Aeroallergen-induced eosinophilic inflammation, lung damage, and airways hyperreactivity in mice can occur independently of IL-4 and allergen-specific immunoglobulins

Critical roles for interleukin-4 and interleukin-5 during respiratory syncytial virus infection in the development of airway hyperresponsiveness after airway sensitization

In mice, respiratory syncytial virus (RSV) infection can enhance the consequences of allergic airway sensitization, resulting in lung eosinophilia and the development of airway hyperresponsiveness (AHR) to inhaled methacholine (MCh). To delineate a role for interleukin-5 (IL-5), interleukin-4 (IL-4), and interferon gamma (IFN-gamma) in mediating the effects of RSV infection on subsequent allergic sensitization, we treated BALB/c mice with anti-IL-5 during acute RSV infection but not during subsequent exposure to ovalbumin (OVA). IL-5-deficient and IL-4-deficient mice were also treated with IL-5 either during acute RSV infection or during the sensitization period. Airway responsiveness to inhaled MCh was assessed and numbers of lung eosinophils were monitored. Anti-IL-5 treatment during RSV infection reduced AHR and lung eosinophilia after subsequent exposure to allergen. In IL-5-deficient or IL-4-deficient mice lung eosinophilia and AHR after RSV infection and allergen exposure were also markedly reduced. IL-5 administration during RSV infection restored the responses to allergen in both IL-5- and IL-4-deficient mice. However, IL-5 administration only during sensitization restored these responses in IL-4-deficient but not in IL-5-deficient animals. IFN-gamma-deficient mice developed AHR and some lung eosinophilia after allergen exposure alone and when RSV infection preceded allergen, these responses were enhanced. We conclude that both IL-5, particularly during acute infection, and IL-4 are critical in mediating the effects of RSV infection on allergic airway sensitization, resulting in the development of AHR and lung eosinophilia.

Interleukin-4-independent production of Th2 cytokines by nasal lymphocytes and nasal eosinophilia in murine allergic rhinitis

BACKGROUND

Interleukin (IL)-4 is believed to play an important role in the atopic pathogenesis. However, the precise role of IL-4 in the in vivo initiation of allergic rhinitis is not fully understood. We have recently found that BALB/c mice sensitized intranasally with Schistosoma mansoni egg antigen (SEA) mount a Th2 response that initiates allergic rhinitis. Thus, we sought to determine the role of IL-4 in the initiation of allergic rhinitis in vivo with this model.

METHODS

IL-4 gene-deficient (IL-4 -/-) BALB/c and wild-type (IL-4 +/+) control mice were sensitized by intranasal SEA administration, and their immunologic responses were examined both in vivo and in vitro.

RESULTS

IL-4 +/+ mice sensitized with SEA displayed significantly higher titers of SEA-specific IgG1 and IgE antibodies than IL-4-/- mice, while the latter produced significantly more SEA-specific IgG2a. Antigen-stimulated nasal lymphocytes from SEA-sensitized IL-4 -/- and IL-4 +/+ mice produced similar amounts of IL-5 and IL-10, but neither produced IFN-gamma. Furthermore, the severity of nasal eosinophilia was similar in both groups.

CONCLUSIONS

These results indicate that although IL-4 is necessary for the production of Th2-associated antibodies--in particular, IgE--it is not required for either the production of the Th2-associated cytokines IL-5 and IL-10, or the induction of nasal eosinophilia.

Abrogation of lung inflammation in sensitized Stat6-deficient mice is dependent on the allergen inhalation procedure

Conflicting results have been reported about the role of Stat6 in allergen-induced airway inflammation. We have studied the influence of the allergen inhalation procedure on the inflammatory response using wild-type and Stat6-deficient mice generated on a C57BL/6 background. Animals were immunized i.p. on day 0 and 7 with ovalbumin (OVA) and then received aerosolized OVA or phosphate buffer saline challenge (acute on day 14; chronic on day 14, 15, 16, 17 and 18) before being sacrificed at different time points. Following an acute challenge, Stat6-deficiency fully abrogated the increase in serum IgE levels and the development of lung inflammation (inflammatory cell infiltration, IL-4 and IL-5 release, and increase in plasma leakage). Following chronic challenge, despite the absence of IgE, IL-4 and IL-5, Stat6-deficient mice develop a characteristic lung inflammation, although the intensity was smaller when compared with the wild-type mice. OVA-induced early bronchoconstriction was observed in wild-type mice only after chronic challenge, and this was totally abrogated in the Stat6-deficient animals. These results suggest that Stat6 signalling is essential for the development of allergic airway inflammation following an acute allergen exposure. However, in a more chronic situation, the airway inflammatory response seems to be only partially mediated by Stat6.

Cytokines in airway inflammation

With over 50 potential asthma mediators, cytokines are the latest group of substances which have been investigated for their potential role in this disease. The use of murine models of allergic inflammation has facilitated the investigation of the role of individual cytokines in this response. The use of targeted gene disruption, overexpression of genes and monoclonal antibodies directed against cytokines have allowed a detailed examination of the role cytokines play in IgE production, eosinophil recruitment and bronchial hyperresponsiveness, which are the characteristic features of the asthma phenotype. Despite the introduction of this new methodology, conflicting reports relating to the role of cytokines in allergic inflammation, highlight the complexity of allergic inflammation and challenge the notion that a single cytokine can explain the asthma phenotype.

Systemically derived large intestinal CD4(+) Th2 cells play a central role in STAT6-mediated allergic diarrhea

Systemically primed BALB/c mice developed severe diarrhea after repeated oral administration of ovalbumin (OVA). Histological analysis demonstrated that dramatic infiltration of eosinophils and mast cells occurred in the large intestine but not in the small intestine of mice with diarrhea. Interestingly, CD4(+) alphabeta T cells of the large intestine secreted IL-4 and IL-13 at high levels. Identically treated STAT6 gene-disrupted mice failed to develop OVA-induced diarrhea. Further, treatment of BALB/c mice with monoclonal anti-IL-4 antibody prevented the development of allergic diarrhea. An adoptive transfer study showed that systemically primed splenic CD4(+) T cells were preferentially recruited into the large intestine upon exposure to oral OVA. These results strongly suggest that systemically derived CD4(+) alphabeta T cells of the large intestine play a critical role in the onset of Th2-mediated intestinal allergic disorders via STAT6 signal transduction.

Integrated signals between IL-13, IL-4, and IL-5 regulate airways hyperreactivity

In this investigation, we have examined the integrated relationship between IL-13, IL-4, and IL-5 for the development of airways hyperreactivity (AHR) in a model of asthma in BALB/c mice. Sensitization and aeroallergen challenge of both wild-type (WT) and IL-13 gene-targeted (IL-13-/-) mice induced allergic disease that was characterized by pulmonary eosinophilia and AHR to beta-methacholine. Although these responses in IL-13-/- mice were heightened compared with WT, they could be reduced to the level in nonallergic mice by the concomitant neutralization of IL-4. Mice in which both IL-4 and IL-13 were depleted displayed a marked reduction in tissue eosinophils, despite the development of a blood eosinophilia. Similar neutralization of IL-4 in WT mice only partially reduced AHR with no effect on tissue eosinophilia. In addition, neutralization of IL-5 in IL-13-/- mice, but not in WT mice, inhibited AHR, suggesting that tissue eosinophilia is linked to the mechanism underlying AHR only in the absence of IL-13. Additionally, mucus hypersecretion was attenuated in IL-13-/- mice, despite the persistence of AHR. Taken together, our data suggest both a modulatory role for IL-13 during sensitization and a proinflammatory role during aeroallergen challenge. The latter process appears redundant with respect to IL-4.

Reducing IgE levels as a strategy for the treatment of asthma

IgE secretion by B lymphocytes defines the allergic state and nearly all asthmatics have higher than normal IgE levels in serum following adjustment for age and sex. It is thought that allergic mechanisms may be responsible for the increasing prevalence of asthma. In particular, in utero changes may encourage T cells to differentiate into Th2 subtypes. Th2 cells produce cytokines such as IL-4 and IL-5, which can act indirectly via B cells, mast cells and eosinophils to mediate the asthma phenotype. Alternatively, IL-4 and IL-13 may act directly on the airway. Th2 lymphocyte inflammation in asthma predisposes subjects to B cell and IgE-mediated airway inflammation. IgE binds to receptors on the surface of a variety of effector cells causing them to release a variety of mediators that promote airway hyperresponsiveness, mucus secretion and increased vascular permeability. Several strategies for decreasing IgE have been developed as a possible treatment for asthma. For example, anti-IgE monoclonal antibodies such as rhuMAb-E25 and CGP 56901 block binding of IgE to its high-affinity receptor and have been shown to reduce IgE levels in humans without causing anaphylaxis. IgE levels must be nearly completely suppressed. Recent clinical studies in subjects with asthma have shown that rhuMAb-E25 attenuates both the early and late phase responses to inhaled allergen, and reduces the associated increase in eosinophils in induced sputum. rhuMAb-E25 is well tolerated and has shown promising results in improving symptoms and lung function in patients with moderate to severe asthma. Other strategies for decreasing IgE levels include interferon gamma, IL-4 antibodies, IL-4 receptor antibodies and soluble IL-4 receptors.

Ligation of IgE receptors causes an anaphylactic response and neutrophil infiltration but does not induce eosinophilic inflammation in mice

BACKGROUND

Eosinophils are selectively recruited into the tissues during chronic allergic inflammation. IgE is considered an initiator of the allergic reaction; however, the roles of IgE in allergic inflammation are not fully understood.

OBJECTIVE

We tested the hypothesis that antigen interaction with specific IgE antibody provokes eosinophilic inflammation.

METHODS

BALB/c mice were actively sensitized with ragweed extract and passively sensitized with anti-dinitrophenyl (anti-DNP) mouse IgE and challenged intraperitoneally by injecting either ragweed extract or DNP-ovalbumin (OVA). Immediate anaphylactic responses were examined by monitoring vascular permeability and by measuring histamine content in peritoneal lavage fluids. Late-phase allergic responses were examined by total cell counts and cell differentials.

RESULTS

Mice sensitized and challenged with ragweed showed immediate anaphylactic responses followed by temporal increases in neutrophils at 3 to 12 hours and sustained increases in eosinophils in their peritoneal cavities after 24 hours. Double-sensitized mice (ie, sensitized actively for ragweed and passively for DNP-OVA) challenged with ragweed showed immediate anaphylactic responses and peritoneal eosinophilia at 48 hours. Double-sensitized mice challenged with DNP-OVA showed comparable immediate anaphylactic responses but no peritoneal eosinophilia. Furthermore, at 8 hours, ragweed-challenged animals recruited both eosinophils and neutrophils, but DNP-OVA-challenged animals recruited only neutrophils. Finally, after active sensitization and challenge with ragweed, mast cell-deficient mice (WBB6F1-W/W(v)) lacked the immediate response but showed comparable eosinophil accumulation as their litter mate controls (WBB6F1-+/+).

CONCLUSION

Interaction of antigen with IgE antibody is insufficient to provoke eosinophilic inflammation in mice.

The role of CD23 on allergen-induced IgE levels, pulmonary eosinophilia and bronchial hyperresponsiveness in mice

BACKGROUND

The role of Immunoglobulin (Ig)E in inflammation is the subject of considerable study and a number of studies have shown conflicting evidence for its role in eosinophil recruitment and bronchial hyperresponsiveness in a number of murine models. The low affinity IgE receptor, CD23, is known to act as a negative regulator of IgE production and we have used knockout mice deficient in CD23 to investigate the role of IgE in eosinophil recruitment and bronchial hyperresponsiveness in a murine model of airway inflammation.

OBJECTIVE

To study the role of the low affinity FcepsilonII receptor, CD23 in IgE production, lung inflammation and bronchial hyperresponsiveness.

METHODS

Wild-type and CD23 knockout C57Bl/6 mice (CD23-/-) were immunized by intraperitoneal injection with ovalbumin on days 0 and 14 and challenged with aerosolized antigen on day 21 for a period of up to 1 week. Blood samples, bronchoalveolar lavage and lung tissue samples were obtained to determine serum IgE levels and inflammatory cell numbers, respectively. Furthermore, airway resistance was measured to increasing concentrations of aerosolized 5-hydroxytryptamine in order to evaluate the effect of CD23 deficiency on bronchial hyperresponsiveness to antigen challenge.

RESULTS

Sensitization of wild-type C57Bl/6 mice to ovalbumin resulted in elevated levels of total serum IgE and ovalbumin-specific IgE, which was significantly augmented in CD23 knockout C57Bl/6 mice (CD23-/-). A significant increase in the percentage of eosinophils recovered in bronchoalveolar lavage fluid from wild-type and CD23-/- mice was observed 24 h following 3 or 7 days aerosol exposure with ovalbumin (10 mg/mL). At 3 days, the increase in the percentage of eosinophils was significantly greater in CD23-/- groups. Immunohistochemical analysis of lungs sections revealed the presence of CD3+, CD4+ and CD23+ cells in wild-type mice but a lack of immunofluorescence of CD23+ cells in CD23-/- mice. In wild-type ovalbumin-immunized mice, bronchial hyperresponsiveness to aerosolized 5-hydroxytryptamine was observed following a 3-day antigen challenge, which was significantly greater in CD23-/- ovalbumin-immunized mice.

CONCLUSION

These studies demonstrate that CD23-/- mice have increased capacity to produce IgE consistent with the view of a negative feedback role for membrane-bound CD23 and under such conditions, may account for the greater numbers of eosinophils recruited to the airways and bronchial hyperresponsiveness observed following acute but not chronic antigen challenge.

Dissociation of inflammatory and epithelial responses in a murine model of chronic asthma

To study pathogenetic mechanisms in chronic asthma, we employed a novel experimental model that replicates characteristic features of the human disease. Chronic inflammation and epithelial changes, specifically localized to the airways, were induced by repeated exposure of systemically sensitized BALB/c mice to low mass concentrations of aerosolized ovalbumin for 6 weeks. The contribution of Th2 cytokine-driven inflammation to the development of airway lesions and hyperreactivity was assessed in cytokine-deficient mice. In interleukin-5-deficient animals, intraepithelial eosinophils and chronic inflammatory cells in the lamina propria of the airways were markedly decreased; however, these animals developed epithelial hypertrophy and subepithelial fibrosis comparable with that observed in sensitized wild type mice. Airway hyperreactivity to inhaled methacholine did not develop in interleukin-5-deficient mice. In contrast, interleukin-4-deficient mice exhibited no decrease in airway inflammation, but had significantly greater epithelial hypertrophy and subepithelial fibrosis, as well as exaggerated hyperreactivity to methacholine. We conclude that interleukin-5, but not interleukin-4, plays a central role in the development of chronic inflammation of the airways and the induction of airway hyperreactivity. Furthermore, chronic epithelial and fibrotic changes occur independently of interleukin-5 and are not required for the development of airway hyperreactivity. The dissociation between airway wall remodeling and airway hyperreactivity has important implications for therapeutic approaches to chronic asthma.

IL-10 reduces Th2 cytokine production and eosinophilia but augments airway reactivity in allergic mice

We investigated the effects of interleukin (IL)-10 administration on allergen-induced Th2 cytokine production, eosinophilic inflammation, and airway reactivity. Mice were sensitized by intraperitoneal injection of ragweed (RW) adsorbed to Alum and challenged by intratracheal instillation of the allergen. Sensitization and challenge with RW increased concentrations of IL-10 in bronchoalveolar lavage (BAL) fluid from undetectable levels to 60 pg/ml over 72 h. Intratracheal instillation of 25 ng of recombinant murine IL-10 at the time of RW challenge further elevated BAL fluid IL-10 concentration to 440 pg/ml but decreased BAL fluid IL-4, IL-5, and interferon-gamma levels by 40-85% and eosinophil numbers by 70% (P < 0.0001). Unexpectedly, the same IL-10 treatment increased airway reactivity to methacholine in spontaneously breathing mice that had been sensitized and challenged with RW (P < 0.001). IL-10 treatment in naive animals or RW-sensitized mice challenged with PBS failed to increase airway reactivity, demonstrating that IL-10 induces an increase in airway reactivity only when it is administered in conjunction with allergic sensitization and challenge. The results demonstrate that IL-10 reduces Th2 cytokine levels and eosinophilic inflammation but augments airway hyperreactivity. Thus, despite its potent anti-inflammatory activity, IL-10 could contribute to the decline in pulmonary function observed in asthma.

An essential role of mast cells in the development of airway hyperresponsiveness in a murine asthma model

Immunization of BALB/c mice with alum-adsorbed OVA, followed by three bronchoprovocations with aerosolized OVA, resulted in the development of airway hyperresponsiveness (AHR) and allergic inflammation in the lung accompanied by severe infiltration of eosinophils into airways. In this murine asthma model, administration of monoclonal anti-IL-5 Ab before each Ag challenge markedly inhibited airway eosinophilia, but the treatment did not affect the development of AHR. Immunization and aerosol challenges with OVA following the same protocol failed to induce AHR in the mast cell-deficient W/Wv mice, but induced AHR in their congenic littermates, i.e., WBB6F1 (+/+) mice. No significant difference was found between the W/Wv mice and +/+ mice with respect to the IgE and IgG1 anti-OVA Ab responses and to the airway eosinophilia after Ag provocations. It was also found that reconstitution of W/Wv mice with bone marrow-derived mast cells cultured from normal littermates restored the capacity of developing Ag-induced AHR, indicating that lack of mast cells was responsible for the failure of W/Wv mice to develop Ag-induced AHR under the experimental conditions. However, the OVA-immunized W/Wv mice developed AHR by increasing the frequency and Ag dose of bronchoprovocations. The results suggested that AHR could be developed by two distinct cellular mechanisms. One would go through mast cell activation and the other is IgE/mast cell independent but an eosinophil/IL-5-dependent mechanism.

Th2 responses induced by epicutaneous or inhalational protein exposure are differentially dependent on IL-4

Atopic individuals are predisposed to mounting vigorous Th2-type immune responses to environmental allergens. To determine the factors responsible, animal models that closely mimic natural modes of allergen exposure should prove most informative. Therefore, we investigated the role of IL-4, a known Th2-promoting cytokine, in generation of Th2 responses after exposure of either the skin or airway to soluble protein. Compared with wild-type (WT) mice, IL-4-deficient (IL-4(-/-)) mice showed markedly impaired Th2 activation after primary exposure to inhaled ovalbumin (OVA), with decreased OVA-specific IgG1 and IgE, and significantly fewer eosinophils in bronchoalveolar lavage (BAL) fluid after airway challenge. In contrast, IL-4(-/-) mice initially exposed to epicutaneous (e.c.) OVA mounted Th2 responses equivalent to responses in WT mice, with high numbers of eosinophils in BAL fluid. Because Th2 responses were not induced by e.c. OVA exposure in Stat6(-/-) mice (mice lacking signal transducer and activator of transcription 6), the role of IL-13 was tested. In vivo depletion of IL-13 prevented Th2 responses induced by e.c. OVA exposure in IL-4(-/-) mice. These data demonstrate a marked difference in the IL-4 dependence of Th2 responses generated at two anatomic sites of natural allergen encounter and identify the skin as a particularly potent site for Th2 sensitization.

The role of lymphocytes in allergic disease

In the last few years strong evidence has accumulated to suggest that allergen-reactive type-2 T helper (T(H)2) cells play an important role in the induction and maintenance of the allergic inflammatory cascade. First, cytokines and chemokines produced by T(H)2 cells (GM-CSF, IL-4, IL-5, IL-6, IL-9, IL-10, IL-13, macrophage-derived chemokine) and those produced by other cell types in response to T(H)2 cytokines or as a reaction to T(H)2-related tissue damage (eotaxin, transforming growth factor-beta, IL-11) account for most pathophysiologic aspects of allergic disorders (production of IgE antibodies; recruitment or activation of mast cells, basophils, and eosinophils; mucus hypersecretion; subepithelial fibrosis; and tissue remodeling). The T(H)2 hypothesis may also explain the complex genetic background responsible for allergic disorders. Several genes are involved in the development and regulation of T(H)2 cells and may provide the reason why the prevalence of atopic allergy is increasing in Western countries. Indeed, a dramatic change has occurred in the last several decades in the "microbial" environment of children, thus probably altering the balance between T(H)1 and T(H)2 responses to "innocuous" antigens (allergens) in favor of T(H)2 responses. Finally, the T(H)2 hypothesis offers exciting opportunities for the development of novel immunotherapeutic strategies targeted to address allergen-specific T(H)2 cells or T(H)2-derived effector molecules in atopic individuals.

The role of IL-12 in the induction of late-phase cellular infiltration in a murine model of allergic conjunctivitis

BACKGROUND

The applied murine model of allergic conjunctivitis mimics human disease, and an immediate hypersensitivity reaction (IHR) and a late-phase cellular reaction typically develop in sensitized mice after topical challenge with the allergen.

OBJECTIVE

We investigated the role of IL-4, IFN-gamma, and IL-12 in the early and late phases of ocular allergy with use of cytokine knockout (KO) mice and neutralizing antibodies.

METHODS

Ragweed-sensitized wild-type or IL-4KO, IL-12KO, IFN-gamma KO, anti-IL-12 mAb-treated, recombinant murine IL-12-treated, and anti-IFN-gamma mAb-treated mice were challenged with the allergen 10 days after the immunization. IHR, cellular infiltration, lymphoproliferative response, and cytokine production from draining lymph nodes were recorded and compared among groups.

RESULTS

We show that IL-12KO mice and anti-IL-12 antibody-treated wild-type animals failed to have a cellular infiltration into the conjunctiva. Treatment with recombinant murine IL-12 also reduced the number of infiltrating PMNs but increased the percentage of mononuclear cells in the conjunctiva compared with controls. IFN-gamma KO mice had a significantly stronger IHR and prolonged infiltration into the conjunctiva after challenge with ragweed than controls.

CONCLUSION

Our data suggest that the presence of IL-12, although better known as a T(H)1-inducing cytokine, is important for the development and the regulation of the late-phase pathologic features in ocular allergy. Furthermore, IFN-gamma is a limiting factor in the late phase of allergy and thus may be important in preventing chronic allergic disease.

IL-13 in allergy: home at last

The immune response to allergic challenge is thought to include important effects mediated by cytokines. Of considerable interest to immunologists and parasitologists is the distinction between two closely related cytokines, IL-4 and IL-13. Although overlapping functions are inevitable, studies over the past year reveal a distinct role for IL-13 in mediating the physiologic response to a diverse array of allergens and parasites.

Interleukin-4 receptor in moderate atopic asthma. A phase I/II randomized, placebo-controlled trial

Interleukin-4 mediates important proinflammatory functions in asthma, including induction of the IgE isotype switch, expression of VCAM-1 on endothelium, mucin production, 15-lipoxygenase activity, and Th2 lymphocyte stimulation leading to the secondary synthesis of IL-4, IL-5, and IL-13. Soluble recombinant human IL-4 receptor (IL-4R; Nuvance; altrakincept) inactivates naturally occurring IL-4 without mediating cellular activation. Nebulized IL-4R has a serum half-life of approximately 1 wk. In this double-blind, placebo-controlled trial, 25 patients with moderate asthma requiring inhaled corticosteroids were randomly assigned to receive a single nebulized dose of IL-4R 1,500 microg, IL-4R 500 microg, or placebo after stopping inhaled corticosteroids. No drug-related toxicity was observed. Treatment with IL-4R produced significant improvement in FEV(1) on Day 4 (1,500 microg versus placebo; p < 0.05) and in FEF(25-75) on Days 2 and 4 (1,500 microg versus placebo; p < 0.05). Asthma symptom scores stabilized among patients treated with IL-4R 1, 500 microg, despite abrupt withdrawal of corticosteroids, but not in the IL-4R 500 microg group or the placebo group (p < 0.05). Patients in the IL-4R 1,500 microg group also required significantly less beta(2)-agonist rescue use (p < 0.05). Anti-inflammatory effects were further demonstrated by significantly reduced exhaled nitric oxide (p < 0.05).

CONCLUSIONS

A single dose of IL-4R appears safe and effective in moderate asthma. The 1,500 microg dose appears as safe but significantly more effective than the 500 microg dose.

Induction and regulation of the IgE response

Immunoglobulin E (IgE) is believed to be one of the major mediators of immediate hypersensitivity reactions that underlie atopic conditions such as urticaria, seasonal allergy, asthma and anaphylaxis. Factors that control IgE production are therefore essential to the pathogenesis of these important afflictions. But a complete understanding of this topic is lacking, while new data have raised questions regarding the precise role of IgE in atopic disease. Evolving concepts of IgE production and elimination are likely to clarify the importance of IgE in health and disease.

Genetic variability in pulmonary physiological, cellular, and antibody responses to antigen in mice

Wide differences among inbred mouse strains in susceptibility to develop components of asthmalike pulmonary changes would provide insights into the nature of the relationships among those components and set the stage for genetic approaches to their etiology. We therefore examined pulmonary pathophysiological and serum immunoglobulin (Ig)E responses in mice of 12 inbred strains sensitized intraperitoneally with ovalbumin (OVA) and repeatedly exposed to aerosolized OVA. One day after the last OVA exposure the intravenous methacholine (MCh) dose required to reduce lung conductance by 50% (ED(50)GL) in OVA-sensitized and exposed mice was reduced by 0 to 2.7-fold, compared with sham-sensitized mice, depending on the strain. In OVA-sensitized mice, bronchoalveolar lavage (BAL) eosinophils comprised from 3.3 +/- 3.1 (SD) to 91.2 +/- 5.0% of BAL cells and eosinophilic pulmonary inflammation varied from being nondetectable to widespread and severe. OVA-specific IgE concentrations ranged from less than 3 ng/ml to 455 ng/ml in different strains. Shifts in responsiveness correlated significantly with pulmonary eosinophilia among strains (r > 0.70, p < 0.001) but not with antigen-specific IgE levels (r = 0.55, p = 0.056). These results demonstrate that allergen- induced enhancement of cholinergic responsiveness, pulmonary eosinophil influx, and elevations of serum antigen-specific IgE levels are each genetically determined and are not always associated.

Cellular sources of enhanced brain-derived neurotrophic factor production in a mouse model of allergic inflammation

The aim of this study was to investigate production and cellular sources of brain-derived neurotrophic factor (BDNF) production in allergic asthma. For this purpose a mouse model of chronic and severe ovalbumin (OVA)-induced airway inflammation was developed. Allergen-exposed mice developed elevated immunoglobulin E titers; airway inflammation with influx of lymphocytes, monocytes, and eosinophils; and airway hyperresponsiveness. In addition to an influx of inflammatory cells, interleukin (IL)-4 and IL-5 production were enhanced, macrophages showed morphologic signs of activation, and airway epithelium was thickened and displayed a goblet-cell hyperplasia with a marked mucus production. BDNF was detected using in situ hybridization and enzyme-linked immunosorbent assay. Constitutive expression of BDNF messenger RNA (mRNA) was observed in the respiratory epithelium of sensitized and nonsensitized mouse lungs. In addition, BDNF mRNA was detected in airway inflammatory infiltrations and bronchoalveolar lavage fluid (BALF) cells of OVA-sensitized and aerosol-challenged mice. Highest BDNF protein levels were detected in BALF after long-term allergen aerosol exposure. Analysis of BDNF production by isolated lymphocyte subsets revealed T but not B cells as a cellular source of BDNF. In addition, activated alveolar macrophages were identified as BDNF-positive cells. These data indicate that in allergic airway inflammation BDNF production is upregulated and immune cells serve as a source of BDNF.

The failure of STAT6-deficient mice to develop airway eosinophilia and airway hyperresponsiveness is overcome by interleukin-5

While signal transducer and activator of transcription protein 6 (STAT6) is important in interleukin-4 (IL-4)-induced commitment of CD4(+) T cells to the T helper cell, type 2 (Th2) phenotype and IgE isotype switching in B cells, its role in other IL-4-mediated events and their impact upon the allergic response is less evident. In the present study we demonstrate the critical role of STAT6 in the development of allergic airway eosinophilia and airway hyperresponsiveness (AHR) after allergen sensitization and challenge. STAT6-deficient (STAT6-/-) mice did not develop a Th2 cytokine response or an allergen-specific IgE response. Further, STAT6-/- mice had a reduced constitutive and allergen-induced expression of CD23 as well as lower mucus production in the airway epithelium. Critically, we show that IL-5 alone can reconstitute airway eosinophilia and AHR in sensitized and challenged STAT6-/- mice. This emphasizes the essential nature of the IL-4-dependent signaling of T cells to the Th2 phenotype and secretion of IL-5, resulting in the airway eosinophilia and AHR. These observations underscore the importance of targeting this pathway in new antiallergic asthma drug development.

Secreted respiratory syncytial virus G glycoprotein induces interleukin-5 (IL-5), IL-13, and eosinophilia by an IL-4-independent mechanism

The attachment glycoprotein G of respiratory syncytial virus (RSV) is produced as both membrane-anchored and secreted forms by infected cells. Immunization with secreted RSV G (Gs) or formalin-inactivated alumprecipitated RSV (FI-RSV) predisposes mice to immune responses involving a Th2 cell phenotype which results in more severe illness and pathology, decreased viral clearance, and increased pulmonary eosinophilia upon subsequent RSV challenge. These responses are associated with increased interleukin-4 (IL-4) production in FI-RSV-primed mice, and the responses are IL-4 dependent. RNase protection assays demonstrated that similar levels of IL-4 mRNA were induced after RSV challenge in mice primed with vaccinia virus expressing Gs (vvGs) or a construct expressing only membrane-anchored G (vvGr). However, upon RSV challenge, vvGs-primed mice produced significantly greater levels of IL-5 and IL-13 mRNA and protein than vvGr-primed mice. Administration of neutralizing anti-IL-4 antibody 11.B11 during vaccinia virus priming did not alter the levels of vvGs-induced IL-5, IL-13, pulmonary eosinophilia, illness, or RSV titers upon RSV challenge, although immunoglobulin G (IgG) isotype profiles revealed that more IgG2a was produced. vvGs-priming of IL-4-deficient mice demonstrated that G-induced airway eosinophilia was not dependent on IL-4. In contrast, airway eosinophilia induced by FI-RSV priming was significantly reduced in IL-4-deficient mice. Thus we conclude that, in contrast to FI-RSV, the secreted form of RSV G can directly induce IL-5 and IL-13, producing pulmonary eosinophilia and enhanced illness in RSV-challenged mice by an IL-4-independent mechanism.

Short ragweed allergen induces eosinophilic lung disease in HLA-DQ transgenic mice

The human leukocyte antigen (HLA) restriction of the IgE response to different allergens in humans has been a subject of numerous published studies. However, the role and contribution of specific HLA class II molecules in the pathogenesis of allergic airway inflammation are unknown and difficult to assess. HLA-DQ6 and HLA-DQ8 transgenic mice lacking endogenous mouse class II gene expression were actively immunized and later challenged intranasally with short ragweed (SRW) allergenic extract. The HLA-DQ transgenic mice developed pulmonary eosinophilia and lung tissue damage. We also found an increase in total protein (TP) level and IL-5 production in bronchoalveolar lavage (BAL) fluid and an increase in SRW-specific Th2-type immunoglobulins (IgG1, IgG2b) and total serum IgE levels. Under similar treatment, DQ-negative full-sib control mice were normal. The allergic response could be significantly inhibited or abrogated in HLA-DQ mice by systemic treatment with anti-DQ mAb. The in vivo responses of HLA-DQ6 and HLA-DQ8 mice showed differences in terms of levels of eosinophilia, BAL protein, IL-5 concentration, and lung hyperreactivity to inhaled methacholine. These findings demonstrate the crucial role for specific HLA-DQ molecules in SRW-specific CD4(+) T-cell activation and resulting recruitment of eosinophils into the airways.

Contribution of nitric oxide synthases 1, 2, and 3 to airway hyperresponsiveness and inflammation in a murine model of asthma

Asthma is a chronic disease characterized by increased airway responsiveness and airway inflammation. The functional role of nitric oxide (NO) and the various nitric oxide synthase (NOS) isoforms in human asthma is controversial. To investigate the role of NO in an established model of allergic asthma, mice with targeted deletions of the three known isoforms of NOS (NOS1, 2, and 3) were studied. Although the inducible (NOS2) isoform was significantly upregulated in the lungs of ovalbumin (OVA)-sensitized and -challenged (OVA/OVA) wild-type (WT) mice and was undetectable in similarly treated NOS2-deficient mice, airway responsiveness was not significantly different between these groups. OVA/OVA endothelial (NOS3)-deficient mice were significantly more responsive to methacholine challenge compared with similarly treated NOS1 and NOS1&3-deficient mice. Airway responsiveness in OVA/OVA neuronal (NOS1)-deficient and neuronal/endothelial (NOS1&3) double-deficient mice was significantly less than that observed in similarly treated NOS2 and WT groups. These findings demonstrate an important function for the nNOS isoform in controlling the inducibility of airway hyperresponsiveness in this model of allergic asthma.

An Adoptive Transfer Model of Allergic Lung Inflammation in Mice Is Mediated by CD4+CD62LlowCD25+ T Cells

Animal models of allergic lung inflammation have provided important insight into the cellular and biochemical factors involved in the pathogenesis of human asthma. Herein, we describe an adoptive transfer model of OVA-specific eosinophilic lung inflammation in the mouse that is used to characterize the cells involved in mediating the pulmonary inflammatory response. We report that freshly isolated spleen cells from OVA-sensitized mice are unable to prime naive recipient mice to respond to a subsequent OVA aerosol challenge. Subjecting the spleen cells to short term restimulation with Ag in vitro, however, renders the cells competent to transfer activity. The magnitude and the kinetics of the eosinophilic pulmonary inflammation in the adoptive transfer recipients are nearly identical with those generated by a more conventional active sensitization/challenge protocol, with the notable exception of differential production of plasma IgE in the two models. Extensive negative and positive selection of splenocyte subtypes indicates that the transfer of Ag-primed CD4+ T cells is both necessary and sufficient to establish full responsiveness in the recipient mice. Additional phenotypic characterization of the transfer-reactive CD4+ T cells indicates that they are found within the CD62LlowCD25+ subset and secrete high levels of IL-5 in response to Ag stimulation. Limiting dilution analysis-derived minimal frequency estimates indicate that approximately 1 in 8500 of the sensitized, cultured spleen cells produces IL-5 in response to OVA stimulation in vitro, suggesting that eosinophilic lung inflammation can be induced in naive mice by the transfer of &lt;1200 Ag-specific CD4+ T cells.

Roles of TH1 and TH2 cytokines in a murine model of allergic dermatitis

Skin lesions in atopic dermatitis (AD) are characterized by hypertrophy of the dermis and epidermis, infiltration by T cells and eosinophils, and expression of the cytokines IL-4, IL-5, and IFN-gamma. The role of these cytokines in the pathogenesis of AD is not known. We took advantage of a recently described murine model of AD elicited by epicutaneous sensitization with ovalbumin (OVA) (1) and of the availability of mice with targeted deletions of the IL-4, IL-5, and IFN-gamma cytokine genes to assess the role of these cytokines in this model.OVA-sensitized skin from IL-5(-/-) mice had no detectable eosinophils and exhibited decreased epidermal and dermal thickening. Sensitized skin from IL-4(-/-) mice displayed normal thickening of the skin layers but had a drastic reduction in eosinophils and a significant increase in infiltrating T cells. These findings were associated with a reduction in eotaxin mRNA and an increase in mRNA for the T-cell chemokines macrophage inflammatory protein-2 (MIP-2), MIP-1beta, and RANTES. Sensitized skin from IFN-gamma-/- mice was characterized by reduced dermal thickening. These results suggest that both the TH2 cytokines IL-4 and IL-5 and the TH1 cytokine IFN-gamma play important roles in the inflammation and hypertrophy of the skin in AD.

IL-5 and Eosinophils Are Essential for the Development of Airway Hyperresponsiveness Following Acute Respiratory Syncytial Virus Infection

Viral respiratory infections can cause bronchial hyperresponsiveness and exacerbate asthma. In mice, respiratory syncytial virus (RSV) infection, which induces an immune response dominated by IFN-γ, results in airway hyperresponsiveness (AHR) and eosinophil influx into the airways, both of which are prevented by pretreatment with anti-IL-5 Ab. To delineate the role of IL-5, IL-4, and IFN-γ in the development of RSV-induced AHR and lung eosinophilia, we tested the ability of mice deficient in each of these cytokines to develop these symptoms of RSV infection. Mice deficient in either IL-5, IL-4, or IFN-γ were administered infectious RSV intranasally, and 6 days later, airway responsiveness to inhaled methacholine was assessed by barometric body plethysmography, and numbers of lung eosinophils and production of IFN-γ, IL-4, and IL-5 by mononuclear cells from peribronchial lymph nodes were monitored. RSV infection resulted in airway eosinophilia and AHR in both IL-4- and IFN-γ-deficient mice, but not in IL-5-deficient mice. Reconstitution of IL-5-deficient mice with IL-5 restored these responses and enhanced the responses in IL-4-deficient mice. Anti-VLA-4 (very late Ag-4) treatment prevented lung eosinophilia and AHR following RSV infection and IL-5 reconstitution. We conclude that in response to RSV, IL-5 is essential for the influx of eosinophils into the lung and that eosinophils in turn are critical for the development of AHR. IFN-γ and IL-4 are not essential for these responses to RSV infection.

Antigen-induced airway hyperresponsiveness, pulmonary eosinophilia, and chemokine expression in B cell-deficient mice

Murine models of allergen-induced pulmonary inflammation share many features with human asthma, including the development of antigen-induced pulmonary eosinophilia, airway hyperresponsiveness, antigen-specific cellular and antibody responses, the elaboration of Th2 cytokines (interleukin [IL]-4 and IL-5), and the expression of chemokines with activity for eosinophils. We examined the role of B cells and antigen-specific antibody responses in such a model by studying the histopathologic and physiologic responses of B cell-deficient mice compared with wild-type controls, following systemic immunization and airway challenge with ovalbumin (OVA). Both OVA-challenged wild-type and B cell-deficient mice developed (1) airway hyperresponsiveness, (2) pulmonary inflammation with activated T cells and eosinophils, (3) IL-4 and IL-5 secretion into the airway lumen, and (4) increased expression of the eosinophil active chemokines eotaxin and monocyte chemotactic protein-3. There were no significant differences in either the pathologic or physiologic responses in the B cell-deficient mice compared with wild-type mice. These data indicate that B cells and antigen-specific antibodies are not required for the development of airway hyperresponsiveness, eosinophilic pulmonary inflammation, and chemokine expression in sensitized mice following aerosol challenge with antigen.

Interleukin-8 receptor modulates IgE production and B-cell expansion and trafficking in allergen-induced pulmonary inflammation

We examined the role of the interleukin-8 (IL-8) receptor in a murine model of allergen-induced pulmonary inflammation using mice with a targeted deletion of the murine IL-8 receptor homologue (IL-8r-/-). Wild-type (Wt) and IL-8r-/- mice were systemically immunized to ovalbumin (OVA) and were exposed with either single or multiple challenge of aerosolized phosphate-buffered saline (OVA/PBS) or OVA (OVA/OVA). Analysis of cells recovered from bronchoalveolar lavage (BAL) revealed a diminished recruitment of neutrophils to the airway lumen after single challenge in IL-8r-/- mice compared with Wt mice, whereas multiply challenged IL-8r-/- mice had increased B cells and fewer neutrophils compared with Wt mice. Both Wt and IL-8r-/- OVA/OVA mice recruited similar numbers of eosinophils to the BAL fluid and exhibited comparable degrees of pulmonary inflammation histologically. Both total and OVA-specific IgE levels were greater in multiply challenged IL-8r-/- OVA/OVA mice than in Wt mice. Both the IL-8r-/- OVA/OVA and OVA/PBS mice were significantly less responsive to methacholine than their respective Wt groups, but both Wt and IL-8r mice showed similar degrees of enhancement after multiple allergen challenge. The data demonstrate that the IL-8r modulates IgE production, airway responsiveness, and the composition of the cells (B cells and neutrophils) recruited to the airway lumen in response to antigen.

The cell surface expression level of the human interleukin-5 receptor alpha subunit determines the agonistic/antagonistic balance of the human interleukin-5 E13Q mutein

The human interleukin-5 (IL-5) receptor consists of an alpha-chain that specifically binds the ligand with intermediate affinity, and a beta c-chain, that associates with the IL-5/IL-5R alpha complex, leading to a high-affinity, signal transducing receptor complex. Structure-function studies showed that modification of the putative beta c-chain binding site in IL-5 (E13Q mutein) converted the molecule into an antagonist. However, analysis of the effect of this mutant IL-5 on COS-1 cells transfected with both receptor subunits, did not show reduced interaction with the beta c subunit [Tavernier, J., Tuypens, T., Verhee, A., Plaetinck, G., Devos, R., Van der Heyden, J., Guisez, Y. & Oefner, C. (1995) Proc. Natl Acad. Sci. USA 89, 7041-7045]. To gain more insight into the mechanism of IL-5 antagonism by E13Q, we tested its biological activity on two FDC-P1 subclones that express clearly different numbers of alpha-subunits yet an almost constant number of murine beta c-subunits. Here we show that E13Q has a biological activity comparable to wild-type IL-5 only when a high number of alpha-chains is present on the cells. Confirming the critical role of the IL5R alpha cell-surface expression level, treatment with suboptimal doses of a neutralising anti-IL-5R alpha antibody results in reduced activity of the mutant but not of wild-type IL-5.

Gene expression of the GATA-3 transcription factor is increased in atopic asthma

BACKGROUND

High expression of IL-5 by T cells in the airways of asthmatic individuals is believed to play a fundamental role in the eosinophilia associated with this disease. Recently, the transcription factor GATA-3 was shown to be critical for IL-5 gene expression in TH2 cells in vitro.

OBJECTIVE

Our aim was to examine the expression of GATA-3 mRNA and its colocalization within the airways of asthmatic and nonasthmatic individuals.

METHODS

We investigated the association between GATA-3 gene expression, airway inflammatory cells, and IL-5 gene expression in bronchoalveolar lavage fluid and bronchial biopsy specimens from atopic asthmatic subjects (n = 10) and normal control subjects (n = 10).

RESULTS

We report that GATA-3 mRNA expression is significantly increased in the airways of asthmatic subjects compared with those of normal control subjects (P <.001). Numbers of cells expressing GATA-3 transcripts correlated significantly with reduced airway caliber (P <.05) and airways hyperresponsiveness (P <.05) in asthmatic subjects. Colocalization studies showed that the majority (approximately 60% to 90%) of GATA-3 mRNA+ cells in asthmatic airways were CD3(+) T cells, with smaller contributions from major basic protein+ eosinophils and tryptase+ mast cells. The density of GATA-3 mRNA+ cells correlated significantly with the numbers of cells expressing IL-5 mRNA (P <.001, r = 0.879 for bronchoalveolar lavage fluid; P <. 05, r = 0.721 for biopsy specimens). Furthermore, double in situ hybridization demonstrated that approximately 76% of GATA-3 mRNA+ cells coexpressed IL-5 mRNA and that 91% of IL-5 mRNA+ cells coexpressed GATA-3 mRNA.

CONCLUSION

The results of this study provide the first evidence of increased GATA-3 gene expression in association with IL-5 mRNA+ cells in asthmatic airways. These findings support a causal association between augmented GATA-3 expression and dysregulated IL-5 expression in atopic asthma.

Immune dysregulation as a cause for allergic asthma

Allergic asthma is being increasingly understood as a disease caused by Th2-mediated immune responses to inhaled allergens. Most individuals fail to respond to allergens with a Th2 response, and thus, allergic asthma can be considered the result of an abnormally regulated or dysregulated immune response. The prevalence of asthma has risen precipitously in urbanized cultures, as contrasted with third world countries. This observation underlies the heightened efforts in the past few years of basic and applied research efforts to gain a better understanding of both normal and dysregulated immunity to antigens introduced via the airways. This review focuses on recent human studies into the immune dysregulation that results in the asthma phenotype, but also cites selected relevant papers from research with experimental animals.

STAT6 deficiency in a mouse model of allergen-induced airways inflammation abolishes eosinophilia but induces infiltration of CD8+ T cells

BACKGROUND

The TH2-type cytokines have been reported to contribute to the asthmatic response. STAT6 has an essential role in IL-4 signalling and in production of TH2 cytokines from T cells and is involved in IgE and IgG1 responses after nematode infections, indicating that STAT6 has an important role in allergic diseases.

OBJECTIVE

In this study we investigated the effects of STAT6 deficiency on allergen-induced airways inflammation in mice.

METHODS

Both ovalbumin (OVA)-sensitized STAT6 deficient (STAT6-/-) mice and wild-type C57BL/6 mice were challenged with aerosolized OVA. Changes in inflammatory cell infiltration and cytokine levels in lung tissue as well as serum immunoglobulin levels were analysed in OVA-challenged STAT6-/- and wild-type mice.

RESULTS

The eosinophilia and lung damage normally resulting from aeroallergen challenge were not seen in STAT6-/- mice. Expression of TH2 cytokines (IL-4 and IL-5) in the lung tissue as well as IgE and IgG1 responses after OVA challenge were profoundly reduced in STAT6-/- mice, whereas expression of IFNgamma was the same in STAT6-/- mice and wild-type mice after OVA challenge. Immunocytochemical analysis of T cells showed the infiltration of CD4+ T cells but not CD8+ T cells increased into the lung of wild-type mice after OVA challenge. However, the OVA-exposed STAT6-/- mice demonstrated the infiltration of both CD4+ T cells and CD8+ T cells with a significant increase in percentage and total number of CD8+ T cells compared with OVA-exposed wild-type mice.

CONCLUSION

These results indicate that factors which signal through STAT6 are important regulators of eosinophilia of allergic airway inflammation, regulating TH2-type cytokine production both in CD4+ T cells and CD8+ T cells.

Cutting Edge: IL-4-Independent Induction of Airway Hyperresponsiveness by Th2, But Not Th1, Cells

We investigated the role of Th1 or Th2 cells in airway hyperresponsiveness (AHR), because both IFN-γ and IL-4 and IL-5-producing CD4 T cells have been identified in the airways of asthmatics. After transfer of in vitro-generated TCR transgenic Th1 or Th2 cells and exposure to inhaled Ag, Th2 cells induced AHR and airway eosinophilia, whereas Th1 cells induced neutrophilic inflammation without AHR. Next, to determine the precise effector function of IL-4 in Th2 cell-induced AHR, we transferred IL-4−/− Th2 cells into wild-type and IL-4−/− recipient mice. After exposure to inhaled Ag, both groups of mice exhibited AHR with markedly reduced airway eosinophilia. Thus, IL-4 production by Th2 cells is not essential for the induction of AHR, but is critical for the migration of eosinophils from lung tissue into the airways.

Expression of interleukin 9 in the lungs of transgenic mice causes airway inflammation, mast cell hyperplasia, and bronchial hyperresponsiveness

Interleukin (IL)-9, a pleiotropic cytokine produced by the Th2 subset of T lymphocytes has been proposed as product of a candidate gene responsible for asthma. Its wide range of biological functions on many cell types involved in the allergic immune response suggests a potentially important role in the complex pathogenesis of asthma. To investigate the contributions of IL-9 to airway inflammation and airway hyperresponsiveness in vivo, we created transgenic mice in which expression of the murine IL-9 cDNA was regulated by the rat Clara cell 10 protein promoter. Lung selective expression of IL-9 caused massive airway inflammation with eosinophils and lymphocytes as predominant infiltrating cell types. A striking finding was the presence of increased numbers of mast cells within the airway epithelium of IL-9-expressing mice. Other impressive pathologic changes in the airways were epithelial cell hypertrophy associated with accumulation of mucus-like material within nonciliated cells and increased subepithelial deposition of collagen. Physiologic evaluation of IL-9-expressing mice demonstrated normal baseline airway resistance and markedly increased airway hyperresponsiveness to inhaled methacholine. These findings strongly support an important role for IL-9 in the pathogenesis of asthma.

Cellular and molecular regulation of eosinophil trafficking to the lung

Airway inflammation is central to the pathogenesis of allergic asthma, and molecules that mediate this process obviously represent targets for therapy. In the present article, we discuss our experiments, which point to CD4+ T cells and IL-5-driven eosinophilia as potential targets for the relief of bronchial hyperreactivity in late-phase asthma.

An improved murine model of asthma: selective airway inflammation, epithelial lesions and increased methacholine responsiveness following chronic exposure to aerosolised allergen

BACKGROUND

Existing murine models of asthma lack many of the inflammatory and epithelial changes that are typical of the human disease. Moreover, these models are frequently complicated by allergic alveolitis.

METHODS

High IgE responder BALB/c mice were systemically sensitised to ovalbumin and chronically challenged with low particle mass concentrations of aerosolised ovalbumin. Titres of antiovalbumin IgE in serum were measured at two weekly intervals by enzyme immunoassay, accumulation of inflammatory cells and histopathological abnormalities of the epithelium were quantified morphometrically in the trachea and the lungs, and airway reactivity was assessed by measuring bronchoconstriction following intravenous administration of methacholine.

RESULTS

Mice sensitised by two intraperitoneal injections of ovalbumin developed high titres of IgE antibodies to ovalbumin. Following exposure to low concentrations of aerosolised antigen for up to eight weeks these animals developed a progressive inflammatory response in the airways, characterised by the presence of intraepithelial eosinophils and by infiltration of the lamina propria with lymphoid/mononuclear cells, without associated alveolitis. Goblet cell hyperplasia/metaplasia was induced in the intrapulmonary airways, while epithelial thickening and subepithelial fibrosis were evident following chronic exposure. In parallel, the mice developed increased sensitivity to induction of bronchospasm, as well as increased maximal reactivity. Non-immunised mice exposed to aerosolised ovalbumin had low or absent antiovalbumin IgE and did not exhibit inflammatory or epithelial changes, but developed airway hyperreactivity.

CONCLUSIONS

This experimental model replicates many of the features of human asthma and should facilitate studies of pathogenetic mechanisms and of potential therapeutic agents.

Interleukin-4 and interleukin-5 as targets for the inhibition of eosinophilic inflammation and allergic airways hyperreactivity

Clinical and experimental investigations suggest that allergen-specific CD4+ T-cells, IgE and the cytokines IL-4 and IL-5 play central roles in initiating and sustaining an asthmatic response by regulating the recruitment and/or activation of airways mast cells and eosinophils. IL-5 plays a unique role in eosinophil development and activation and has been strongly implicated in the aetiology of asthma. The present paper summarizes our recent investigations on the role of these cytokines using cytokine knockout mice and a mouse aeroallergen model. Investigations in IL-5-/-mice indicate that this cytokine is critical for regulating aeroallergen-induced eosinophilia, the onset of lung damage and airways hyperreactivity during allergic airways inflammation. While IL-4 and allergen-specific IgE play important roles in the regulation of allergic disease, recent investigations in IL-4-/- mice suggest that allergic airways inflammation can occur via pathways which operate independently of these molecules. Activation of these IL-4 independent pathways are also intimately associated with CD4+ T-cells, IL-5 signal transduction and eosinophilic inflammation. Such IL-5 regulated pathways may also play a substantive role in the aetiology of asthma. Thus, evidence is now emerging that allergic airways disease is regulated by humoral and cell mediated processes. The central role of IL-5 in both components of allergic disease highlights the requirements for highly specific therapeutic agents which inhibit the production or action of this cytokine.

A Novel T Cell-Regulated Mechanism Modulating Allergen-Induced Airways Hyperreactivity in BALB/c Mice Independently of IL-4 and IL-5

The immunoregulatory functions of IL-4 and IL-5 have identified these cytokines as primary targets for the resolution of airways inflammation and bronchial hyperreactivity in asthma. However, the individual contribution of each of these cytokines and of IL-5-regulated eosinophilia to the induction of airways hyperreactivity in mouse models of asthma remains highly controversial. In this investigation, we have used IL-4- and IL-5-deficient mice of the same genetic background in combination with inhibitory mAbs to these cytokines to identify unequivocally the contribution of these factors to the induction of airways hyperreactivity. Sensitization and aeroallergen challenge of wild-type mice with OVA induced pathological changes to the respiratory epithelium, airways eosinophilia, and hyperreactivity to β-methacholine. Inhibition of the actions of IL-4 and/or IL-5 did not abolish airways hyperreactivity, and in the case of IL-4-deficient mice pretreated with anti-IL-5 mAb, airways hyperreactivity persisted in the absence of pronounced airways inflammation. Airways hyperreactivity was abolished only by anti-CD4+ mAb treatment. However, aeroallergen challenge of IL-5−/− mice showed that morphologic changes to the airways were critically linked to IL-5 and eosinophilia. This investigation demonstrates the existence in BALB/c mice of a novel CD4+ T cell pathway for modulating airways hyperreactivity. These findings may provide an explanation for the dissociation of airways eosinophilia from the development of airways hyperreactivity observed in some cases of asthma and in animal models of this disease.

Abrogation of bronchial eosinophilic inflammation and airway hyperreactivity in signal transducers and activators of transcription (STAT)6-deficient mice

Signal transducers and activators of transcription 6 (STAT6) is essential for interleukin 4-mediated responses, including class switching to IgE and induction of type 2 T helper cells. To investigate the role of STAT6 in allergic asthma in vivo, we developed a murine model of allergen-induced airway inflammation. Repeated exposure of actively immunized C57BL/6 mice to ovalbumin (OVA) aerosol increased the level of serum IgE, the number of eosinophils in bronchoalveolar lavage (BAL) fluid, and airway reactivity. Histological analysis revealed peribronchial inflammation with pulmonary eosinophilia in OVA-treated mice. In STAT6-deficient (STAT6-/-) C57BL/6 mice treated in the same fashion, there were no eosinophilia in BAL and significantly less peribronchial inflammation than in wild-type mice. Moreover STAT6-/- mice had much less airway reactivity than wild-type mice. These findings suggest that STAT6 plays a crucial role in the pathogenesis of allergen-induced airway inflammation.

Requirements for allergen-induced airway hyperreactivity in T and B cell-deficient mice

BACKGROUND

The pathogenesis of asthma is believed to reflect antigen-induced airway inflammation leading to the recruitment of eosinophils and activation of mast cells through cell-associated IgE. Controversies persist however, regarding the relative importance of different pathogenic cells and effector molecules.

MATERIALS AND METHODS

A variety of gene-targeted mice were examined for the induction of cholinergic airway hyperresponsiveness (AH), allergic airway inflammation, mucus production, and serum IgE reactivity following intratracheal challenge with a potent allergen. AH was determined using whole-body plethysmography following acetylcholine challenge. Where possible, results were confirmed using neutralizing antibodies and cell-specific reconstitution of immune deficient mice.

RESULTS

T and B cell-deficient, recombinase-activating-gene-deficient mice (RAG -/-) failed to develop significant allergic inflammation and AH following allergen challenge. Reconstitution of RAG -/- mice with CD4+ T cells alone was sufficient to restore allergen-induced AH, allergic inflammation, and goblet cell hyperplasia, but not IgE reactivity. Sensitized B cell-deficient mice also developed airway hyperreactivity and lung inflammation comparable to that of wild-type animals, confirming that antibodies were dispensable. Treatment with neutralizing anti-IL-4 antibody or sensitization of IL-4-deficient mice resulted in loss of airway hyperreactivity, whereas treatment with anti-IL-5 antibody or sensitization of IL-5-deficient mice had no effect.

CONCLUSIONS

In mice, CD4+ T cells are alone sufficient to mediate many of the pathognomonic changes that occur in human asthma by a mechanism dependent upon IL-4, but independent of IL-5, IgE, or both. Clarification of the role played by CD4+ T cells is likely to stimulate important therapeutic advances in treatment of asthma.