In vivo depletion of lung CD11c+ dendritic cells during allergen challenge abrogates the characteristic features of asthma

Nociceptin reduces the inflammatory immune microenvironment in a conventional murine model of airway hyperresponsiveness

BACKGROUND

Nociceptin/orphanin FQ (N/OFQ) and its receptor (NOP) are involved in airway hyperresponsiveness (AHR) and inflammation. However, the role of nociceptin at modulating the inflammatory immune microenvironment in asthma is still unclear.

OBJECTIVE

To understand the role of N/OFQ in the regulation of a Th2-like environment, we used a conventional murine model of AHR.

METHODS

Balb/c and CD1 mice were sensitized to ovalbumin (OVA) and treated with saline solution or N/OFQ, at days 0 and 7. A group of Balb/c mice were killed at 7 and 14 days from the first sensitization for the inflammatory profile evaluation while a group of Balb/c and CD1 mice were aerosol-challenged from day 21 to 23 with OVA and killed 24 h later for functional evaluations.

RESULTS

In OVA-sensitized mice, N/OFQ significantly reduced IL-4+ CD4+ T cells in lymph nodes (LN) and IL-13 in the lungs, while it induced IFN-γ increase in the lung. The efflux of dendritic cells (DCs) to the mediastinic LN and into the lung of OVA-sensitized mice was reduced in N/OFQ-treated and sensitized mice. N/OFQ reduced the expression of CD80 on DCs, indicating its ability to modulate the activation of DCs. In a less prone Th2-like environment mice strain, such as CD1 mice, N/OFQ did not modify lung resistances as observed in BALB/c mice. Finally, spectroscopic data showed the N/OFQ was able to interact onto the membrane of DCs obtained from Balb/c rather than CD1 mice, indicating its ability to modulate AHR in a Th2-like environment with a direct activity on DCs.

CONCLUSIONS AND CLINICAL RELEVANCE

Our data confirmed the capability of N/OFQ to modulate the immune microenvironment in the lung of Th2-biased, OVA-sensitized Balb/c mice, suggesting N/OFQ-NOP axis as a novel pharmacological tool to modulate the inflammatory immune microenvironment in asthma.

Basophil-derived IL-6 regulates TH17 cell differentiation and CD4 T cell immunity

Basophils are rare, circulating granulocytes proposed to be involved in T helper (T_H) type 2 immunity, mainly through secretion of interleukin (IL)-4. In addition to IL-4, basophils produce IL-6 and tumor necrosis factor (TNF)-α in response to immunoglobulin E (IgE) crosslinking. Differentiation of T_H17 cells requires IL-6 and transforming growth factor (TGF)-β, but whether basophils play a significant role in T_H17 induction is unknown. Here we show a role for basophils in T_H17 cell development by using in vitro T cell differentiation and in vivo T_H17-mediated inflammation models. Bone marrow derived-basophils (BMBs) and splenic basophils produce significant amounts of IL-6 as well as IL-4 following stimulation with IgE crosslink or cholera toxin (CT). In addition, through IL-6 secretion, BMBs cooperate with dendritic cells to promote T_H17 cell differentiation. In the T_H17 lung inflammation model, basophils are recruited to the inflamed lungs following CT challenge, and T_H17 responses are significantly reduced in the absence of basophils or IL-6. Furthermore, reconstitution with wild-type, but not IL-6-deficient, basophils restored CT-mediated lung inflammation. Lastly, basophil-deficient mice showed reduced phenotypes of T_H17-dependent experimental autoimmune encephalomyelitis. Therefore, our results indicate that basophils are an important inducer of T_H17 cell differentiation, which is dependent on IL-6 secretion.

IgE-Related Chronic Diseases and Anti-IgE-Based Treatments

IgE is an immunoglobulin that plays a central role in acute allergic reactions and chronic inflammatory allergic diseases. The development of a drug able to neutralize this antibody represents a breakthrough in the treatment of inflammatory pathologies with a probable allergic basis. This review focuses on IgE-related chronic diseases, such as allergic asthma and chronic urticaria (CU), and on the role of the anti-IgE monoclonal antibody, omalizumab, in their treatment. We also assess the off-label use of omalizumab for other pathologies associated with IgE and report the latest findings concerning this drug and other new related drugs. To date, omalizumab has only been approved for severe allergic asthma and unresponsive chronic urticaria treatments. In allergic asthma, omalizumab has demonstrated its efficacy in reducing the dose of inhaled corticosteroids required by patients, decreasing the number of asthma exacerbations, and limiting the effect on airway remodeling. In CU, omalizumab treatment rapidly improves symptoms and in some cases achieves complete disease remission. In systemic mastocytosis, omalizumab also improves symptoms and its prophylactic use to prevent anaphylactic reactions has also been discussed. In other pathologies such as atopic dermatitis, food allergy, allergic rhinitis, nasal polyposis, and keratoconjunctivitis, omalizumab significantly improves clinical manifestations. Omalizumab acts in two ways: by sequestering free IgE and by accelerating the dissociation of the IgE-Fcε receptor I complex.

Thiol peroxiredoxin, a novel allergen from Bombyx mori, modulates functions of macrophages and dendritic cells

Bombyx mori (B.mori, also known as silkworm) plays a role in the pathogenesis of allergic diseases. However, its allergens are to be characterized. The aim of this paper is to identify new silkworm allergens. Two-dimensional gel electrophoresis (2-DE) and mass spectrometry were employed to separate and identify potential allergens from silkworm pupa. Six potential allergens were identified in this study. Thiol peroxiredoxin (TP), one of the 6 allergens, reacted to serum IgE from patients sensitized to silkworm. By sensitizing with TP allergic asthma like symptoms were induced in mice, including elevation of the levels of serum IgE, IL-4 from bronchoalveolar lavage fluid and culture supernatant of spleen cells. In vitro experiments showed that TP significantly induced RAW264.7 cells (a macrophage cell line) apoptosis via modulating the BCL2 and Caspase9 pathways. The levels of CD80, CD40, CD83 and TNF-α in DC2.4 cells (a dendritic cell line) were increased in the culture after exposure to TP. In summary, TP is an allergic component of silkworm. It induces allergic asthma, and modulates the functions of macrophages and dendritic cells.

Nerve growth factor promotes expression of costimulatory molecules and release of cytokines in dendritic cells involved in Th2 response through LPS-induced p75NTR

INTRODUCTION

Nerve growth factor (NGF) plays an important role in asthmatic inflammatory responses. However, the effects of NGF on dendritic cells (DCs) in asthmatic inflammation remain unknown. Therefore, we examined the effects of NGF on co-stimulatory molecules and the release of cytokines after ovalbumin (OVA) and a low dose of LPS (low LPS) stimulation of dendritic cells.

METHODS

Bone-marrow-derived dendritic cells (BMDCs) were collected from 6- to 8-week-old wide or TLR4(-/-) mice. BMDCs were treated with OVA and/or low LPS for 12h, and then stimulated with NGF for 24h. ELISA and flow cytometry were performed to measure TSLP, IL-6, IL-10, and IL-12 production and MHCII and CD86 expression on BMDCs. BMDCs were exposed to p75 neurotrophin receptor (p75NTR) inhibitor (TAT-Pep5) or NF-kB inhibitor (QNZ) 30 min prior to NGF 1 h after NGF intervention, the levels of RelA and RelB in cytoplasmic and nuclear were detected by west blot. Co-cultured BMDCs with naïve CD4(+) T cells, and ELISA was used to detect IL-4 and INF-γ levels.

RESULTS

NGF was found to markedly promote OVA and low LPS-induced expression of MHCII, CD86, secretion of TSLP and IL-6, and Th2-response-stimulating capacity of BMDCs. NGF affected BMDCs through LPS-induced p75NTR expression. TAT-Pep5 or QNZ could attenuate the promotive effect of NGF.

CONCLUSIONS

NGF facilitates OVA with lowLPS-induced maturation of mouse BMDCs through LPS-up-regulated p75 NTR via activation of NF-κB pathways, providing another mechanism for the involvement of NGF in the Th2 response.

Dectin-1 Plays an Important Role in House Dust Mite-Induced Allergic Airway Inflammation through the Activation of CD11b+ Dendritic Cells

It is well known that sensitization against fungi is closely associated with severity of asthma. Dectin-1 (gene symbol Clec7a), a C-type lectin receptor, recognizes the fungal cell wall component β-glucan, as well as some component(s) in house dust mite (HDM) extract. However, the roles of Dectin-1 in HDM-induced allergic airway inflammation remain unclear. In this study, we used Dectin-1-deficient (Clec7a^-/-) mice to examine whether Dectin-1 is involved in HDM-induced allergic airway inflammation. We found that HDM-induced eosinophil and neutrophil recruitment into the airways was significantly attenuated in Clec7a^-/- mice compared with that in wild-type mice. In addition, HDM-induced IL-5, IL-13, and IL-17 production from mediastinum lymph node cells was reduced in HDM-sensitized Clec7a^-/- mice. Dectin-1 was expressed on CD11b⁺ dendritic cells (DCs), an essential DC subset for the development of allergic inflammation, but not on CD103⁺ DCs, plasmacytoid DCs, or lung epithelial cells. Transcriptome analysis revealed that the expression of chemokine/chemokine receptors, including CCR7, which is indispensable for DC migration to draining lymph nodes, was decreased in Clec7a^-/- DCs. In accordance with these results, the number of HDM-labeled CD11b⁺ DCs in mediastinum lymph nodes was significantly reduced in Clec7a^-/- mice compared with wild-type mice. Taken together, these results suggest that Dectin-1 expressed on CD11b⁺ DCs senses some molecule(s) in HDM extract and plays a critical role in the induction of HDM-induced allergic airway inflammation by inducing the expression of chemokine/chemokine receptors in DCs.

Scaffolding protein Gab1 regulates myeloid dendritic cell migration in allergic asthma

Asthma is a common allergic disorder involving a complex interplay among multiple genetic and environmental factors. Recent studies identified genetic variants of human GAB1 as a novel asthma susceptibility factor. However, the functions of Gab1 in lung remain largely unexplored. In this study, we first observed an elevation of Gab1 level in peripheral blood mononuclear cells from asthmatic patients during acute exacerbation compared with convalescence. Mice with a selectively disrupted Gab1 in myeloid dendritic cells (mDCs) considerably attenuated allergic inflammation in experimental models of asthma. Further investigations revealed a prominent reduction in CCL19-mediated migration of Gab1-deficient mDCs to draining lymph nodes and subsequent impairment of Th2-driven adaptive activation. Mechanistically, Gab1 is an essential component of the CCL19/CCR7 chemokine axis that regulates mDC migration during asthmatic responses. Together, these findings provide the first evidence for the roles of Gab1 in lung, giving us deeper understanding of asthmatic pathogenesis.

House dust mite-driven asthma and allergen-specific T cells depend on B cells when the amount of inhaled allergen is limiting

BACKGROUND

Allergic asthma is a CD4 T_H2-lymphocyte driven disease characterized by airway hyperresponsiveness and eosinophilia. B cells can present antigens to CD4 T cells and produce IgE immunoglobulins that arm effector cells; however, mouse models are inconclusive on whether B cells are necessary for asthma development.

OBJECTIVES

We sought to address the role of B cells in a house dust mite (HDM)-driven T_H2-high asthma mouse model.

METHODS

Wild-type and B cell-deficient muMT mice were sensitized and challenged through the airways with HDM extracts. The antigen-presenting capacities of B cells were studied by using new T-cell receptor transgenic 1-DER mice specific for the Der p 1 allergen.

RESULTS

In vitro-activated B cells from HDM-exposed mice presented antigen to 1-DER T cells and induced a T_H2 phenotype. In vivo B cells were dispensable for activation of naive 1-DER T cells but necessary for full expansion of primed 1-DER T cells. At high HDM challenge doses, B cells were not required for development of pulmonary asthmatic features yet contributed to T_H2 expansion in the mediastinal lymph nodes but not in the lungs. When the amount of challenge allergen was decreased, muMT mice had reduced asthma features. Under these limiting conditions, B cells contributed also to expansion of T_H2 effector cells in the lungs and central memory T cells in the mediastinal lymph nodes.

CONCLUSION

B cells are a major part of the adaptive immune response to inhaled HDM allergen, particularly when the amount of inhaled allergen is low, by expanding allergen-specific T cells.

Interferon response factor-3 promotes the pro-Th2 activity of mouse lung CD11b+ conventional dendritic cells in response to house dust mite allergens

Very few transcription factors have been identified that are required by antigen-presenting cells (APCs) to induce T helper type 2 (Th2) responses. Because lung CD11b⁺ conventional dendritic cells (CD11b⁺ cDCs) are responsible for priming Th2 responses in house-dust mite (HDM)-induced airway allergy, we used them as a model to identify transcriptional events regulating the pro-Th2 activity of cDCs. Transcriptomic profiling of lung CD11b⁺ cDCs exposed to HDM in vivo revealed first that HDM triggers an antiviral defence-like response, and second that the majority of HDM-induced transcriptional changes depend on the transcription factor Interferon Response Factor-3 (Irf3). Validating the functional relevance of these observations, Irf3-deficient CD11b⁺ cDCs displayed reduced pro-allergic activity. Indeed, Irf3-deficient CD11b⁺ cDCs induced less Th2, more regulatory T cell, and similar Th1 differentiation in naïve CD4⁺ T cells compared to their wild-type counterparts. The altered APC activity of Irf3 CD11b⁺ cDCs was associated with reduced expression of CD86 and was phenocopied by blocking CD86 activity in wild-type CD11b⁺ cDCs. Altogether, these results establish Irf3, known mostly for its role in antiviral responses, as a transcription factor involved in the induction of Th2 responses through the promotion of pro-Th2 costimulation in CD11b⁺ DCs.

Secondary allergic T cell responses are regulated by dendritic cell-derived thrombospondin-1 in the setting of allergic eye disease

Allergic eye disease, as in most forms of atopy, ranges in severity among individuals from immediate hypersensitivity to a severe and debilitating chronic disease. Dendritic cells play a key role in stimulating pathogenic T cells in allergen re-exposure, or secondary responses. However, molecular cues by dendritic cells underpinning allergic T cell response levels and the impact that this control has on consequent severity of allergic disease are poorly understood. Here, we show that a deficiency in thrombospondin-1, a matricellular protein known to affect immune function, has subsequent effects on downstream T cell responses during allergy, as revealed in an established mouse model of allergic eye disease. More specifically, we demonstrate that a thrombospondin-1 deficiency specific to dendritic cells leads to heightened secondary T cell responses and consequent clinical disease. Interestingly, whereas thrombospondin-1-deficient dendritic cells augmented activity of allergen-primed T cells, this increase was not recapitulated with naïve T cells in vitro. The role of dendritic cell-derived thrombospondin-1 in regulating secondary allergic T cell responses was confirmed in vivo, as local transfer of thrombospondin-1-sufficient dendritic cells to the ocular mucosa of thrombospondin-1 null hosts prevented the development of augmented secondary T cell responses and heightened allergic eye disease clinical responses. Finally, we demonstrate that topical instillation of thrombospondin-1-derived peptide reduces T cell activity and clinical progression of allergic eye disease. Taken together, this study reveals an important modulatory role of dendritic cell-derived thrombospondin-1 on secondary allergic T cell responses and suggests the possible dysregulation of dendritic cell-derived thrombospondin-1 expression as a factor in allergic eye disease severity.

Endosomal recognition of Lactococcus lactis G121 and its RNA by dendritic cells is key to its allergy-protective effects

BACKGROUND

Bacterial cowshed isolates are allergy protective in mice; however, the underlying mechanisms are largely unknown. We examined the ability of Lactococcus lactis G121 to prevent allergic inflammatory reactions.

OBJECTIVE

We sought to identify the ligands and pattern recognition receptors through which L lactis G121 confers allergy protection.

METHODS

L lactis G121-induced cytokine release and surface expression of costimulatory molecules by untreated or inhibitor-treated (bafilomycin and cytochalasin D) human monocyte-derived dendritic cells (moDCs), bone marrow-derived mouse dendritic cells (BMDCs), and moDC/naive CD4⁺ T-cell cocultures were analyzed by using ELISA and flow cytometry. The pathology of ovalbumin-induced acute allergic airway inflammation after adoptive transfer of BMDCs was examined by means of microscopy.

RESULTS

L lactis G121-treated murine BMDCs and human moDCs released T_H1-polarizing cytokines and induced T_H1 T cells. Inhibiting phagocytosis and endosomal acidification in BMDCs or moDCs impaired the release of T_H1-polarizing cytokines, costimulatory molecule expression, and T-cell activation on L lactis G121 challenge. In vivo allergy protection mediated by L lactis G121 was dependent on endosomal acidification in dendritic cells (DCs). Toll-like receptor (Tlr) 13^-/- BMDCs showed a weak response to L lactis G121 and were unresponsive to its RNA. The T_H1-polarizing activity of L lactis G121-treated human DCs was blocked by TLR8-specific inhibitors, mediated by L lactis G121 RNA, and synergistically enhanced by activation of nucleotide-binding oligomerization domain-containing protein (NOD) 2.

CONCLUSION

Bacterial RNA is the main driver of L lactis G121-mediated protection against experimentally induced allergy and requires both bacterial uptake by DCs and endosomal acidification. In mice L lactis G121 RNA signals through TLR13; however, the most likely intracellular receptor in human subjects is TLR8.

Cysteinyl leukotriene receptor antagonist epigenetically modulates cytokine expression and maturation of human myeloid dendritic cells

BACKGROUND

Cysteinyl leukotriene receptor antagonists are important controllers in treating asthma. Human myeloid DCs (mDCs) play critical roles in the pathogenesis of asthma. However, the effects of cysteinyl leukotriene receptor antagonist on human mDCs are unknown.

METHODS

To investigate the effects of cysteinyl leukotriene receptor antagonist on the function of human mDCs, circulating mDCs were isolated from six health subjects. Human mDCs were pretreated with montelukast and were stimulated with toll-like receptor (TLR) ligands lipopolysaccharide (LPS) or polyinosinic-polycytidylic acid (poly I:C). Tumor necrosis factor (TNF)-α and interleukin (IL)-10 were measured by ELISA. Intracellular signaling was investigated by pathway inhibitors, western blot and chromatin immunoprecipitation. Costimulatory molecules expression was investigated by flow cytometry. T cell polarization function of mDCs was investigated by measuring interferon (IFN)-γ, IL-13, IL-10 and IL-17A production by T cells using mDC/T cell coculture assay.

RESULTS

Montelukast suppressed TLR-mediated TNF-α expression via the NFκB-p65 and mitogen-activated protein kinase (MAPK)-JNK pathway, and enhanced TLR-mediated IL-10 expression via the MAPK-p38 pathway and epigenetic regulation by histone H3 acetylation. Montelukast suppressed LPS-induced CD80, CD86, CD40 and HLA-DR expression. Montelukast-treated mDCs suppressed IFN-γ and IL-13 production by T cells.

CONCLUSION

Cysteinyl leukotriene receptor antagonist alters the function of human mDCs by epigenetically modulating cytokine expression, suppressing costimulatory molecules expression and inhibiting the ability to initiate Th1/Th2 responses. The effects of cysteinyl leukotriene receptor antagonist on human mDCs can be an important mechanism in treating asthma.

CD11c.DTR mice develop a fatal fulminant myocarditis after local or systemic treatment with diphtheria toxin

To assess the role of alveolar macrophages (AMs) during a pulmonary Aspergillus fumigatus infection AMs were depleted by intratracheal application of diphtheria toxin (DTX) to transgenic CD11c.DTR mice prior to fungal infection. Unexpectedly, all CD11c.DTR mice treated with DTX died within 4-5 days, whether being infected with A. fumigatus or not. Despite measurable impact of DTX on lung functional parameters, these constrictions could not explain the high mortality rate. Instead, DTX-treated CD11c.DTR animals developed fulminant myocarditis (FM) characterized by massive leukocyte infiltration and myocardial cell destruction, including central parts of the heart's stimulus transmission system. In fact, standard limb lead ECG recordings of diseased but not healthy mice showed a "Brugada"-like pattern with an abnormally high ST segment pointing to enhanced susceptibility for potential lethal arrhythmias. While CD11c.DTR mice are extensively used for the characterization of CD11c(+) cells, including dendritic cells, several studies have already mentioned adverse side effects following DTX treatment. Our results demonstrate that this limitation is based on severe myocarditis but not on the expected lung constrictions, and has to be taken into consideration if this animal model is used. Based on these properties, however, the CD11c.DTR mouse might serve as useful animal model for FM.

Circulating Dendritic Cells, Farm Exposure and Asthma at Early Age

Farm environment has been shown to protect from childhood asthma. Underlying immunological mechanisms are not clear yet, including the role of dendritic cells (DCs). The aim was to explore whether asthma and farm exposures are associated with the proportions and functional properties of DCs from 4.5-year-old children in a subgroup of the Finnish PASTURE birth cohort study. Myeloid DCs (mDCs), plasmacytoid DCs (pDCs) and CD86 expression on mDCs ex vivo (n = 100) identified from peripheral blood mononuclear cells (PBMCs) were analysed using flow cytometry. MDCs and production of interleukin (IL)-6 and tumour necrosis factor alpha (TNF-α) by mDCs were analysed after 5 h in vitro stimulation with lipopolysaccharide (LPS) (n = 88). Prenatal and current farm exposures (farming, stables, hay barn and farm milk) were assessed from questionnaires. Asthma at age 6 years was defined as a doctor's diagnosis and symptoms; atopic sensitization was defined by antigen-specific IgE measurements. Asthma was positively associated with CD86 expression on mDCs ex vivo [adjusted odds ratio (aOR) 4.83, 95% confidence interval (CI) 1.51-15.4] and inversely with IL-6 production in mDCs after in vitro stimulation with LPS (aOR 0.19, 95% CI 0.04-0.82). In vitro stimulation with LPS resulted in lower percentage of mDCs in the farm PBMC cultures as compared to non-farm PBMC cultures. Our results suggest an association between childhood asthma and functional properties of DCs. Farm exposure may have immunomodulatory effects by decreasing mDC proportions.

Tissue-resident dendritic cells and diseases involving dendritic cell malfunction

Dendritic cells (DCs) control immune responses and are central to the development of immune memory and tolerance. DCs initiate and orchestrate immune responses in a manner that depends on signals they receive from microbes and cellular environment. Although DCs consist mainly of bone marrow-derived and resident populations, a third tissue-derived population resides the spleen and lymph nodes (LNs), different subsets of tissue-derived DCs have been identified in the blood, spleen, lymph nodes, skin, lung, liver, gut and kidney to maintain the tolerance and control immune responses. Tissue-resident DCs express different receptors for microbe-associated molecular patterns (MAMPs) and damage-associated molecular patterns (DAMPs), which were activated to promote the production of pro- or anti-inflammatory cytokines. Malfunction of DCs contributes to diseases such as autoimmunity, allergy, and cancer. It is therefore important to update the knowledge about resident DC subsets and diseases associated with DC malfunction.

Regulation of Th2 Cell Immunity by Dendritic Cells

Th2 cell immunity is required for host defense against helminths, but it is detrimental in allergic diseases in humans. Unlike Th1 cell and Th17 cell subsets, the mechanism by which dendritic cells modulate Th2 cell responses has been obscure, in part because of the inability of dendritic cells to provide IL-4, which is indispensable for Th2 cell lineage commitment. In this regard, immune cells other than dendritic cells, such as basophils and innate lymphoid cells, have been suggested as Th2 cell inducers. More recently, multiple independent researchers have shown that specialized subsets of dendritic cells mediate Th2 cell responses. This review will discuss the current understanding related to the regulation of Th2 cell responses by dendritic cells and other immune cells.

Immunomodulation of airway epithelium cell activation by mesenchymal stromal cells ameliorates house dust mite-induced airway inflammation in mice

Allergic asthma is underpinned by T helper 2 (Th2) inflammation. Redundancy in Th2 cytokine function and production by innate and adaptive immune cells suggests that strategies aimed at immunomodulation may prove more beneficial. Hence, we sought to determine whether administration of mesenchymal stromal cells (MSCs) to house dust mite (HDM) (Dermatophagoides pteronyssinus)-sensitized mice would suppress the development of Th2 inflammation and airway hyperresponsiveness (AHR) after HDM challenge. We report that the intravenous administration of allogeneic donor MSCs 1 hour before allergen challenge significantly attenuated the features of allergic asthma, including tissue eosinophilia, Th2 cytokine (IL-5 and IL-13) levels in bronchoalveolar lavage fluid, and AHR. The number of infiltrating type 2 innate lymphoid cells was not affected by MSC transfer, suggesting that MSCs may modulate the adaptive arm of Th2 immunity. The effect of MSC administration was long lasting; all features of allergic airway disease were significantly suppressed in response to a second round of HDM challenge 4 weeks after MSC administration. Further, we observed that MSCs decreased the release of epithelial cell-derived alarmins IL-1α and high mobility group box-1 in an IL-1 receptor antagonist-dependent manner. This significantly decreased the expression of the pro-Th2 cytokine IL-25 and reduced the number of activated and antigen-acquiring CD11c(+)CD11b(+) dendritic cells in the lung and mediastinal lymph nodes. Our findings suggest that MSC administration can ameliorate allergic airway inflammation by blunting the amplification of epithelial-derived inflammatory cytokines induced by HDM exposure and may offer long-term protection against Th2-mediated allergic airway inflammation and AHR.

Dendritic cells revisited in human allergic rhinitis and asthma

The role of dendritic cells (DCs) in airway allergy has been studied for 15 years; recent data has highlighted the cross talk with airway epithelial cells and environmental factors (allergens, virus) during the inception and exacerbation of allergic asthma. Although murine models have provided key information, it remains uncertain to what extent these basic mechanisms take place in human allergic disease, notably with regard to different clinical phenotypes. In the present review, we discuss new evidence regarding mechanisms of DC regulation in the mouse which could be important in human asthma. Finally, after discussing the effects of current therapies on DC biology, we focus on pathways that could represent targets for future therapies.

Indoor Pollutant Hexabromocyclododecane Has a Modest Immunomodulatory Effect on House Dust Mite Induced Allergic Asthma in Mice

Hexabromocyclododecane (HBCD) has been recognized as an indoor pollutant. HBCD is added as a flame retardant to many consumer products and leaches from the products into house dust. HBCD might be potentially hazardous to the airways because of inhalation of house dust. Sensitization to house dust mite (HDM) is a risk factor for the development of allergic asthma. In this study, we examined whether HBCD can affect the immune response to HDM allergens. Bone-marrow-derived dendritic cells (BMDCs) were exposed simultaneously to HBCD and HDM in vitro. HBCD enhanced oxidative stress in HDM-pulsed BMDCs, which was accompanied by a higher production of Interleukin (IL)-6 and -10. Adoptive transfer of HDM/HBCD-exposed BMDCs into naı̈ve mice resulted in enhanced levels of IL-17A after inhalational challenge with HDM. Direct mucosal exposure to HBCD during HDM inhalation enhanced IL-4 or IL-17A production, depending on the HDM extract used, but did not aggravate the eosinophilic airway inflammation or airway hyper-reactivity. Our results indicate that exposure to HBCD can have a mild immune-modulating effect by enhancing the inflammatory cytokine production in response to inhaled HDM in mice.

Macrophages are critical to the maintenance of IL-13-dependent lung inflammation and fibrosis

The roles of macrophages in type 2-driven inflammation and fibrosis remain unclear. Here, using CD11b-diphtheria toxin receptor (DTR) transgenic mice and three models of interleukin 13 (IL-13)-dependent inflammation, fibrosis, and immunity, we show that CD11b(+) F4/80(+) Ly6C(+) macrophages are required for the maintenance of type 2 immunity within affected tissues but not secondary lymphoid organs. Direct depletion of macrophages during the maintenance or resolution phases of secondary Schistosoma mansoni egg-induced granuloma formation caused a profound decrease in inflammation, fibrosis, and type 2 gene expression. Additional studies with CD11c-DTR and CD11b/CD11c-DTR double-transgenic mice suggested that macrophages but not dendritic cells were critical. Mechanistically, macrophage depletion impaired effector CD4(+) T helper type 2 (Th2) cell homing and activation within the inflamed lung. Depletion of CD11b(+) F4/80(+) Ly6C(+) macrophages similarly reduced house dust mite-induced allergic lung inflammation and suppressed IL-13-dependent immunity to the nematode parasite Nippostrongylus brasiliensis. Consequently, therapeutic strategies targeting macrophages offer a novel approach to ameliorate established type 2 inflammatory diseases.

Group 2 innate lymphoid cells license dendritic cells to potentiate memory TH2 cell responses

Rapid activation of memory CD4(+) T helper 2 (TH2) cells during allergic inflammation requires their recruitment into the affected tissue. Here we demonstrate that group 2 innate lymphoid (ILC2) cells have a crucial role in memory TH2 cell responses, with targeted depletion of ILC2 cells profoundly impairing TH2 cell localization to the lungs and skin of sensitized mice after allergen re-challenge. ILC2-derived interleukin 13 (IL-13) is critical for eliciting production of the TH2 cell-attracting chemokine CCL17 by IRF4(+)CD11b(+)CD103(-) dendritic cells (DCs). Consequently, the sentinel function of DCs is contingent on ILC2 cells for the generation of an efficient memory TH2 cell response. These results elucidate a key innate mechanism in the regulation of the immune memory response to allergens.

Antigen-specific cytotoxic T lymphocytes target airway CD103+ and CD11b+ dendritic cells to suppress allergic inflammation

Allergic airway inflammation is driven by the recognition of inhaled allergen by T helper type 2 (Th2) cells in the airway and lung. Allergen-specific cytotoxic T lymphocytes (CTLs) can strongly reduce airway inflammation, however, the mechanism of their inhibitory activity is not fully defined. We used mouse models to show that allergen-specific CTLs reduced early cytokine production by Th2 cells in lung, and their subsequent accumulation and production of interleukin (IL)-4 and IL-13. In addition, treatment with specific CTLs also increased the proportion of caspase(+) dendritic cells (DCs) in mediastinal lymph node (MLN), and decreased the numbers of CD103(+) and CD11b(+) DCs in the lung. This decrease required expression of the cytotoxic mediator perforin in CTLs and of the appropriate MHC-antigen ligand on DCs, suggesting that direct CTL-DC contact was necessary. Lastly, lung imaging experiments revealed that in airway-challenged mice XCR1-GFP(+) DCs, corresponding to the CD103(+) DC subset, and XCR1-GFP(-) CD11c(+) cells, which include CD11b(+) DCs and alveolar macrophages, both clustered in the areas surrounding the small airways and were closely associated with allergen-specific CTLs. Thus, allergen-specific CTLs reduce allergic airway inflammation by depleting CD103(+) and CD11b(+) DC populations in the lung, and may constitute a mechanism through which allergic immune responses are regulated.

In Vivo Analysis of Intestinal Mononuclear Phagocytes

The study of the intestinal dendritic cell (DC) compartment, its homeostasis, regulation, and response to challenges calls for the investigation within the physiological tissue context comprising the unique anatomic constellation of the epithelial single cell layer and the luminal microbiota, as well as neighboring immune and nonimmune cells. Here we provide protocols we developed that use a combination of conditional cell ablation, conditional compartment mutagenesis, and adoptive precursor transfers to study DC and other intestinal mononuclear phagocytes in in vivo context. We will highlight pitfalls and strengths of these approaches.

Human Respiratory Syncytial Virus: Role of Innate Immunity in Clearance and Disease Progression

Human respiratory syncytial virus (HRSV) infections have worldwide records. The virus is responsible for bronchiolitis, pneumonia, and asthma in humans of different age groups. Premature infants, young children, and immunocompromised individuals are prone to severe HRSV infection that may lead to death. Based on worldwide estimations, millions of cases were reported in both developed and developing countries. In fact, HRSV symptoms develop mainly as a result of host immune response. Due to inability to establish long lasting adaptive immunity, HRSV infection is recurrent and hence impairs vaccine development. Once HRSV attached to the airway epithelia, interaction with the host innate immune components starts. HRSV interaction with pulmonary innate defenses is crucial in determining the disease outcome. Infection of alveolar epithelial cells triggers a cascade of events that lead to recruitment and activation of leukocyte populations. HRSV clearance is mediated by a number of innate leukocytes, including macrophages, natural killer cells, eosinophils, dendritic cells, and neutrophils. Regulation of these cells is mediated by cytokines, chemokines, and other immune mediators. Although the innate immune system helps to clear HRSV infection, it participates in disease progression such as bronchiolitis and asthma. Resolving the mechanisms by which HRSV induces pathogenesis, different possible interactions between the virus and immune components, and immune cells interplay are essential for developing new effective vaccines. Therefore, the current review focuses on how the pulmonary innate defenses mediate HRSV clearance and to what extent they participate in disease progression. In addition, immune responses associated with HRSV vaccines will be discussed.

A central role for hepatic conventional dendritic cells in supporting Th2 responses during helminth infection

Dendritic cells (DCs) are the key initiators of T-helper (Th) 2 immune responses against the parasitic helminth Schistosoma mansoni. Although the liver is one of the main sites of antigen deposition during infection with this parasite, it is not yet clear how distinct DC subtypes in this tissue respond to S. mansoni antigens in vivo, or how the liver microenvironment might influence DC function during establishment of the Th2 response. In this study, we show that hepatic DC subsets undergo distinct activation processes in vivo following murine infection with S. mansoni. Conventional DCs (cDCs) from schistosome-infected mice upregulated expression of the costimulatory molecule CD40 and were capable of priming naive CD4(+) T cells, whereas plasmacytoid DCs (pDCs) upregulated expression of MHC class II, CD86 and CD40 but were unable to support the expansion of either naive or effector/memory CD4(+) T cells. Importantly, in vivo depletion of pDCs revealed that this subset was dispensable for either maintenance or regulation of the hepatic Th2 effector response during acute S. mansoni infection. Our data provides strong evidence that S. mansoni infection favors the establishment of an immunogenic, rather than tolerogenic, liver microenvironment that conditions cDCs to initiate and maintain Th2 immunity in the context of ongoing antigen exposure.

Estrogen Signaling Modulates Allergic Inflammation and Contributes to Sex Differences in Asthma

Asthma is a chronic airway inflammatory disease that affects ~300 million people worldwide. It is characterized by airway constriction that leads to wheezing, coughing, and shortness of breath. The most common treatments are corticosteroids and β2-adrenergic receptor antagonists, which target inflammation and airway smooth muscle constriction, respectively. The incidence and severity of asthma is greater in women than in men, and women are more prone to develop corticosteroid-resistant or “hard-to-treat” asthma. Puberty, menstruation, pregnancy, menopause, and oral contraceptives are known to contribute to disease outcome in women, suggesting a role for estrogen and other hormones impacting allergic inflammation. Currently, the mechanisms underlying these sex differences are poorly understood, although the effect of sex hormones, such as estrogen, on allergic inflammation is gaining interest. Asthma presents as a heterogeneous disease. In typical Th2-type allergic asthma, interleukin (IL)-4 and IL-13 predominate, driving IgE production and recruitment of eosinophils into the lungs. Chronic Th2-inflammation in the lung results in structural changes and activation of multiple immune cell types, leading to a deterioration of lung function over time. Most immune cells express estrogen receptors (ERα, ERβ, or the membrane-bound G-protein-coupled ER) to varying degrees and can respond to the hormone. Together these receptors have demonstrated the capacity to regulate a spectrum of immune functions, including adhesion, migration, survival, wound healing, and antibody and cytokine production. This review will cover the current understanding of estrogen signaling in allergic inflammation and discuss how this signaling may contribute to sex differences in asthma and allergy.

Dendritic cell and epithelial cell interactions at the origin of murine asthma

Dendritic cells (DCs) are ideally placed in the airways and lungs to capture inhaled allergens. Different subsets of DCs perform different tasks. Migratory conventional DCs (cDCs) expressing CD11b mediate Th2 priming to respiratory allergens, whereas cDCs expressing CD103 mediate tolerance to them. Monocyte-derived DCs are poorly migratory antigen-presenting cells that mainly produce proinflammatory chemokines and are necessary for maintaining allergic airway inflammation once initiated. The function of the airway DC network is closely controlled by cytokines released from airway epithelial cells. Airway epithelial cells react to pathogen-associated molecular patterns and damage-associated molecular patterns released on allergen inhalation by producing pro-Th2 polarizing cytokines and chemokines that attract and activate DCs. This conceptual framework of epithelial and DC collaboration is very helpful in explaining the process of allergic sensitization and how this is influenced by genetics and environment.

Blockage of thymic stromal lymphopoietin signaling improves acute lung injury in mice by regulating pulmonary dendritic cells

OBJECTIVES

To investigate the effects of blockage of thymic stromal lymphopoietin (TSLP) signaling by TSLP receptor (TSLPR)-immunoglobulin (Ig) on acute lung injury (ALI) induced by lipopolysaccharide (LPS).

METHODS

C57BL/6 mice received TSLPR-Ig or controlled-Ig before being induced ALI. Lung wet/dry (W/D) weight ratio was recorded. Neutrophil number and albumin concentration of bronchoalveolar lavages fluids (BALF) were determined. Besides, bone marrow dendritic cells (BMDCs) were separated and cultured with medium, TSLP, TSLP plus TSLPR-Ig or TSLP plus controlled-Ig. Protein expression levels of TSLP in lung tissues, phosphorylation extracellular regulated protein kinases (pERK) 1/2, p38, and signal transducers and activators of transcription (STAT) 3 in BMDCs were analyzed using Western blotting. Expression of CD40, CD80 and CD86 on pulmonary DCs and BMDCs was determined using flow cytometry (FCM).

RESULTS

The W/D ratio, neutrophil number and albumin concentration were significantly decreased in the TSLPR-Ig group compared with the controlled-Ig and model group. Moreover, there was a noticeable decrease in CD40, CD80 or CD86 expression by TSLPR-Ig on both pulmonary DCs and BMDCs. The protein levels of TSLP, pERK1 and STAT3 were significantly decreased by TSLPR-Ig. However, no significant differences were found in p38 and pERK2.

CONCLUSION

These results suggest that TSLP may be involved in ALI, and blockage of TSLP signaling using TSLPR-Ig improves ALI at least in part by regulation of DCs functions. The underling downstream signaling mediated by TSLP might be associated with activating the ERK1 and STAT3 signaling pathway.

Amelioration of allergic airway inflammation in mice by regulatory IL-35 through dampening inflammatory dendritic cells

BACKGROUND

IL-35, a new member of the IL-12 family, is an inhibitory cytokine produced by regulatory T and B lymphocytes that play a suppressive role in the inflammatory diseases. This study focuses on the cellular mechanism regulating the anti-inflammatory activity of IL-35 in asthmatic mice.

METHODS

Ovalbumin-induced asthmatic and humanized asthmatic mice were adopted to evaluate the in vivo anti-inflammatory activities of IL-35. For monitoring the airway, Penh value (% baseline) was measured using a whole-body plethysmograph.

RESULTS

In this study using ovalbumin-induced asthmatic mice, we observed that intraperitoneal injection of IL-35 during the allergen sensitization stage was more efficient than administration in the challenge stage for the amelioration of airway hyper-responsiveness. This was reflected by the significantly reduced concentration of asthma-related Th2 cytokines IL-5 and IL-13, as well as eosinophil counts in bronchoalveolar lavage fluid (all P < 0.05). IL-35 also significantly attenuated the accumulation of migratory CD11b+CD103(-) dendritic cells (DC) in the mediastinal lymph node (mLN) and lung of mice (all P < 0.05). IL-35 markedly inhibited the ovalbumin-induced conversion of recruited monocytes into inflammatory DC, which were then substantially reduced in mLN to cause less T-cell proliferation (all P < 0.05). Further study using the humanized asthmatic murine model also indicated human IL-35 exhibited a regulatory impact on allergic asthma.

CONCLUSION

Our findings suggest that IL-35 can act as a crucial regulatory cytokine to inhibit the development of allergic airway inflammation via suppressing the formation of inflammatory DC at the inflammatory site and their accumulation in the draining lymph nodes.

Expression of adenosine receptors in monocytes from patients with bronchial asthma

Adenosine is generated from adenosine triphosphate, which is released by stressed and damaged cells. Adenosine levels are significantly increased in patients with bronchial asthma (BA) and mediate mast cell degranulation and bronchoconstriction. Over the last decade, increasing evidence has shown that adenosine can modulate the innate immune response during monocytes differentiation towards mature myeloid cells. These adenosine-differentiated myeloid cells, characterized by co-expression of monocytes/macrophages and dendritic cell markers such as CD14 and CD209, produce high levels of pro-inflammatory cytokines, thus contributing to the pathogenesis of BA and chronic obstructive pulmonary disease. We found that expression of ADORA2A and ADORA2B are increased in monocytes obtained from patients with BA, and are associated with the generation of CD14(pos)CD209(pos) pro-inflammatory cells. A positive correlation between expression of ADORA2B and IL-6 was identified in human monocytes and may explain the increased expression of IL-6 mRNA in asthmatics. Taken together, our results suggest that monocyte-specific expression of A2 adenosine receptors plays an important role in pro-inflammatory activation of human monocytes, thus contributing to the progression of asthma.

DNGR-1(+) dendritic cells are located in meningeal membrane and choroid plexus of the noninjured brain

The role and different origin of brain myeloid cells in the brain is central to understanding how the central nervous system (CNS) responds to injury. C-type lectin receptor family 9, member A (DNGR-1/CLEC9A) is a marker of specific DC subsets that share functional similarities, such as CD8α(+) DCs in lymphoid tissues and CD103(+) CD11b(low) DCs in peripheral tissues. Here, we analyzed the presence of DNGR-1 in DCs present in the mouse brain (bDCs). Dngr-1/Clec9a mRNA is expressed mainly in the meningeal membranes and choroid plexus (m/Ch), and its expression is enhanced by fms-like tyrosine kinase 3 ligand (Flt3L), a cytokine involved in DC homeostasis. Using Clec9a(egfp/egfp) mice, we show that Flt3L induces accumulation of DNGR-1-EGFP(+) cells in the brain m/Ch. Most of these cells also express major histocompatibility complex class II (MHCII) molecules. We also observed an increase in specific markers of cDC CD8α+ cells such as Batf-3 and Irf-8, but not of costimulatory molecules such as Cd80 and Cd86, indicating an immature phenotype for these bDCs in the noninjured brain. The presence of DNGR-1 in the brain provides a potential marker for the study of this specific brain cell subset. Knowledge and targeting of brain antigen presenting cells (APCs) has implications for the fight against brain diseases such as neuroinflammation-based neurodegenerative diseases, microbe-induced encephalitis, and brain tumors such as gliomas.

The B subunit of Escherichia coli heat-labile toxin alters the development and antigen-presenting capacity of dendritic cells

Escherichia coli's heat-labile enterotoxin (Etx) and its non-toxic B subunit (EtxB) have been characterized as adjuvants capable of enhancing T cell responses to co-administered antigen. Here, we investigate the direct effect of intravenously administered EtxB on the size of the dendritic and myeloid cell populations in spleen. EtxB treatment appears to enhance the development and turnover of dendritic and myeloid cells from precursors within the spleen. EtxB treatment also gives a dendritic cell (DC) population with higher viability and lower activation status based on the reduced expression of MHC-II, CD80 and CD86. In this respect, the in vivo effect of EtxB differs from that of the highly inflammatory mediator lipopolysaccharide. In in vitro bone marrow cultures, EtxB treatment was also found to enhance the development of DC from precursors dependent on Flt3L. In terms of the in vivo effect of EtxB on CD4 and CD8 T cell responses in mice, the interaction of EtxB directly with DC was demonstrated following conditional depletion of CD11c(+) DC. In summary, all results are consistent with EtxB displaying adjuvant ability by enhancing the turnover of DC in spleen, leading to newly mature myeloid and DC in spleen, thereby increasing DC capacity to perform as antigen-presenting cells on encounter with T cells.

Re-defining the unique roles for eosinophils in allergic respiratory inflammation

The role of eosinophils in the progression and resolution of allergic respiratory inflammation is poorly defined despite the commonality of their presence and in some cases their use as a biomarker for disease severity and/or symptom control. However, this ambiguity belies the wealth of insights that have recently been gained through the use of eosinophil-deficient/attenuated strains of mice that have demonstrated novel immunoregulatory and remodelling/repair functions for these cells in the lung following allergen provocation. Specifically, studies of eosinophil-deficient mice suggest that eosinophils contribute to events occurring in the lungs following allergen provocation at several key moments: (i) the initiating phase of events leading to Th2-polarized pulmonary inflammation, (ii) the suppression Th1/Th17 pathways in lung-draining lymph nodes, (iii) the recruitment of effector Th2 T cells to the lung, and finally, (iv) mechanisms of inflammatory resolution that re-establish pulmonary homoeostasis. These suggested functions have recently been confirmed and expanded upon using allergen provocation of an inducible eosinophil-deficient strain of mice (iPHIL) that demonstrated an eosinophil-dependent mechanism(s) leading to Th2 dominated immune responses in the presence of eosinophils in contrast to neutrophilic as well as mixed Th1/Th17/Th2 variant phenotypes in the absence of eosinophils. These findings highlighted that eosinophils are not exclusively downstream mediators controlled by T cells, dendritic cells (DC) and/or innate lymphocytic cells (ILC2). Instead, eosinophils appear to be more aptly described as significant contributors in complex interrelated pathways that lead to pulmonary inflammation and subsequently promote resolution and the re-establishment of homoeostatic baseline. In this review, we summarize and put into the context the evolving hypotheses that are now expanding our understanding of the roles eosinophils likely have in the lung following allergen provocation.

Dendritic cell-bound IgE functions to restrain allergic inflammation at mucosal sites

Antigen-mediated cross-linking of Immunoglobulin E (IgE) bound to mast cells/basophils via FcɛRI, the high affinity IgE Fc-receptor, is a well-known trigger of allergy. In humans, but not mice, dendritic cells (DCs) also express FcɛRI that is constitutively occupied with IgE. In contrast to mast cells/basophils, the consequences of IgE/FcɛRI signals for DC function remain poorly understood. We show that humanized mice that express FcɛRI on DCs carry IgE like non-allergic humans and do not develop spontaneous allergies. Antigen-specific IgE/FcɛRI cross-linking fails to induce maturation or production of inflammatory mediators in human DCs and FcɛRI-humanized DCs. Furthermore, conferring expression of FcɛRI to DCs decreases the severity of food allergy and asthma in disease-relevant models suggesting anti-inflammatory IgE/FcɛRI signals. Consistent with the improved clinical parameters in vivo, antigen-specific IgE/FcɛRI cross-linking on papain or lipopolysaccharide-stimulated DCs inhibits the production of pro-inflammatory cytokines and chemokines. Migration assays confirm that the IgE-dependent decrease in cytokine production results in diminished recruitment of mast cell progenitors; providing a mechanistic explanation for the reduced mast cell-dependent allergic phenotype observed in FcɛRI-humanized mice. Our study demonstrates a novel immune regulatory function of IgE and proposes that DC-intrinsic IgE signals serve as a feedback mechanism to restrain allergic tissue inflammation.

Mesenchymal stem cells abrogate experimental asthma by altering dendritic cell function

Mesenchymal stem cells (MSCs) have been investigated in the treatment of numerous autoimmune diseases. However, the immune properties of MSCs on the development of asthma have remained to be fully elucidated. Airway dendritic cells (DCs) have an important role in the pathogenesis of allergic asthma, and disrupting their function may be a novel therapeutic approach. The present study used a mouse model of asthma to demonstrate that transplantation of MSCs suppressed features of asthma by targeting the function of lung myeloid DCs. MSCs suppressed the maturation and migration of lung DCs to the mediastinal lymph nodes, and thereby reducing the allergen-specific T helper type 2 (Th2) response in the nodes. In addition, MSC-treated DCs were less potent in activating naive and effector Th2 cells and the capacity of producing chemokine (C-C motif) ligand 17 (CCL17) and CCL22, which are chemokines attracting Th2 cells, to the airways was reduced. These results supported that MSCs may be used as a potential treatment for asthma.

Airway epithelium interactions with aeroallergens: role of secreted cytokines and chemokines in innate immunity

Airway epithelial cells are the first line of defense against the constituents of the inhaled air, which include allergens, pathogens, pollutants, and toxic compounds. The epithelium not only prevents the penetration of these foreign substances into the interstitium, but also senses their presence and informs the organism’s immune system of the impending assault. The epithelium accomplishes the latter through the release of inflammatory cytokines and chemokines that recruit and activate innate immune cells at the site of assault. These epithelial responses aim to eliminate the inhaled foreign substances and minimize their detrimental effects to the organism. Quite frequently, however, the innate immune responses of the epithelium to inhaled substances lead to chronic and high level release of pro-inflammatory mediators that may mediate the lung pathology seen in asthma. The interactions of airway epithelial cells with allergens will be discussed with particular focus on interactions-mediated epithelial release of cytokines and chemokines and their role in the immune response. As pollutants are other major constituents of inhaled air, we will also discuss how pollutants may alter the responses of airway epithelial cells to allergens.

Identification of Pathogenic Cardiac CD11c+ Macrophages in Nod1-Mediated Acute Coronary Arteritis

OBJECTIVE

Nod1 is an intracellular pattern recognition receptor for bacterial peptidoglycan fragments. We previously reported that a synthetic Nod1 ligand, FK565, induced acute coronary arteritis in mice similar to that of Kawasaki disease. However, the molecular mechanisms underlying this characteristic inflammation have remained elusive.

APPROACH AND RESULTS

We found that CD11c(+)MHC class II(+) cells accumulated in the heart of FK565-treated mice before arteritis development. Morphological features and gene expression signatures of the cardiac CD11c(+)MHC class II(+) cells suggested that this population is closely related to macrophages, and thus, we designated them cardiac CD11c(+) macrophages. Nod1 in nonhematopoietic cells, rather than hematopoietic cells, was required for the increase of cardiac CD11c(+) macrophages and arteritis development. Among nonhematopoietic cells, cardiac endothelial cells produced a large amount of chemokines in response to FK565. Endothelial cell-specific blockade of Nod1 signaling suppressed FK565-induced expression of these chemokines, accumulation of cardiac CD11c(+) macrophages, and subsequent coronary arteritis development. We also found that CCR2(+)Ly6C(hi) inflammatory monocytes in peripheral blood supplied precursors of cardiac CD11c(+) macrophages. CCR2-deficient mice or pertussis toxin-treated mice exhibited decreased numbers of cardiac CD11c(+) macrophages and reduced arteritis.

CONCLUSIONS

These results suggest that Ly6C(hi) monocytes are recruited to FK565-activated endothelial cells to generate cardiac CD11c(+) macrophages, which play a pivotal role in the pathogenesis of acute coronary arteritis.

A critical role for dendritic cells in the evolution of IL-1β-mediated murine airway disease

Chronic airway inflammation and fibrosis, known as airway remodeling, are defining features of chronic obstructive pulmonary disease and are refractory to current treatments. How and whether chronic inflammation contributes to airway fibrosis remain controversial. In this study, we use a model of chronic obstructive pulmonary disease airway disease utilizing adenoviral delivery of IL-1β to determine that adaptive T cell immunity is required for airway remodeling because mice deficient in α/β T cells (tcra(-/-)) are protected. Dendritic cells (DCs) accumulate around chronic obstructive pulmonary disease airways and are critical to prime adaptive immunity, but they have not been shown to directly influence airway remodeling. We show that DC depletion or deficiency in the crucial DC chemokine receptor ccr6 both protect from adenoviral IL-1β-induced airway adaptive T cell immune responses and fibrosis in mice. These results provide evidence that chronic airway inflammation, mediated by accumulation of α/β T cells and driven by DCs, is critical to airway fibrosis.

The immunology of asthma

Asthma is a common disease that affects 300 million people worldwide. Given the large number of eosinophils in the airways of people with mild asthma, and verified by data from murine models, asthma was long considered the hallmark T helper type 2 (TH2) disease of the airways. It is now known that some asthmatic inflammation is neutrophilic, controlled by the TH17 subset of helper T cells, and that some eosinophilic inflammation is controlled by type 2 innate lymphoid cells (ILC2 cells) acting together with basophils. Here we discuss results from in-depth molecular studies of mouse models in light of the results from the first clinical trials targeting key cytokines in humans and describe the extraordinary heterogeneity of asthma.

Myeloid dendritic cells type 2 after allergen inhalation in asthmatic subjects

BACKGROUND

Dendritic cells (DCs) are professional antigen-presenting cells that mediate the response to inhaled allergen. A major division in DC ontogeny exists between myeloid DCs (mDCs) and plasmacytoid DCs (pDCs). A subtype of mDC expressing thrombomodulin, termed myeloid DCs type 2 (mDC2s), has been identified in both the circulation and lung and has recently been suggested to have a role in allergic asthma.

OBJECTIVE

To investigate changes in circulating and sputum mDC2s after allergen inhalation in subjects with asthma.

METHODS

Peripheral blood and induced sputum were obtained before and 3, 7, and 24 h after inhalation of diluent and allergen from allergic asthmatic subjects who develop both allergen-induced early- and late-phase responses. mDC2s were measured by flow cytometry. Soluble BDCA-3 (thrombomodulin) was measured in sputum by ELISA.

RESULTS

The number of sputum mDC2s significantly increased 24 h after allergen challenge compared with diluent. The expression of BDCA-3 on sputum mDCs also increased, albeit non-significantly, at 7 and 24 h after allergen. Soluble BDCA-3 in sputum and the number of circulating mDC2s were not different between allergen and diluent.

CONCLUSIONS AND CLINICAL RELEVANCE

Myeloid DCs type 2 (mDC2s) increase in the sputum of subjects with asthma after allergen challenge, suggesting this subtype of mDC is involved in the regulation of allergen responses in the lung.

The varieties of immunological experience: of pathogens, stress, and dendritic cells

In the 40 years since their discovery, dendritic cells (DCs) have been recognized as central players in immune regulation. DCs sense microbial stimuli through pathogen-recognition receptors (PRRs) and decode, integrate, and present information derived from such stimuli to T cells, thus stimulating immune responses. DCs can also regulate the quality of immune responses. Several functionally specialized subsets of DCs exist, but DCs also display functional plasticity in response to diverse stimuli. In addition to sensing pathogens via PRRs, emerging evidence suggests that DCs can also sense stress signals, such as amino acid starvation, through ancient stress and nutrient sensing pathways, to stimulate adaptive immunity. Here, I discuss these exciting advances in the context of a historic perspective on the discovery of DCs and their role in immune regulation. I conclude with a discussion of emerging areas in DC biology in the systems immunology era and suggest that the impact of DCs on immunity can be usefully contextualized in a hierarchy-of-organization model in which DCs, their receptors and signaling networks, cell-cell interactions, tissue microenvironment, and the host macroenvironment represent different levels of the hierarchy. Immunity or tolerance can then be represented as a complex function of each of these hierarchies.

Role of growth arrest-specific gene 6 in the development of fungal allergic airway disease in mice

Growth arrest-specific gene (Gas)6 is a secreted vitamin K-dependent protein with pleiotropic effects via activation of receptor tyrosine kinase Tyro3, Axl, and Mertk receptors, but little is known about its role in allergic airway disease. We investigated the role of Gas6 in the development of fungal allergic airway disease in mice. The immune response was evaluated in Gas6-deficient (Gas6-/-) and wild-type (WT) mice and in recombinant Gas6-treated WT mice during Aspergillus fumigatus-induced allergic airway disease. Gas6 plasma levels were significantly elevated in adult clinical asthma of all severities compared with subjects without asthma. In a murine model of fungal allergic airway disease, increased protein expression of Axl and Mertk were observed in the lung. Airway hyperresponsiveness (AHR), whole lung Th2 cytokine levels, goblet cell metaplasia, and peribronchial fibrosis were ameliorated in Gas6-/- mice compared with WT mice with fungal allergic airway disease. Intranasal Gas6 administration into WT mice had a divergent effect on airway inflammation and AHR. Specifically, a total dose of 2 μg of exogenous Gas6 (i.e., low dose) significantly increased whole lung Th2 cytokine levels and subsequent AHR, whereas a total dose of 7 μg of exogenous Gas6 (i.e., high dose) significantly suppressed Th1 and Th2 cytokines and AHR compared with appropriate control groups. Mechanistically, Gas6 promoted Th2 activation via its highest affinity receptor Axl expressed by myeloid DCs. Intranasal administration of Gas6 consistently exacerbated airway remodeling compared with control WT groups. These results demonstrate that Gas6 enhances several features of fungal allergic airway disease.

The role of dendritic cells and monocytes in the maintenance and loss of respiratory tolerance

Promoting tolerance to inhaled antigens is an active area of study with the potential to benefit the millions of Americans currently suffering from respiratory allergies and asthma. Interestingly, not all individuals with atopy are symptomatic, arguing that sensitization alone does not lead to an allergic clinical phenotype. Respiratory dendritic cells (rDCs), classically associated with inducing inflammatory responses, can actively promote tolerance. Tolerance can be broken when inflammatory stimuli, including viral infections and other environmental exposures, inhibit rDC-mediated tolerance by allowing innocuous antigen to be presented to initiate type-2 immunity. Importantly, rDCs are composed of multiple subsets, each with a unique response to an inhaled antigen that can lead to either tolerance or inflammation. In this review, we will discuss how rDC subsets actively maintain tolerance or, alternatively, break tolerance in response to environmental cues.

Historic overview of allergy research in the Netherlands

Research in allergy has a long history in the Netherlands, although the relation with immunology has not always been appreciated. In many aspects Dutch researchers have made major contribution in allergy research. This ranges from the first characterization of house dust mite as an important allergen, the first characterization of human Th2 and Th1 T cell clones, to the development of diagnostic test systems. In this overview Aalberse and Knol have made an overview of the major contributions of Dutch immunologists in allergy.

Small interfering RNA against CD86 during allergen challenge blocks experimental allergic asthma

Background

CD86-CD28 interaction has been suggested as the principal costimulatory pathway for the activation and differentiation of naïve T cells in allergic inflammation. However, it remains uncertain whether this pathway also has an essential role in the effector phase. We sought to determine the contribution of CD86 on dendritic cells in the reactivation of allergen-specific Th2 cells.

Methods

We investigated the effects of the downregulation of CD86 by short interfering RNAs (siRNAs) on Th2 cytokine production in the effector phase in vitro and on asthma phenotypes in ovalbumin (OVA)-sensitized and -challenged mice.

Results

Treatment of bone marrow-derived dendritic cells (BMDCs) with CD86 siRNA attenuated LPS-induced upregulation of CD86. CD86 siRNA treatment impaired BMDCs’ ability to activate OVA-specific Th2 cells. Intratracheal administration of CD86 siRNA during OVA challenge downregulated CD86 expression in the airway mucosa. CD86 siRNA treatment ameliorated OVA-induced airway eosinophilia, airway hyperresponsiveness, and the elevations of OVA-specific IgE in the sera and IL-5, IL-13, and CCL17 in the bronchoalveolar lavage fluid, but not the goblet cell hyperplasia.

Conclusion

These results suggest that local administration of CD86 siRNA during the effector phase ameliorates lines of asthma phenotypes. Targeting airway dendritic cells with siRNA suppresses airway inflammation and hyperresponsiveness in an experimental model of allergic asthma.

Distinct dendritic cell subsets actively induce Th2 polarization

The mechanisms by which dendritic cells induce Th2 polarization (DC(Th2) cells) have been controversial. Many have argued that DC(Th2) cells are not a distinct functional DC subset, but rather, DC-induced polarization of Th2 cells is a default pathway that occurs in the absence of inflammatory signals leading to DC-induced polarization of Th1/Th17 cells. However, recent studies demonstrate that distinct subsets of tissue DCs actively polarize Th2 cells after stimulation with type-2 inducing stimuli. DC(Th2) cells development is marked by the upregulation of specific transcription factors, cell surface molecules, and cytokines. These findings counter previous hypotheses that Th2 skewing by DCs is a passive response and support a model in which DCs are actively programmed to induce Th2 differentiation.