Background
Signaling through histamine receptors on dendritic cells (DCs) may be involved in the effector phase of peanut‐induced intestinal anaphylaxis.
Objectives
The objective of this study was to ...determine the role of histamine H1 (H1R) and H4 receptors (H4R) in intestinal allergic responses in a model of peanut allergy.
Methods
Balb/c mice were sensitized and challenged with peanut. During the challenge phase, mice were treated orally with the H1R antagonist, loratadine, and/or the H4R antagonist, JNJ7777120. Bone marrow‐derived DCs (BMDCs) were adoptively transferred to nonsensitized WT mice. Symptoms, intestinal inflammation, and mesenteric lymph node and intestine mucosal DCs were assessed. Effects of the drugs on DC chemotaxis, calcium mobilization, and antigen‐presenting cell function were measured.
Results
Treatment with loratadine or JNJ7777120 individually partially suppressed the development of diarrhea and intestinal inflammation and decreased the numbers of DCs in the mesenteric lymph nodes and lamina propria. Combined treatment with both drugs prevented the development of diarrhea and intestinal inflammation. In vitro, the combination suppressed DC antigen‐presenting cell function to T helper cells and DC calcium mobilization and chemotaxis to histamine.
Conclusion
Blockade of both H1R and H4R in the challenge phase had additive effects in preventing the intestinal consequences of peanut sensitization and challenge. These effects were mediated through the limitation of mesenteric lymph node and intestinal DC accumulation and function. Identification of this histamine H1R/H4R‐DC‐CD4+ T‐cell axis provides new insights into the development of peanut‐induced intestinal allergic responses and for prevention and treatment of peanut allergy.
Background
The role of CD8 T lymphocytes in the pathogenesis of asthma is not well understood. We investigated whether a subset of IL‐13‐producing BLT1‐positive CD8 T lymphocytes are present in ...asthmatic airways and are associated with impaired lung function.
Methods
Bronchoalveolar lavage (BAL) cells were obtained from asthmatic (n = 39) and healthy control (n = 28) subjects. Cells were stimulated with phorbol ester and ionomycin in the presence of brefeldin A and stained for CD8, BLT1, and intracellular IL‐13. The frequency of IL‐13‐producing BLT1‐positive CD8 T lymphocytes was compared between the two groups and related to lung function, serum IgE levels, and reticular basement membrane (RBM) thickness.
Results
A subset of CD8 T lymphocytes expressing BLT1 and producing IL‐13 were detected in the airways of all asthmatic subjects. The frequency of this subset among recovered lymphocytes was significantly higher in the airways of asthmatic subjects compared with controls (mean ± SEM: 16.2 ± 1.4 vs 5.3 ± 0.5, respectively, P < 0.001) and correlated positively with serum IgE levels and RBM thickness. More importantly, the frequency of CD8 T lymphocytes co‐expressing BLT1 and IL‐13 was inversely related to FEV1 and FEF25–75 percent predicted values (P < 0.001).
Conclusions
A subset of CD8 T lymphocytes expressing BLT1 and producing IL‐13 is present in the airways of asthmatics. The accumulation of these cells is associated with airway obstruction, suggesting that they may play a significant pathogenic role in bronchial asthma.
To study the mechanisms and kinetics underlying the development of increased airway responsiveness (AR) after allergic sensitization, animal models have been invaluable. Using barometric whole-body ...plethysmography and increases in enhanced pause (Penh) as an index of airway obstruction, we measured responses to inhaled methacholine in conscious, unrestrained mice after sensitization and airway challenge with ovalbumin (OVA). Sensitized and challenged animals had significantly increased AR to aerosolized methacholine compared with control animals. AR measured as Penh was associated with increased IgE production and eosinophil lung infiltration. In a separate approach we confirmed the involvement of the lower airways in the response to aerosolized methacholine using tracheotomized mice. Increases in Penh values after methacholine challenge were also correlated with increased intrapleural pressure, measured via an esophageal tube. Lastly, mice demonstrating AR using a noninvasive technique also demonstrated increased pulmonary resistance responses to aerosolized methacholine when measured using an invasive technique the following day in the same animals. The increases in Penh values were inhibited by pretreatment of the mice with a beta 2-agonist. These data indicate that measurement of AR to inhaled methacholine by barometric whole-body plethysmography is a valid indicator of airway hyperresponsiveness after allergic sensitization in mice. The measurement of AR in unrestrained, conscious animals provides new opportunities to evaluate the mechanisms and kinetics underlying the development and maintenance of airway hyperresponsiveness and to assess various therapeutic interventions.
Summary
Background
Prostaglandin D2 (PGD2) plays an important role in allergic inflammation. The PGD2 receptor, CRTH2, is expressed on basophils, eosinophils, and Th2 lymphocytes and mediates ...chemotactic activity.
Objective
To define the role of CRTH2 in allergen‐induced nasal responses in a mouse model of allergic rhinitis (AR), a potent, selective CRTH2 receptor antagonist, ARRY‐063 was administered in a model of allergic rhinitis in mice.
Methods
ARRY‐063 was administered orally to ovalbumin (OVA) sensitized and challenged mice. To assess nasal obstruction, respiratory frequency (RF) was monitored by whole‐body plethysmography immediately after the 4th challenge (early‐phase response, EPR) and 24 h after the 6th challenge (late‐phase response, LPR). Nasal resistance (RNA) was also measured in the LPR. PGD2 was administered with or without OVA to determine the effect of PGD2 on nasal responsiveness. Cytokine levels and histopathological changes in nasal tissue were analysed.
Results
Instillation of PGD2 in the nose of sensitized mice together with a low concentration of OVA induced both an EPR and LPR. Treatment with the CRTH2 receptor antagonist prevented the decreases in RF seen immediately following the 4th challenge of sensitized mice (EPR). In the LPR, decreases in RF and increases in RNA were also prevented by antagonist treatment associated with reduced cytokine levels and inflammation in nasal tissues.
Conclusions
These data identify PGD2 as a mediator of both the EPR and LPR in this model of AR and suggest that antagonism of CRTH2 prevents the development of both the EPR and LPR as well as nasal inflammation.
Bronchial asthma is a chronic inflammatory airway disease defined by reversible airway obstruction and non‐specific airway hyper‐responsiveness (AHR). Although profound insights have been made into ...the pathophysiology of asthma, the exact mechanisms inducing and regulating the disease are still not fully understood. Yet, it is generally accepted that the pathological changes in asthma are induced by a chronic inflammatory process which is characterized by infiltration of the bronchial mucosa with lymphocytes and eosinophils, increased mucus production and submucosal edema. There is increasing evidence that an imbalance in the T‐helper (Th) cell response of genetically predisposed individuals to common environmental antigens plays a pivotal role in the pathogenesis of allergic bronchial asthma and other atopic disorders. Following allergic sensitization, T cells from atopic patients tend to produce elevated levels of Th2‐type cytokines, especially interleukin (IL)‐4, IL‐13, IL‐5 and IL‐6, which induce and regulate IgE production and eosinophil airway infiltration. In this review, the role of Th2‐type cytokines, IgE and airway eosinophils in the induction of airway inflammation and AHR is discussed, and animal studies of asthma and AHR, mainly in rodents will be considered. A better understanding of the underlying mechanisms leading to asthma pathology may yield more specific immunological strategies for the treatment of this disease which is increasing worldwide.
I thank the many colleagues in the laboratory of Dr. E. W. Gelfand, National Jewish Research Center, Denver CO, USA, for continuous support and encouragement. E.H. is a fellow of the Deutsche Forschungsgemeinschaft (DFG Ha 2162/1‐1 and 2‐1).
The importance of IgE in airway inflammation and development of AHR in allergen-sensitized mice has been compared and contrasted in different models of sensitization and challenge. Using different ...modes of sensitization in normal and genetically manipulated mice after anti-IgE treatment, we have been able to distinguish the role of IgE under these different conditions. Striking differences in the three sensitization protocols were delineated in terms of the role of allergen-specific IgE, extent of eosinophilic airway inflammation, and development of AHR (Table 1). The highest levels of IgE and eosinophil infiltration (approximately 20-fold increases) were achieved after systemic sensitization with allergen (plus adjuvant) followed by repeated airway challenge. Passive sensitization with allergen-specific IgE followed by limited airway challenge induced a modest eosinophilic inflammatory response in the airways despite high levels of serum IgE. Exposure to allergen exclusively via the airways also resulted in a modest serum IgE response and a limited eosinophilic inflammatory response (approximately fourfold increases). Under all of these conditions, inhibition of IL-5-mediated eosinophilic airway inflammation was associated with attenuation of AHR. In contrast, the differences in the responses to the different modes of allergen exposure were associated with differences in the requirements for IgE in the development of AHR (Table 1). In the two models associated with mild eosinophil infiltration (passive sensitization and exclusive airway exposure), IgE was required for the development of AHR but did not substantially enhance airway inflammation on its own. However, IgE-allergen interaction was able to enhance T-cell function in vitro and induce T-cell expansion in vivo. In mice systemically sensitized and challenged via the airways, IgE (or IgE-mediated mast-cell activation) was not required for T-cell activation, eosinophilic inflammation and activation in the airways, or development of AHR. This was most clearly seen in B-cell-deficient and mast-cell-deficient, low-IgE-responder mouse strains (B6, B10) and in anti-IgE-treated high-IgEresponder mice (BALB/c). At the same time, we confirmed the importance of IgE in the induction of immediate-type hypersensitivity (mast-cell activation, immediate cutaneous hypersensitivity, passive cutaneous and systemic anaphylaxis). These differences were also highlighted by the means used to detect altered airway function. Passive sensitization and limited airway challenge or exclusive airway exposure to allergen over 10 days elicited changes in airway function that could be detected only in tracheal smooth-muscle preparations exposed to EFS. In contrast, systemic sensitization followed by repeated airway challenge resulted not only in changes in the contractile response to EFS but also in increased responsiveness to inhaled MCh. Thus, these results distinguish not only the differential involvement of IgE and eosinophil numbers but also their contribution to the readouts used to monitor airway function. Based on these studies, we conclude that IgE plays an important role in the development of airway inflammation and AHR under conditions in which limited IL-5-mediated eosinophilic airway infiltration is induced. In conditions where a robust eosinophilic inflammation of the airways is elicited, IgE (and IgE-mediated mast-cell activation) does not appear to be essential for airway inflammation and the development of AHR, detected as increased responsiveness to inhaled MCh. These findings reveal the potential importance of differential targeting in the treatment of allergic diseases with a predominance of IgE-mediated symptoms, e.g., allergic rhinitis and conjunctivitis, where anti-IgE may be an effective therapy, compared to those diseases with a predominant inflammatory component, e.g., AHR in atopic bronchial asthma, where anti-inflammatory or anti-IL-5 therapy may be more beneficial.
Background
Asthma is a complex lung disease resulting from the interplay of genetic and environmental factors. To understand the molecular changes that occur during the development of allergic asthma ...without genetic and environmental confounders, an experimental model of allergic asthma in mice was used. Our goals were to (1) identify changes at the small molecule level due to allergen exposure, (2) determine perturbed pathways due to disease, and (3) determine whether small molecule changes correlate with lung function.
Methods
In this experimental model of allergic asthma, matched bronchoalveolar lavage (BAL) fluid and plasma were collected from three groups of C57BL6 mice (control vs sensitized and/or challenged with ovalbumin, n=3‐5/group) 6 hour, 24 hour, and 48 hour after the last challenge. Samples were analyzed using liquid chromatography‐mass spectrometry‐based metabolomics. Airway hyper‐responsiveness (AHR) measurements and differential cell counts were performed.
Results
In total, 398 and 368 dysregulated metabolites in the BAL fluid and plasma of sensitized and challenged mice were identified, respectively. These belonged to four, interconnected pathways relevant to asthma pathogenesis: sphingolipid metabolism (P=6.6×10−5), arginine and proline metabolism (P=1.12×10−7), glycerophospholipid metabolism (P=1.3×10−10), and the neurotrophin signaling pathway (P=7.0×10−6). Furthermore, within the arginine and proline metabolism pathway, a positive correlation between urea‐1‐carboxylate and AHR was observed in plasma metabolites, while ornithine revealed a reciprocal effect. In addition, agmatine positively correlated with lung eosinophilia.
Conclusion
These findings point to potential targets and pathways that may be central to asthma pathogenesis and can serve as novel therapeutic targets.
Different strains of mice exhibit different degrees of airway hyperresponsiveness after sensitization to and airway challenge with ovalbumin. Antibody responses in BALB/c mice far exceeded those in ...C57BL/6 mice; in contrast, although responsiveness to methacholine was much higher in the BALB/c mice, the number of eosinophils in the bronchoalveolar lavage fluid was higher in C57BL/6 animals. Sensitized and challenged BALB/c mice developed increases in lung resistance and decreases in dynamic compliance after methacholine or 5-hydroxytryptamine inhalation. C57BL/6 mice only exhibited significant levels of responsiveness when dynamic compliance was monitored in response to inhaled 5-hydroxytryptamine. Eosinophils accumulated in the peribronchial and peripheral lung tissue in BALB/c mice but were distributed diffusely in the peripheral lung tissue of C57BL/6 mice. Thus, in addition to differences in antibody responses and cholinergic agonist reactivity, differences in the responses of large and small airways may reflect the selective distribution of eosinophils in lung tissue.
Respiratory virus infections can trigger exacerbations of asthma and may also contribute to allergic sensitization to aeroallergens and the development of asthma. Conversely, atopy may predispose to ...more severe virus-induced airway disease. The animal models reviewed in this article support the hypothesis that respiratory virus infections can promote allergic sensitization and the development of asthma. Respiratory viruses can prevent induction of tolerance and enhance sensitization to inhaled allergens resulting in increased airway inflammation and airway hyperresponsiveness. Probable mechanisms involved in this enhanced sensitization are increased permeability of the airway mucosa to allergens and recruitment of dendritic cells to the respiratory epithelium during acute infection. Factors involved in augmenting the consequences of allergic airway sensitization appear to be T-cells, especially CD8+ T-cells as regulators of this process, interleukin-5 as a pivotal cytokine for eosinophilic airway inflammation and eosinophils themselves as effector cells triggering airway hyperresponsiveness. Depending on the timing of allergen exposure, respiratory virus infections which elicit a significant type 1 T-helper cell cytokine response may also downregulate allergic sensitization. Respiratory virus infections in animals previously sensitized to aeroallergens result in prolonged increases in inflammation and airway responsiveness, indicating that critical interactions between immune responses to allergen sensitization and the responses to infection can lead to more severe disease. Taken together, animal models have proved valuable in generating a number of plausible pathogenetic concepts, and can be used to address a host of unresolved questions regarding the immunology of respiratory virus infections, allergic sensitization and asthma.
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