CpG-C immunostimulatory oligodeoxyribonucleotide activation of plasmacytoid dendritic cells in rhesus macaques to augment the activation of IFN-gamma-secreting simian immunodeficiency virus-specific T cells

There are two principle subsets of dendritic cells (DCs); CD11c(+)CD123(-) myeloid DCs (MDCs) and CD11c(-)CD123(+) plasmacytoid DCs (PDCs). DC activation via TNF-TNFRs (e.g., CD40L) and TLRs (e.g., immunostimulatory oligodeoxyribonucleotides (ISS-ODNs)) is crucial for maximal stimulation of innate and adaptive immunity. Macaque DC biology is being studied to improve HIV vaccines using the SIV macaque model. Using lineage (Lin) markers to exclude non-DCs, Lin(-)HLA-DR(+)CD11c(+)CD123(-) MDCs and Lin(-)HLA-DR(+)CD11c(-)CD123(+) PDCs were identified in the blood of uninfected macaques and healthy macaques infected with SIV or simian-human immunodeficiency virus. Overnight culture of DC-enriched Lin-depleted cells increased CD80 and CD86 expression. IL-12 production and CD80/CD86 expression by MDC/PDC mixtures was further enhanced by CD40L and ISS-ODN treatment. A CpG-B ISS-ODN increased CD80/CD86 expression by PDCs, but resulted in little IFN-alpha secretion unless IL-3 was added. In contrast, a CpG-C ISS-ODN and aldrithiol-2-inactivated (AT-2) SIV induced considerable PDC activation and IFN-alpha release without needing exogenous IL-3. The CpG-C ISS-ODN also stimulated IL-12 release (unlike AT-2 SIV) and augmented DC immunostimulatory activity, increasing SIV-specific T cell IFN-gamma production induced by AT-2 SIV-presenting MDC/PDC-enriched mixtures. These data highlight the functional capacities of MDCs and PDCs in naive as well as healthy, infected macaques, revealing a promising CpG-C ISS-ODN-driven DC activation strategy that boosts immune function to augment preventative and therapeutic vaccine efficacy.     

Differential regulation of human blood dendritic cell subsets by IFNs

Based on the relative expression of CD11c and CD1a, we previously identified subsets of dendritic cells (DCs) or DC precursors in human peripheral blood. A CD1a(+)/CD11c(+) population (CD11c(+) DCs), also called myeloid DCs, is an immediate precursor of Langerhans cells, whereas a CD1a(-)/CD11c(-) population (CD11c(-) DCs), sometimes called lymphoid DCs but better known as plasmacytoid DCs, is composed of type I IFN (IFN-alpha beta)-producing cells. Here, we investigate the effects of IFN-alpha beta and IFN-gamma as well as other cytokines on CD11c(+) and CD11c(-) DC subsets, directly isolated from the peripheral blood, instead of in vitro-generated DCs. IFN-gamma and IFN-alpha, rather than GM-CSF, were the most potent cytokines for enhancing the maturation of CD11c(+) DCs. Incubation of CD11c(+) DCs with IFN-gamma also resulted in increased IL-12 production, and this IL-12 allowed DCs to increase Th1 responses by alloreactive T cells. In contrast, IFN-alpha did not induce IL-12 but, rather, augmented IL-10 production. IFN-alpha-primed matured CD11c(+) DCs induced IL-10-producing regulatory T cells; however, this process was independent of the DC-derived IL-10. On the other hand, IFN-alpha by itself neither matured CD11c(-) DCs nor altered the polarization of responding T cells, although this cytokine was a potent survival factor for CD11c(-) DCs. Unlike IFN-alpha, IL-3 was a potent survival factor and induced the maturation of CD11c(-) DCs. The IL-3-primed CD11c(-) DCs activated T cells to produce IL-10, IFN-gamma, and IL-4. Thus, CD11c(+) and CD11c(-) DC subsets play distinct roles in the cytokine network, especially their responses to IFNs.     

Costimulation of chemokine receptor signaling by matrix metalloproteinase-9 mediates enhanced migration of IFN-alpha dendritic cells

Type I IFNs induce differentiation of dendritic cells (DCs) with potent Ag-presenting capacity, termed IFN-alpha DCs, that have been implicated in the pathogenesis of systemic lupus erythematosus. In this study, we found that IFN-alpha DCs exhibit enhanced migration across the extracellular matrix (ECM) in response to chemokines CCL3 and CCL5 that recruit DCs to inflammatory sites, but not the lymphoid-homing chemokine CCL21. IFN-alpha DCs expressed elevated matrix metalloproteinase-9 (MMP-9), which mediated increased migration across ECM. Unexpectedly, MMP-9 and its cell surface receptors CD11b and CD44 were required for enhanced CCL5-induced chemotaxis even in the absence of a matrix barrier. MMP-9, CD11b, and CD44 selectively modulated CCL5-dependent activation of JNK that was required for enhanced chemotactic responses. These results establish the migratory phenotype of IFN-alpha DCs and identify an important role for costimulation of chemotactic responses by synergistic activation of JNK. Thus, cell motility is regulated by integrating signaling inputs from chemokine receptors and molecules such as MMP-9, CD11b, and CD44 that also mediate cell interactions with inflammatory factors and ECM.     

Induction of CD83+CD14+ nondendritic antigen-presenting cells by exposure of monocytes to IFN-alpha

IFN-alpha is a well-known agent for treatment of viral and malignant diseases. It has several modes of actions, including direct influence on the immune system. We investigated IFN-alpha effects on PBMC in terms of dendritic cell (DC) differentiation, as PBMC are exposed to high IFN-alpha levels during treatment of infections and cancers. We show that in vitro IFN-alpha exposure induced rapid and strong up-regulation of the DC-maturation markers CD80, CD86, and CD83 in bulk PBMC. Consistently, IFN-alpha induced up-regulation of these molecules on purified monocytes within 24 h. Up-regulation of CD80 and CD83 expression was IFN-alpha concentration-dependent. In contrast to GM-CSF + IL-4-generated DCs, most of the IFN-alpha-challenged CD83(+) cells coexpressed the monocyte marker CD14. Despite a typical mature DC immunophenotype, IFN-alpha-treated monocytes conserved phagocytic activity and never acquired a dendritic morphology. In mixed lymphocyte reactions IFN-alpha-treated monocytes were less potent than GM-CSF + IL-4-generated DCs but significantly more potent than untreated monocytes to induce T cell proliferation in bulk PBMC. However, only GM-CSF + IL-4-generated DCs were able to induce a significant proliferation of naive CD4(+) T cells. Notably, autologous memory CD4(+) T cells proliferated when exposed to tetanus toxoid-pulsed IFN-alpha-treated monocytes. At variance with untreated or GM-CSF + IL-4-exposed monocytes, those challenged with IFN-alpha showed long-lasting STAT-1 phosphorylation. Remarkably, CD83(+)CD14(+) cells were present in varicella skin lesions in close contact with IFN-alpha-producing cells. The present findings suggest that IFN-alpha alone promptly generates nondendritic APCs able to stimulate memory immune responses. This may represent an additional mode of action of IFN-alpha in vivo.     

Murine plasmacytoid dendritic cells produce IFN-gamma upon IL-4 stimulation

IL-4 plays a key role in inducing IL-4 production in CD4+ T cells, functioning as an important determinant for Th2 cell differentiation. We show here that IL-4 induces IFN-gamma production in B220+ plasmacytoid dendritic cells (PDCs). By searching for cell populations that produce IFN-gamma upon IL-4 stimulation, we found that PDCs were a major IFN-gamma-producing cell upon IL-4 stimulation in wild-type and Rag-2-/- splenocytes. Isolated PDCs, but not CD11b+ DCs or CD8+ DCs, produced IFN-gamma upon IL-4 stimulation. In vivo, the depletion of PDCs by anti-Ly6G/C Ab prevented IFN-gamma production induced by IL-4 administration. We also found that IL-4 induced IFN-gamma production, but not IL-12 or IFN-alpha production, in PDCs and also strongly enhanced CpG oligodeoxynucleotide-induced IFN-gamma production, but not CpG oligodeoxynucleotide-induced IL-12 or IFN-alpha production. However, IL-4 did not induce IFN-gamma production in Stat6-/- PDCs. Moreover, IL-4 induced Stat4 expression in PDCs through a Stat6-dependent mechanism, and only the Stat4-expressing PDCs produced IFN-gamma. Furthermore, IL-4 did not induce IFN-gamma production in Stat4-/- PDCs. These results indicate that PDCs preferentially produce IFN-gamma upon IL-4 stimulation by Stat6- and Stat4-dependent mechanisms.     

Critical role of MHC class I-related chain A and B expression on IFN-alpha-stimulated dendritic cells in NK cell activation: impairment in chronic hepatitis C virus infection

Dendritic cells (DCs) augment effector functions of NK cells, but the underlying mechanisms are not fully understood. Here we show in an in vitro coculture system that human monocyte-derived DCs enhance IFN-gamma production, CD69 expression, and K562 cytolytic ability of NK cells when DCs are prestimulated with various maturation stimuli such as IFN-alpha or LPS. Of interest is the finding that NK cell activation mediated by LPS-stimulated DCs was dependent on IL-12 produced in DC/NK coculture, but that IFN-alpha-stimulated DC-mediated activation was not. Alternatively, MHC class I-related chain A and B (MICA/B), ligands for NKG2D activating receptor, were found to be induced on DCs upon IFN-alpha stimulation and to be responsible for the NK activation because mAb-mediated masking of MICA/B as well as inhibition of direct cell-to-cell contact using transwell insert completely abolished DC-dependent NK cell activation by IFN-alpha. Finally, DCs recovered from chronic hepatitis C virus-infected patients showed defects in the induction of MICA/B and impaired ability to activate NK cells in response to IFN-alpha stimulation. These findings suggested that MICA/B induction on DCs may be one of the mechanisms by which IFN-alpha activates NK cells; this impairment might affect IFN-alpha responsiveness in hepatitis C virus infection.     

Mucosally delivered dendritic cells activate T cells independently of IL-12 and endogenous APCs

In vitro manipulated dendritic cells (DC) have increasingly been used as a promising vaccine formulation against cancer and infectious disease. However, improved understanding of the immune mechanisms is needed for the development of safe and efficacious mucosal DC immunization. We have developed a murine model of respiratory mucosal immunization by using a genetically manipulated DC vaccine. Within 24 h of intranasal delivery, the majority of vaccine DCs migrated to the lung mucosa and draining lymph nodes and elicited a significant level of T cells capable of IFN-gamma secretion and CTL in the airway lumen as well as substantial T cell responses in the spleen. And such T cell responses were associated with enhanced protection against respiratory mucosal intracellular bacterial challenge. In comparison, parenteral i.m. DC immunization did not elicit marked airway luminal T cell responses and immune protection regardless of strong systemic T cell activation. Although repeated mucosal DC delivery boosted Ag-specific T cells in the airway lumen, added benefits to CD8 T cell activation and immune protection were not observed. By using MHC-deficient vaccine DCs, we further demonstrated that mucosal DC immunization-mediated CD8 and CD4 T cell activation does not require endogenous DCs. By using IL-12-deficient vaccine DCs, we also observed that IL-12(-/-) DCs failed to migrate to the lymph nodes but remained capable of T cell activation. Our observations indicate that mucosal delivery of vaccine DCs represents an effective approach to enhance mucosal T cell immunity, which may operate independent of vaccine IL-12 and endogenous DCs.     

IL-12-impaired and IL-12-secreting dendritic cells produce IL-23 upon CD154 restimulation

Experimental studies in monkeys on the basis of ex vivo-generated, reinjected dendritic cells (DCs) allow investigations of primate DC biology in vivo. To study in vitro and in vivo properties of DCs with a reduced capacity to produce IL-12, we adapted findings obtained in vitro with human cells to the rhesus macaque model. Following exposure of immature monocyte-derived monkey DCs to the immunomodulating synthetic polypeptide glatiramer acetate (GA) and to dibutyryl-cAMP (d-cAMP; i.e., a cAMP enhancer that activates DCs but inhibits the induction of Th1 immune responses), the resulting DCs displayed a mature phenotype with enhanced Ag-specific T cell stimulatory function, notably also for memory Th1 cells. Phosphorylation of p38 MAPK was not induced in GA/d-cAMP-activated DCs. Accordingly, these cells secreted significantly less IL-12p40 (p < or = 0.001) than did cytokine-activated cells. However, upon restimulation with rhesus macaque CD154, GA/d-cAMP-activated DCs produced IL-12p40/IL-23. Additionally, DCs activated by proinflammatory cytokines following protocols for the generation of cells used in clinical studies secreted significantly more IL-23 upon CD154 restimulation than following prior activation. Two days after intradermal injection, GA/d-cAMP-activated fluorescence-labeled DCs were detected in the T cell areas of draining lymph nodes. When similarly injected, GA/d-cAMP as well as cytokine-activated protein-loaded DCs induced comparable Th immune responses characterized by secretion of IFN-gamma, TNF, and IL-17, and transiently expanded FOXP3(+) regulatory T cells. Reactivation of primate DCs through CD154 considerably influences their immmunostimulatory properties. This may have a substantial impact on the development of innovative vaccine approaches.     

Severe acute respiratory syndrome coronavirus fails to activate cytokine-mediated innate immune responses in cultured human monocyte-derived dendritic cells

Activation of host innate immune responses was studied in severe acute respiratory syndrome coronavirus (SCV)-infected human A549 lung epithelial cells, macrophages, and dendritic cells (DCs). In all cell types, SCV-specific subgenomic mRNAs were seen, whereas no expression of SCV proteins was found. No induction of cytokine genes (alpha interferon [IFN-alpha], IFN-beta, interleukin-28A/B [IL-28A/B], IL-29, tumor necrosis factor alpha, CCL5, or CXCL10) or IFN-alpha/beta-induced MxA gene was seen in SCV-infected A549 cells, macrophages, or DCs. SCV also failed to induce DC maturation (CD86 expression) or enhance major histocompatibility complex class II expression. Our data strongly suggest that SCV fails to activate host cell cytokine gene expression in human macrophages and DCs.     

Augmentation of antigen-presenting and Th1-promoting functions of dendritic cells by WSX-1(IL-27R) deficiency

WSX-1 is the alpha subunit of the IL-27R complex expressed by T, B, NK/NKT cells, as well as macrophages and dendritic cells (DCs). Although it has been shown that IL-27 has both stimulatory and inhibitory effects on T cells, little is known on the role of IL-27/WSX-1 on DCs. LPS stimulation of splenic DCs in vivo resulted in prolonged CD80/CD86 expression on WSX-1-deficient DCs over wild-type DCs. Upon LPS stimulation in vitro, WSX-1-deficient DCs expressed Th1-promoting molecules higher than wild-type DCs. In an allogeneic MLR assay, WSX-1-deficient DCs were more potent than wild-type DCs in the induction of proliferation of and IFN-gamma production by responder cell proliferation. When cocultured with purified NK cells, WSX-1-deficient DCs induced higher IFN-gamma production and killing activity of NK cells than wild-type DCs. As such, Ag-pulsed WSX-1-deficient DCs induced Th1-biased strong immune responses over wild-type DCs when transferred in vivo. WSX-1-deficient DCs were hyperreactive to LPS stimulation as compared with wild-type DCs by cytokine production. IL-27 suppressed LPS-induced CD80/86 expression and cytokine production by DCs in vitro. Thus, our study demonstrated that IL-27/WSX-1 signaling potently down-regulates APC function and Th1-promoting function of DCs to modulate overall immune responses.     

IL-10 from regulatory T cells determines vaccine efficacy in murine Leishmania major infection

Leishmaniasis affects 12 million people, but there are no vaccines. Immunological correlates of vaccine efficacy are unclear. Polarized Th1 vs Th2 responses in Leishmania major-infected mice suggested that a shift in balance from IL-4 to IFN-gamma was the key to vaccine success. Recently, a role for IL-10 and regulatory T cells in parasite persistence was demonstrated, prompting re-evaluation of vaccine-induced immunity. We compared DNA/modified vaccinia virus Ankara heterologous prime-boost with Leishmania homolog of the receptor for activated C kinase (LACK) or tryparedoxin peroxidase (TRYP). Both induced low IL-4 and high IFN-gamma prechallenge. Strikingly, high prechallenge CD4 T cell-derived IL-10 predicted vaccine failure using LACK, whereas low IL-10 predicted protection with TRYP. The ratio of IFN-gamma:IL-10 was thus a clear prechallenge indicator of vaccine success. Challenge infection caused further polarization to high IL-10/low IFN-gamma with LACK and low IL-10/high IFN-gamma with TRYP. Ex vivo quantitative RT-PCR and in vitro depletion and suppression experiments demonstrated that Ag-driven CD4+ CD25+ T regulatory 1-like cells were the primary source of IL-10 in LACK-vaccinated mice. Anti-IL-10R treatment in vivo demonstrated that IL-10 was functional in determining vaccine failure, rendering LACK protective in the presence of high IFN-gamma/low IL-5 responses.     

IFN-alpha skews monocyte differentiation into Toll-like receptor 7-expressing dendritic cells with potent functional activities

IFN-alpha is an important cytokine for the generation of a protective T cell-mediated immune response to viruses. In this study, we asked whether IFN-alpha can regulate the functional properties of dendritic cells (DCs). We show that monocytes cultured in the presence of GM-CSF and IFN-alpha can differentiate into DCs (IFN-alpha-derived DCs (IFN-DCs)). When compared with DCs generated in the presence of GM-CSF and IL-4 (IL-4-derived DCs), IFN-DCs exhibited a typical DC morphology and expressed, in addition to DC markers CD1a and blood DC Ag 4, a similar level of costimulatory and class II MHC molecules, but a significantly higher level of MHC class I molecules. After maturation with CD40 ligand, IFN-DCs up-regulated costimulatory, class I and II MHC molecules and expressed mature DC markers such as CD83 and DC-lysosome-associated membrane protein. IFN-DCs were endowed with potent functional activities. IFN-DCs secreted large amounts of the inflammatory cytokines IL-6, IL-10, TNF-alpha, IL-1beta, and IL-18, and promoted a Th1 response that was independent of IL-12p70 and IL-18, but substantially inhibited by IFN-alpha neutralization. Furthermore, immature IFN-DCs induced a potent autologous Ag-specific immune response, as evaluated by IFN-gamma secretion and expansion of CD8(+) T cells specific for CMV. Also, IFN-DCs expressed a large number of Toll-like receptors (TLRs), including acquisition of TLR7, which is classically found on the natural type I IFN-producing plasmacytoid DCs. Like plasmacytoid DCs, IFN-DCs could secrete IFN-alpha following viral stimulation or TLR7-specific stimulation. Taken together, these results illustrate the critical role of IFN-alpha at the early steps of immune response to pathogens or in autoimmune diseases.     

Double-stranded RNA stimulation or CD40 ligation of monocyte-derived dendritic cells as models to study their activation and maturation process

Monocyte-derived dendritic cells (DCs) were used as an in vitro model of myeloid DCs in order to determine a minimum marker pattern with which to characterize and distinguish different stages of DC activation and maturation. Phenotypic changes induced on immature DCs by two prototypic stimuli, poly I:C and CD40 ligation, were first examined. Both elicited HLA-DR, CD40, CD86 and CXCR4 upregulation, and CCR5 downregulation, but only CD40 ligand-stimulated DCs became CD83(+)\CCR7(+), whereas poly I:C-stimulated DCs expressed lower CD83 levels and were mostly CCR7(--). CD40 ligation and poly I:C elicited increased production of inflammatory cytokines interleukin (IL)-6 and tumor necrosis factor-alpha, of IL-10 and the CCL5 chemokine, but profiles differed as to higher IL-10, IL-12 and CCL22 (a CCR4 ligand important for T cell recruitment) levels for the former, and of CCL4 and CCL5 for the latter. Thus, a limited set of phenotypic markers, cytokine and chemokine production assays, may be used to distinguish the three stages in the life of DCs: immaturity, activation and full maturation. The ability of purified protein derivative-loaded DCs to stimulate autologous T cells to produce IL-2, IL-4 and interferon-gamma indeed depended on their activation stage and endocytic activity, which decreased upon maturation. We then examined whether ligation of CD4, CCR5 and\or CXCR4, the receptor and coreceptors of human immunodeficiency virus envelope gp120, respectively, affected DC activation or maturation, neither a monoclonal antibody to the gp120-binding site on CD4 nor CCL5 nor CXCL12, the natural ligands of CCR5 and CXCR4, respectively, nor gp120 altered the DC activation and maturation processes.     

Toll-like receptor ligands modulate dendritic cells to augment cytomegalovirus- and HIV-1-specific T cell responses

Optimal Ag targeting and activation of APCs, especially dendritic cells (DCs), are important in vaccine development. In this study, we report the effects of different Toll-like receptor (TLR)-binding compounds to enhance immune responses induced by human APCs, including CD123(+) plasmacytoid DCs (PDCs), CD11c(+) myeloid DCs (MDCs), monocytes, and B cells. PDCs, which express TLR7 and TLR9, responded to imidazoquinolines (imiquimod and R-848) and to CpG oligodeoxynucleotides stimulation, resulting in enhancement in expression of costimulatory molecules and induction of IFN-alpha and IL-12p70. In contrast, MDCs, which express TLR3, TLR4, and TLR7, responded to poly(I:C), LPS, and imidazoquinolines with phenotypic maturation and high production of IL-12 p70 without producing detectable IFN-alpha. Optimally TLR ligand-stimulated PDCs or MDCs exposed to CMV or HIV-1 Ags enhanced autologous CMV- and HIV-1-specific memory T cell responses as measured by effector cytokine production compared with TLR ligand-activated monocytes and B cells or unstimulated PDCs and MDCs. Together, these data show that targeting specific DC subsets using TLR ligands can enhance their ability to activate virus-specific T cells, providing information for the rational design of TLR ligands as adjuvants for vaccines or immune modulating therapy.     

Lutzomyia longipalpis salivary peptide maxadilan alters murine dendritic cell expression of CD80/86, CCR7, and cytokine secretion and reprograms dendritic cell-mediated cytokine release from cultures containing allogeneic T cells

Leishmania protozoan parasites, the etiologic agent of leishmaniasis, are transmitted exclusively by phlebotomine sand flies of the genera Phlebotomus and Lutzomyia. In addition to parasites, the infectious bite inoculum contains arthropod salivary components. One well-characterized salivary component from Lutzomyia longipalpis is maxadilan (MAX), a vasodilator acting via the type I receptor for the pituitary cyclic AMP activating peptide. MAX has been shown to elicit immunomodulatory effects potentially dictating immune responses to Leishmania parasites. When exposed to MAX, both resting and LPS-stimulated dendritic cells (DCs) show reduced CD80 and CD86 expression on most DCs in vitro. However, CD86 expression is increased significantly on a subpopulation of DCs. Furthermore, MAX treatment promoted secretion of type 2 cytokines (IL-6 and IL-10) while reducing production of type 1 cytokines (IL-12p40, TNF-alpha, and IFN-gamma) by LPS-stimulated DCs. A similar trend was observed in cultures of MAX-treated DCs containing naive allogeneic CD4(+) T cells: type 2 cytokines (IL-6 and IL-13) increased while type 1 cytokines (TNF-alpha and IFN-gamma) decreased. Additionally, the proinflammatory cytokine IL-1beta was increased in cultures containing MAX-treated mature DCs. MAX treatment of LPS-stimulated DCs also prevented optimal surface expression of CCR7 in vitro. These MAX-dependent effects were evident in DCs from both Leishmania major-susceptible (BALB/c) and -resistant (C3H/HeN) murine strains. These data suggest that modification of DC phenotype and function by MAX likely affects crucial cellular components that determine the pathological response to infection with Leishmania.     

The Toll-like receptor 5 stimulus bacterial flagellin induces maturation and chemokine production in human dendritic cells

Toll-like receptors (TLRs) are pattern recognition receptors that serve an important function in detecting pathogens and initiating inflammatory responses. Upon encounter with foreign Ag, dendritic cells (DCs) go through a maturation process characterized by an increase in surface expression of MHC class II and costimulatory molecules, which leads to initiation of an effective immune response in naive T cells. The innate immune response to bacterial flagellin is mediated by TLR5, which is expressed on human DCs. Therefore, we sought to investigate whether flagellin could induce DC maturation. Immature DCs were cultured in the absence or presence of flagellin and monitored for expression of cell surface maturation markers. Stimulation with flagellin induced increased surface expression of CD83, CD80, CD86, MHC class II, and the lymph node-homing chemokine receptor CCR7. Flagellin stimulated the expression of chemokines active on neutrophils (IL-8/CXC chemokine ligand (CXCL)8, GRO-alpha/CXCL1, GRO-beta/CXCL2, GRO-gamma/CXCL3), monocytes (monocyte chemoattractant protein-1/CC chemokine ligand (CCL)2), and immature DCs (macrophage-inflammatory protein-1 alpha/CCL3, macrophage-inflammatory protein-1 beta/CCL4), but not chemokines active on effector T cells (IFN-inducible protein-10 kDa/CXCL10, monokine induced by IFN-gamma/CXCL9, IFN-inducible T cell alpha chemoattractant/CXCL11). However, stimulating DCs with both flagellin and IFN-inducible protein-10 kDa, monokine induced by IFN-gamma, and IFN-inducible T cell alpha chemoattractant expression, whereas stimulation with IFN-beta or flagellin alone failed to induce these chemokines. In functional assays, flagellin-matured DCs displayed enhanced T cell stimulatory activity with a concomitant decrease in endocytic activity. Finally, DCs isolated from mouse spleens or bone marrows were shown to not express TLR5 and were not responsive to flagellin stimulation. These results demonstrate that flagellin can directly stimulate human but not murine DC maturation, providing an additional mechanism by which motile bacteria can initiate an acquired immune response.     

Inhibition of myeloid dendritic cell accessory cell function and induction of T cell anergy by alcohol correlates with decreased IL-12 production

Alcohol consumption inhibits accessory cell function and Ag-specific T cell responses. Myeloid dendritic cells (DCs) coordinate innate immune responses and T cell activation. In this report, we found that in vivo moderate alcohol intake (0.8 g/kg of body weight) in normal volunteers inhibited DC allostimulatory capacity. Furthermore, in vitro alcohol treatment during DC differentiation significantly reduced allostimulatory activity in a MLR using naive CD4(+) T cells, and inhibited tetanus toxoid Ag presentation by DCs. Alcohol-treated DCs showed reduced IL-12, increased IL-10 production, and a decrease in expression of the costimulatory molecules CD80 and CD86. Addition of exogenous IL-12 and IL-2, but not neutralization of IL-10, during MLR ameliorated the reduced allostimulatory capacity of alcohol-treated DCs. Naive CD4(+) T cells primed with alcohol-treated DCs showed decreased IFN-gamma production that was restored by exogenous IL-12, indicating inhibition of Th1 responses. Furthermore, CD4(+) T cells primed with alcohol-treated DCs were hyporesponsive to subsequent stimulation with the same donor-derived normal DCs, suggesting the ability of alcohol-treated DCs to induce T cell anergy. LPS-induced maturation of alcohol-treated immature DCs partially restored the reduced allostimulatory activity, whereas alcohol given only during DC maturation failed to inhibit DC functions, suggesting that alcohol primarily impairs DC differentiation rather than maturation. NFkappaB activation, a marker of DC maturation was not affected by alcohol. Taken together, alcohol both in vitro and in vivo can impair generation of Th1 immune responses via inhibition of DC differentiation and accessory cell function through mechanisms that involve decreased IL-12 induction.     

TRANCE, a TNF family member, is differentially expressed on T cell subsets and induces cytokine production in dendritic cells

TNF-related activation-induced cytokine (TRANCE) is a member of the TNF family recently identified in activated T cells. We report here that TRANCE mRNA is constitutively expressed in memory, but not naive, T cells and in single-positive thymocytes. Upon TCR/CD3 stimulation, TRANCE mRNA and surface protein expression are rapidly up-regulated in CD4+ and CD8+ T cells, which can be further enhanced on CD4+ T cells by CD28-mediated costimulation. However, TRANCE induction is significantly suppressed when cells are stimulated in the presence of IL-4, but is not modified in the presence of IFN-alpha, IFN-gamma, TGF-beta, TNF-alpha, or IL-2. High levels of TRANCE receptor expression are found on mature dendritic cells (DCs). In this study we show that activated T and B cells also express TRANCE receptor, but only at low levels. TRANCE, however, does not exert any significant effect on the proliferation, activation, or survival of those cells. In DCs, TRANCE induces the expression of proinflammatory cytokines (IL-6, IL-1) and T cell growth and differentiation factors (IL-12, IL-15) in addition to enhancing DC survival. Moreover, TRANCE cooperates with CD40 ligand or TNF-alpha to further increase the viability of DCs, suggesting that several TNF-related molecules on activated T cells may cooperatively regulate the function and survival of DCs to enhance T cell-mediated immune responses.     

NKp46 and NKG2D recognition of infected dendritic cells is necessary for NK cell activation in the human response to influenza infection

At an early phase of viral infection, contact and cooperation between dendritic cells (DCs) and NK cells activates innate immunity, and also influences recruitment, when needed, of adaptive immunity. Influenza, an adaptable fast-evolving virus, annually causes acute, widespread infections that challenge the innate and adaptive immunity of humanity. In this study, we dissect and define the molecular mechanisms by which influenza-infected, human DCs activate resting, autologous NK cells. Three events in NK cell activation showed different requirements for soluble mediators made by infected DCs and for signals arising from contact with infected DCs. IFN-alpha was mainly responsible for enhanced NK cytolysis and also important for CD69 up-regulation, whereas IL-12 was necessary for enhancing IFN-gamma production. Increased CD69 expression and IFN-gamma production, but not increased cytolysis, required recognition of influenza-infected DCs by two NK cell receptors: NKG2D and NKp46. Abs specific for these receptors or their known ligands (UL16-binding proteins 1-3 class I-like molecules for NKG2D and influenza hemagglutinin for NKp46) inhibited CD69 expression and IFN-gamma production. Activation of NK cells by influenza-infected DCs and polyinosinic:polycytidylic acid (poly(I:C))-treated DCs was distinguished. Poly(I:C)-treated DCs did not express the UL16-binding protein 3 ligand for NKG2D, and in the absence of the influenza hemagglutinin there was no involvement of NKp46.