moreover, NK(-)DC showed reduced ability to direct primary and established Ag-specific Th1 CD4(+) T cell responses in DC-T coculture systems. More importantly, adoptive transfer of NK(-)DC, in contrast to NK(+)DC, failed to induce type 1 protective immunity in recipients after challenge infection. Finally, NK cells showed strong direct enhancing effect on IL-12 production by DC in an NK-DC coculture system, which was partially reduced by blocking NKG2D receptors signaling and virtually abolished by neutralizing IFN-γ activity. The data demonstrate a critical role of NK cells in modulating DC function in an intracellular bacterial infection.     

Regulation of mucosal dendritic cell function by receptor activator of NF-kappa B (RANK)/RANK ligand interactions: impact on tolerance induction

The mucosal immune system is uniquely equipped to discriminate between potentially invasive pathogens and innocuous food proteins. While the mechanisms responsible for induction of mucosal immunity vs tolerance are not yet fully delineated, recent studies have highlighted mucosal dendritic cells (DC) as being important in determining the fate of orally administered Ag. To further investigate the DC:T cell signals involved in regulating the homeostatic balance between mucosal immunity and tolerance, we have examined the expression and function of the TNFR family member receptor activator of NF-kappaB (RANK) and its cognate ligand, RANKL, in vitro and in vivo. Our data show that although DC isolated from mucosal lymphoid tissues expressed similar levels of surface RANK compared with DC isolated from peripheral lymphoid tissues, DC from the distinct anatomical sites displayed differential responsiveness to RANK engagement with soluble RANKL. Whereas splenic DC responded to RANKL stimulation with elevated IL-12 p40 mRNA expression, Peyer's patch DC instead preferentially displayed increased IL-10 mRNA expression. Our data also show that the in vivo functional capacity of mucosal DC can be modulated by RANKL. Treatment with RANKL in vivo at the time of oral administration of soluble OVA enhanced the induction of tolerance in two different mouse models. These studies underscore the functional differences between mucosal and peripheral DC and highlight a novel role for RANK/RANKL interactions during the induction of mucosal immune responses.     

Diversity of interferon gamma and granulocyte-macrophage colony-stimulating factor in restoring immune dysfunction of dendritic cells and macrophages during polymicrobial sepsis

The development of immunosuppression during polymicrobial sepsis is associated with the failure of dendritic cells (DC) to promote the polarization of T helper (Th) cells toward a protective Th1 type. The aim of the study was to test potential immunomodulatory approaches to restore the capacity of splenic DC to secrete interleukin (IL) 12 that represents the key cytokine in Th1 cell polarization. Murine polymicrobial sepsis was induced by cecal ligation and puncture (CLP). Splenic DC were isolated at different time points after CLP or sham operation, and stimulated with bacterial components in the presence or absence of neutralizing anti-IL-10 antibodies, murine interferon (IFN) gamma, and/or granulocyte macrophage colony-stimulating factor (GM-CSF). DC from septic mice showed an impaired capacity to release the pro-inflammatory and Th1-promoting cytokines tumor necrosis factor alpha, IFN-gamma, and IL-12 in response to bacterial stimuli, but secreted IL-10. Endogenous IL-10 was not responsible for the impaired IL-12 secretion. Up to 6 h after CLP, the combined treatment of DC from septic mice with IFN-gamma and GM-CSF increased the secretion of IL-12. Later, DC from septic mice responded to IFN-gamma and GM-CSF with increased expression of the co-stimulatory molecule CD86, while IL-12 secretion was no more enhanced. In contrast, splenic macrophages from septic mice during late sepsis responded to GM-CSF with increased cytokine release. Thus, therapy of sepsis with IFN-gamma/GM-CSF might be sufficient to restore the activity of macrophages, but fails to restore DC function adequate for the development of a protective Th1-like immune response.     

Different toll-like receptor stimuli have a profound impact on cytokines required to break tolerance and induce autoimmunity

Although toll-like receptor (TLR) signals are critical for promoting antigen presenting cell maturation, it remains unclear how stimulation via different TLRs influence dendritic cell (DC) function and the subsequent adaptive response in vivo. Furthermore, the relationship between TLR-induced cytokine production by DCs and the consequences on the induction of a functional immune response is not clear. We have established a murine model to examine whether TLR3 or TLR4 mediated DC maturation has an impact on the cytokines required to break tolerance and induce T-cell-mediated autoimmunity. Our study demonstrates that IL-12 is not absolutely required for the induction of a CD8 T-cell-mediated tissue specific immune response, but rather the requirement for IL-12 is determined by the stimuli used to mature the DCs. Furthermore, we found that IFNα is a critical pathogenic component of the cytokine milieu that circumvents the requirement for IL-12 in the induction of autoimmunity. These studies illustrate how different TLR stimuli have an impact on DC function and the induction of immunity.     

Activation, stimulation and uptake of bacterial ghosts in antigen presenting cells

Bacterial ghosts have been shown to be an innovative system to prepare vaccines of various bacteria with all features of the intact bacterial cell envelopes, especially all antigenic epitopes, but also to target recombinant proteins inserted in the cell envelopes of the ghost preparations to specific antigen presenting cells. To investigate the activation of the antigen presenting cell by bacterial ghosts in more detail we studied the uptake of bacterial ghosts in dendritic porcine cells and RAW macrophages and the induction of inflammatory mediators or mediators directing the immune response in THP-1 human macrophage cell line. The synthesis of inflammatory macrophage mediators such as TNFalpha in the THP1 cell line was stimulated by a hundred-fold higher dose of ghosts from Vibrio cholerae than the corresponding LPS using ELISA-analysis. These results confirm in vivo experiments indicating no toxic effects of ghosts in rabbits even after intravenous administration in doses stimulating significant humoral responses. We were also able to see a significant activation of IL-12 indicated by the analysis of IL-12(p70) synthesis and IL-12(p40) mRNA accumulation. This interleukine is of special importance in the activation of cellular TH1 immune responses. A rapid uptake of bacterial ghosts in macrophages within 10-30 min could be confirmed by electron microscopy. As antigen presentation is especially effective in porcine dendritic cells (DC) and even a low capacity of antigen uptake is sufficient for an induction of immune responses we investigated uptake and activation of bacterial ghosts by DC. DC are known to be phagocytic in specific immature stages. We found a significant uptake of bacterial ghosts from Actinobacillus pleuropneumoniae (App) and V. cholerae conjugated with FITC (fluorescinisothiocyanate) within 2 h. These data suggest that bacterial ghosts effectively stimulate monocytes and macrophages for the induction of TH1 directed immune responses and dendritic cells treated with bacterial ghosts may serve as a promising vehicle for active immunization and immunotherapy in situ.     

IL-10- and IL-12-independent down-regulation of allergic sensitization by stimulation of CD40 signaling

Interaction between CD154 (CD40 ligand) on activated T lymphocytes and its receptor CD40 has been shown to be critically involved in the generation of cell-mediated as well as humoral immunity. CD40 triggering activates dendritic cells (DC), enhances their cytokine production, up-regulates the expression of costimulatory molecules, and induces their maturation. It is unknown how stimulation of CD40 during sensitization to an airborne allergen may affect the outcome of allergic airway inflammation. We took advantage of a mouse model of allergic asthma and a stimulatory mAb to CD40 (FGK45) to study the effects of CD40-mediated DC activation on sensitization to OVA and subsequent development of OVA-induced airway inflammation. Agonistic anti-CD40 mAb (FGK45) injected during sensitization with OVA abrogated the development of allergic airway inflammation upon repeated airway challenges with OVA. Inhibition of bronchial eosinophilia corresponded with reduced Th2 cytokine production and was independent of IL-12, as evidenced by a similar down-regulatory effect of anti-CD40 mAb in IL-12 p40-deficient mice. In addition, FGK45 equally down-regulated allergic airway inflammation in IL-10-deficient mice, indicating an IL-10-independent mechanism of action of FGK45. In conclusion, our results show that CD40 signaling during sensitization shifts the immune response away from Th2 cytokine production and suppresses allergic airway inflammation in an IL-12- and IL-10-independent way, presumably resulting from enhanced DC activation during sensitization.     

Effects of beta-glucan extracted from Saccharomyces cerevisiae on humoral and cellular immunity in weaned piglets

Twenty-four barrows were used to investigate the effects of beta-glucan on immune function in weaned piglets. Pigs (8.09 +/- 0.20 kg, 28 d of age) were fed a diet without or with supplemented beta-glucan (50 mg/kg feed). All pigs were injected with ovalbumin (OVA) on day 14 to investigate their humoral immune response. On day 28, lymphocytes were isolated from all pigs to determine the effects of beta-glucan on cellular immunity of pigs in vitro. Lymphocytes from six pigs of each group were incubated with 16 microg lipopolysaccharide (LPS) per ml culture medium, the remainder with an equivalent volume of culture medium alone. Samples were collected at 0, 3, 6, 12, 18, 24, and 48 h after LPS addition for determination of interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), and interleukin-10 (IL-10). On day 31, six pigs of each group were injected with either LPS (25 microg/kg BW) or an equivalent amount of sterile saline. Blood samples were collected at 3 h after LPS injection for analysis of IL-6, TNF-alpha, and IL-10 in plasma. The results indicated that dietary beta-glucan enhanced pig antibody response to OVA only in the first week after injection. In vitro, the increases of IL-6 and TNF-alpha in culture medium were partially dampened in pigs supplemented with beta-glucan when their lymphocytes were incubated with LPS, whereas the increase of IL-10 was potentiated. In vivo, dietary beta-glucan attenuated the increase of plasma IL-6 and TNF-alpha, and enhanced the increase of plasma IL-10 when pigs were challenged with LPS. These results demonstrate that beta-glucan can improve the humoral immunity of pigs and modulate cellular immunity of pigs by mitigating the elevation of pro-inflammatory cytokines and enhancing the increase of anti-inflammatory cytokines after an immunological challenge.     

Antigen-independent immune responses after dendritic cell vaccination

The ability of cultured, antigen-loaded dendritic cells (DCs) to induce antigen-specific T cell immunity in vivo has previously been demonstrated and confirmed. Immune monitoring naturally focuses on immunity against vaccine antigens and may thus ignore other effects of DC vaccination. Here we therefore focused on antigen-independent responses induced by DC vaccination of renal cell carcinoma patients. In addition to the anticipated response against the vaccine antigen KLH, vaccination with CD83⁺ monocyte-derived DCs resulted in a strong increase in the ex vivo proliferative and cytokine responses of PBMCs stimulated with LPS or BCG. In addition, LPS strongly enhanced the KLH-induced proliferative and cytokine response of PBMCs. Moreover, proliferative and cytokine responses of PBMCs stimulated with the homeostatic cytokines IL-7 and IL-15 were also clearly enhanced after DC vaccination. In contrast to LPS induced proliferation, which is well known to depend on monocytes, IL-7 induced proliferation was substantially enhanced after monocyte depletion indicating that monocytes limit IL-7 induced lymphocyte expansion. Our data indicate that DC vaccination leads to an increase in the ex vivo responsiveness of patient PBMCs consistent with a DC vaccination induced enhancement of T cell memory. Our findings also suggest that incorporation of bacterial components and homeostatic cytokines into immunotherapy protocols may be useful in order to enhance the efficacy of DC vaccination and that monocytes may limit DC vaccination induced immunity. Supported by a grant to Martin Thurnher from the kompetenzzentrum medizin tirol (kmt), a center of excellence.     

Gamma-ray irradiation impairs dendritic cell migration to CCL19 by down-regulation of CCR7 and induction of cell apoptosis

Dendritic cells (DCs) are the most potent antigen-presenting cells and play a crucial role in the regulation of immune response and migration of DCs into secondary lymphoid tissues also play an important role in the initiation of innate and adaptive immunity. Radiation therapy is now a routine treatment for certain types of cancer and over 20 percent of cancer patients will require radiation therapy during the treatment of their disease. However, the influence of ionizing irradiation on the migratory ability of DCs is largely unknown. In this article, we report that γ ray irradiation can significantly inhibit LPS-triggered up regulation of CCR7 expression and PGE2 production by DC, thus impairing DC migration towards CCL19 in vitro and in vivo. Moreover, γ ray exposed DC also displayed an increased apoptosis rate and decreased cell viability. Furthermore, we demonstrate that exogenous PGE2 can partly reduce the gamma-ray induced migratory impairment and restored CCR7 expression of DC. Our work suggests that γ irradiation affects DC function at multiple steps during the immune response including DC migration, and that PGE2, via control of CCR7 expression, is an important regulator of DC migration.     

Exosomes from bone marrow dendritic cells pulsed with diphtheria toxoid preferentially induce type 1 antigen-specific IgG responses in naive recipients in the absence of free antigen

Exosomes derived from dendritic cells (DC) activate T cells in vivo, but whether exosomes are able to induce and/or modulate humoral immune responses is still unknown. We show that murine bone marrow DC pulsed in vitro with an intact protein (diphtheria toxoid (DT)) produce exosomes that induce, in the absence of free protein, in vivo Ig responses specific for DT in naive recipients. Furthermore, these exosomes stimulate secondary IgG anti-DT responses in mice primed with intact DT. Exosomes from mature, relative to immature, DC were more effective at inducing primary, although not secondary, IgG anti-DT responses. Whereas intact DT preferentially induced a type 2 (IgG1) anti-DT response, exosomes from DT-pulsed bone marrow DC favored induction of type 1 (IgG2b and IgG2a) DT-specific IgG. These results are the first to demonstrate the ability of exosomes derived from Ag-pulsed DC to induce and modulate Ag-specific humoral immunity in vivo.     

Modulation of dendritic cell function by naive and regulatory CD4+ T cells

The consequences of interactions between dendric cells (DCs) and either naive CD4+ T cells or regulatory CD4+CD25+ T cells on the expression of proinflammatory IL-6 and anti-inflammatory IL-10 in DC were examined over a period of 12 h, spanning the time frame during which stable T cell-DC interactions shape the development of tolerance and immunity in vivo. We demonstrate that the basal production of IL-6 and IL-10, which is initiated following DC stimulation with LPS, is modified in distinctly different ways by interaction with the two T cell populations. Naive CD4 T cells skew DC cytokine production toward IL-6 and suppress IL-10, whereas CD4+CD25+ T cells have the opposite effect. CD8 T cells or memory CD4 T cells do not influence basal cytokine production by stimulated DC. The effect of CD4+CD25+ T cells is dominant in coculture with naive CD4 T cells as long as inflammatory LPS is absent; the addition of LPS abrogates the suppression of IL-6. However, the modulating influence of CD4+CD25+ T cells remains evident in the enhancement of IL-10 production. Thus, mutual interactions between DC and CD4+ T cell subpopulations following contact with pathogens are likely to influence the strength and quality of incipient immune responses in the local microenvironment.     

Oxidized low-density lipoprotein promotes mature dendritic cell transition from differentiating monocyte

Proinflammatory oxidized phospholipids are generated during oxidative modification of low-density lipoproteins (LDL). The production of these proinflammatory oxidized phospholipids is controlled by secreted enzymes that circulate as proteins complexed with LDL and high-density lipoprotein. During the acute phase response to tissue injury, profound changes occur in lipoprotein enzymatic composition that alter their anti-inflammatory function. Monocytes may encounter oxidized phospholipids in vivo during their differentiation to macrophages or dendritic cells (DC). In this study we show that the presence of oxidized LDL (oxLDL) at the first day of monocyte differentiation to DC in vitro yielded phenotypically atypical cells with some functional characteristics of mature DC. Addition of oxLDL during the late stage of monocyte differentiation gave rise directly to phenotypically mature DC with reduced uptake capacity, secreting IL-12 but not IL-10, and supporting both syngeneic and allogeneic T cell stimulation. In contrast to known mediators of DC activation, oxLDL did not trigger maturation of immature DC. An intriguing possibility is that a burst of oxidized phospholipids is an endogenous activation signal for the immune system, which is tightly controlled by lipoproteins during the acute phase response.     

The multifaceted relationship between IL-10 and adaptive immunity: putting together the pieces of a puzzle

Interleukin-10 (IL-10) is a pleiotropic cytokine that modulates the function of several adaptive immunity-related cells. Although generally considered an immunosuppressive molecule, IL-10 possesses immunostimulatory properties in several in vitro and in vivo models. These very different outcomes are believed to depend upon experimental conditions, the dominant immune effector mediating a given immune response, the timing of IL-10 production/administration, and IL-10 dose and/or location of expression. In the present work, we review the current knowledge regarding IL-10 activity on adaptive immunity related cells, emphasize new insights on IL-10 molecular/cellular targets, and summarize the available data on the relationship between IL-10 and some pathological conditions (e.g. infectious diseases, autoimmunity, allergy, cancer and transplantation) involving adaptive immunity.     

T and B cells are not required for clearing Staphylococcus aureus in systemic infection despite a strong TLR2-MyD88-dependent T cell activation

Staphylococcus aureus infection elicits through its mature lipoproteins an innate immune response by TLR2-MyD88 signaling, which improves bacterial clearing and disease outcome. The role of dendritic cells (DCs) and T cells in this immune activation and the function of T and B cells in defense against S. aureus infection remain unclear. Therefore, we first evaluated DC and T cell activation after infection with S. aureus wild type (WT) and its isogenic mutant, which is deficient in lipoprotein maturation, in vitro. Lipoproteins in viable S. aureus contributed via TLR2-MyD88 to activation of DCs, which promoted the release of IFN-γ and IL-17 in CD4(+) T cells. This strong effect was independent of superantigens and MHC class II. We next evaluated the function of T cells and their cytokines IFN-γ and IL-17 in infection in vivo. Six days after systemic murine infection IFN-γ, IL-17, and IL-10 production in total spleen cells were MyD88-dependent and their levels increased until day 21. The comparison of CD3(-/-), Rag2(-/-), and C57BL/6 mice after infection revealed that IFN-γ and IL-17 originated from T cells and IL-10 originated from innate immune cells. Furthermore, vaccination of mice to activate T and B cells did not improve eradication of S. aureus from organs. In conclusion, S. aureus enhances DC activation via TLR2-MyD88 and thereby promotes T(H)1 and T(H)17 cell differentiation. However, neither T cells and their MyD88-regulated products, IFN-γ and IL-17, nor B cells affected bacterial clearing from organs and disease outcome.     

Increased survival in sepsis by in vivo adenovirus-induced expression of IL-10 in dendritic cells

The dendritic cell (DC) is the most potent APC of the immune system, capable of stimulating naive T cells to proliferate and differentiate into effector T cells. Recombinant adenovirus (Adv) readily transduces DCs in vitro allowing directed delivery of transgenes that modify DC function and immune responses. In this study we demonstrate that footpad injection of a recombinant Adv readily targets transduction of myeloid and lymphoid DCs in the draining popliteal lymph node, but not in other lymphoid organs. Popliteal DCs transduced with an empty recombinant Adv undergo maturation, as determined by high MHC class II and CD86 expression. However, transduction with vectors expressing human IL-10 limit DC maturation and associated T cell activation in the draining lymph node. The extent of IL-10 expression is dose dependent; transduction with low particle numbers (10(5)) yields only local expression, while transduction with higher particle numbers (10(7) and 10(10)) leads additionally to IL-10 appearance in the circulation. Furthermore, local DC expression of human IL-10 following in vivo transduction with low particle numbers (10(5)) significantly improves survival following cecal ligation and puncture, suggesting that compartmental modulation of DC function profoundly alters the sepsis-induced immune response.     

Immunosuppression during Acute Infection with Foot-and-Mouth Disease Virus in Swine Is Mediated by IL-10

Foot-and-mouth disease virus (FMDV) is one of the most contagious animal viruses, causing a devastating disease in cloven-hoofed animals with enormous economic consequences. Identification of the different parameters involved in the immune response elicited against FMDV remains unclear, and it is fundamental the understanding of such parameters before effective control measures can be put in place. In the present study, we show that interleukin-10 (IL-10) production by dendritic cells (DCs) is drastically increased during acute infection with FMDV in swine. In vitro blockade of IL-10 with a neutralizing antibody against porcine IL-10 restores T cell activation by DCs. Additionally, we describe that FMDV infects DC precursors and interferes with DC maturation and antigen presentation capacity. Thus, we propose a new mechanism of virus immunity in which a non-persistent virus, FMDV, induces immunosuppression by an increment in the production of IL-10, which in turn, reduces T cell function. This reduction of T cell activity may result in a more potent induction of neutralizing antibody responses, clearing the viral infection.     

Maturation of monocyte-derived dendritic cells with Toll-like receptor 3 and 7/8 ligands combined with prostaglandin E2 results in high interleukin-12 production and cell migration

Dendritic cells (DC) are professional antigen-presenting cells of the immune system that play a key role in regulating T cell-based immunity. In vivo, the capacity of DC to activate T cells depends on their ability to migrate to the T cell areas of lymph nodes as well as on their maturation state. Depending on their cytokine-secreting profile, DC are able to skew the immune response in a specific direction. In particular, IL-12p70 producing DC drive T cells towards a T helper 1 type response. A serious disadvantage of current clinical grade ex vivo generated monocyte-derived DC is the poor IL-12p70 production. We have investigated the effects of Toll-like receptor (TLR)-mediated maturation on ex vivo generated human monocyte-derived DC. We demonstrate that in contrast to cytokine-matured DC, DC matured with poly(I:C) (TLR3 ligand) and/or R848 (TLR7/8 ligand) are able to produce vast amounts of IL-12p70, but exhibit a reduced migratory capacity. The addition of prostaglandin E(2) (PGE(2)) improved the migratory capacity of TLR-ligand matured DC while maintaining their IL-12p70 production upon T cell encounter. We propose a novel clinical grade maturation protocol in which TLR ligands poly(I:C) and R848 are combined with PGE(2) to generate DC with both high migratory capacity and IL-12p70 production upon T cell encounter.     

NK dendritic cells are innate immune responders to Listeria monocytogenes infection

NK dendritic cells (NKDC) are recently described immunologic cells that possess both lytic and Ag-presenting function and produce prolific quantities of IFN-gamma. The role of NKDC in innate immunity to bacterial infection is unknown. Because IFN-gamma is important in the immune response to Listeria monocytogenes (LM), we hypothesized that NKDC play a critical role during LM infection in mice. We found that LM increased the frequency and activation state of NKDC in vivo. Using in vivo intracellular cytokine analysis, we demonstrated that NKDC are a major source of early IFN-gamma during infection with LM. Adoptive transfer of wild-type NKDC into IFN-gamma-deficient recipients that were subsequently infected with LM decreased bacterial burden in the liver and spleen and prolonged survival. In contrast, NK cells were depleted early during LM infection, produced less IFN-gamma, and conferred less protection upon adoptive transfer into IFN-gamma-deficient mice. In vitro, LM induction of IFN-gamma secretion by NKDC depended on TLR9, in addition to IL-18 and IL-12. Our study establishes NKDC as innate immune responders to bacterial infection by virtue of their ability to secrete IFN-gamma.