Dendritic cells as regulators of the immune response to inhaled allergen: recent findings in animal models of asthma

IL-23 plays a significant role in the augmentation of particulate matter-mediated allergic airway inflammation

It has been recently that particulate matter (PM) exposure increases the risk and exacerbation of allergic asthma. However, the underlying mechanisms and factors associated with increased allergic responses remain elusive. We evaluated IL-23 and IL-23R (receptor) expression, as well as changes in the asthmatic phenotype in mice administered PM and a low dose of house dust mite (HDM). Next, changes in the phenotype and immune responses were evaluated after intranasal administration of anti-IL-23 antibody during co-exposure to PM and low-dose HDM. We also performed in vitro experiments to investigate the effect of IL-23. IL-23 expression was significantly increased in Epcam+CD45- and CD11c+ cells, while that of IL-23R was increased in Epcam+CD45- cells only in mice administered PM and low-dose HDM. Administration of anti-IL-23 antibody led to decreased airway hyperresponsiveness, eosinophils, and activation of dendritic cells, reduced populations of Th2 Th17, ILC2, the level of IL-33 and granulocyte-macrophage colony-stimulating factor (GM-CSF). Inhibition of IL-23 in PM and low-dose HDM stimulated airway epithelial cell line resulted in decreased IL-33, GM-CSF and affected ILC2 and the activation of BMDCs. PM augmented the phenotypes and immunologic responses of asthma even at low doses of HDM. Interestingly, IL-23 affected immunological changes in airway epithelial cells.

The Association between Tobacco Smoke and Serum Immunoglobulin E Levels in Korean Adults

Objective Smoking is common in patients with allergic diseases. The aim of this study was to evaluate the cross-sectional association between the current smoking status and total and specific Immunoglobulin E (IgE) levels in Korean adults. Methods Data were obtained from the 2010 Korean National Health and Nutrition Examination Survey, a national cross-sectional study. We analyzed the data of subjects whose smoking status and serum IgE levels were of acceptable quality. Results A total of 1,963 subjects (1,118 never smokers, 340 ex-smokers, and 505 current smokers) were included. The total IgE levels and specific IgE levels to house dust mite Dermatophagoides farinae (Df), cockroach, and dog allergens in never smokers were significantly (p<0.0001) lower than in ex-smokers or current smokers. After adjusting for other variables, current smokers independently had significantly higher levels of total IgE and cockroach-specific IgE than ex-smokers or never smokers. The proportions of subjects with total IgE ≥150 kU/L and specific IgE ≥0.35 kU/L to Df-specific IgE were significantly (p value for trend <0.05) increased in ex-smokers and current smokers. The total IgE levels and IgE levels specific to Df, cockroaches, and dogs significantly (p value for trend <0.05) and proportionally increased with increasing numbers of cigarettes smoked daily. Conclusion Smoking was associated with elevated total IgE levels and IgE levels specific to Df, cockroach, and dog allergens in a cumulative, dose-dependent manner. Furthermore, current smoking status was an independent risk factor for elevated total IgE levels and IgE levels specific to cockroach allergen.

The effects of targeted deletion of cannabinoid receptors CB1 and CB2 on intranasal sensitization and challenge with adjuvant-free ovalbumin

The mechanisms by which cannabinoid receptors CB(1) and CB(2) modulate immune function are not fully elucidated. Critical tools for the determination of the role of both receptors in the immune system are CB(1)/CB(2) double null mice (CB(1)/CB(2) null), and previous studies have shown that CB(1)/CB(2) null mice exhibit exaggerated responses to various immunological stimuli. The objective of these studies was to determine the magnitude to which CB(1)/CB(2) null mice responded to the respiratory allergen ovalbumin (OVA) as compared with wild-type C57BL/6 mice. The authors determined that in the absence of adjuvant, both wild-type and CB(1)/CB(2) null mice mounted a marked response to intranasally instilled OVA as assessed by inflammatory cell infiltrate in the bronchoalveolar lavage fluid (BALF), eosinophilia, induction of mucous cell metaplasia, and IgE production. Many of the endpoints measured in response to OVA were similar in wild-type versus CB(1)/CB(2) null mice, with exceptions being modest reductions in OVA-induced IgE and attenuation of BALF neutrophilia in CB(1)/CB(2) null mice as compared with wild-type mice. These results suggest that T-cell responses are not universally exaggerated in CB(1)/CB(2) null mice.

Thymic stromal lymphopoietin, OX40-ligand, and interleukin-25 in allergic responses

Allergic diseases are often triggered by environmental allergens that induce dominant type 2 immune responses, characterized by the infiltrated T-helper type 2 (TH2) lymphocytes, eosinophils, and elevated TH2 cytokines. In addition to TH2 type immune responses, epithelial stress and injury linked to tissue remodelling are often observed, suggesting that epithelial cells may play important role in regulating allergic responses. Dendritic cells (DCs), the professional antigen-presenting cells with the capabilities of sampling allergens, are considered as the key player on instructing TH2 immune responses. Whether inflamed epithelium can regulate innate immunity, such as macrophages and DCs, which in turn instructs adaptive immunity has long been hypothesized. Studies of thymic stromal lymphopoietin (TSLP), an epithelial cells-derived cytokine, that can strongly activate DCs, provide important evidences that the epithelial barrier can trigger allergic diseases by regulating immune responses. The finding that OX40/OX40Ligand (OX40L) interactions are the molecular trigger responsible for the induction and maintenance of TH2 responses by TSLP-activated DCs provides a plausible molecular explanation for TSLP-mediated allergy. Recent progresses in characterizing the pro-inflammatory IL-17 cytokine family have added an additional layer of complexity on the regulation of allergic inflammation. TSLP-DCs can induce a robust expansion of TH2 memory cells and strengthen functional attributes by up-regulating their surface expression of IL-17RB (IL-25R), the receptor for cytokine IL-17E (IL-25), a distinct member of IL-17 cytokine family. IL-17E (also known as IL-25) produced by epithelial cells, and other innate cells, such as eosinphils, basophils, and mast cells, are shown to regulate adaptive immunity by enhancing TH2 cytokine productions. These exciting findings expand our knowledge of the complex immunological cascades that result in allergic inflammation and may provide novel therapeutic approaches for the treatment of allergic diseases.

Distinct responses of lung and spleen dendritic cells to the TLR9 agonist CpG oligodeoxynucleotide

Dendritic cells (DCs) sense various components of invading pathogens via pattern recognition receptors such as TLRs. CpG oligodeoxynucleotides (ODNs), which mimic bacterial DNA, inhibit allergic airways disease and promote responses in the spleen to bacterial components. Because many TLR agonists are currently being tested for potential therapeutic effects, it is important to characterize the expression and function of TLRs in different tissues. We show that both myeloid and plasmacytoid DCs in the spleen express TLR9, the receptor for CpG ODNs, but lung DCs show no detectable expression in either subset. TLR4 expression in contrast was detected on both lung and spleen DCs. LPS was superior to CpG ODN in increasing the allostimulatory potential of lung DCs and their expression of CD40. However, both agonists efficiently stimulated spleen DCs. CpG ODNs administered to mice efficiently inhibited Th2 cytokine production both in the lung draining lymph node and in the spleen. Surprisingly, inhibition of Th2 cytokine production was evident despite high levels of expression of GATA-3 and additional transcription factors that regulate Th2 responses. Although in the spleen CpG ODNs induced IL-6, a key cytokine induced via TLR9-MyD88 signaling, no IL-6 was detectable in lung LN cells. These studies show for the first time that lung DCs lack TLR9 expression, but, despite this deficiency, CpG ODNs induce potent inhibitory effects on Th2 cytokine production in the lung without inducing expression of the proinflammatory cytokine, IL-6, which has been linked to chronic diseases in the lung and the gut.

Maintenance and polarization of human TH2 central memory T cells by thymic stromal lymphopoietin-activated dendritic cells

The identity of TH2 memory cells and the mechanism regulating their maintenance during allergic inflammation remain elusive. We report that circulated human CD4+ T cells expressing the prostaglandin D2 receptor (CRTH2) are TH2 central memory T cells, characterized by their phenotype, TH2 cytokine production, gene-expression profile, and the ability to respond to allergens. Only dendritic cells (DCs) activated by thymic stromal lymphopoietin (TSLP) can induce a robust expansion of CRTH2+CD4+ TH2 memory cells, while maintaining their central memory phenotype and TH2 commitments. CRTH2+CD4+ TH2 memory cells activated by TSLP-DCs undergo further TH2 polarization and express cystatin A, Charcot-Leydon crystal protein, and prostaglandin D2 synthase, implying their broader roles in allergic inflammation. Infiltrated CRTH2+CD4+ TH2 effector memory T cells in skin lesion of atopic dermatitis were associated with activated DCs, suggesting that TSLP-DCs play important roles not only in TH2 priming, but also in the maintenance and further polarization of TH2 central memory cells in allergic diseases.

Leukocyte infiltration of the periarterial space of the lung after allergen provocation in a rat asthma model

The periarterial space has recently been described and its physiological and pathophysiological role during inflammatory and allergic reactions has been reviewed. The present studies used a light-/electron-microscopic approach to characterize the periarterial space in an asthma model in Brown Norway rats. After repeated sensitization with ovalbumin and heat-killed Bordetella pertussis bacilli, airway challenge was carried out after 1 further week. Four or 24 h after challenge, rats were fixed by perfusion or instillation and processed for microscopy. Several periarterial capillaries and connective tissue characterized the tissue between small pulmonary arteries, bronchioles and alveolar septa. Additionally, a partly pronounced interstitial edema was seen independent of the kind of fixation. Not only small arteries but also arterioles and venules were partly surrounded by edematous fluid already visible by light microscopy. Within the connective tissue and within the periarterial fluid, numerous leukocytes, predominantly eosinophils, were found. However, leukocytes were detected only rarely in the vascular lumen. Only sporadically were eosinophils seen in the wall of small arteries or venules. Eosinophils transmigrating the endothelium of capillaries or arterioles were not visible 4 or 24 h after challenge. Thus, granulocytes transmigrate in the periarterial space very rapidly or even earlier than 4 h after challenge. The location of transmigration in the periarterial space needs further investigation.

Intranasal exposure to bacterial superantigens induces airway inflammation in HLA class II transgenic mice

Staphylococcus aureus is widely prevalent in the nasopharynges of healthy individuals (carriers) but can also cause serious infections. S. aureus can elaborate a variety of superantigen exotoxins in "carrier" or "pathogenic" states. Streptococcus pyogenes can also colonize the nasopharynx and elaborate superantigens. Unlike the acute effects of superantigen exotoxins absorbed through the gut or vaginal mucosa, little is known regarding the pathogenesis of superantigens entering through the intranasal route. In the current study, we evaluated the local and systemic effects of staphylococcal enterotoxin B (SEB) and streptococcal pyrogenic exotoxin A (SPEA) delivered through the intranasal route. Superantigens were administered intranasally on multiple occasions, and experimental animals were sacrificed on day 8 for experimental analyses. SEB-induced airway inflammation was more pronounced for HLA-DR3 transgenic mice than for BALB/c mice, consistent with bacterial superantigens binding more efficiently to human than murine major histocompatibility complex class II. The nature of the airway inflammation in HLA-DR3 mice was determined by the concentration of SEB applied intranasally. Low concentrations (20 ng) induced eosinophilic airway inflammation as well as eosinophil degranulation, whereas intranasal exposure to higher concentrations (2,000 ng) resulted in neutrophilic airway inflammation, permanent airway destruction, toxic shock, and mortality. SEB-induced eosinophilic inflammatory response was enhanced in signal transducer and activator of transcription (STAT)-4-deficient HLA-DQ8 transgenic mice with defective interleukin-12 signaling. Intranasal administration of SPEA induced airway inflammation and systemic immune activation in HLA-DQ8 transgenic mice. In conclusion, repeated chronic intranasal exposure to bacterial superantigens causes airway inflammation and systemic immune activation.

Effects of various anti-asthmatic agents on mite allergen-pulsed murine bone marrow-derived dendritic cells

BACKGROUND

Dendritic cells (DCs) play an important role in the immune response and are critically involved in asthma. beta2-agonists could potentially exacerbate type 2 T helper (Th2) cell-mediated immune response.

OBJECTIVES

To determine the effects of various anti-asthmatic agents on DCs function both in vitro and in vivo.

METHODS

Murine bone marrow-derived DCs were pulsed with mite allergen in the presence of pranlukast, salbutamol, salmeterol or fluticasone. These DCs were then inoculated intranasally into naïve mice to induce allergic airway inflammation in vivo.

RESULTS

Pranlukast reduced IL-10 and increased IL-12, while fluticasone reduced both IL-10 and IL-12 production by mite allergen-pulsed DCs. Allergic airway inflammation in pranlukast- and fluticasone-treated and mite allergen pulsed DCs-harbouring mice was attenuated and such response was associated with inhibition of Th2 response in the airway. Salbutamol did not alter cytokine production, while salmeterol reduced IL-12 production by mite allergen-pulsed DCs. Lung pathology in beta2-agonist-harbouring mice was comparable with those of mite allergen-pulsed DCs-harbouring mice.

CONCLUSIONS

Our results indicate that leukotriene receptor antagonists and corticosteroids inhibit DCs-induced Th2 skewed immune response, and that short- and long-acting beta2-agonists do not modify DCs-induced allergic airway inflammation.

A mouse model for in vivo tracking of the major dust mite allergen Der p 2 after inhalation

Inhaled environmental antigens, i.e. allergens, cause allergic symptoms in millions of patients worldwide. As little is known about the fate of an allergen upon inhalation, we addressed this issue for a major dust mite allergen, Der p 2. First, a model for Der p 2-sensitization was established in C57BL/6 J mice, in which sensitized mice mounted a Der p 2-specific IgE-response with eosinophilic lung inflammation after allergen challenge in the airways. In this model, we applied recombinant Der p 2 carrying a novel C-terminal tetrapeptide Sel-tag enabling labelling with the gamma-emitting radionuclide 75Se at a single selenocysteine residue ([75Se]Der p 2). In vivo tracking of intratracheally administered [75Se]Der p 2 using whole-body autoradiography revealed that [75Se]Der p 2-derived radioactivity persisted in the lungs of sensitized mice as long as 48 h. Radioactivity was also detected in kidneys, liver and in enlarged lung-associated lymph nodes. Interestingly, a larger proportion of radioactivity was found in the lungs of sensitized compared with nonsensitized mice 24 h after intratracheal instillation of [75Se]Der p 2. A radioactive protein corresponding to intact Der p 2 could only be detected in the lungs, whereas [75Se]Der p 2-derived radioactivity was recovered in known selenoproteins both in lung and other organs. Hence, using the recently developed Sel-tag method in a mouse model for Der p 2-sensitization, we could track the fate of an inhaled allergen in vivo. Based upon our findings, we conclude that the inflammatory state of the lung influences the rate of metabolism and clearance of Der p 2. Thus, an allergic response to the inhaled allergen may lead to prolonged retention of Der p 2 in the lung.

Short-term cigarette smoke exposure enhances allergic airway inflammation in mice

RATIONALE

Epidemiologic studies suggest that tobacco smoke contributes to the prevalence and occurrence of exacerbations in asthma. The effect of active smoking in adolescents with atopy is poorly understood.

OBJECTIVES

We developed an experimental model to investigate the influence of smoking on antigen-induced airway inflammation and airway responsiveness in mice that were previously sensitized.

METHODS

Ovalbumin (OVA)-sensitized BALB/c mice were exposed to air or mainstream smoke (5 days/week) and to phosphate-buffered saline (PBS) or OVA aerosol (3 times/week) for 2 weeks (n = 8 for each group).

RESULTS

Airway responsiveness to intravenously injected carbachol was increased (p < 0.05) in smoke- and OVA-exposed mice compared with all other groups. There was an additive effect of smoke and OVA exposure on total cell numbers, macrophages, and dendritic cells in bronchoalveolar lavage fluid and on CD4+ and CD8+ T lymphocytes and dendritic cells in lung tissue (p < 0.05 compared with mice exposed to smoke and PBS and to mice exposed to air and OVA). Concurrent smoke and OVA exposure augmented OVA-specific IgE in serum compared with air and OVA exposure. In lavage fluid supernatant, eotaxin was increased in air- and OVA-exposed mice. The further increase observed in the group exposed to both OVA and cigarette smoke came close to formal significance (p = 0.06). Thymus- and activation-regulated chemokine was augmented in mice exposed to either smoke or OVA, without additional effect.

CONCLUSIONS

Our data indicate that acute concurrent exposure to allergen and mainstream cigarette smoke enhances airway inflammation and airway responsiveness in previously sensitized mice.

The Periarterial Space in the Lung: Its Important Role in Lung Edema, Transplantation, and Microbial or Allergic Inflammation

In mammal lungs different compartments for leukocytes can be identified during health and disease, e.g. lung interstitium, bronchoalveolar space, the epithelium and lamina propria of the air-conducting part. A so far neglected compartment is the space around the branches of the pulmonary arteries, characterized by a unique architecture of capillaries running in parallel to the pulmonary artery. This compartment - the periarterial space - is described and its physiological and pathophysiological role reviewed. The periarterial space is infiltrated by different leukocyte subsets during edema formation in the early stages of a lung transplant rejection and, in particular, during inflammatory and allergic reactions. The periarterial compartment seems to be of major relevance in all these situations.

The lung cytokine microenvironment influences molecular events in the lymph nodes during Th1 and Th2 respiratory mucosal sensitization to antigen in vivo

Originally defined by their patterns of cytokine production, Th1 and Th2 cells have been described more recently to express other genes differentially as well, at least in vitro. In this study we compared the expression of Th1- and Th2-associated genes directly during in vivo sensitization to ovalbumin (OVA) in Th1- and Th2-polarized models of airways inflammation. Th1-polarized airway inflammation was achieved by the intranasal instillation of adenoviral vectors (Ad) encoding granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin (IL)-12, followed by daily aerosolizations of OVA; instillation of Ad/GM-CSF alone with OVA aerosolization led to Th2-polarized responses. Lymph nodes were obtained at various time-points, RNA extracted, and analysed by real-time quantitative polymerase chain reaction (PCR). Consistent with reports from in vitro and human studies, mice undergoing Th1-polarized inflammation showed preferential expression of the transcription factor t-bet, the chemokines IFN-gamma inducible protein (IP)-10 and macrophage inflammatory protein 1 alpha (MIP-1-alpha), and the chemokine receptor CCR5. In contrast, the transcription factor GATA-3, the chemokines I-309 and thymus and activation regulated chemokine (TARC), and the chemokine receptors CCR3 and CCR4 were preferentially expressed in the Th2 model. Importantly, we also show that Ad/transgene expression remains compartmentalized to the lung after intranasal instillation. Flow cytometric analysis of lung myeloid dendritic cells indicated that B7.1 was expressed more strongly in the Th1 model than in the Th2 model. These studies provide a direct comparison of gene expression in in vivo Th1- and Th2-polarized models, and demonstrate that molecular events in the lymph nodes can be altered fundamentally by cytokine expression at distant mucosal sites.

Inflammation in allergic asthma: initiating events, immunological response and risk factors

Allergic asthma affects 155 million people worldwide. Currently, it is a disease that can be controlled by diverse therapeutic approaches but that cannot be cured. This means that asthma is one of the most expensive diseases for healthcare systems in developed countries. Efficient prevention strategies are therefore greatly needed to reduce both individual morbidity and national economic burdens. This requires a detailed knowledge of the immunological and physiological mechanisms involved in asthma. This review synthesizes current understanding about the immunobiology of IgE-mediated asthma. It discusses the initiating events, the main immunological and inflammatory processes, and addresses the importance of risk factors in the development and maintenance of allergic diseases. Finally, it integrates these concepts in a theoretical causal model for atopic asthma.

Expression of genes for B7-H3 and other T cell ligands by nasal epithelial cells during differentiation and activation

Epithelial cells of the human respiratory tract express human leukocyte antigen (HLA) and the costimulatory molecules B7-1 and B7-2. Little is known, however, about the constitutive expression of genes encoding for the more recently identified members of the B7 homolog family of costimulatory molecules or about the influence of cellular differentiation and cytokines on their activity or on that of HLA or B7-1 and B7-2. Human nasal epithelial (HNE) cells were grown at the air-liquid interface (ALI) for 2 or 21 days to model in vivo conditions. Expression of genes for HLA-B and HLA-DR1 increased during mucociliary differentiation during this period and became more similar to HNE cells obtained fresh by brush biopsy from nasal turbinates. Gene transcripts for B7-H3 and B7-H2 were abundantly expressed in cells cultured at the ALI, but neither their activities nor that of B7-2 was significantly altered during differentiation. IFN-gamma and TNF-alpha upregulated mRNA encoding for both HLA molecules, but not for the B7 molecules. This study describes, for the first time, the expression of B7-H3 and B7-H2 by HNE cells and thus expands the range of potential costimulatory signals through which these cells may interact with activated mucosal T lymphocytes. In addition, the results suggest that the extent of mucociliary differentiation of cultured cells may influence this capability.

Do mouse models of allergic asthma mimic clinical disease?

Experimental mouse models of allergic asthma established almost 10 years ago offered new opportunities to study disease pathogenesis and to develop new therapeutics. These models focused on the factors governing the allergic immune response, on modeling clinical behavior of allergic asthma, and led to insights into pulmonary pathophysiology. Although mouse models rarely completely reproduce all the features of human disease, after sensitization and respiratory tract challenges with antigen, wild-type mice develop a clinical syndrome that closely resembles allergic asthma, characterized by eosinophilic lung inflammation, airway hyperresponsiveness (AHR), increased IgE, mucus hypersecretion, and eventually, airway remodeling. There are, however, differences between mouse and human physiology that threaten to limit the value of mouse models. Three examples of such differences relate to both clinical manifestations of disease and underlying pathogenesis. First, in contrast to patients who have increased methacholine-induced AHR even when they are symptom-free, mice exhibit only transient methacholine-induced AHR following allergen exposure. Second, chronic allergen exposure in patients leads to chronic allergic asthma, whereas repeated exposures in sensitized mice causes suppression of disease. Third, IgE and mast cells, in humans, mediate early- and late-phase allergic responses, though both are unnecessary for the generation of allergic asthma in mice. Taken together, these observations suggest that mouse models of allergic asthma are not exact replicas of human disease and thus, question the validity of these models. However, observations from mouse models of allergic asthma support many existing paradigms, although some novel discoveries in mice have yet to be verified in patients. This review presents an overview of the clinical aspects of disease in mouse models of allergic asthma emphasizing (1). the factors influencing the pathophysiological responses during the initiation and perpetuation of disease, (2). the utility of mouse models for studying clinical manifestations of disease, and (3). the applicability of mouse models for testing new treatments for allergic asthma.

Animal models for asthma: controversial aspects and unsolved problems

The incidence of asthma in children and adults is continuously increasing in the developed countries. Its pathophysiology is still not yet clarified in sufficient detail. Despite a large number of animal models for asthma (mainly rodents), these only partly mimic the situation in humans. Some examples of limitations of using the mouse as an animal model for asthma will be discussed and directions of future research outlined.

Bordetella bronchiseptica persists in the nasal cavities of mice and triggers early delivery of dendritic cells in the lymph nodes draining the lower and upper respiratory tract

Early after the intranasal instillation of Bordetella bronchiseptica into mice, not only are mature dendritic leukocytes recovered from lung parenchyma and bronchoalveolar lavage fluid but their numbers are also increased in the mediastinal lymph nodes and the nasal mucosa-associated lymphoid tissue. Later during the infectious process, the bacteria persist mainly in the nasal cavity.

Perivascular capillaries in the lung: an important but neglected vascular bed in immune reactions?

In allergic and inflammatory immune reactions of the respiratory tract, leukocytes migrate into the different compartments of the lung. The air space can easily be sampled by means of bronchoalveolar lavage. However, the subset composition in the bronchial wall or the lung interstitium often differs considerably from that of the bronchoalveolar lavage fluid. A further compartment involved in very heterogeneous immune reactions in the lung has thus far not been mentioned: the periarterial space. In numerous experiments in different species with virus, bacteria, fungi, or allergens, there was not only a leukocyte infiltration of the bronchial lamina propria but also infiltration around branches of the pulmonary artery. This thus far neglected compartment consists of a different type of capillary. Thus it is important not to overlook this area in studies on allergic or inflammatory immune reactions of the lung.

Targeting epidermal Langerhans cells by epidermal powder immunization

Immune reactions to foreign or self-antigens lead to protective immunity and, sometimes, immune disorders such as allergies and autoimmune diseases. Antigen presenting cells (APC) including epidermal Langerhans cells (LCs) play an important role in the course and outcome of the immune reactions. Epidermal powder immunization (EPI) is a technology that offers a tool to manipulate the LCs and the potential to harness the immune reactions towards prevention and treatment of infectious diseases and immune disorders.