Histamine induces CD86 expression and chemokine production by human immature dendritic cells

Mast cells and immature dendritic cells (DC) are in close contact in peripheral tissues. Upon activation, mast cells release histamine, a mediator involved in the immediate hypersensitivity reaction. We therefore tested whether histamine could affect human DC activation and maturation. Histamine induces CD86 expression on immature DC in a dose-dependent (significant at 10(-7) M) and transient manner (maximal after 24-h stimulation). Histamine also transiently up-regulates the expression of the costimulatory and accessory molecules, CD40, CD49d, CD54, CD80, and MHC class II. As a consequence, immature DC exposed for 24 h to histamine stimulate memory T cells more efficiently than untreated DC. In addition, histamine induces a potent production of IL-6, IL-8, monocyte chemoattractant protein 1, and macrophage-inflammatory protein 1alpha by immature DC and also up-regulates IL-1beta, RANTES, and macrophage-inflammatory protein 1beta but not TNF-alpha and IL-12 mRNA expression. Histamine activates immature DC through both the H1 and H2 receptors. However, histamine-treated DC do not have a phenotype of fully mature cells, as they do neither show significant changes in the expression of the chemokine receptors, CCR5, CCR7 and CXC chemokine receptor 4, nor expression of CD83 de novo. These data demonstrate that histamine activates immature DC and induces chemokine production, thereby suggesting that histamine, via stimulation of resident DC, may participate locally in T cell stimulation and in the late inflammatory reaction associated with allergic disorders.     

Cutting edge: mTORC1 in intestinal CD11c+ CD11b+ dendritic cells regulates intestinal homeostasis by promoting IL-10 production

The mammalian target of rapamycin (mTOR) controls cell growth and survival through two distinct complexes called mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2). Although several reports have suggested the involvement of mTORC1 in development and function of dendritic cells (DCs), its physiological roles remain obscure. We therefore established mTORC1 signal-deficient mice lacking Raptor, an essential component of mTORC1 signal, specifically in DC lineage (referred to here as Raptor(DC-/-)). Raptor(DC-/-) mice exhibited cell expansion in specific subsets of DCs such as splenic CD8(+) DCs and intestinal CD11c(+)CD11b(+) DCs. We also found that impaired mTORC1 signal resulted in the suppression of IL-10 production along with enhanced CD86 expression in intestinal CD11c(+)CD11b(+) DCs and that Raptor(DC-/-) mice were highly susceptible to dextran sodium sulfate-induced colitis. Our results uncover mTORC1-mediated anti-inflammatory programs in intestinal CD11c(+)CD11b(+) DCs to limit the intestinal inflammation.     

Cutting edge: differential chemokine production by myeloid and plasmacytoid dendritic cells

To examine the different roles of myeloid dendritic cells (M-DCs) and plasmacytoid dendritic cells (P-DCs) in the induction and regulation of immune response, we have studied chemokine secretion by freshly isolated DC subsets in response to bacterial, viral, and T cell-derived stimuli. M-DCs selectively produced very high levels of the homeostatic chemokines CC chemokine ligand (CCL)17 and CCL22, while P-DCs produced very little if any. In contrast, the proinflammatory chemokine CCL3 was secreted mostly by P-DCs, whereas CCL4 and CXC chemokine ligand 8 were produced by both subsets. The selective production of CCL17 and CCL22 by M-DCs but not P-DCs was confirmed in vivo by immunohistology on human reactive lymph node sections. The high production of CCR4 ligands by M-DCs suggests their capacity to selectively recruit at sites of inflammation T cells with regulatory properties or with a Th2 phenotype, whereas P-DCs, by preferentially secreting CCR1/CCR5 ligands, would mostly recruit effector T cells and, in particular, Th1-type cells.     

G-CSF suppresses allergic pulmonary inflammation, downmodulating cytokine, chemokine and eosinophil production

AimsGranulocyte Colony-Stimulating Factor (G-CSF), which mobilizes hemopoietic stem cells (HSC), is believed to protect HSC graft recipients from graft-versus-host disease by enhancing Th2 cytokine secretion. Accordingly, G-CSF should aggravate Th2-dependent allergic pulmonary inflammation and the associated eosinophilia. We evaluated the effects of G-CSF in a model of allergic pulmonary inflammation.Main methodsAllergic pulmonary inflammation was induced by repeated aerosol allergen challenge in ovalbumin-sensitized C57BL/6J mice. The effects of allergen challenge and of G-CSF pretreatment were evaluated by monitoring: a) eosinophilia and cytokine/chemokine content of bronchoalveolar lavage fluid, pulmonary interstitium, and blood; b) changes in airway resistance; and c) changes in bone-marrow eosinophil production.Key findingsContrary to expectations, G-CSF pretreatment neither induced nor enhanced allergic pulmonary inflammation. Instead, G-CSF: a) suppressed accumulation of infiltrating eosinophils in bronchoalveolar, peribronchial and perivascular spaces of challenged lungs; and b) prevented ovalbumin challenge-induced rises in airway resistance. G-CSF had multiple regulatory effects on cytokine and chemokine production: in bronchoalveolar lavage fluid, levels of IL-1 and IL-12 (p40), eotaxin and MIP-1a were decreased; in plasma, KC, a neutrophil chemoattractant, was increased, while IL-5 was decreased and eotaxin was unaffected. In bone-marrow, G-CSF: a) prevented the increase in bone-marrow eosinophil production induced by ovalbumin challenge of sensitized mice; and b) selectively stimulated neutrophil colony formation.SignificanceThese observations challenge the view that G-CSF deviates cytokine production towards a Th2 profile in vivo, and suggest that this neutrophil-selective hemopoietin affects eosinophilic inflammation by a combination of effects on lung cytokine production and bone-marrow hemopoiesis.     

An adoptive transfer model of allergic lung inflammation in mice is mediated by CD4+CD62LlowCD25+ T cells

Animal models of allergic lung inflammation have provided important insight into the cellular and biochemical factors involved in the pathogenesis of human asthma. Herein, we describe an adoptive transfer model of OVA-specific eosinophilic lung inflammation in the mouse that is used to characterize the cells involved in mediating the pulmonary inflammatory response. We report that freshly isolated spleen cells from OVA-sensitized mice are unable to prime naive recipient mice to respond to a subsequent OVA aerosol challenge. Subjecting the spleen cells to short term restimulation with Ag in vitro, however, renders the cells competent to transfer activity. The magnitude and the kinetics of the eosinophilic pulmonary inflammation in the adoptive transfer recipients are nearly identical with those generated by a more conventional active sensitization/challenge protocol, with the notable exception of differential production of plasma IgE in the two models. Extensive negative and positive selection of splenocyte subtypes indicates that the transfer of Ag-primed CD4+ T cells is both necessary and sufficient to establish full responsiveness in the recipient mice. Additional phenotypic characterization of the transfer-reactive CD4+ T cells indicates that they are found within the CD62LlowCD25+ subset and secrete high levels of IL-5 in response to Ag stimulation. Limiting dilution analysis-derived minimal frequency estimates indicate that approximately 1 in 8500 of the sensitized, cultured spleen cells produces IL-5 in response to OVA stimulation in vitro, suggesting that eosinophilic lung inflammation can be induced in naive mice by the transfer of <1200 Ag-specific CD4+ T cells.     

n-Nonanoyl-CC chemokine ligand 14, a potent CC chemokine ligand 14 analogue that prevents the recruitment of eosinophils in allergic airway inflammation

CCR3 is responsible for tissue infiltration of eosinophils, basophils, mast cells, and Th2 cells, particularly in allergic diseases. In this context, CCR3 has emerged as a target for the treatment of allergic asthma. It is well known that the N-terminal domain of chemokines is crucial for receptor binding and, in particular, its activation. Based on this background, we investigated a number of N-terminally truncated or modified peptides derived from the chemokine CCL14/hemofiltrate CC chemokine-1 for their ability to modulate the activity of CCR3. Among 10 derivatives tested, n-nonanoyl (NNY)-CCL14[10-74] (NNY-CCL14) was the most potent at evoking the release of reactive oxygen species and inducing chemotaxis of human eosinophils. In contrast, NNY-CCL14 has inactivating properties on human eosinophils, because it is able to induce internalization of CCR3 and to desensitize CCR3-mediated intracellular calcium release and chemotaxis. In contrast to naturally occurring CCL11, NNY-CCL14 is resistant to degradation by CD26/dipeptidyl peptidase IV. Because inhibition of chemokine receptors through internalization is a reasonable therapeutic strategy being pursued for HIV infection, we tested a potential inhibitory effect of NNY-CCL14 in two murine models of allergic airway inflammation. In both OVA- and Aspergillus fumigatus-sensitized mice, i.v. treatment with NNY-CCL14 resulted in a significant reduction of eosinophils in the airways. Moreover, airway hyper-responsiveness was shown to be reduced by NNY-CCL14 in the OVA model. It therefore appears that an i.v. administered agonist internalizing and thereby inhibiting CCR3, such as NNY-CCL14, has the potential to alleviate CCR3-mediated diseases.     

Regulation of chemokine expression by IL-10 in lung inflammation

We have been interested in understanding the mechanisms regulating the inflammatory process underlying acute lung injury. The current studies have employed a model of acute lung inflammation in mice triggered by bacterial lipopolysaccharide. The development of this injury was associated with increased expression of the chemokines, MIP-1alpha and MIP-2, that coordinate recruitment of neutrophils to the lung. IL-10 is a potent, endogenous anti-inflammatory molecule that has been shown to decrease lung inflammation partly on the basis of TNF-alpha and IL-1beta inhibition. In these studies we tested the hypothesis that endogenous IL-10 modulates chemokine expression using the IL-10 knock-out mouse, and then explored the molecular mechanisms by which IL-10 might do so. The results demonstrate that significant elevations in both chemokines were observed in the absence of IL-10 and that these findings were associated with significant increases in lung neutrophil accumulation. In vitro studies defined two, gene-specific, mechanisms by which IL-10 regulated chemokine expression: mRNA destabilization and NF-kappaB inhibition. These results suggested that IL-10 is an important, endogenous regulator of chemokine expression in acute lung inflammation.     

Th2 cells and cytokine networks in allergic inflammation of the lung

The cytokines released from Th2 and Th2-like cells are likely to be central to the pathophysiolgy of asthma and allergy, contributing to aberrant IgE production, eosinophilia and, perhaps, mucosal susceptibility to viral infection. IL-4 has emerged as a central target, not only for B cell IgE production, but also in the commitment of both CD4+ and CD8+ T cells to cells with Th2 effector function capable of secreting IL-5 resultlng in eosinophilic inflammation. In view of the central role of this cytokine and the evidence that glucocorticoids are unable to modify many IL-4 dependent effects, Th2 inhibitors may prove to be novel therapies for the treatment of bronchial asthma.     

Protease-activated receptor 2 activation of myeloid dendritic cells regulates allergic airway inflammation

Background

A common characteristic of allergens is that they contain proteases that can activate protease-activated receptor (PAR-2); however the mechanism by which PAR-2 regulates allergic airway inflammation is unclear.

Methods

Mice (wild type and PAR-2-deficient) were sensitized using German cockroach (GC) feces (frass), the isolated protease from GC frass, or through adoptive transfer of GC frass-treated bone marrow-derived dendritic cells (BMDC) and measurements of airway inflammation (cellular infiltration, cytokine expression, and mucin production), serum IgE levels and airway hyperresponsiveness (AHR) were assessed. BMDC were cultured, treated with GC frass and assessed for cytokine production. PAR-2 expression on pulmonary mDCs was determined by flow cytometry.

Results

Exposure to GC frass induced AHR and airway inflammation in wild type mice; however PAR-2-deficient mice had significantly attenuated responses. To directly investigate the role of the protease, we isolated the protease from GC frass and administered the endotoxin-free protease into the airways of mice in the presence of OVA. GC frass proteases were sufficient to promote the development of AHR, serum IgE, and Th2 cytokine production. PAR-2 expression on mDC was upregulated following GC frass exposure, but the presence of a functional PAR-2 did not alter antigen uptake. To determine if PAR-2 activation led to differential cytokine production, we cultured BMDC in the presence of GM-CSF and treated these cells ex vivo with GC frass. PAR-2-deficient BMDC released significantly less IL-6, IL-23 and TNFα compared to BMDC from wild type mice, suggesting PAR-2 activation was important in Th2/Th17 skewing cytokine production. To determine the role for PAR-2 on mDCs on the initiation of allergic airway inflammation, BMDCs from wild type and PAR-2-deficient mice were treated in the presence or absence of GC frass and then adoptively transferred into the airway of wild type mice. Importantly, GC frass-stimulated wild type BMDCs were sufficient to induce AHR and allergic airway inflammation, while GC frass-stimulated PAR-2-deficient BMDC had attenuated responses.

Conclusions

Together these data suggest an important role for allergen activation of PAR-2 on mDCs in mediating Th2/Th17 cytokine production and allergic airway responses.     

CD1d‐mediated lipid presentation by CD11c+ cells regulates intestinal homeostasis

Intestinal homeostasis relies on a continuous dialogue between the commensal bacteria and the immune system. Natural killer T (NKT) cells, which recognize CD1d‐restricted microbial lipids and self‐lipids, contribute to the regulation of mucosal immunity, yet the mechanisms underlying their functions remain poorly understood. Here, we demonstrate that NKT cells respond to intestinal lipids and CD11c⁺ cells (including dendritic cells (DCs) and macrophages) are essential to mediate lipid presentation within the gut ultimately controlling intestinal NKT cell homeostasis and activation. Conversely, CD1d and NKT cells participate in the control of the intestinal bacteria composition and compartmentalization, in the regulation of the IgA repertoire and in the induction of regulatory T cells within the gut. These changes in intestinal homeostasis require CD1d expression on DC/macrophage populations as mice with conditional deletion of CD1d on CD11c⁺ cells exhibit dysbiosis and altered immune homeostasis. These results unveil the importance of CD11c⁺ cells in controlling lipid‐dependent immunity in the intestinal compartment and reveal an NKT cell–DC crosstalk as a key mechanism for the regulation of gut homeostasis.     

Effective chemokine secretion by dendritic cells and expansion of cross-presenting CD4-/CD8+ dendritic cells define a protective phenotype in the mouse model of coxsackievirus myocarditis

Enteroviruses such as coxsackievirus B3 (CVB3) are able to induce lethal acute and chronic myocarditis. In resistant C57BL/6 mice, CVB3 myocarditis is abrogated by T-cell-dependent mechanisms, whereas major histocompatibility complex (MHC)-matched permissive A.BY/SnJ mice develop chronic myocarditis based on virus persistence. To define the role of T-cell-priming dendritic cells (DCs) in the outcome of CVB3 myocarditis, DCs were analyzed in this animal model in the course of CVB3 infection. In both mouse strains, DCs were found to be infectible with CVB3; however, formation of infectious virions was impaired. In DCs derived from C57BL/6 mice, significantly higher quantities of interleukin-10 (IL-10) and the proinflammatory cytokines IL-6 and tumor necrosis factor alpha were measured compared to those from A.BY/SnJ mice. Additionally, the chemokines interferon-inducible protein 10 (IP-10) and RANTES were secreted by DCs from resistant C57BL/6 mice earlier in infection and at significantly higher levels. The protective role of IP-10 in CVB3 myocarditis was confirmed in IP-10^−/− mice, which had increased myocardial injury compared to the immunocompetent control animals. Also, major differences in resistant and permissive mice were found in DC subsets, with C57BL/6 mice harboring more cross-priming CD4⁻ CD8⁺ DCs. As CD4⁻ CD8⁺ DCs are known to express 10 times more Toll-like receptor 3 (TLR3) than other DC subsets, we followed the course of CVB3 infection in TLR3^−/− mice. These mice developed a fulminant acute myocarditis and secreted sustained low amounts of type I interferons; secretion of IP-10 and RANTES was nearly abrogated in DCs. We conclude that MHC-independent genetic factors involving DC-related IP-10 secretion and TLR3 expression are beneficial in the prevention of chronic coxsackievirus myocarditis.     

Endogenous attenuation of allergic lung inflammation by syndecan-1

The airway plays a vital role in allergic lung diseases by responding to inhaled allergens and initiating allergic inflammation. Various proinflammatory functions of the airway epithelium have been identified, but, equally important, anti-inflammatory mechanisms must also exist. We show in this study that syndecan-1, the major heparan sulfate proteoglycan of epithelial cells, attenuates allergic lung inflammation. Our results show that syndecan-1-null mice instilled with allergens exhibit exaggerated airway hyperresponsiveness, glycoprotein hypersecretion, eosinophilia, and lung IL-4 responses. However, administration of purified syndecan-1 ectodomains, but not ectodomain core proteins devoid of heparan sulfate, significantly inhibits these inflammatory responses. Furthermore, syndecan-1 ectodomains are shed into the airway when wild-type mice are intranasally instilled with several biochemically distinct inducers of allergic lung inflammation. Our results also show that syndecan-1 ectodomains bind to the CC chemokines (CCL7, CCL11, and CCL17) implicated in allergic diseases, inhibit CC chemokine-mediated T cell migration, and suppress allergen-induced accumulation of Th2 cells in the lung through their heparan sulfate chains. Together, these findings uncover an endogenous anti-inflammatory mechanism of the airway epithelium where syndecan-1 ectodomains attenuate allergic lung inflammation via suppression of CC chemokine-mediated Th2 cell recruitment to the lung.     

Endogenously expressed nef uncouples cytokine and chemokine production from membrane phenotypic maturation in dendritic cells

Immature dendritic cells (DCs), unlike mature DCs, require the viral determinant nef to drive immunodeficiency virus (SIV and HIV) replication in coculture with CD4(+) T cells. Since immature DCs may capture and get infected by virus during mucosal transmission, we hypothesized that Nef associated with the virus or produced during early replication might modulate DCs to augment virus dissemination. Adenovirus vectors expressing nef were used to introduce nef into DCs in the absence of other immunodeficiency virus determinants to examine Nef-induced changes that might activate immature DCs to acquire properties of mature DCs and drive virus replication. Nef expression by immature human and macaque DCs triggered IL-6, IL-12, TNF-alpha, CXCL8, CCL3, and CCL4 release, but without up-regulating costimulatory and other molecules characteristic of mature DCs. Coincident with this, nef-expressing immature DCs stimulated stronger autologous CD4(+) T cell responses. Both SIV and HIV nef-expressing DCs complemented defective SIVmac239 delta nef, driving replication in autologous immature DC-T cell cultures. In contrast, if DCs were activated after capturing delta nef, virus growth was not exacerbated. This highlights one way in which nef-defective virus-bearing immature DCs that mature while migrating to draining lymph nodes could induce stronger immune responses in the absence of overwhelming productive infection (unlike nef-containing wild-type virus). Therefore, Nef expressed in immature DCs signals a distinct activation program that promotes virus replication and T cell recruitment but without complete DC maturation, thereby lessening the likelihood that wild-type virus-infected immature DCs would activate virus-specific immunity, but facilitating virus dissemination.     

Processing and degradation of exogenous prion protein by CD11c(+) myeloid dendritic cells in vitro

The immune system plays an important role in facilitating the spread of prion infections from the periphery to the central nervous system. CD11c(+) myeloid dendritic cells (DC) could, due to their subepithelial location and their migratory capacity, be early targets for prion infection and contribute to the spread of infection. In order to analyze mechanisms by which these cells may affect prion propagation, we studied in vitro the effect of exposing such DC to scrapie-infected GT1-1 cells, which produce the scrapie prion protein PrP(Sc). In this system, the DC efficiently engulfed the infected GT1-1 cells. Unexpectedly, PrP(Sc), which is generally resistant to protease digestion, was processed and rapidly degraded. Based on this observation we speculate that CD11c(+) DC may play a dual role in prion infections: on one hand they may facilitate neuroinvasion by transfer of the infectious agent as suggested from in vivo studies, but on the other hand they may protect against the infection by causing an efficient degradation of PrP(Sc). Thus, the migrating and highly proteolytic CD11c(+) myeloid DC may affect the balance between propagation and clearance of PrP(Sc) in the organism.     

The immune response modifier and Toll-like receptor 7 agonist S-27609 selectively induces IL-12 and TNF-alpha production in CD11c+CD11b+CD8- dendritic cells

IL-12 and TNF-alpha production by dendritic cells (DCs) is a critical step in the initiation of local inflammation and adaptive immune responses. We show in this study that a small molecule immune response modifier that is a Toll-like receptor 7 (TLR7) agonist induces IL-12 and TNF-alpha production from murine CD11c(+)CD11b(+)CD8(-) DCs, a subset not previously known for this activity. Stimulation of these DCs through TLR7 in vivo induces significant cytokine production even 12 h after initial stimulation, as well as migration of the DC into T cell zones of the lymphoid tissue. In contrast, stimulation through TLR4 and TLR9 induced IL-12 production predominantly from CD8(+) DCs, consistent with previously published data. All TLR stimuli induced the increase in surface expression of the activation markers B7-1, B7-2, and class II in both CD8(+) and CD8(-) DCs, demonstrating that CD8(+) DCs do respond to TLR7-mediated stimuli. To date this is the only known stimuli to induce preferential cytokine production from CD8(-) DCs. Given the efficacy of TLR7 agonists as antiviral agents, the data collectively indicate that stimulation of CD8(-) DCs through TLR7 most likely plays a role in the generation of antiviral immune responses.     

Dendritic cells in allergic airway inflammation

Dendritic cells (DCs) are primary antigen-presenting cells involved in interactions with T cells leading to the proliferation of TH1 or TH2 cell types. In asthma, predominance of TH2 cells appears to be responsible for disease pathogenesis. Differentiation of TH2 cells is driven by a variety of factors such as the expression of high levels of costimulatory molecules, the cytokine profile, and the subset of DCs. Many inflammatory cells involved in the pathogenesis of asthma either directly or indirectly modulate DC function. Traditional treatments for asthma decrease the number of airway DCs in animals as well as in patients with asthma. Immunomodulators including interleukin (IL)-10, transforming growth factor (TGF)-beta, cytosine-phosphate-guanosine-containing oligodeoxynucleotides (CpG-ODN), 1alpha,25-dihydroxyvitamin D3, and fetal liver tyrosine kinase 3 ligand (Flt3L) are involved in the modulation of the function of DCs. Based on the critical review of the interaction between DCs and other inflammatory cells, we propose that activation of T cells by DCs and sensitization to inhaled allergen and resulting airway inflammation are dependent on plasmacytoid and myeloid subset of lung DCs to induce an immune response or tolerance and are tightly regulated by T-regulatory cells. Effects of various therapeutic agents to modulate the function of lung myeloid DCs have been discussed.     

Expression of a functional eotaxin (CC chemokine ligand 11) receptor CCR3 by human dendritic cells

Critical to the function of Ag-presenting dendritic cells (DCs) is their capacity to migrate to lymphoid organs and to sites of inflammation. A final stage of development, termed maturation, yields DCs that are strong stimulators of T cell-mediated immunity and is associated with a remodeling of the cell surface that includes a change in the levels of expression of many molecules, including chemokine receptors. We show in this study that CCR3, a chemokine receptor initially discovered on eosinophils, is also expressed by human DCs that differentiate from blood monocytes, DCs that emigrate from skin (epidermal and dermal DCs), and DCs derived from CD34+ hemopoietic precursors in bone marrow, umbilical cord blood, and cytokine-elicited peripheral blood leukapheresis. Unlike other chemokine receptors, such as CCR5 and CCR7, the expression of CCR3 is not dependent on the state of maturation. All DC subsets contain a large intracellular pool of CCR3. The surface expression of CCR3 is not modulated following uptake of particulate substances such as zymosan or latex beads. CCR3 mediates in vitro chemotactic responses to the known ligands, eotaxin and eotaxin-2, because the DC response to these chemokines is inhibited by CCR3-specific mAbs. We postulate that expression of CCR3 may underlie situations where both DCs and eosinophils accumulate in vivo, such as the lesions of patients with Langerhans cell granulomatosis.