Endotoxins and allergy: lessons from the murine model.

Exposure early in life to organic dusts containing immunomodulatory components such as endotoxins and immunizing components such as aeroallergens may greatly influence whether subsequent encounters with allergens lead rather to sensitization or unresponsiveness. We investigated the effects of endotoxin in the context of allergen-mediated immune responses in a murine model of allergen sensitization. Systemic sensitization with ovalbumin induced high serum levels of allergen-specific IgE, predominant Th2-type cytokine production, eosinophilic airway inflammation and in vivo airway hyperreactivity. Endotoxins were either applied systemically prior to sensitization, or via the airways prior to airway challenges, or by repeated inhalation during the first weeks of life prior to subsequent sensitization. Different effects of endotoxins on allergen-induced immune responses may be attributed to differences in dosing, route of application, time relationship with allergen sensitization and the concurrent exposure to endotoxin and allergen. The results of these studies may help to define the effects of endotoxin on allergen-mediated immune reactions and to further delineate the important interrelationships between environment and disease development. Finally, this may lead to new strategies in the prevention and treatment of allergic diseases.     

The role of allergen-specific IgE,IgG and IgA in allergic disease

Immunoglobulin E (IgE)-mediated allergy is the most common hypersensitivity disease affecting more than 30% of the population. Exposure to even minute quantities of allergens can lead to the production of IgE antibodies in atopic individuals. This is termed allergic sensitization, which occurs mainly in early childhood. Allergen-specific IgE then binds to the high (FcεRI) and low-affinity receptors (FcεRII, also called CD23) for IgE on effector cells and antigen-presenting cells. Subsequent and repeated allergen exposure increases allergen-specific IgE levels and, by receptor cross-linking, triggers immediate release of inflammatory mediators from mast cells and basophils whereas IgE-facilitated allergen presentation perpetuates T cell–mediated allergic inflammation. Due to engagement of receptors which are highly selective for IgE, even tiny amounts of allergens can induce massive inflammation. Naturally occurring allergen-specific IgG and IgA antibodies usually recognize different epitopes on allergens compared with IgE and do not efficiently interfere with allergen-induced inflammation. However, IgG and IgA antibodies to these important IgE epitopes can be induced by allergen-specific immunotherapy or by passive immunization. These will lead to competition with IgE for binding with the allergen and prevent allergic responses. Similarly, anti-IgE treatment does the same by preventing IgE from binding to its receptor on mast cells and basophils. Here, we review the complex interplay of allergen-specific IgE, IgG and IgA and the corresponding cell receptors in allergic diseases and its relevance for diagnosis, treatment and prevention of allergy.     

Role of IgE in the development of allergic airway inflammation and airway hyperresponsiveness – a murine model

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.     

Anti-IgE therapy in asthma: rationale and therapeutic potential

Airway inflammation is found in virtually all individuals with asthma symptoms. The factors contributing to asthma-related airway inflammation are multiple and involve a number of different inflammatory cells and mediators. Allergic responses at the level of the respiratory system are mostly mediated by IgE-dependent mechanisms. After sensitization of a susceptible individual and the synthesis and binding of allergen-specific IgE to target cells, atopic individuals respond immunologically to common, naturally occurring allergens by releasing mast cell-derived mediators. Subsequent allergen exposure in susceptible individuals produces a characteristic cascade of events orchestrated by immune effector cells, most prominently, mast cells, T lymphocytes and eosinophils. A new strategy, neutralizing IgE antibodies, inhibits expression of allergic symptoms by preventing the initial trigger of the allergic reaction, IgE binding to IgE-receptor bearing cells. rhuMAb-E25 is a recombinant humanized monoclonal anti-IgE antibody currently under investigation that has been shown to reduce allergic responses in atopic individuals and to improve symptoms and reduce rescue medication and corticosteroid use in patients with allergic asthma. Thus, the clinical effectiveness of rhuMAb-E25 supports the central role of IgE in allergic reactions and the viability of anti-IgE therapy as a potentially effective treatment option for asthma.     

Common vaccine antigens inhibit allergen-induced sensitization and airway hyperresponsiveness in a murine model

BACKGROUND: Co-vaccination with cellular pertussis vaccine down-regulates allergic sensitization to diphtheria and tetanus antigens. Using a murine model, we investigated whether vaccination with diphtheria/tetanus toxoids, administered separately or simultaneously with the whole cell vaccine of Bordetella pertussis, inhibits subsequent allergen-induced immune and inflammatory responses. METHODS: BALB/c-mice were vaccinated intracutaneously with a combination of diphtheria and tetanus toxoids or a combination of diphtheria and tetanus toxoids with a whole cell vaccine of B. pertussis (three times, days -21 to -7) prior to systemic sensitization (days 1-14) and repeated airway challenges (days 28-30) with ovalbumin. RESULTS: Compared with negative controls, systemic sensitization and airway allergen challenges induced high serum levels of allergen-specific IgE, predominant Th2-type cytokine production, airway inflammation and development of in vivo airway hyperreactivity. Vaccination with diphtheria and tetanus toxoids prior to sensitization suppressed IgE formation and development of eosinophilic airway inflammation. Co-vaccination with a whole cell pertussis vaccine inhibited allergen sensitization, airway inflammation and development of in vivo airway hyperreactivity. Prevention was due to an allergen-specific and general shift from a predominant Th2 towards a predominant Th1 immune response. CONCLUSION: Vaccination with diphtheria and tetanus toxoids alone or in combination with whole cell pertussis vaccine prior to allergen sensitization prevented allergen-induced Th2 immune responses. Vaccine antigens may down-regulate allergic responses to a range of common allergens.     

Repeated aerosol allergen exposure suppresses inflammation in B-cell-deficient mice with established allergic asthma

BACKGROUND: Repeated allergen administration is a well-established therapeutic strategy for desensitizing patients with allergic disease. Similarly, repeated inhalation of antigen by mice with established allergen-induced asthma suppresses allergic inflammation. The mechanisms underlying antigen-dependent suppression of allergic immune responses remain unknown. In previous studies, we found that repeated aerosol antigen challenges in sensitized mice reduced eosinophils while increasing plasma cells and antibody in the lungs. We sought to test whether plasma cells and antibody played a role in suppression of allergic disease. METHODS: We primed wild-type and B-cell-deficient (microMT) mice with 25 microg ovalbumin (OVA) precipitated in alum on days 0 and 5, nebulized weekly with 1% OVA, 1 h, twice daily, for up to 6 weeks, and assessed lung inflammation, mucus hypersecretion, and IgE/IgG1. RESULTS: Kinetic studies revealed that initial aerosol exposure induced high numbers of eosinophils, lymphocytes, and macrophages within lung infiltrates and increased mucus production in wild-type mice. After 3-4 weeks of antigen exposure, eosinophils diminished while lymphocytes, plasma cells, and macrophages and mucus hypersecretion increased. However, by 6 weeks, lung inflammation and mucus hypersecretion were dramatically reduced. In contrast, repeated aerosol challenges maintained OVA-specific IgG1 and IgE production. Repeated aerosol antigen challenges in microMT mice resulted in reduced lung inflammation and mucus hypersecretion and the development of smooth muscle hypertrophy of the pulmonary microvasculature. CONCLUSIONS: B cells and antibody do not appear to play a role in antigen-dependent suppression of allergic responses in mice.     

Complete inhibition of allergic airway inflammation and remodelling in quadruple IL-4/5/9/13−/− mice

BACKGROUND: T-helper type 2 (Th2)-derived cytokines such as IL-4, IL-5, IL-9 and IL-13 play an important role in the synthesis of IgE and in the promotion of allergic eosinophilic inflammation and airway wall remodelling. OBJECTIVE: We determined the importance of IL-13 alone, and of the four Th2 cytokines together, by studying mice in which either IL-13 alone or the Th2 cytokine cluster was genetically disrupted. METHODS: The knock-out mice and their BALB/c wild-type (wt) counterparts were sensitized and repeatedly exposed to ovalbumin (OVA) aerosol. RESULTS: Bronchial responsiveness measured as the concentration of acetylcholine aerosol needed to increase baseline lung resistance by 100% (PC100) was decreased in IL-13-/-, but increased in IL-4/5/9/13-/- mice. Chronic allergen exposure resulted in airway hyperresponsiveness (AHR) in wt mice but not in both genetically modified mice. After allergen exposure, eosinophil counts in bronchoalveolar lavage fluid and in airways mucosa, and goblet cell numbers were not increased in IL-4/5/9/13-/- mice, and were only attenuated in IL-13-/- mice. Airway smooth muscle (ASM) hyperplasia after allergen exposure was prevented in both IL-13-/- and IL-4/5/9/13-/- mice to an equal extent. Similarly, the rise in total or OVA-specific serum IgE levels was totally inhibited. CONCLUSION: IL-13 is mainly responsible for AHR, ASM hyperplasia and increases in IgE, while IL-4, -5 and -9 may contribute to goblet cell hyperplasia and eosinophilic inflammation induced by chronic allergen exposure in a murine model. Both redundancy or complementariness of Th2 cytokines can occur in vivo, according to specific aspects of the allergic response.     

Interleukin (IL)-5 but not immunoglobulin E reconstitutes airway inflammation and airway hyperresponsiveness in IL-4-deficient mice

We studied the role of interleukin (IL)-4, IL-5, and allergen-specific immunoglobulin (Ig) E in the development of allergen-induced sensitization, airway inflammation, and airway hy-perresponsiveness (AHR). Normal, IL-4-, and IL-5-deficient C57BL/6 mice were sensitized intraperitoneally to ovalbumin (OVA) and repeatedly challenged with OVA via the airways. After allergen sensitization and airway challenge, normal and IL-5-deficient, but not IL-4-deficient, mice developed increased serum levels of total and antigen-specific IgE levels and increased IL-4 production in the lung tissue compared with nonsensitized control mice. Only normal mice showed significantly increased IL-5 production in the lung tissue and an eosinophilic infiltration of the peribronchial regions of the airways, whereas both IL-4- and IL-5-deficient mice had little or no IL-5 production and no significant eosinophilic airway inflammation. Associated with the inflammatory responses in the lung, only normal mice developed increased airway responsiveness to methacholine after sensitization and airway challenge; in both IL-4- and IL-5-deficient mice, airway responsiveness was similar to that in nonsensitized control mice. Reconstitution of sensitized, IL-4-deficient mice before allergen airway challenge with IL-5, but not with allergen-specific IgE, restored eosinophilic airway inflammation and the development of AHR. These data demonstrate the importance of IL-4 for allergen-driven airway sensitization and that IL-5, but not allergen-specific IgE, is required for development of eosinophilic airway inflammation and AHR after this mode of sensitization and challenge.     

Toll-like receptor 4 or 2 agonists decrease allergic inflammation

Toll-like receptors (TLRs) recognize highly conserved microbial molecular patterns, such as found in endotoxin. This study tested whether TLR4 and TLR2 stimulation in vivo would modulate subsequent adaptive (allergic) immune responses. We analyzed the effects of pulmonary administration of a TLR4 agonist, lipid A (LpA), and two TLR2 agonists, peptidoglycan (Ppg) and PamCys, in a murine model of allergic inflammation. The TLR agonists were administered during allergen sensitization or challenge. Both TLR agonists decreased the allergen-induced pulmonary recruitment of eosinophils when administered at sensitization or challenge. When given before sensitization, the TLR4 and TLR2 agonists decreased additional allergen-induced parameters of inflammation (pulmonary eosinophilia, bronchoalveolar lavage IL-13, total serum IgE, and airway hyperresponsiveness). Interestingly, TLR4 and TLR2 agonists decreased the number of CD4+ cells in the lung. Also, at the site of local allergen stimulation, the draining thoracic lymph nodes, allergen-induced lymphocyte proliferation, and IL-13 secretion were decreased by administration of LpA and Ppg. These data provide a distinct example of the modulation of adaptive (allergic) responses by non-antigen-dependent stimuli. Our findings also demonstrate that both TLR4 and TLR2 agonists decrease allergic responses, supporting the concept that exposure to bacterial components under defined conditions may protect against allergic disease.     

Intranasal delivery of whole influenza vaccine prevents subsequent allergen-induced sensitization and airway hyper-reactivity in mice

BACKGROUND: Infection with influenza virus has been associated with seemingly opposing effects on the development of asthma. However, there are no data about the effects of mucosal vaccination with inactivated influenza on the inception of allergic asthma. OBJECTIVE: To assess the immunological effects of inhaled inactivated influenza vaccine, using two different types of flu vaccines, on the inception of allergic sensitization and allergen-mediated airway disease in a mouse model. METHODS: BALB/c mice were intranasally or intratracheally vaccinated with whole or split influenza virus vaccine (days -1 or -1, 27) before systemic sensitization with ovalbumin (OVA) (days 1, 14) and repeated airway allergen challenges (days 28-30). Allergen sensitization (IgE serum levels), airway inflammation (differential cells in bronchoalveolar lavage fluid) and airway hyper-reactivity (AHR) (in vivo lung function) were analysed. RESULTS: The intranasal instillation of whole influenza vaccine before allergen sensitization significantly reduced the serum levels of total and OVA-specific IgE as well as allergen-induced AHR. Prevention was due to an allergen-specific shift from a predominant T helper (Th)2- towards a Th1-immune response. Application of split influenza vaccine did not show the same preventive effect. CONCLUSION: Intranasal administration of inactivated whole influenza vaccine reduced subsequent allergen sensitization and prevented allergen-induced AHR. Our results show that the composition of the influenza vaccine has a major influence on subsequent development of allergen-induced sensitization and AHR, and suggest that mucosal inactivated whole influenza vaccination may represent a step towards the development of a preventive strategy for atopic asthma.     

Oral administration of desloratadine prior to sensitization prevents allergen-induced airway inflammation and hyper-reactivity in mice

BACKGROUND: Histamine-1-receptor (H1R)-antagonists were shown to influence various immunological functions on different cell types and may thus be employed for immune-modulating strategies for the prevention of primary immune responses. OBJECTIVE: The aim of this study was to investigate the effects of an H1R-antagonist on allergen-induced sensitization, airway inflammation (AI) and airway hyper-reactivity (AHR) in a murine model. METHODS: BALB/c mice were systemically sensitized with ovalbumin (OVA) (six times, days 1-14) and challenged with aerosolized allergen (days 28-30). One day prior to the first and 2 h prior to every following sensitization, mice received either 1 or 0.01 microg of desloratadine (DL) or placebo per os. RESULTS: Sensitization with OVA significantly increased specific and total IgE and IgG1 serum levels, as well as in vitro IL-5 and IL-4 production by spleen and peribronchial lymph node (PBLN) cells. Sensitized and challenged mice showed a marked eosinophilic infiltration in broncho-alveolar lavage fluids and lung tissues, and developed in vivo AHR to inhaled methacholine. Oral treatment with DL prior to OVA sensitization significantly decreased production of OVA-specific IgG1, as well as in vitro Th2-cytokine production by spleen and PBLN cells, compared with OVA-sensitized mice. Moreover, eosinophilic inflammation and development of in vivo AHR were significantly reduced in DL-treated mice, compared with sensitized controls. CONCLUSION: Treatment with H1R-anatagonist prior to and during sensitization suppressed allergen-induced Th2 responses, as well as development of eosinophilic AI and AHR. This underscores an important immune modulating function of histamine, and implies a potential role of H1R-anatagonists in preventive strategies against allergic diseases.     

Therapeutic effects of DNA vaccine on allergen-induced allergic airway inflammation in mouse model

Vaccination with DNA encoding Dermatophagoides pteronyssinus group 2 （Der p 2） allergen previously showed its effects of immunologic protection on Der p 2 allergen-induced allergic airway inflammation in mice. In present study, we investigated whether DNA vaccine encoding Der p 2 could exert therapeutic role on allergen-induced allergic airway inflammation in mouse model and explored the mechanism of DNA vaccination in asthma specific-allergen immunotherapy. After sensitized and challenged by Der p 2, the BALB/c mice were immunized with DNA vaccine. The degrees of cellular infiltration were scored. IgE levels in serum and IL-4/IL-13 levels in BALF were determined by ELISA. The lung tissues were assessed by histological examinations. Expressions of STAT6 and NF-kB in lung were determined by immunohistochemistry staining. Vaccination of mice with DNA vaccine inhibited the development of airway inflammation and the production of mucin induced by allergen, and reduced the level of Der p 2-specific IgE level. Significant reductions of eosinophil infiltration and levels of IL-4 and IL-13 in BALF were observed after vaccination. Further more, DNA vaccination inhibited STAT6 and NF-kB expression in lung tissue in Der p 2-immunized mice. These results indicated that DNA vaccine encoding Der p 2 allergen could be used for therapy of allergen-induced allergic airway inflammation in our mouse model. Cellular ＆ Molecular Immunology.     

Inhibition of Pim1 kinase activation attenuates allergen-induced airway hyperresponsiveness and inflammation

Pim kinases are a family of serine/threonine kinases whose activity can be induced by cytokines involved in allergy and asthma. These kinases play a role in cell survival and proliferation, but have not been examined, to the best of our knowledge, in the development of allergic disease. This study sought to determine the role of Pim1 kinase in the development of allergic airway responses. Mice were sensitized and challenged with antigen (primary challenge), or were sensitized, challenged, and rechallenged with allergen in a secondary model. To assess the role of Pim1 kinase, a small molecule inhibitor was administered orally after sensitization and during the challenge phase. Airway responsiveness to inhaled methacholine, airway and lung inflammation, cell composition, and cytokine concentrations were assessed. Lung Pim1 kinase concentrations were increased after ovalbumin sensitization and challenge. In the primary allergen challenge model, treatment with the Pim1 kinase inhibitor after sensitization and during airway challenges prevented the development of airway hyperresponsiveness, eosinophilic airway inflammation, and goblet cell metaplasia, and increased Th2 cytokine concentrations in bronchoalveolar fluid in a dose-dependent manner. These effects were also demonstrated after a secondary allergen challenge, where lung allergic disease was established before treatment. After treatment with the inhibitor, a significant reduction was evident in the number of CD4(+) and CD8(+) T cells and concentrations of cytokines in the airways. The inhibition of Pim1 kinase was effective in preventing the development of airway hyperresponsiveness, airway inflammation, and cytokine production in allergen-sensitized and allergen-challenged mice. These data identify the important role of Pim1 kinase in the full development of allergen-induced airway responses.     

Respiratory syncytial virus-induced airway hyperresponsiveness is independent of IL-13 compared with that induced by allergen

BACKGROUND: IL-13 is a central mediator of allergen-induced airway hyperresponsiveness (AHR), but its role in respiratory syncytial virus (RSV)-induced AHR is not defined. The combination of allergen exposure and RSV infection is known to increase AHR and lung inflammation, but whether IL-13 regulates this increase is similarly not known. OBJECTIVE: Our objective was to determine the role of RSV infection and IL-13 on airway responsiveness and lung inflammation on sensitized and challenged mice. METHODS: Using a murine model of RSV infection and allergen exposure, we examined the role of IL-13 in the development of AHR and lung inflammation in IL-13 knockout mice, as well as using a potent IL-13 inhibitor (IL-13i). Mice were sensitized and challenged to allergen, and 6 days after the last challenge, they were infected with RSV. IL-13 was inhibited using an IL-13 receptor alpha(2)-human IgG fusion protein. AHR to inhaled methacholine was measured 6 days after infection, as was bronchoalveolar lavage fluid and lung inflammatory and cytokine responses. RESULTS: RSV-induced AHR was unaffected by the IL-13i, despite prevention of goblet cell hyperplasia. Similar results were seen in IL-13-deficient mice. In sensitized and challenged mice, RSV infection significantly increased AHR, and after IL-13i treatment, AHR was significantly reduced, but to the levels seen in RSV-infected mice alone. CONCLUSIONS: These results indicate that despite some similarities, the mechanisms leading to AHR induced by RSV are different from those that follow allergen sensitization and challenge. Because IL-13 inhibition is effective in preventing the increases in AHR and mucus production in sensitized and challenged mice infected with RSV, IL-13i could play an important role in preventing the consequences of viral infection in patients with allergic asthma.     

Surface plasmon resonance analysis of free IgE in allergic patients receiving omalizumab (Xolair)

The diagnosis of human allergic disease involves an initial clinical history based association of allergic symptoms with an allergen exposure. This is followed by confirmation of sensitization (IgE antibody positivity) with skin test, serology or provocation testing. Once diagnosed, the allergic individual can be managed using one or several modalities that involve allergen avoidance, pharmacotherapy, allergen immunotherapy and anti-IgE therapy. This report examines Law of Mass Action considerations for the design of immunological methods which permit the quantification of free (non-Omalizumab bound) IgE in the serum of patients receiving anti-IgE therapy. The rationale for and design and performance of a surface plasmon resonance assay for the detection of "free" IgE (unbound with anti-IgE) is presented as an alternative to microtiter plate based ELISAs.     

The anti-inflammatory effects of omalizumab confirm the central role of IgE in allergic inflammation

Anti-IgE therapy with omalizumab reduces serum levels of free IgE and downregulates expression of IgE receptors (Fc epsilonRI) on mast cells and basophils. In the airways of patients with mild allergic asthma, omalizumab reduces Fc epsilonRI+ and IgE+ cells and causes a profound reduction in tissue eosinophilia, together with reductions in submucosal T-cell and B-cell numbers. In patients with seasonal allergic rhinitis, omalizumab inhibits the allergen-induced seasonal increases in circulating and tissue eosinophils. Omalizumab decreases Fc epsilonRI expression on circulating dendritic cells, which might lead to a reduction in allergen presentation, T(H)2 cell activation, and proliferation. As a systemic anti-IgE agent, omalizumab has demonstrated clinical efficacy in patients with moderate and severe allergic asthma and in those with seasonal and perennial allergic rhinitis, as well as in patients with concomitant allergic asthma and allergic rhinitis. The anti-inflammatory effects of omalizumab at different sites of allergic inflammation and the clinical benefits of anti-IgE therapy in patients with allergic asthma and allergic rhinitis emphasize the fundamental importance of IgE in allergic inflammation.     

Interleukin-13-dependent bronchial hyper-responsiveness following isolated upper-airway allergen challenge in a murine model of allergic rhinitis and asthma

BACKGROUND: We have previously shown that isolated allergic sensitization and challenge of the upper airway results in lower-airway inflammation, which supports the concept of the united airways. OBJECTIVE: This study investigates the hypothesis that isolated upper-airway allergic sensitization is sufficient to induce bronchial hyper-responsiveness (BHR), characteristic of asthma, and that IL-13 is an essential mediator in both the upper and lower airways. METHODS: BALB/c mice were sensitized and challenged by intranasal instillation of allergen ovalbumin (OVA) using our standard protocol. BHR to methacholine was determined and inflammation in nares and lung was assessed. RESULTS: Isolated intranasal application of allergen in awake animals resulted in almost exclusive deposition in the upper airways while in anaesthetized mice there was almost equal distribution in the upper and lower airways. We have demonstrated significant BHR to methacholine challenge in animals receiving OVA only in the upper airway. Also noted was concomitant increase in eosinophilic infiltrates in lung and nares as well as increased granulocytes and IL-13 levels in bronchoalveolar lavage (BAL) fluid. Using a polyclonal anti-IL-13 antibody we have shown inhibition of airways inflammation, both in nares and in lung with significant reduction of granulocytes in BAL from anti-IL-13 treated mice (P<0.0001). Anti-IL-13 treatment also abrogates allergen-induced BHR (P<0.01). CONCLUSION: These data suggest that isolated upper-airway allergen deposition initiates allergic responses along the entire airway. IL-13 mediates both airway inflammation and BHR and may play a role in the communication between the upper and lower airways.     

Fexofenadine modulates T-cell function,preventing allergen-induced airway inflammation and hyperresponsiveness

BACKGROUND: Antihistamines have been evaluated for usefulness in the treatment of asthma for more than 50 years. Interest was limited until the introduction of newer compounds that were free of much of the dose-limiting sedation associated with the earlier drugs. OBJECTIVE: In a murine model of allergen-induced airway inflammation and hyperresponsiveness, the efficacy of an H1 receptor antagonist to prevent allergic inflammation and altered airway function was evaluated. METHODS: Mice were sensitized and challenged to an allergen, ovalbumin, which elicited marked airway and tissue eosino-philia and airway hyperresponsiveness. Fexofenadine was administered before challenge, and airway responsiveness to inhaled methacholine, airway and tissue eosinophilia, bronchoalveolar lavage fluid cytokine levels, and serum IgE levels were assayed. In a second group of experiments, sensitized and challenged mice were treated or not treated with fexofenadine before challenge. T cells were isolated from the lungs and adoptively transferred into naive recipients before exposure to limited airway allergen challenge, and lung function and inflammation were evaluated. RESULTS: Fexofenadine treatment of sensitized mice prevented the development of airway hyperresponsiveness in both the primary sensitization and challenge, as well as in the adoptive transfer experiments. These changes were accompanied by decreases in bronchoalveolar lavage and tissue eosinophilia, lymphocyte numbers, and T(H)2 cytokine production. CONCLUSION: The results demonstrate the efficacy of an H1 receptor antagonist in preventing allergen-induced alterations in pulmonary inflammation and airway function. The data support the evaluation of drugs such as fexofenadine in the treatment of allergic asthma.     

Prenatal initiation of endotoxin airway exposure prevents subsequent allergen-induced sensitization and airway inflammation in mice

BACKGROUND: New preventive strategies against the development of allergic diseases focus on potentially immunomodulatory components, such as bacterial LPSs. Optimal time frames for initiating immunomodulation to receive a sufficient effect against allergen sensitization are still unclear. OBJECTIVE: Using a mouse model, we investigated the influence of prenatal LPS exposure on later allergen-mediated sensitization and airway inflammation in the offspring. METHODS: Pregnant BALB/c mice were repeatedly exposed to aerosolized LPS (LPS Escherichia coli; 3x per week, day 7 of gestation time up to delivery). Some of the offspring were further exposed to aerosolized LPS before allergen sensitization with ovalbumin (OVA; administered intraperitoneally day 28 up to day 42) and OVA airway challenges (days 56-58). Positive control animals were placebo exposed to PBS instead of LPS, and negative control animals were first placebo exposed and later placebo sensitized with PBS instead of OVA. RESULTS: Compared with positive control animals, prenatal LPS exposure suppressed (1) allergen-specific sensitization (IgE production), (2) eosinophilic airway inflammation (reduced numbers of eosinophils in bronchoalveolar lavage fluids), and (3) in vivo airway reactivity in response to methacholine. These effects occurred only when prenatal was combined with further postnatal LPS exposure. Suppression of allergen-mediated inflammatory responses was associated with increased Toll-like receptor and T-bet expression by lung tissues and a shift toward predominantly T(H)1 immune responses in spleen cells cultured with OVA in vitro. CONCLUSION: Prenatal initiated and postnatal sustained LPS exposure increased endotoxin susceptibility and prevented later allergen sensitization in offspring through inhibition of T(H)2 immune responses. CLINICAL IMPLICATIONS: Immunomodulation with bacterial compounds during gestation time might be an effective mode for first-step primary prevention against allergic diseases.     

Effect of ozone exposure on allergic sensitization and airway inflammation induced by dendritic cells

BACKGROUND: Epidemiological studies suggest that ozone exposure is related to increased asthma symptoms. Dendritic cells (DCs) are the principal antigen-presenting cells in the airways. OBJECTIVE: We have examined whether ambient doses of ozone (100 ppb for 2 h) enhance allergic sensitization and/or airway inflammation in a mouse model. METHODS: C57BL/6 mice were sensitized to inhaled ovalbumin (OVA) by intratracheal instillation of OVA-pulsed DCs on day 0. Daily exposure to OVA aerosol on days 14-20 resulted in an eosinophilic airway inflammation, as reflected in bronchoalveolar lavage fluid and lung histology. In a first experiment, mice were exposed to ozone or room air immediately prior to and following sensitization. Subsequently, we tested the effect of ozone exposure during antigen challenge in DC-sensitized mice. RESULTS: Exposure to ozone during sensitization did not influence airway inflammation after subsequent allergen challenge. In contrast, in sensitized mice, challenge with OVA together with ozone (days 14-20) resulted in enhanced airway eosinophilia and lymphocytosis, as compared with mice exposed to OVA and room air (1.91 x 106 +/- 0.46 x 106 vs. 0.16 x 106 +/- 0.06 x 106 eosinophils/mL lavage fluid; P = 0.015; 0.49 x 106 +/- 0.11 x 106 vs. 0.08 x 106 +/- 0.03 x 106 lymphocytes/mL lavage fluid; P = 0.004). Ozone exposure without subsequent OVA exposure did not cause airway inflammation. CONCLUSION: Ozone exposure does not increase allergic sensitization but enhances antigen-induced airway inflammation in mice that are sensitized via the airways.