Streptococcus mutans Wall‐Associated Protein A Promotes TLR4‐Induced Dendritic Cell Maturation

Dendritic cells orchestrate innate and adaptive immune responses, which are central to establishing efficient responses to vaccination. Wall‐associated protein A (WapA) of Streptococcus mutans was previously used as a vaccine in animal studies for immunization against dental caries. However, as a cell surface protein, whether WapA activates innate immune responses and the effects of WapA on DCs remain unclear. In this study, WapA was cloned into the GST fusion vector pEBG, which can be expressed efficiently in mammalian cells. We found that when added before stimulation with LPS, purified WapA‐GST protein increased TLR4‐induced NF‐κB and MAPK signalling pathway activation. Pretreatment with WapA‐GST also increased LPS‐induced proinflammatory cytokine production by DCs, including IL‐12, IL‐6 and TNF‐α. Furthermore, expression of the DC maturation markers CD80/86, CD40 and MHC II was also increased by WapA pretreatment. These data indicate that WapA is recognized by DCs and promotes DC maturation.     

A20 expression in dendritic cells protects mice from LPS‐induced mortality

DCs contribute to immune homeostasis under physiological conditions and regulate the immune activation during infection. The deubiquitinase A20 inhibits the activation of NF‐κB‐dependent immune reactions, and prevents the hyperactivation of DCs under steady‐state conditions. However, the role of DC‐specific A20 under pathological conditions is unknown. Here, we demonstrate that upon injection of low‐dose LPS, mice with DC‐specific A20 deletion (CD11c‐Cre A20^fl/fl) died within 6 h, whereas A20^fl/fl controls survived. LPS‐induced mortality in CD11c‐Cre A20^fl/fl mice was characterized by increased serum levels of IL‐2, IL‐10, IL‐12, IFN‐γ, and TNF. Upon LPS stimulation, the activation of NF‐κB and ERK‐NFATc3 pathways were enhanced in A20‐deficient DCs, resulting in an increased production of IL‐2, IL‐12, and TNF both in vitro and in vivo. Targeted inhibition of ERK in A20‐deficient DCs abolished the increased production of IL‐2. A20‐deficient DCs failed to induce LPS tolerance, which was independent of T cells and the intestinal flora, since T‐cell depletion and decolonization of CD11c‐Cre A20^fl/fl mice could not prevent death of LPS‐challenged CD11c‐Cre A20^fl/fl mice. In conclusion, these findings show that DC‐specific A20 preserves immune homeostasis in steady‐state conditions and is also required for LPS tolerance.     

Activation of dendritic cells by the Gal-lectin of Entamoeba histolytica drives Th1 responses in vitro and in vivo

Amebiasis is a human disease caused by the protozoan intestinal parasite Entamoeba histolytica. Vaccine development has focused on the parasite's surface galactose‐N‐acetyl‐d‐ galactosamine inhibitable lectin (Gal‐lectin) as a protective antigen. The Gal‐lectin is immunogenic and has been shown to induce Th1 cytokines in vitro and in vivo. The immunological basis of the protective immune response elicited by the Gal‐lectin is unknown. In this study, we investigated the response of BALB/c bone marrow‐derived DC to E. histolytica Gal‐lectin. Incubation of immature DC with Gal‐lectin resulted in activation and maturation after 24 h. FACS analysis demonstrated an up‐regulation of DC maturation markers CD80, CD86, CD40 and MHC class II upon exposure to Gal‐lectin. The Gal‐lectin also induced DC production of IL‐12, indicating a Th1 response. Gal‐lectin‐activated DC were able to stimulate T cell proliferation in an allogeneic mixed leukocyte reaction and adoptive transfer of Gal‐lectin‐treated DC into naïve mice resulted in IFN‐γ‐producing Gal‐lectin‐sensitized T cells. The activation of DC by Gal‐lectin was mediated by MAPK and NF‐κB. These findings indicate that E. histolytica Gal‐lectin is a potent vaccine antigen capable of directly initiating DC maturation and activation characterized by Th1 cytokine production.     

Human primary gastric dendritic cells induce a Th1 response to H. pylori

Adaptive CD4 T-cell responses are important in the pathogenesis of chronic Helicobacter pylori gastritis. However, the gastric antigen-presenting cells that induce these responses have not yet been identified. Here we show that dendritic cells (DCs) are present in the gastric mucosa of healthy subjects and are more prevalent and more activated in the gastric mucosa of H. pylori-infected subjects. H. pylori induced gastric DCs isolated from noninfected subjects to express increased levels of CD11c, CD86 and CD83, and to secrete proinflammatory cytokines, particularly interleukin (IL)-6 and IL-8. Importantly, gastric DCs pulsed with live H. pylori, but not control DCs, mediated T-cell secretion of interferon-γ. The ability of H. pylori to induce gastric DC maturation and stimulate gastric DC activation of Th1 cells implicates gastric DCs as initiators of the immune response to H. pylori.     

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

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

Chemokine programming dendritic cell antigen response: part II – programming antigen presentation to T lymphocytes by partially maintaining immature dendritic cell phenotype

In a companion article to this study,¹ the successful programming of a JAWSII dendritic cell (DC) line's antigen uptake and processing was demonstrated based on pre‐treatment of DCs with a specific ‘cocktail’ of select chemokines. Chemokine pre‐treatment modulated cytokine production before and after DC maturation [by lipopolysaccharide (LPS)]. After DC maturation, it induced an antigen uptake and processing capacity at levels 36% and 82% higher than in immature DCs, respectively. Such programming proffers a potential new approach to enhance vaccine efficiency. Unfortunately, simply enhancing antigen uptake does not guarantee the desired activation and proliferation of lymphocytes, e.g. CD4⁺ T cells. In this study, phenotype changes and antigen presentation capacity of chemokine pre‐treated murine bone marrow‐derived DCs were examined in long‐term co‐culture with antigen‐specific CD4⁺ T cells to quantify how chemokine pre‐treatment may impact the adaptive immune response. When a model antigen, ovalbumin (OVA), was added after intentional LPS maturation of chemokine‐treated DCs, OVA‐biased CD4⁺T‐cell proliferation was initiated from ~ 100% more undivided naive T cells as compared to DCs treated only with LPS. Secretion of the cytokines interferon‐γ, interleukin‐1β, interleukin‐2 and interleukin‐10 in the CD4⁺ T cell : DC co‐culture (with or without chemokine pre‐treatment) were essentially the same. Chemokine programming of DCs with a 7 : 3 ratio of CCL3 : CCL19 followed by LPS treatment maintained partial immature phenotypes of DCs, as indicated by surface marker (CD80 and CD86) expression over time. Results here and in our companion paper suggest that chemokine programming of DCs may provide a novel immunotherapy strategy to obviate the natural endocytosis limit of DC antigen uptake, thus potentially increasing DC‐based vaccine efficiency.     

Dendritic cells phenotype fitting under hypoxia or lipopolysaccharide; adenosine 5′‐triphosphate‐binding cassette transporters far beyond an efflux pump

This study examines adenosine 5′‐triphosphate‐binding cassette (ABC) transporters as a potential therapeutic target in dendritic cell (DC) modulation under hypoxia and lipopolysaccharide (LPS). Functional capacity of dendritic cells (DCs) (mixed lymphocyte reaction: MLR) and maturation of iDCs were evaluated in the presence or absence of specific ABC‐transporter inhibitors. Monocyte‐derived DCs were cultured in the presence of interleukin (IL)‐4/granulocyte–macrophage colony‐stimulating factor (GM‐CSF). Their maturation under hypoxia or LPS conditions was evaluated by assessing the expression of maturation phenotypes using flow cytometry. The effect of ABC transporters on DC maturation was determined using specific inhibitors for multi‐drug resistance (MDR1) and multi‐drug resistance proteins (MRPs). Depending on their maturation status to elicit T cell alloresponses, the functional capacity of DCs was studied by MLR. Mature DCs showed higher P‐glycoprotein (Pgp) expression with confocal microscopy. Up‐regulation of maturation markers was observed in hypoxia and LPS‐DC, defining two different DC subpopulation profiles, plasmacytoid versus conventional‐like, respectively, and different cytokine release T helper type 2 (Th2) versus Th1, depending on the stimuli. Furthermore, hypoxia‐DCs induced more B lymphocyte proliferation than control‐iDC (56% versus 9%), while LPS‐DCs induced more CD8‐lymphocyte proliferation (67% versus 16%). ABC transporter‐inhibitors strongly abrogated DC maturation [half maximal inhibitory concentration (IC₅₀): P‐glycoprotein inhibition using valspodar (PSC833) 5 μM, CAS 115104‐28‐4 (MK571) 50 μM and probenecid 2·5 μM], induced significantly less lymphocyte proliferation and reduced cytokine release compared with stimulated‐DCs without inhibitors. We conclude that diverse stimuli, hypoxia or LPS induce different profiles in the maturation and functionality of DC. Pgp appears to play a role in these DC events. Thus, ABC‐transporters emerge as potential targets in immunosuppressive therapies interfering with DCs maturation, thereby abrogating innate immune response when it is activated after ischaemia.     

Immunotherapy using lipopolysaccharide‐stimulated bone marrow‐derived dendritic cells to treat experimental autoimmune encephalomyelitis

Lipopolysaccharide (LPS) produced by Gram‐negative bacteria induces tolerance and suppresses inflammatory responses in vivo; however, the mechanisms are poorly understood. In this study we show that LPS induces apoptosis of bone marrow‐derived dendritic cells (DCs) and modulates phenotypes of DCs. LPS treatment up‐regulates expression of tolerance‐associated molecules such as CD205 and galectin‐1, but down‐regulates expression of Gr‐1 and B220 on CD11c⁺ DCs. Moreover, LPS treatment regulates the numbers of CD11c⁺CD8⁺, CD11c⁺CD11b^low and CD11c⁺CD11b^hi DCs, which perform different immune functions in vivo. Our data also demonstrated that intravenous transfer of LPS‐treated DCs blocks experimental autoimmune encephalomyelitis (EAE) development and down‐regulates expression of retinoic acid‐related orphan receptor gamma t (ROR‐γt), interleukin (IL)‐17A, IL‐17F, IL‐21, IL‐22 and interferon (IFN)‐γ in myelin oligodendrocyte glycoprotein (MOG)‐primed CD4⁺ T cells in the peripheral environment. These results suggest that LPS‐induced apoptotic DCs may lead to generation of tolerogenic DCs and suppress the activity of MOG‐stimulated effector CD4⁺ T cells, thus inhibiting the development of EAE in vivo. Our results imply a potential mechanism of LPS‐induced tolerance mediated by DCs and the possible use of LPS‐induced apoptotic DCs to treat autoimmune diseases such as multiple sclerosis.     

Mycobacterium tuberculosis RpfE promotes simultaneous Th1‐ and Th17‐type T‐cell immunity via TLR4‐dependent maturation of dendritic cells

Reciprocal induction of the Th1 and Th17 immune responses is essential for optimal protection against Mycobacterium tuberculosis (Mtb); however, only a few Mtb antigens are known to fulfill this task. A functional role for resuscitation‐promoting factor (Rpf) E, a latency‐associated member of the Rpf family, in promoting naïve CD4⁺ T‐cell differentiation toward both Th1 and Th17 cell fates through interaction with dendritic cells (DCs) was identified in this study. RpfE induces DC maturation by increasing expression of surface molecules and the production of IL‐6, IL‐1β, IL‐23p19, IL‐12p70, and TNF‐α but not IL‐10. This induction is mediated through TLR4 binding and subsequent activation of ERK, p38 MAPKs, and NF‐κB signaling. RpfE‐treated DCs effectively caused naïve CD4⁺ T cells to secrete IFN‐γ, IL‐2, and IL‐17A, which resulted in reciprocal expansions of the Th1 and Th17 cell response along with activation of T‐bet and RORγt but not GATA‐3. Furthermore, lung and spleen cells from Mtb‐infected WT mice but not from TLR4^?/? mice exhibited Th1 and Th17 polarization upon RpfE stimulation. Taken together, our data suggest that RpfE has the potential to be an effective Mtb vaccine because of its ability to activate DCs that simultaneously induce both Th1‐ and Th17‐polarized T‐cell expansion.     

Virulence‐dependent induction of interleukin‐10‐producing‐tolerogenic dendritic cells by Mycobacterium tuberculosis impedes optimal T helper type 1 proliferation

Mycobacterium tuberculosis inhibits optimal T helper type 1 (Th1) responses during infection. However, the precise mechanisms by which virulent M. tuberculosis limits Th1 responses remain unclear. Here, we infected dendritic cells (DCs) with the virulent M. tuberculosis strain H37Rv or the attenuated strain H37Ra to investigate the phenotypic and functional alterations in DCs and resultant T‐cell responses. H37Rv‐infected DCs suppressed Th1 responses more strongly than H37Ra‐infected DCs. Interestingly, H37Rv, but not H37Ra, impaired DC surface molecule expression (CD80, CD86 and MHC class II) due to prominent interleukin‐10 (IL‐10) production while augmenting the expression of tolerogenic molecules including PD‐L1, CD103, Tim‐3 and indoleamine 2,3‐dioxygenase on DCs in a multiplicity‐of‐infection (MOI) ‐dependent manner. These results indicate that virulent M. tuberculosis drives immature DCs toward a tolerogenic phenotype. Notably, the tolerogenic phenotype of H37Rv‐infected DCs was blocked in DCs generated from IL‐10^−/− mice or DCs treated with an IL‐10‐neutralizing monoclonal antibody, leading to restoration of Th1 polarization. These findings suggest that IL‐10 induces a tolerogenic DC phenotype. Interestingly, p38 mitogen‐activated protein kinase (MAPK) activation predominantly mediates IL‐10 production; hence, H37Rv tends to induce a tolerogenic DC phenotype through expression of tolerogenic molecules in the p38 MAPK–IL‐10 axis. Therefore, suppressing the tolerogenic cascade in DCs is a novel strategy for stimulating optimal protective T‐cell responses against M. tuberculosis infection.     

Human milk oligosaccharides promote immune tolerance via direct interactions with human dendritic cells

Human milk oligosaccharides (HMOS) are a complex mixture of bioactive components supporting the immune development of breastfed‐infants. Dendritic cells (DCs) play a central role in the regulation of immune responses, being specialized in antigen presentation and driving T‐cell priming as well as differentiation. However, little is known about the direct effects of HMOS on human DC phenotypes and functions. Here, we report that HMOS mixture isolated from pooled human milk, induced semi‐maturation of human monocytes‐derived DCs (moDCs), and elevated levels of IL‐10, IL‐27 and IL‐6 but not IL‐12p70 and TNF‐α. Consistently, HMOS‐conditioned human moDCs promoted Treg generation from naïve CD4⁺ T cells. Interestingly, HMOS limited LPS‐induced maturation of human moDCs, while maintained IL‐10 and IL‐27 secretion and reduced LPS‐induced production of IL‐12p70, IL‐6 and TNF‐α. Furthermore, HMOS+LPS‐stimulated DCs induced a higher frequency of Tregs and increased IL‐10 production, while a reduction in Tbet+Th1 frequency and IFN‐γ production was detected as compared to LPS‐DCs. The regulatory effects of HMOS seemed to be mediated by interactions of HMOS with receptors, including but not limited to TLR4 and DC‐SIGN on human moDCs. In conclusion, HMOS contain tolerogenic factors influencing human moDCs and thereby modulating the development of the neonatal immune system.     

IL‐10 promotes homeostatic proliferation of human CD8+ memory T cells and,when produced by CD1c+ DCs,shapes naive CD8+ T‐cell priming

IL‐10 is an anti‐inflammatory cytokine that inhibits maturation and cytokine production of dendritic cells (DCs). Although mature DCs have the unique capacity to prime CD8⁺ CTL, IL‐10 can promote CTL responses. To understand these paradoxic findings, we analyzed the role of IL‐10 produced by human APC subsets in T‐cell responses. IL‐10 production was restricted to CD1c⁺ DCs and CD14⁺ monocytes. Interestingly, it was differentially regulated, since R848 induced IL‐10 in DCs, but inhibited IL‐10 in monocytes. Autocrine IL‐10 had only a weak inhibitory effect on DC maturation, cytokine production, and CTL priming with high‐affinity peptides. Nevertheless, it completely blocked cross‐priming and priming with low‐affinity peptides of a self/tumor‐antigen. IL‐10 also inhibited CD1c⁺ DC‐induced CD4⁺ T‐cell priming and enhanced Foxp3 induction, but was insufficient to induce T‐cell IL‐10 production. CD1c⁺ DC‐derived IL‐10 had also no effect on DC‐induced secondary expansions of memory CTL. However, IL‐15‐driven, TCR‐independent proliferation of memory CTL was enhanced by IL‐10. We conclude that DC‐derived IL‐10 selects high‐affinity CTL upon priming. Moreover, IL‐10 preserves established CTL memory by enhancing IL‐15‐dependent homeostatic proliferation. These combined effects on CTL priming and memory maintenance provide a plausible mechanism how IL‐10 promotes CTL responses in humans.     

Manipulation of mitogen-activated protein kinase/nuclear factor-κB-signaling cascades during intracellular Toxoplasma gondii infection

Summary: The intracellular protozoan Toxoplasma gondii exerts profound effects on nuclear factor‐κB (NF‐κB)‐ and mitogen‐activated protein kinase (MAPK)‐signaling cascades in macrophages. During early infection, nuclear translocation of NF‐κB is blocked, and later, the cells display defects in lipopolysaccharide (LPS)‐induced MAPK phosphorylation after undergoing initial activation in response to Toxoplasma itself. Infected macrophages that are subjected to triggering through Toll‐like receptor 4 (TLR4) with LPS display defective production of tumor necrosis factor‐α and IL‐12 (IL‐12) that likely reflects interference with NF‐κB‐ and MAPK‐signaling cascades. Nevertheless, T. gondii possesses molecules that themselves induce eventual proinflammatory cytokine synthesis. For interleukin‐12, this occurs through both myeloid differentiation factor 88‐dependent and chemokine receptor CCR5‐dependent pathways. The balance between activation and interference with proinflammatory signaling is likely to reflect the need to achieve an appropriate level of immunity that allows the host and parasite to maintain a stable interaction.     

The CRTH2 agonist Pyl A prevents lipopolysaccharide‐induced fetal death but induces preterm labour

We have previously demonstrated that the anti‐inflammatory prostaglandin 15‐deoxy‐Δ 12,14‐prostaglandin J₂ (15dPGJ₂) delays inflammation‐induced preterm labour in the mouse and improves pup survival through the inhibition of nuclear factor‐κB (NF‐κB) by a mechanism yet to be elucidated. 15dPGJ₂ is an agonist of the second prostaglandin D₂ receptor, chemoattractant receptor homologous to the T helper 2 cell (CRTH2). In human T helper cells CRTH2 agonists induce the production of the anti‐inflammatory interleukins IL‐10 and IL‐4. We hypothesized that CRTH2 is involved in the protective effect of 15dPGJ₂ in inflammation‐induced preterm labour in the murine model. We therefore studied the effects of a specific small molecule CRTH2 agonist on preterm labour and pup survival. An intrauterine injection of lipopolysaccharide (LPS) was administered to CD1 mice at embryonic day 16, ± CRTH2 agonist/vehicle controls. Mice were killed at 4.5 hr to assess fetal wellbeing and to harvest myometrium and pup brain for analysis of NF‐κB, and T helper type 1/2 interleukins. To examine the effects of the CRTH2 agonist on LPS‐induced preterm labour, mice were allowed to labour spontaneously. Direct effects of the CRTH2 agonist on uterine contractility were examined ex vivo on contracting myometrial strips. The CRTH2 agonist increased fetal survival from 20 to 100% in LPS‐treated mice, and inhibited circular muscle contractility ex vivo. However, it augmented LPS‐induced labour and significantly increased myometrial NF‐κB, IL‐1β, KC‐GRO, interferon‐γ and tumour necrosis factor‐α. This suggests that the action of 15dPGJ₂ is not via CRTH2 and therefore small molecule CRTH2 agonists are not likely to be beneficial for the prevention of inflammation‐induced preterm labour.     

Triggering of NF‐κB in cytokine‐matured human DCs generates superior DCs for T‐cell priming in cancer immunotherapy

Understanding the signaling that governs the immunogenicity of human dendritic cells (DCs) is a prerequisite for improving DC‐based therapeutic vaccination strategies, in which the ability of DCs to induce robust and lasting Ag‐specific CTL responses is of critical importance. Cytokine‐matured DCs are regularly used, but to induce memory‐type CTLs, they require additional activation stimuli, such as CD4⁺ T‐cell help or TLR activation. One common denominator of these stimuli is the activation of NF‐κB. Here, we show that human monocyte‐derived, cytokine cocktail‐matured DCs transfected with constitutively active mutants of IκB kinases (caIKKs) by mRNA electroporation, further upregulated maturation markers, and secreted enhanced amounts of cytokines, including IL‐12p70, which was produced for more than 48 h after transfection. Most importantly, cytotoxic T cells induced by caIKK‐transfected DCs combined high CD27 expression, indicating a more memory‐like phenotype, and a markedly enhanced secondary expandability with a high lytic capacity. In contrast, CTLs primed and expanded with unmodified cytokine cocktail‐matured DCs did not maintain their proliferative capacity upon repetitive stimulations. We hypothesize that “designer” DCs expressing constitutively active IκB kinases will prove highly immunogenic also in vivo and possibly emerge as a new strategy to improve the clinical efficacy of therapeutic vaccinations against cancer and other chronic diseases.     

Contribution of dendritic cells to measles virus induced immunosuppression

Measles virus (MV) remains an important pathogen in children worldwide. The morbidity and mortality of MV is associated with severe immune suppression. Dendritic cells (DCs) were identified as initial target cells in vivo, and DCs were efficiently infected by MV in vitro. MV infection of DCs likely contributes to functional deficiency in these cells; therefore playing a role in MV‐induced immunosuppression. DCs appeared to mature phenotypically; however, the ability of infected cells to stimulate T cells was compromised. Phenotypic maturation of infected immature DCs was partially controlled by IFN production; however, infected DCs also maintained markers of an immature phenotype such as the continued uptake of antigen and lack of expression of chemokine receptor CCR7. Furthermore, mature DCs did not appear to maintain phenotypic maturation following infection demonstrated by decreased MHC and co‐stimulatory molecule expression. Several mechanisms of MV‐induced DC dysfunction have been suggested, each likely contributing to the immunosuppressive effect of MV‐infected DCs. Infected DCs responded aberrantly to secondary maturation stimuli such as CD40L or TLR4 stimulation. MV infection resulted in apoptosis in DC/T‐cell cocultures, which may contribute to a reduced T‐cell response. Additionally, the immunological synapse between infected DCs and T cells was compromised resulting in reduced T‐cell interaction times and activation signaling. The mechanisms of MV contribution to DC dysfunction appear multifaceted and central to MV‐induced immunosuppression. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.