Prevention of house dust mite induced allergic airways disease in mice through immune tolerance

Allergic airways disease is a consequence of a Th2 response to an allergen leading to a series of manifestations such as production of allergen-specific IgE, inflammatory infiltrates in the airways, and airway hyper-reactivity (AHR). Several strategies have been reported for tolerance induction to allergens leading to protection from allergic airways disease. We now show that CD4 blockade at the time of house dust mite sensitization induces antigen-specific tolerance in mice. Tolerance induction is robust enough to be effective in pre-sensitized animals, even in those where AHR was pre-established. Tolerant mice are protected from airways eosinophilia, Th2 lung infiltration, and AHR. Furthermore, anti-CD4 treated mice remain immune competent to mount immune responses, including Th2, to unrelated antigens. Our findings, therefore, describe a strategy for tolerance induction potentially applicable to other immunogenic proteins besides allergens.     

Acinetobacter baumannii infection inhibits airway eosinophilia and lung pathology in a mouse model of allergic asthma

Allergic asthma is a dysregulation of the immune system which leads to the development of Th2 responses to innocuous antigens (allergens). Some infections and microbial components can re-direct the immune response toward the Th1 response, or induce regulatory T cells to suppress the Th2 response, thereby inhibiting the development of allergic asthma. Since Acinetobacter baumannii infection can modulate lung cellular and cytokine responses, we studied the effect of A. baumannii in modulating airway eosinophilia in a mouse model of allergic asthma. Ovalbumin (OVA)-sensitized mice were treated with live A. baumannii or phosphate buffered saline (PBS), then intranasally challenged with OVA. Compared to PBS, A. baumannii treatment significantly reduced pulmonary Th2 cytokine and chemokine responses to OVA challenge. More importantly, the airway inflammation in A. baumannii-treated mice was strongly suppressed, as seen by the significant reduction of the proportion and the total number of eosinophils in the bronchoalveolar lavage fluid. In addition, A. baumannii-treated mice diminished lung mucus overproduction and pathology. However, A. baumannii treatment did not significantly alter systemic immune responses to OVA. Serum OVA-specific IgE, IgG1 and IgG2a levels were comparable between A. baumannii- and PBS-treated mice, and tracheobronchial lymph node cells from both treatment groups produced similar levels of Th1 and Th2 cytokines in response to in vitro OVA stimulation. Moreover, it appears that TLR-4 and IFN-γ were not directly involved in the A. baumannii-induced suppression of airway eosinophilia. Our results suggest that A. baumannii inhibits allergic airway inflammation by direct suppression of local pulmonary Th2 cytokine responses to the allergen.     

Airway house dust extract exposures modify allergen-induced airway hypersensitivity responses by TLR4-dependent and independent pathways

TLR ligands and other allergen-nonspecific immunostimulatory molecules are ubiquitous in ambient air and have profound modulatory activities in animal models of allergic asthma. However, several of these molecules have been shown to promote exaggerated Th2-biased airway hypersensitivity responses (AHRs), whereas others attenuate the asthmatic phenotype. Therefore, it has proven difficult to extrapolate experimental results with purified molecules toward a more general understanding of the allergen-nonspecific immunomodulatory influence of living environments on the natural history of allergic asthma. These investigations determined how regular and intermittent airway exposures to an unpurified, but sterile house dust extract standard (HDEst) affected the OVA-specific AHR and immune status of previously Th2-sensitized mice. Low-dose daily and high-dose intermittent HDEst exposures modulated ongoing AHRs considerably, reducing eosinophil recruitment and methacholine responsiveness, while increasing neutrophilic inflammation. However, only daily airway delivery of low-dose HDEst attenuated OVA-specific Th2 cytokine production and Th2-biased AHRs to allergen challenge 1 mo later. Finally, whereas LPS mimicked many of the immunomodulatory characteristics of HDEst in this murine asthma model, daily airway HDEst delivery was highly effective in attenuating the AHR of OVA/alum-sensitized TLR4-deficient mice. Taken together, these investigations provide direct evidence that living environments contain allergen-nonspecific immunostimulatory molecules that influence the airway hypersensitivity status of allergen-sensitized mice by TLR4-dependent and independent mechanisms.     

Airway IgG counteracts specific and bystander allergen-triggered pulmonary inflammation by a mechanism dependent on Fc gamma R and IFN-gamma

Besides IgE, the Ab isotype that gives rise to sensitization and allergic asthma, the immune response to common inhalant allergens also includes IgG. Increased serum titers of allergen-specific IgG, induced spontaneously or by allergen vaccination, have been implicated in protection against asthma. To verify the interference of topical IgG with the allergen-triggered eosinophilic airway inflammation that underlies asthma, sensitized mice were treated by intranasal instillation of specific IgG, followed by allergen challenge. This treatment strongly reduced eosinophilic inflammation and goblet cell metaplasia, and increased Th1 reactivity and IFN-gamma levels in bronchoalveolar lavage fluid. In contrast, inflammatory responses were unaffected in IFN-gamma-deficient mice or when applying F(ab')(2). Although dependent on specific allergen-IgG interaction, inflammation triggered by bystander allergens was similarly repressed. Perseverance of inflammation repression, apparent after secondary allergen challenge, and increased allergen capture by alveolar macrophages further characterized the consequences of topical IgG application. These results assign a novel protective function to anti-allergen IgG namely at the local level interference with the inflammatory cascade, resulting in repression of allergic inflammation through an FcgammaR- and IFN-gamma-dependent mechanism. Furthermore, these results provide a basis for topical immunotherapy of asthma by direct delivery of anti-allergen IgG to the airways.     

Proteinase-activated receptor-2 promotes allergic sensitization to an inhaled antigen through a TNF-mediated pathway

The reason why particular inhaled Ags induce allergic sensitization while others lead to immune tolerance is unclear. Along with a genetic predisposition to atopy, intrinsic characteristics of these Ags must be important. A common characteristic of many allergens is that they either possess proteinase activity or are inhaled in particles rich in proteinases. Many allergens, such as house dust mite and cockroach allergens, have the potential to activate the proteinase-activated receptor (PAR)-2. In this study, we report that PAR-2 activation in the airways at the same time as exposure to inhaled Ags induces allergic sensitization, whereas exposure to Ag alone induces tolerance. BALB/c mice were administered OVA with a PAR-2 activating peptide intranasally. Upon allergen re-exposure mice developed airway inflammation and airway hyperresponsiveness, as well as OVA-specific T cells with a Th2 cytokine profile when restimulated with OVA in vitro. Conversely, mice given OVA alone or OVA with a PAR-2 control peptide developed tolerance. These tolerant mice did not develop airway inflammation or airway hyperresponsiveness, and developed OVA-specific T cells that secreted high levels of IL-10 when restimulated with OVA in vitro. Furthermore, pulmonary dendritic cell trafficking was altered in mice following intranasal PAR-2 activation. Finally, we showed that PAR-2-mediated allergic sensitization was TNF-dependent. Thus, PAR-2 activation in the airways could be a critical factor in the development of allergic sensitization following mucosal exposure to allergens with serine proteinase activity. Interfering with this pathway may prove to be useful for the prevention or treatment of allergic diseases.     

Immunosuppression in Early Postnatal Days Induces Persistent and Allergen-Specific Immune Tolerance to Asthma in Adult Mice

Bronchial asthma is a chronic airway inflammatory condition with high morbidity, and effective treatments for asthma are limited. Allergen-specific immunotherapy can only induce peripheral immune tolerance and is not sustainable. Exploring new therapeutic strategies is of great clinical importance. Recombinant adenovirus (rAdV) was used as a vector to make cells expressing cytotoxic T lymphocyte-associated antigen-4-immunoglobulin (CTLA4Ig) a soluble CTLA4 immunoglobulin fusion protein. Dendritic cells (DCs) were modified using the rAdVs together with allergens. Then these modified DCs were transplanted to mice before allergen sensitization. The persistence and specificity of immune tolerance were evaluated in mice challenged with asthma allergens at 3 and 7 months. DCs modified by CTLA4Ig showed increased IL-10 secretion, decreased IL-12 secretion, and T cell stimulation in vitro. Mice treated with these DCs in the early neonatal period developed tolerance against the allergens that were used to induce asthma in the adult stage. Asthma symptoms, lung damage, airway reactivity, and inflammatory response all improved. Humoral immunity indices showed that this therapeutic strategy strongly suppressed mice immune responses and was maintained for as long as 7 months. Furthermore, allergen cross-sensitization and challenge experiments demonstrated that this immune tolerance was allergen-specific. Treatment with CTLA4Ig modified DCs in the early neonatal period, inducing persistent and allergen-specific immune tolerance to asthma in adult mice. Our results suggest that it may be possible to develop a vaccine for asthma.     

Airway exposure levels of lipopolysaccharide determine type 1 versus type 2 experimental asthma

Allergic asthma is characterized by airway inflammation initiated by adaptive immune responses to aeroallergens. Recent data suggest that severe asthma may be a different form of asthma rather than an increase in asthma symptoms and that innate immune responses to LPS can modulate adaptive immune responses to allergens. In this study, we evaluated the hypothesis that airway exposure to different doses of LPS induces different form of asthma. Our study showed that neutrophilic inflammation and IFN-gamma expression were higher in induced sputum from severe asthma patients than from mild to moderate asthmatics. Animal experiments indicated that allergen sensitization with low-dose LPS (0.1 microg) induced type 2 asthma phenotypes, i.e., airway hyperresponsiveness, eosinophilic inflammation, and allergen-specific IgE up-regulation. In contrast, allergen sensitization with high-dose LPS (10 microg) induced asthma phenotypes, i.e., airway hyperresponsiveness and noneosinophilic inflammation that were not developed in IFN-gamma-deficient mice, but unaffected in the absence of IL-4. During the allergen sensitization period, TNF-alpha expression was found to be enhanced by both low- and high-dose LPS, whereas IL-12 expression was only enhanced by high-dose LPS. Interestingly, the asthma phenotypes induced by low-dose LPS, but not by high-dose LPS, were completely inhibited in TNF-alpha receptor-deficient mice, whereas the asthma phenotypes induced by high-dose LPS were abolished in the homozygous null mutation of the STAT4 gene. These findings suggest that airway exposure levels of LPS induces different forms of asthma that are type 1 and type 2 asthma phenotypes by high and low LPS levels, respectively.     

Induction of prolonged asthma tolerance by IL-10-differentiated dendritic cells: differential impact on airway hyperresponsiveness and the Th2 immunoinflammatory response

IL-10-differentiated dendritic cells (DC10s) can prevent allergen sensitization and reverse the asthma phenotype in mice with established disease. However, little is known about the time-frames over which this tolerance is effective. We report that at 2 wk after i.p. or transtracheal delivery of 1 × 10(6) OVA-, but not house dust mite- presenting, DC10s to OVA-asthmatic mice, significant diminution of airway hyperresponsiveness (AHR) was first apparent, whereas AHR was abrogated between 3 and 10 wk posttreatment. At 13 wk, AHR returned to pretreatment levels but could again be reversed by DC10 retreatment. The impact of a single DC10 treatment on airway eosinophil and Th2 cytokine responses to recall OVA challenge, and on OVA-specific IgE/IgG1 responses, was substantial at 3 wk posttreatment, but progressively increased thereafter, such that at 8 mo, airway eosinophil and Th2 responses to recall allergen challenge remained ～85-95% suppressed relative to saline-treated asthmatic mice. Four biweekly DC10 treatments, whether transtracheal or i.p., reduced all asthma parameters to near background by 8 wk, whereas s.c. DC10 treatments did not affect AHR but did reduce the airway Th2 responses (i.v. DC10 had no discernible effects). Repeated challenge of the DC10-treated mice with aerosolized OVA (100 μg/ml) did not reverse tolerance, but treatment with the indoleamine-2,3-dioxygenase antagonist 1-methyltryptophan or neutralizing anti-IL-10R from days 12 to 21 after DC10 therapy partially reversed tolerance (Th2 cytokine responses, but not AHR). These findings indicate that DC10-induced Th2 tolerance in asthmatic animals is long lived, but that DC10s employ distinct mechanisms to affect AHR versus Th2 immunoinflammatory parameters.     

A protease-activated pathway underlying Th cell type 2 activation and allergic lung disease

The respiratory allergens that induce experimental Th cell type 2-dependent allergic lung inflammation may be grouped into two functional classes. One class of allergens, in this study termed type I, requires priming with adjuvants remote from the lung to overcome airway tolerogenic mechanisms that ordinarily preclude allergic responses to inhaled Ags. In contrast, the other, or type II, allergen class requires neither remote priming nor additional adjuvants to overcome airway tolerance and elicit robust allergic lung disease. In this study, we show in an experimental model that diverse type II allergens share in common proteolytic activity that is both necessary and sufficient for overcoming airway tolerance and induction of pulmonary allergic disease. Inactivated protease and protease-free Ag fragments showed no allergenic potency, demonstrating that only active protease acting on endogenous substrates was essential. Furthermore, induction of airway tolerance could be aborted and allergic lung disease established by simply adding purified protease to a type I allergen. Thus, exogenous proteases are common to type II allergens and may be generally required to overcome the innate resistance of the airway to Th cell type 2 activation and allergic inflammation, raising concern for their potential contribution to diseases such as asthma.     

The danger signal, extracellular ATP, is a sensor for an airborne allergen and triggers IL-33 release and innate Th2-type responses

The molecular mechanisms underlying the initiation of innate and adaptive proallergic Th2-type responses in the airways are not well understood. IL-33 is a new member of the IL-1 family of molecules that is implicated in Th2-type responses. Airway exposure of naive mice to a common environmental aeroallergen, the fungus Alternaria alternata, induces rapid release of IL-33 into the airway lumen, followed by innate Th2-type responses. Biologically active IL-33 is constitutively stored in the nuclei of human airway epithelial cells. Exposing these epithelial cells to A. alternata releases IL-33 extracellularly in vitro. Allergen exposure also induces acute extracellular accumulation of a danger signal, ATP; autocrine ATP sustains increases in intracellular Ca(2+) concentration and releases IL-33 through activation of P2 purinergic receptors. Pharmacological inhibitors of purinergic receptors or deficiency in the P2Y2 gene abrogate IL-33 release and Th2-type responses in the Alternaria-induced airway inflammation model in naive mice, emphasizing the essential roles for ATP and the P2Y(2) receptor. Thus, ATP and purinergic signaling in the respiratory epithelium are critical sensors for airway exposure to airborne allergens, and they may provide novel opportunities to dampen the hypersensitivity response in Th2-type airway diseases such as asthma.     

Influenza A virus infection inhibits the efficient recruitment of Th2 cells into the airways and the development of airway eosinophilia

Most infections with respiratory viruses induce Th1 responses characterized by the generation of Th1 and CD8(+) T cells secreting IFN-gamma, which in turn have been shown to inhibit the development of Th2 cells. Therefore, it could be expected that respiratory viral infections mediate protection against asthma. However, the opposite seems to be true, because viral infections are often associated with the exacerbation of asthma. For this reason, we investigated what effect an influenza A (flu) virus infection has on the development of asthma. We found that flu infection 1, 3, 6, or 9 wk before allergen airway challenge resulted in a strong suppression of allergen-induced airway eosinophilia. This effect was associated with strongly reduced numbers of Th2 cells in the airways and was not observed in IFN-gamma- or IL-12 p35-deficient mice. Mice infected with flu virus and immunized with OVA showed decreased IL-5 and increased IFN-gamma, eotaxin/CC chemokine ligand (CCL)11, RANTES/CCL5, and monocyte chemoattractant protein-1/CCL2 levels in the bronchoalveolar lavage fluid, and increased airway hyperreactivity compared with OVA-immunized mice. These results suggest that the flu virus infection reduced airway eosinophilia by inducing Th1 responses, which lead to the inefficient recruitment of Th2 cells into the airways. However, OVA-specific IgE and IgG1 serum levels, blood eosinophilia, and goblet cell metaplasia in the lung were not reduced by the flu infection. Flu virus infection also directly induced AHR and goblet cell metaplasia. Taken together, our results show that flu virus infections can induce, exacerbate, and suppress features of asthmatic disease in mice.     

Respiratory tolerance is inhibited by the administration of corticosteroids

Corticosteroids constitute the most effective current anti-inflammatory therapy for acute and chronic forms of allergic diseases and asthma. Corticosteroids are highly effective in inhibiting the effector function of Th2 cells, eosinophils, and epithelial cells. However, treatment with corticosteroids may also limit beneficial T cell responses, including respiratory tolerance and the development of regulatory T cells (T(Reg)), which actively suppress inflammation in allergic diseases. To examine this possibility, we investigated the effects of corticosteroid administration on the development of respiratory tolerance. Respiratory exposure to Ag-induced T cell tolerance and prevented the subsequent development of allergen-induced airway hyperreactivity. However, treatment with dexamethasone during the delivery of respiratory Ag prevented tolerance, such that allergen sensitization and severe airway hyperreactivity subsequently occurred. Treatment with dexamethasone during respiratory exposure to allergen eliminated the development of IL-10-secreting dendritic cells, which was required for the induction of IL-10-producing allergen-specific T(Reg) cells. Therefore, because allergen-specific T(Reg) cells normally develop to prevent allergic disease and asthma, our results suggest that treatment with corticosteroids, which limit the development of T(Reg) cells and tolerance to allergens, could enhance subsequent Th2 responses and aggravate the long-term course of allergic diseases and asthma.     

Effects of systemic versus local administration of corticosteroids on mucosal tolerance

Respiratory exposure to allergen induces T cell tolerance and protection against the development of airway hyperactivity in animal models of asthma. Whereas systemic administration of dexamethasone during the delivery of respiratory Ag has been suggested to prevent the development of mucosal tolerance, the effects of local administration of corticosteroids, first-line treatment for patients with bronchial asthma, on mucosal tolerance remain unknown. To analyze the effects of systemic versus local administration of different types of corticosteroids on the development of mucosal tolerance, mice were exposed to respiratory allergen to induce mucosal tolerance with or without systemic or intranasal application of different doses of dexamethasone or prednisolone. After the induction of mucosal tolerance, proliferation of T cells was inhibited in tolerized mice, whereas systemic applications of corticosteroids restored T cell proliferation and secretion of Th2 cytokines. In contrast, inhaled corticosteroids showed no effect on both T cell proliferation and cytokine secretion. In addition, mice systemically treated with corticosteroids showed an increased airway hyperactivity with a significant lung inflammation, but also an increased T effector cells/regulatory T cells ratio in the second lymphoid organs when compared with mice that receive corticosteroids by inhalation. These results demonstrate that local administration of corticosteroids has no effect on the development of immune tolerance in contrast to systemically applied corticosteroids. Furthermore, although different concentrations of corticosteroids are administered to patients, our results demonstrated that the route of administration rather than the doses affects the effect of corticosteroids on respiratory tolerance induction. Considering the broad application of corticosteroids in patients with allergic disease and asthma, the route of administration of steroid substances seems crucial in terms of treatment and potential side effects. These findings may help elucidate the apparently contradicting results of corticosteroid treatment in allergic diseases.     

Allergic airways disease develops after an increase in allergen capture and processing in the airway mucosa

Airway mucosal dendritic cells (AMDC) and other airway APCs continuously sample inhaled Ags and regulate the nature of any resulting T cell-mediated immune response. Although immunity develops to harmful pathogens, tolerance arises to nonpathogenic Ags in healthy individuals. This homeostasis is thought to be disrupted in allergic respiratory disorders such as allergic asthma, such that a potentially damaging Th2-biased, CD4(+) T cell-mediated inflammatory response develops against intrinsically nonpathogenic allergens. Using a mouse model of experimental allergic airways disease (EAAD), we have investigated the functional changes occurring in AMDC and other airway APC populations during disease onset. Onset of EAAD was characterized by early and transient activation of airway CD4(+) T cells coinciding with up-regulation of CD40 expression exclusively on CD11b(-) AMDC. Concurrent enhanced allergen uptake and processing occurred within all airway APC populations, including B cells, macrophages, and both CD11b(+) and CD11b(-) AMDC subsets. Immune serum transfer into naive animals recapitulated the enhanced allergen uptake observed in airway APC populations and mediated activation of naive allergen-specific, airway CD4(+) T cells following inhaled allergen challenge. These data suggest that the onset of EAAD is initiated by enhanced allergen capture and processing by a number of airway APC populations and that allergen-specific Igs play a role in the conversion of normally quiescent AMDC subsets into those capable of inducing airway CD4(+) T cell activation.     

B Cells Play Key Roles in Th2-Type Airway Immune Responses in Mice Exposed to Natural Airborne Allergens

Humans are frequently exposed to various airborne allergens. In addition to producing antibodies, B cells participate in immune responses via various mechanisms. The roles of B cells in allergic airway inflammation and asthma have been controversial. We examined the functional importance of B cells in a mouse model of asthma, in which mice were exposed repeatedly to common airborne allergens. Naïve wild-type BALB/c mice or B cell-deficient JH^−/− mice were exposed intranasally to a cocktail of allergen extracts, including Alternaria, Aspergillus, and house dust mite, every other day for two weeks. Ovalbumin was included in the cocktail to monitor the T cell immune response. Airway inflammation, lung pathology, and airway reactivity were analyzed. The airway exposure of naïve wild type mice to airborne allergens induced robust eosinophilic airway inflammation, increased the levels of Th2 cytokines and chemokines in the lung, and increased the reactivity to inhaled methacholine. These pathological changes and immune responses were attenuated in B cell-deficient JH^−/− mice. The allergen-induced expansion of CD4⁺ T cells was impaired in the lungs and draining lymph nodes of JH^−/− mice. Furthermore, lymphocytes from JH^−/− mice failed to produce Th2 cytokines in response to ovalbumin re-stimulation in vitro. Our results suggest that B cells are required for the optimal development of Th2-type immune responses and airway inflammation when exposed to common airborne allergens. The therapeutic targeting of B cells may be beneficial to treat asthma in certain patients.     

IL-33-responsive lineage- CD25+ CD44(hi) lymphoid cells mediate innate type 2 immunity and allergic inflammation in the lungs

Innate immunity provides the first line of response to invading pathogens and a variety of environmental insults. Recent studies identified novel subsets of innate lymphoid cells that are capable of mediating immune responses in mucosal organs. In this paper, we describe a subset of lymphoid cells that is involved in innate type 2 immunity in the lungs. Airway exposure of naive BALB/c or C57BL/6J mice to IL-33 results in a rapid (<12 h) production of IL-5 and IL-13 and marked airway eosinophilia independently of adaptive immunity. In the lungs of nonsensitized naive mice, IL-33-responsive cells were identified that have a lymphoid morphology, lack lineage markers, highly express CD25, CD44, Thy1.2, ICOS, Sca-1, and IL-7Rα (i.e., Lin(-)CD25(+)CD44(hi) lymphoid cells), and require IL-7Rα for their development. Airway exposure of naive mice to a clinically relevant ubiquitous fungal allergen, Alternaria alternata, increases bronchoalveolar lavage levels of IL-33, followed by IL-5 and IL-13 production and airway eosinophilia without T or B cells. This innate type 2 response to the allergen is nearly abolished in mice deficient in IL-33R (i.e., ST2), and the Lin(-)CD25(+)CD44(hi) lymphoid cells in the lungs are required and sufficient to mediate the response. Thus, a subset of innate immune cells that responds to IL-33 and vigorously produces Th2-type cytokines is present in mouse lungs. These cells may provide a novel mechanism for type 2 immunity in the airways and induction of allergic airway diseases such as asthma.     

Intratracheal priming with ovalbumin- and ovalbumin 323-339 peptide-pulsed dendritic cells induces airway hyperresponsiveness, lung eosinophilia, goblet cell hyperplasia, and inflammation

Dendritic cells (DC) are the primary APC responsible for the capture of allergens in the airways and the shuttling of processed allergens to the draining lymph nodes where Ag presentation and T cell activation take place. The mechanism of this Ag handling and presentation in asthma is poorly understood. In addition, the feasibility of asthma induction by DC priming has not been directly tested. In this report an asthma model using intratracheally (i.t.) injected splenic DC was used to address these issues. DC pulsed with a model Ag OVA or the major MHC class II-restricted OVA T epitope peptide OVA(323-339) and instilled i.t. primed mice to exhibit asthma-like diseases. With OVA as the Ag, mice exhibit airway hyperresponsiveness (AHR), lung eosinophilia and inflammation, and pulmonary goblet cell hyperplasia. In OVA(323-339)-immunized mice, AHR and goblet cell hyperplasia were noted, with little eosinophilia and parenchymal inflammation. The latter finding provides evidence for dissociating AHR from eosinophilia. In both cases mediastinal node hypertrophy occurred, and high levels of Th2 cytokines were produced by the lung and mediastinal lymph node cells (LNC). Interestingly, mediastinal LNC also produced high levels of Th1 cytokines. Lung cells produced much less Th1 cytokines than these LNC. These results demonstrate that DC when introduced i.t. are potent in inducing asthma-like diseases by recruiting lymphocytes to the lung-draining lymph nodes and by stimulating Th2 responses and also suggest that the lung environment strongly biases T cell responses to Th2.     

An endothelin receptor antagonist,SB-217242, inhibits airway hyperresponsiveness in allergic mice

Within the airways, endothelin-1 (ET-1) can exert a range of prominent effects, including airway smooth muscle contraction, bronchial obstruction, airway wall edema, and airway remodeling. ET-1 also possesses proinflammatory properties and contributes to the late-phase response in allergic airways. However, there is no direct evidence for the contribution of endogenous ET-1 to airway hyperresponsiveness in allergic airways. Allergic inflammation induced in mice by sensitization and challenge with the house dust mite allergen Der P1 was associated with elevated levels of ET-1 within the lung, increased numbers of eosinophils within bronchoalveolar lavage fluid and tissue sections, and development of airway hyperresponsiveness to methacholine (P < 0.05, n = 6 mice per group). Treatment of allergic mice with an endothelin receptor antagonist, SB-217242 (30 mg x kg(-1) x day(-1)), during allergen challenge markedly inhibited airway eosinophilia (bronchoalveolar lavage fluid and tissue) and development of airway hyperresponsiveness. These findings provide direct evidence for a mediator role for ET-1 in development of airway hyperresponsiveness and airway eosinophilia in Der P1-sensitized mice after antigen challenge.     

Nitrogen dioxide promotes allergic sensitization to inhaled antigen

Allergen sensitization and allergic airway disease are likely to come about through the inhalation of Ag with immunostimulatory molecules. However, environmental pollutants, including nitrogen dioxide (NO2), may promote adaptive immune responses to innocuous Ags that are not by themselves immunostimulatory. We tested in C57BL/6 mice whether exposure to NO2, followed by inhalation of the innocuous protein Ag, OVA, would result in allergen sensitization and the subsequent development of allergic airway disease. Following challenge with aerosolized OVA alone, mice previously exposed via inhalation to NO2 and OVA developed eosinophilic inflammation and mucus cell metaplasia in the lungs, as well as OVA-specific IgE and IgG1, and Th2-type cytokine responses. One hour of exposure to 10 parts per million NO2 increased bronchoalveolar lavage fluid levels of total protein, lactate dehydrogenase activity, and heat shock protein 70; promoted the activation of NF-kappaB by airway epithelial cells; and stimulated the subsequent allergic response to Ag challenge. Furthermore, features of allergic airway disease were not induced in allergen-challenged TLR2-/- and MyD88-/- mice exposed to NO2 and aerosolized OVA during sensitization. These findings offer a mechanism whereby allergen sensitization and asthma may result under conditions of high ambient or endogenous NO2 levels.     

Mucosal immunotherapy with CpG oligodeoxynucleotides reverses a murine model of chronic asthma induced by repeated antigen exposure

Murine models of acute atopic asthma may be inadequate to study the effects of recurrent exposure to inhaled allergens, such as the epithelial changes seen in asthmatic patients. We developed a murine model in which chronic airway inflammation is maintained by repeated allergen [ovalbumin (OVA)] inhalation; using this model, we examined the response to mucosal administration of CpG DNA (oligonucleotides) and specific antigen immunotherapy. Mice repeatedly exposed to OVA developed significantly greater airway hyperresponsiveness and goblet cell hyperplasia, but not airway eosinophilia, compared with those exposed only twice. CpG-based immunotherapy significantly reversed both acute and chronic markers of inflammation as well as airway hyperresponsiveness. We further examined the effect of mucosal immunotherapy on the response to a second, unrelated antigen. Mice sensitized to both OVA and schistosome eggs, challenged with inhaled OVA, and then treated with OVA-directed immunotherapy demonstrated significant reduction of airway hyperresponsiveness and a moderate reduction in eosinophilia, after inhalation challenge with schistosome egg antigens. In this model, immunotherapy treatment reduced bronchoalveolar lavage (BAL) levels of Th2 cytokines (IL-4, IL-5, IL-13, and IL-10) without changing BAL IFN-gamma. Antigen recall responses of splenocytes from these mice demonstrated an antigen-specific (OVA) enhanced release of IL-10 from splenocytes of treated mice. These results suggest that CpG DNA may provide the basis for a novel form of immunotherapy of allergic asthma. Both antigen-specific and, to a lesser extent, antigen-nonspecific responses to mucosal administration of CpG DNA are seen.