Lysophosphatidic acid modulates the activation of human monocyte-derived dendritic cells

Lysophosphatidic acid (LPA) is a biologically active lysophospholipid that can regulate immune activation. LPA can activate T cells and dendritic cells (DCs), but the effects of LPA on the ability of DCs to influence T cell polarization are not well understood. Human monocyte-derived DCs were differentiated in vitro in the presence of interleukin-4 (IL-4) and granulocyte-macrophage colonystimulating factor (GM-CSF), and matured with LPA and lipopolysaccharide (LPS) alone or in combination. DC activation was monitored by analyzing cell-surface expression of co-stimulatory receptors and cytokine production. The ability of DCs to influence T cell activation was determined using two models of DC:T cell co-culture. Maturation with LPS induced dose-dependent DC activation characterized by enhanced expression of co-stimulatory molecules (e.g., CD86) and production of cytokines including IL-6 and IL-10. Co-incubation with LPA attenuated the LPS-induced production of IL-6, without significantly affecting IL-10 secretion or the ability of DC to promote T cell proliferation. DCs matured in the presence of both LPA and LPS enhanced the production of interferon-gamma (IFN-gamma) when co-cultured with allogeneic T cells, compared with DC matured by LPS alone. Similar results were found using a model of allogeneic na?ve T cell differentiation, where LPA- plus LPS-matured DC enhanced IFN-gamma as well as IL-4 secretion after restimulation. Lysophosphatidic acid fine-tunes the effects of LPS on human myeloid DC maturation, but does not exert a dominant effect on the ability of DC to influence Th cell polarization.     

IL-10-treated dendritic cells decrease airway hyperresponsiveness and airway inflammation in mice

BACKGROUND: IL-10 affects dendritic cell (DC) function, but the effects on airway hyperresponsiveness (AHR) and inflammation are not defined. OBJECTIVE: We sought to determine the importance of IL-10 in regulating DC function in allergen-induced AHR and airway inflammation. METHODS: DCs were generated from bone marrow in the presence or absence of IL-10. In vivo IL-10-treated DCs from IL-10(+/+) and IL-10(-/-) donors pulsed with ovalbumin (OVA) were transferred to naive or sensitized mice before challenge. In recipient mice AHR, cytokine levels, cell composition of bronchoalveolar lavage (BAL) fluid, and lung histology were monitored. RESULTS: In vitro, IL-10-treated DCs expressed lower levels of CD11c, CD80, and CD86; expressed lower levels of IL-12; and suppressed T(H)2 cytokine production. In vivo, after transfer of OVA-pulsed IL-10-treated DCs, naive mice did not have AHR, airway eosinophilia, T(H)2 cytokine increase in BAL fluid, or goblet cell metaplasia when challenged, and in sensitized and challenged mice IL-10-treated DCs suppressed these responses. Levels of IL-10 in BAL fluid and numbers of lung CD4(+)IL-10(+) T cells were increased in mice that received OVA-pulsed IL-10-treated DCs. Transfer of IL-10-treated DCs from IL-10-deficient mice were ineffective in suppressing the responses in sensitized and challenged mice. CONCLUSIONS: These data demonstrate that IL-10-treated DCs are potent suppressors of the development of AHR, inflammation, and T(H)2 cytokine production; these regulatory functions are at least in part through the induction of endogenous (DC) production of IL-10. CLINICAL IMPLICATIONS: Modification of DC function by IL-10 can attenuate lung allergic responses, including the development of AHR.     

IL-21 enhances SOCS gene expression and inhibits LPS-induced cytokine production in human monocyte-derived dendritic cells

Dendritic cells (DCs) play an important role in innate and adaptive immune responses. In addition to their phagocytic activity, DCs present foreign antigens to na?ve T cells and regulate the development of adaptive immune responses. Upon contact with DCs, activated T cells produce large quantities of cytokines such as interferon-gamma (IFN-gamma) and interleukin (IL)-21, which have important immunoregulatory functions. Here, we have analyzed the effect of IL-21 and IFN-gamma on lipopolysaccharide (LPS)-induced maturation and cytokine production of human monocyte-derived DCs. IL-21 and IFN-gamma receptor genes were expressed in high levels in immature DCs. Pretreatment of immature DCs with IL-21 inhibited LPS-stimulated DC maturation and expression of CD86 and human leukocyte antigen class II (HLAII). IL-21 pretreatment also dramatically reduced LPS-stimulated production of tumor necrosis factor alpha, IL-12, CC chemokine ligand 5 (CCL5), and CXC chemokine ligand 10 (CXCL10) but not that of CXCL8. In contrast, IFN-gamma had a positive feedback effect on immature DCs, and it enhanced LPS-induced DC maturation and the production of cytokines. IL-21 weakly induced the expression Toll-like receptor 4 (TLR4) and translation initiation region (TIR) domain-containing adaptor protein (TIRAP) genes, whereas the expression of TIR domain-containing adaptor-inducing IFN-beta (TRIF), myeloid differentiation (MyD88) 88 factor, or TRIF-related adaptor molecule (TRAM) genes remained unchanged. However, IL-21 strongly stimulated the expression of suppressor of cytokine signaling (SOCS)-1 and SOCS-3 genes. SOCS are known to suppress DC functions and interfere with TLR4 signaling. Our results demonstrate that IL-21, a cytokine produced by activated T cells, can directly inhibit the activation and cytokine production of myeloid DCs, providing a negative feedback loop between DCs and T lymphocytes.     

Role of c-Jun N-terminal kinase on lipopolysaccharide induced maturation of human monocyte-derived dendritic cells

Dendritic cells (DCs) are potent antigen-presenting cells that play a pivotal role in the initiation of T cell-dependent immune responses. Immature DCs obtained from peripheral blood CD14+ monocytes by culture with granulocyte macrophage-colony stimulating factor (GM-CSF) and interleukin-4 (IL-4) differentiate into mature DCs upon stimulation with lipopolysaccharide (LPS). At least three families of mitogen-activated protein kinases (MAPKs), that is, extracellular signal-regulated kinases (ERK), c-Jun N-terminal kinases (JNK) and p38 MAPK, are involved in the DC maturation process. We report investigations of the role of JNK in the maturation of human monocyte-derived DCs. SP600125, a specific inhibitor of JNK, inhibited the LPS-induced up-regulation of CD80, CD83, CD86 and CD54, but augmented the up-regulation of HLA-DR. SP600125 slightly inhibited the down-regulation of FITC-dextran uptake during DC maturation. However, SP600125 did not affect the LPS induced up-regulation of allostimulatory capacity of DCs. SP600125 inhibited the release of IL-12 p70 and TNF-alpha from mature DCs. Although autologous T cells primed by the ovalbumin (OVA)-pulsed mature DCs produced IFN-gamma, but not IL-4, OVA-pulsed SP600125-treated mature DCs could initiate IL-4 production from autologous T cells. In contrast, a p38 MAPK inhibitor, SB203580, profoundly inhibited the phenotypic and functional maturation of DCs, while an ERK inhibitor, PD98059, had little or no effect. Taken together, the JNK signaling pathway appears to have a role that is distinct from the p38 MAPK and ERK cascades in the maturation process of DCs, and may be involved in the augmentation of Th2-prone T cell responses when it is suppressed.     

Commensal bacteria trigger a full dendritic cell maturation program that promotes the expansion of non-Tr1 suppressor T cells

Dendritic cells (DCs) orchestrate the immune response establishing immunity versus tolerance. These two opposite functions may be dictated by DC maturation status with maturity linked to immunogenicity. DCs directly interact with trillions of noninvasive intestinal bacteria in vivo, a process that contributes to gut homeostasis. We here evaluated the maturation program elicited in human DCs by direct exposure to commensal-related bacteria (CB) in the absence of inflammatory signals. We showed that eight gram(+) and gram(-) CB strains up-regulated costimulatory molecule expression in DCs and provoked a chemokine receptor switch similar to that activated by gram(+) pathogens. CB strains may be classified into three groups according to DC cytokine release: high IL-12 and low IL-10; low IL-12 and high IL-10; and low IL-12 and IL-10. All CB-treated DCs produced IL-1beta and IL-6 and almost no TGF-beta. Yet, CB instructed DCs to convert naive CD4+ T cells into hyporesponsive T cells that secreted low or no IFN-gamma, IL-10, and IL-17 and instead, displayed suppressor function. These data demonstrate that phenotypic DC maturation combined to an appropriate cytokine profile is insufficient to warrant Th1, IL-10-secreting T regulatory Type 1 (Tr1), or Th17 polarization. We propose that commensal flora and as such, probiotics manipulate DCs by a yet-unidentified pathway to enforce gut tolerance.     

Stimulatory and inhibitory differentiation of human myeloid dendritic cells

Dendritic cells (DCs) play a critical obligate role in presenting antigens to T cells for activation. In the process, upon antigen capture, DCs undergo maturation and become more stimulatory. Human myeloid DCs can be generated from various sources, including blood, bone marrow, and CD34(+) stem cells. As such, plastic-adherent monocytes from circulation have served as a ready source for generating myeloid DCs in culture in granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4) for translational research in active specific immunotherapy, especially in cancer, with the belief that they are essentially stimulatory or "immunogenic." Here we show that in vitro cultures of plastic-adherent circulating monocytes in GM-CSF and IL-4 followed by further maturation in interferon-gamma plus bacterial superantigens (DC maturing agents) can give rise to two diametrically opposite types of DCs-one stimulatory and another inhibitory. The stimulatory DCs express higher amounts of costimulatory molecules, synthesize IL-12, and efficiently stimulate naive allogeneic T cells in mixed lymphocyte reaction (MLR). The inhibitory DCs, in contrast, express lower concentrations of the critical costimulatory molecules, synthesize large amounts of IL-10, and are nonstimulatory in allogeneic primary MLR. Moreover, while the stimulatory DCs further amplify proliferation of T cells in lectin-driven proliferation assays, the inhibitory DCs totally block T cell proliferation in similar assays, in vitro. Most interestingly, neutralization of the endogenously derived IL-10 with anti-IL-10 antibody in DC cultures repolarizes the inhibitory DCs toward stimulatory phenotype. Accordingly, these observations have important implications in translational research involving myeloid DCs.     

Galectin-9 induces maturation of human monocyte-derived dendritic cells]

We investigated the role of galectin-9 (Gal-9) in maturation of dendritic cells (DC). Culture of immature DCs with exogenous Gal-9 markedly increased the surface expression of CD40, CD54, CD80, CD83, CD86, and HLA-DR in a concentration-dependent manner, although Gal-9 had no effect on differentiation of human monocytes into immature DCs. Gal-9-treated DCs secreted IL-12 but not IL-10, and they elicited the production of Th1 cytokines (IFN-gamma and IL-2), but not that of the Th2 cytokines (IL-4 and IL-5) by allogeneic CD4(+) T cells. These effects of Gal-9 on immature DCs were not essentially dependent on its lectin properties, given that they were only slightly inhibited by lactose. We further found that a Gal-9 mutant that lacks beta-galactoside binding activity reproduced the above activities, and that an anti-Gal-9 mAb suppressed them. Gal-9 induced phosphorylation of the p38 MAPK and ERK1/2 in DCs, and an inhibitor of p38 signaling, but not inhibitors of signaling by either ERK1/2 or phosphatidylinositol 3-kinase, blocked Gal-9-induced up-regulation of costimulatory molecule expression and IL-12 production. These findings suggest that Gal-9 plays a role not only in innate immunity but also in acquired immunity by inducing DC maturation and promoting Th1 immune responses.     

Plasmodium falciparum-free merozoites and infected RBCs distinctly affect soluble CD40 ligand-mediated maturation of immature monocyte-derived dendritic cells

Free plasmodium merozoites released from the parasitized hepatocytes and erythrocytes represent a transitory, extracellular stage in its mammalian host. In this study, we compared the effect of Plasmodium falciparum-free merozoites with infected RBCs (iRBCs) on the maturation of human monocyte-derived dendritic cells (DCs) in vitro. Phagocytosed-free merozoites prevented soluble CD40 ligand (sCD40L)-induced, phenotypic maturation of DCs and secretion of IL-12p70 but enhanced IL-10 production and primed, naive CD4+ cells to produce a high level of IL-10 compared with IFN-gamma. Free merozoites augmented sCD40L-induced ERK1/2 activation, and inhibition of ERK1/2 with its inhibitor PD98059 markedly abrogated IL-10 production and rescued IL-12 production. Therefore, the molecular mechanisms by which free merozoites antagonized sCD40L-induced DC maturation appeared to involve the activation of the ERK pathway. In contrast, phagocytosed iRBCs by itself induced DCs to semi-maturation, responded to CD40 signaling by maturing and secreting increased levels of TNF-alpha, IL-6, and also IL-12p70, and led to a pronounced, proinflammatory response by the allogenic CD4+ T cells. iRBCs regulate CD40-induced p38MAPK. Studies using inhibitors selective for p38MAPK (SB203580) showed that p38MAPK played an essential role in the maturation and function of DCs. Our results reveal the ability of free merozoites and iRBCs to distinctly alter the sCD40L-induced DC functioning by regulating the activation of the MAPK pathway that can inactivate or exacerbate immune responses to promote their survival and the development of parasite-specific pathologies.     

Amyloid beta peptide promotes differentiation of pro-inflammatory human myeloid dendritic cells

A key event of Alzheimer's disease (AD) pathogenesis is the production of amyloid beta peptides (A beta), which are hypothesized to lead to neurodegeneration by still unclear mechanisms, including a chronic inflammatory response characterized by innate immune cell activation and pro-inflammatory molecule release. Since dendritic cells (DCs) are central players of innate immune response and brain dendritic-like cells may have a crucial role in AD pathogenesis, this study investigates the effects of A beta on human DC functions. Myeloid DCs differentiated in the presence of A beta 42 showed an increase in survival and soluble antigen uptake, a reduction in HLA molecule expression and in IL-10 and IL-12 production. Accordingly, A beta 42-treated DCs were impaired in inducing T cell proliferation and IL-2 production. On the other hand, A beta 42 treatment provided DCs with the ability to release higher levels of IL-1 beta, IL-6 and IL-18, than control DCs. These results demonstrate that A beta 42 can modulate the immune system by inducing pro-inflammatory DC differentiation, thus gaining new insights into AD pathogenesis and immune-based therapeutic intervention.     

Impact of Helicobacter pylori virulence factors and compounds on activation and maturation of human dendritic cells

Recently, we and others have shown that Helicobacter pylori induces dendritic cell (DC) activation and maturation. However, the impact of virulence factors on the interplay between DCs and H. pylori remains elusive. Therefore, we investigated the contribution of cag pathogenicity island (PAI) and VacA status on cytokine release and up-regulation of costimulatory molecules in H. pylori-treated DCs. In addition, to characterize the stimulatory capacity of H. pylori compounds in more detail, we studied the effect of formalin-inactivated and sonicated H. pylori, as well as secreted H. pylori molecules, on DCs. Incubation of DCs with viable or formalin-inactivated H. pylori induced comparable secretion of interleukin-6 (IL-6), IL-8, IL-10, IL-12, IL-1beta, and tumor necrosis factor (TNF). In contrast, IL-12 and IL-1beta release was significantly reduced in DCs treated with sonicated bacteria and secreted bacterial molecules. Treatment of sonicated H. pylori preparations with polymyxin B resulted in a significant reduction of IL-8 and IL-6 secretion, suggesting that H. pylori-derived lipopolysaccharide at least partially contributes to activation of immature DCs. In addition, the capacity of H. pylori-pulsed DCs to activate allogeneic T cells was not affected by cag PAI and VacA. Pretreatment of DC with cytochalasin D significantly inhibited secretion of IL-12, IL-1beta, and TNF, indicating that phagocytosis of H. pylori contributes to maximal activation of DCs. Taken together, our results suggest that DC activation and maturation, as well as DC-mediated T-cell activation, are independent of the cag PAI and VacA status of H. pylori.     

Induction of IL-10 producing CD4+ T cells with regulatory activities by stimulation with IL-10 gene-modified bone marrow derived dendritic cells

Dendritic cells (DCs) can induce both tolergenic as well as effective immune responses in the lung. Pulmonary DCs producing interleukin (IL)-10 mediated tolerance induced by respiratory exposure to antigen. IL-10 is an important immunosuppressive cytokine, which inhibits maturation and function of DC. To assess whether IL-10 producing DCs can exert the tolergenic effect through the differentiation of regulatory T cells, bone marrow derived DCs were genetically modified by IL-10 expressing adenovirus. IL-10 gene modified DCs (Ad-IL-10-DC) displayed a characteristic phenotype of immature DCs. Here we showed that in vitro repetitive stimulation of naïve DO11·10 CD4⁺ T cells with Ad-IL-10-DCs resulted in a development of IL-10 producing T-cell regulatory cells. These T cells could not proliferate well but also lost their ability to produce interferon-γ upon restimulation with irradiated splenocytes and ovalbumin peptide. Furthermore, in co-culture experiments these T cells inhibited the antigen-driven proliferation of naïve CD4+ T cells in a dose-dependent manner. Our findings demonstrated that IL-10 producing DCs had the potential to induce the differentiation of Tr1-like cells and suggested their therapeutic use.     

Immunomodulation by semi-mature dendritic cells: A novel role of Toll-like receptors and interleukin-6

Dendritic cells (DCs) are key players in activation of the adaptive immune system by their ability of antigen presentation to and priming of T cells. An increasing body of evidence suggests that DCs may also play an important role in induction of tolerance, predominantly by induction of regulatory T cells (T_reg). More recently, data have been published on how Toll-like receptor (TLR) ligands and cytokines affect DC differentiation, and how DC subsets might be involved in immunoregulation and tolerance rather than in T cell activation. The most important features of tolerance-inducing DCs appear to be their maturation state and their cytokine secretion pattern. The following types of tolerance-inducing DCs have been reported: immature DCs (DCs^im) or DCs in the steady state (DCs^st), DCs^IL-10, semi-mature DCs^TNF-α, semi-mature DCs^IL-6. With this review article we would like to discuss the aforementioned types of tolerogenic DCs with a focus on semi-mature DCs^IL-6 and discuss their potential role in maintenance of (hepatic or intestinal) immune homeostasis and inflammatory diseases such as inflammatory bowel disease.     

IL-27 renders DC immunosuppressive by induction of B7-H1

IL-27, an IL-12 family member, was initially described as a proinflammatory cytokine. Nevertheless, it also poses anti-inflammatory activity, being involved in suppressing development of TH-17 cells as well as in the induction of inhibitory Tr1 cells. Recent data obtained in mice suggest that it can down-modulate the function of APCs. However, until now, nothing was known about the influence of IL-27 on human DCs. We investigated the effect of IL-27 on in vitro human MoDCs and on ex vivo blood DCs. Our results show that treatment of mDCs with IL-27 led to specific up-regulation of surface expression of several molecules, including B7-H1, in the absence of general DC maturation. Moreover, we demonstrated that IL-27-treated DCs exhibit a reduced capacity to stimulate proliferation and cytokine production of allogeneic T cells as compared with control DCs. Decisively, we identified B7-H1 as a crucial molecule, responsible for suppressive effects of "IL-27 DC" on T cells. Our data demonstrate for the first time that in addition to the dual role of IL-27 in the modulation of T cell activation and differentiation, human IL-27 modulates an immune response through DCs, i.e., by inducing immunosuppressive B7-H1 molecules and reducing the stimulatory potential of DCs.     

Recombinant adenovirus-transduced human dendritic cells engineered to secrete interleukin-10 (IL-10) suppress Th1-type responses while selectively activating IL-10-producing CD4+ T cells

Recombinant adenoviruses (rAd) are efficient tools for genetic modification of human dendritic cells (DC) in vitro. Infection of DCs by rAd encoding beta-galactosidase (betagal) results in partial maturation of DCs, as witnessed by the upregulation of major histocompatibility complex and costimulatory molecules. Accordingly, these DCs are more potent stimulators of Th1-type proliferative responses. We now demonstrate that infection of immature DCs with rAd encoding human interleukin (IL)-10 results in the secretion by the DCs of large amounts of IL-10, while not affecting expression of activation markers indicative of partial DC maturation. In contrast to rAd-betagal-infected DCs, rAdIL-10-infected DCs are very poor stimulators of monoclonal and polyclonal Th1-type responses. Instead, stimulation of nonpolarized CD4+ T-cell cultures with rAdIL-10-infected DCs selectively activates and expands an IL-10-producing CD4+ T-cell subset capable of suppressing Th1 responses in vitro. Our data argue that rAd-infected human DCs genetically engineered to produce IL-10 may be exploited for the modulation of harmful Th1-type responses in transplantation and autoimmune diseases.     

Dexamethasone turns tumor antigen-presenting cells into tolerogenic dendritic cells with T cell inhibitory functions

BackgroundDendritic cells (DCs) are usually immunogenic, but they are also capable of inducing tolerance under anti-inflammatory conditions. Immunotherapy based on autologous DCs loaded with an allogeneic melanoma cell lysate (TRIMEL/DCs) induces immunological responses and increases melanoma patient survival. Glucocorticoids can suppress DC maturation and function, leading to a DC-mediated inhibition of T cell responses.MethodsThe effect of dexamethasone, a glucocorticoid extensively used in cancer therapies, on TRIMEL/DCs phenotype and immunogenicity was examined.ResultsDexamethasone induced a semi-mature phenotype on TRIMEL/DC with low maturation surface marker expressions, decreased pro-inflammatory cytokine induction (IL-1β and IL-12) and increased release of regulatory cytokines (IL-10 and TGF-β). Dexamethasone-treated TRIMEL/DCs inhibited allogeneic CD4⁺ T cell proliferation and cytokine release (IFNγ, TNF-α and IL-17). Co-culturing melanoma-specific memory tumor-infiltrating lymphocytes with dexamethasone-treated TRIMEL/DC inhibited proliferation and effector T cell activities, including cytokine secretion and anti-melanoma cytotoxicity.ConclusionsThese findings suggest that dexamethasone repressed melanoma cell lysate-mediated DC maturation, generating a potent tolerogenic-like DC phenotype that inhibited melanoma-specific effector T cell activities. These results suggest that dexamethasone-induced immunosuppression may interfere with the clinical efficacy of DC-based melanoma vaccines, and must be taken into account for optimal design of cellular therapy against cancer.     

Maturation of murine bone marrow-derived dendritic cells with poly(I:C) produces altered TLR-9 expression and response to CpG DNA

Although poly(I:C) and LPS induced differential dendritic cell (DC) cytokine profiles and toll-like receptor (TLR) expression, all were capable of causing phenotypic and functional DC maturation. Both LPS and poly(I:C) downregulated TLR-4/MD-2 expression on DCs. Although poly(I:C) highly upregulated their cell surface TLR-9 expression, LPS upregulated the intracellular TLR-9 expression. LPS-treated DCs could not produce IL-12p70 in response to subsequent both LPS- and CpG DNA-stimulation. On the other hand, poly(I:C)-treated DCs retained to produce IL-12p70 by subsequent CpG DNA-stimulation, while subsequent LPS-stimulation did not induce IL-12p70 production. Chloroquine, inhibitor of endosomal maturation, completely inhibited cytokine production of LPS-treated DCs as well as unstimulated control in response to subsequent CpG DNA-stimulation, while it failed to delete the IL-12p40 and IL-10 production in poly(I:C)-treated DCs. These data suggest that poly(I:C) may induce a novel DC phenotype that preserves the capacity of cytokine production to subsequent CpG DNA-stimulation.     

Stimulatory and inhibitory maturation of human macrophage-derived dendritic cells.

Circulating human macrophages are often used to generate dendritic cells (DCs) by culturing them in granulocyte macrophage-colony stimulating factor (GM-CSF) and interleukin-4 (IL-4). As DCs are superb antigen-presenting cells, these types of myeloid DCs are now used in many DC-based vaccination protocols, especially in cancer, with the belief that they are essentially stimulatory or 'immunogenic'. Here we show that just as peripheral macrophage-derived myeloid DCs can be stimulatory, in vitro cultures of myeloid DCs in GM-CSF and IL-4 followed by further maturation in interferon-gamma plus bacterial superantigens (as DC maturing agents) can give rise to DCs that are functionally inhibitory. The stimulatory DCs express higher amounts of costimulatory molecules, synthesize IL-12, and efficiently stimulate naive allogeneic T cells in mixed lymphocyte reaction (MLR). The inhibitory DCs, in contrast, express lower concentrations of the critical costimulatory molecules, synthesize large amounts of IL-10, and are either marginally stimulatory or nonstimulatory in MLR. Moreover, while the stimulatory DCs further amplify proliferation of T cells in lectin-driven proliferation assays, the inhibitory DCs suppress T cell proliferation in similar assays, in vitro. Most interestingly, neutralization of the endogenously derived IL-10 with anti-IL-10 antibody with DC cultures as well as exposure of the inhibitory DCs to CpG oligonucleotides or to in vitro activated autologous CD4+ T helper cells repolarize them into stimulatory phenotype. Accordingly, these observations have important implications in translational research involving myeloid DCs.     

Interferon-alpha2a is sufficient for promoting dendritic cell immunogenicity

Type I interferons (IFNs) are widely used therapeutically. IFN-alpha2a in particular is used as an antiviral agent, but its immunomodulatory properties are poorly understood. Dendritic cells (DCs) are the only antigen-presenting cells able to prime naive T cells and therefore play a crucial role in initiating the adaptive phase of the immune response. We studied the effects of IFN-alpha2a on DC maturation and its role in determining Th1/Th2 equilibrium. We found that IFN-alpha2a induced phenotypic maturation of DCs and increased their allostimulatory capacity. When dendritic cells were stimulated simultaneously by CD40 ligation and IFN-alpha2a, the production of interleukin (IL)-10 and IL-12 was increased. In contrast, lipopolysaccharide (LPS) stimulation in the presence of IFN-alpha2a mainly induced IL-10 release. The production of IFN-gamma and IL-5 by the responder naive T cells was also amplified in response to IFN-alpha2a-treated DCs. Furthermore, IL-12 production by IFN-alpha2a-treated DCs was enhanced further in the presence of anti-IL-10 antibody. Different results were obtained when DCs were treated simultaneously with IFN-alpha2a and other maturation factors, in particular LPS, and then stimulated by CD40 ligation 36 h later. Under these circumstances, IFN-alpha2a did not modify the DC phenotype, and the production of IL-10/IL-12 and IFN-gamma/IL-5 by DCs and by DC-stimulated naive T cells, respectively, was inhibited compared to the effects on DCs treated with maturation factors alone. Altogether, this work suggests that IFN-alpha2a in isolation is sufficient to promote DC activation, however, other concomitant events, such as exposure to LPS during a bacterial infection, can inhibit its effects. These results clarify some of the in vivo findings obtained with IFN-alpha2a and have direct implications for the design of IFN-alpha-based vaccines for immunotherapy.     

Dendritic cells phagocytose and are activated by Treponema pallidum

Cell-mediated immune processes play a prominent role in the clinical manifestations of syphilis, a sexually transmitted disease of humans caused by spirochetal bacterium Treponema pallidum. The immune cell type that initiates the early immune response to T. pallidum thus far has not been identified. However, dendritic cells (DCs) are the first immune-competent cells to encounter antigens within skin or mucous membranes, the principal sites of early syphilitic infection. In the present study, immature DC line XS52, derived from murine skin, was utilized to examine T. pallidum-DC interactions and subsequent DC activation (maturation). Electron microscopy revealed that T. pallidum was engulfed by DCs via both coiling and conventional phagocytosis and was delivered to membrane-bound vacuoles. The XS52 DC line expressed surface CD14 and mRNA for Toll-like receptors 2 and 4, molecules comprising important signaling components for immune cell activation by bacterial modulins. Both T. pallidum and a synthetic lipopeptide (corresponding to the 47-kDa major membrane lipoprotein) activated the XS52 DC line, as indicated by the secretion of interleukin-12 (IL-12), IL-1beta, tumor necrosis factor alpha, and IL-6 and elevated surface expression of CD54. The combined data support the contention that DCs stimulated by T. pallidum and/or its proinflammatory membrane lipoproteins are involved in driving the cellular immune processes that typify syphilis.     

The dialogue between human natural killer cells and dendritic cells

The interaction of NK cells with dendritic cells (DCs) appears to play an important role in both innate and adaptive immune responses to pathogens. In peripheral inflamed tissues the simultaneous engagement of receptors for danger (e.g. Toll-like receptors), which are expressed by both NK cells and DCs, results in cell activation and the acquisition of functional properties necessary for controlling, and possibly rapidly eliminating, pathogens by innate effector mechanisms. Moreover, NK cells are needed to select the most appropriate DCs that display the functional properties suitable for subsequent T-cell priming. This NK-cell-mediated programming of DC maturation is modulated by cytokines released during the early stages of inflammatory responses (i.e. IL-12, IFN-gamma, IL-4). NK cells and DCs continue their interactions in secondary lymphoid organs where both cell types play a role in the control of T-cell priming.