Effect of acute and chronic antigen inhalation on airway morphology and responsiveness in actively sensitized rats

Asthma: The Use of Animal Models and Their Translational Utility

Asthma is characterized by chronic lower airway inflammation that results in airway remodeling, which can lead to a permanent decrease in lung function. The pathophysiology driving the development of asthma is complex and heterogenous. Animal models have been and continue to be essential for the discovery of molecular pathways driving the pathophysiology of asthma and novel therapeutic approaches. Animal models of asthma may be induced or naturally occurring. Species used to study asthma include mouse, rat, guinea pig, cat, dog, sheep, horse, and nonhuman primate. Some of the aspects to consider when evaluating any of these asthma models are cost, labor, reagent availability, regulatory burden, relevance to natural disease in humans, type of lower airway inflammation, biological samples available for testing, and ultimately whether the model can answer the research question(s). This review aims to discuss the animal models most available for asthma investigation, with an emphasis on describing the inciting antigen/allergen, inflammatory response induced, and its translation to human asthma.

Differences in allergic inflammatory responses in murine lungs: comparison of PM2.5 and coarse PM collected during the hazy events in a Chinese city

Urban particulate matter (PM) is associated with an increase in asthma. PM2.5 (<PM2.5 μm) and coarse PM (CPM: PM2.5-PM10 μm) were collected from the air in a Chinese city during haze events. The amounts of polycyclic aromatic hydrocarbons (PAHs) were higher in PM2.5 than in CPM. Conversely, microbial elements LPS and β-glucan were much higher in CPM than in PM2.5. Concentrations of Si, Al, Fe, and Ti in CPM were greater than in PM2.5, while Pb, Cu and As concentrations were lower than in PM2.5. When RAW264.7 cells were treated with PM2.5 and CPM, the pro-inflammatory response in the cells was associated with the microbial element levels and attenuated partly by both polymyxin B (PMB) and N-acetylcystein (NAC). The expression of the oxidative stress response gene heme oxygenase1 was associated with PAHs levels. The exacerbating effects of the two-types of PM on murine lung eosinophilia were compared to clarify the role of toxic materials. When BALB/c mice were intratracheally instilled with PM2.5 or CPM (total 0.4 mg) + ovalbumin (OVA), both exacerbated lung eosinophilia along with allergy-relevant biological indicators, such as OVA-specific IgE in serum; enhancement of lung pathology when compared with counterpart samples without OVA. The exacerbating effects were greater in microbial element-rich CPM than in organic chemical-rich PM2.5. These results indicate that microbial elements have more potently exacerbating effects on the development of lung eosinophilia than do organic chemicals. In addition, oxidative stress and transition metals might be associated with the exacerbation of this negative effect.

Desert dust induces TLR signaling to trigger Th2-dominant lung allergic inflammation via a MyD88-dependent signaling pathway

Asian sand dust (ASD) is known to exacerbate asthma, although its mechanism is not yet well understood. In this study, when the effects on inflammatory response by LPS present in ASD was investigated by measuring the gene expression of cytokines and chemokines in RAW264.7 cells treated with ASD and/or polymyxin B (PMB), the ASD effects were attenuated by PMB, but not completely. When an in vitro study was performed using bone marrow-derived macrophages (BMDMs) from WT, TLR2(-/-), TLR4(-/-), and MyD88(-/-) BALB/c mice and BMDMs from WT, TLR2(-/-), TLR4(-/-), TLR2/4(-/-), TLR7/9(-/-), and MyD88(-/-) C57BL/6J mice, cytokine (IL-6, IL-12) production in BMDMs was higher in ASD-stimulated TLR2(-/-) cells than in TLR4(-/-) cells, whereas it was lower or undetectable in TLR2/4(-/-) and MyD88(-/-) cells. These results suggest that ASD causes cytokine production predominantly in a TLR4/MyD88-dependent pathway. When WT and TLRs 2(-/-), 4(-/-), and MyD88(-/-) BALB/c mice were intratracheally challenged with OVA and/or ASD, ASD caused exacerbation of lung eosinophilia along with Th2 cytokine and eosinophil-relevant chemokine production. Serum OVA-specific IgE and IgG1 similar to WT was observed in TLRs 2(-/-), 4(-/-) mice, but not in MyD88(-/-) mice. The Th2 responses in TLR2(-/-) mice were attenuated remarkably by PMB. These results indicate that ASD exacerbates lung eosinophilia in a MyD88-dependent pathway. TLRs 2 and 4 signaling may be important in the increase in lung eosinophilia. Also, the TLR4 ligand LPS and TLR2 ligand like β-glucan may be strong candidates for exacerbation of lung eosinophilia.

Silica-carrying particulate matter enhances Bjerkandera adusta-induced murine lung eosinophilia

Bjerkandera adusta (B. adusta) causes fungus-associated chronic cough. However, the inflammatory response is not yet fully understood. Recently, B. adusta was identified in Asian sand dust (ASD) aerosol. This study investigated the enhancing effects of ASD on B. adusta-induced lung inflammation. B. adusta was inactivated by formalin. ASD was heated to remove toxic organic substances. ICR mice were intratracheally instilled with saline, B. adusta 0.2 µg, or B. adusta 0.8 µg with or without heated ASD 0.1 mg (H-ASD), four times at 2-week intervals. Two in vitro experiments were conducted to investigate any enhancing effects using bone marrow-derived macrophages (BMDM) from Toll-like receptor (TLR) knockout mice and ICR mice. Co-exposure to H-ASD and B. adusta, especially at high doses, caused eosinophil infiltration, proliferation of goblet cells in the airway, and fibrous thickening of the subepithelial layer, and remarkable increases in expression of Th2 cytokines and eosinophil-related cytokine and chemokine expression in bronchoalveolar lavage fluid. In the in vitro study using BMDM from wild-type, TLR2-/-, and TLR4-/- mice, the TLR-signaling pathway for cytokine production caused by B. adusta was predominantly TLR2 rather than TLR4. H-ASD increased the expression of NF-κB and cytokine production by B. adusta in BMDM from ICR mice. The results suggest that co-exposure to H-ASD and B. adusta caused aggravated lung eosinophilia via remarkable increases of pro-inflammatory mediators. The aggravation of inflammation may be related, at least in part, to the activation of the TLR2-NF-κB signaling pathway in antigen presenting cells by H-ASD.

Effect of combined nitrogen dioxide and carbon nanoparticle exposure on lung function during ovalbumin sensitization in Brown Norway rat

The interaction of particulate and gaseous pollutants in their effects on the severity of allergic inflammation and airway responsiveness are not well understood. We assessed the effect of exposure to NO₂ in the presence or absence of repetitive treatment with carbon nanoparticle (CNP) during allergen sensitization and challenges in Borwn-Norway (BN) rat, in order to assess their interactions on lung function and airway responses (AR) to allergen and methacholine (MCH), end-expiratory lung volume (EELV), bronchoalveolar lavage fluid (BALF) cellular content, serum and BALF cytokine levels and histological changes. Animals were divided into the following groups (n = 6): Control; CNP (Degussa-FW2): 13 nm, 0.5 mg/kg instilled intratracheally ×3 at 7-day intervals; OVA: ovalbumin-sensitised; OVA+CNP: both sensitized and exposed to CNP. Rats were divided into equal groups exposed either to air or to NO₂, 10 ppm, 6 h/d, 5d/wk for 4 weeks. Exposure to NO₂, significantly enhanced lung inflammation and airway reactivity, with a significantly larger effect in animals sensitized to allergen, which was related to a higher expression of TH1 and TH2-type cytokines. Conversely, exposure to NO₂ in animals undergoing repeated tracheal instillation of CNP alone, increased BALF neutrophilia and enhanced the expression of TH1 cytokines: TNF-α and IFN-γ, but did not show an additive effect on airway reactivity in comparison to NO₂ alone. The exposure to NO₂ combined with CNP treatment and allergen sensitization however, unexpectedly resulted in a significant decrease in both airway reactivity to allergen and to methacholine, and a reduction in TH2-type cytokines compared to allergen sensitization alone. EELV was significantly reduced with sensitization, CNP treatment or both. These data suggest an immunomodulatory effect of repeated tracheal instillation of CNP on the proinflammatory effects of NO₂ exposure in sensitized BN rat. Furthermore, our findings suggest that NO₂, CNP and OVA sensitization may significantly slow overall lung growth in parenchymally mature animals.

Preclinical animal models of asthma and chronic obstructive pulmonary disease

Animal models of disease serve a vital function in the search for novel therapeutic approaches. While these systems cannot replicate human disease, they can be used to mimic and investigate mechanisms believed to be central to disease pathogenesis. In this review, we discuss the most relevant and commonly used animal models for asthma and chronic obstructive pulmonary disease (COPD); specifically, models developed for the mouse, rat and guinea pig. Allergens, such as ovalbumin, can be used to induce an IgE-dependent response characterized by early- and late-phase bronchoconstriction, inflammation and airway hyper-responsiveness similar to what occurs in asthmatics. Similarly, elastase and cigarette smoke can be used to replicate steroid-insensitive and progressive inflammation, which leads to lung pathologies that are observed in COPD patients. We also discuss how these models are developing in new ways to more closely reflect the clinical disease. Unfortunately, these models have limitations due to differences in genetics, anatomy and physiology among the species, many of which we have highlighted; however, understanding these differences, careful characterization of these models and parallel in vitro or ex vivo studies using human and relevant animal tissues will overcome some of these issues. In spite of these limitations, as long as studies are designed and interpreted appropriately, in vivo models will continue to be vital for furthering our understanding of disease pathogenesis and for developing new therapies.

Oral tolerance attenuates airway inflammation and remodeling in a model of chronic pulmonary allergic inflammation

We investigated the effects of oral tolerance (OT) in controlling inflammatory response, hyperresponsiveness and airway remodeling in guinea pigs (GP) with chronic allergic inflammation. Animals received seven inhalations of ovalbumin (1-5mg/mL-OVA group) or normal saline (NS group). OT was induced by offering ad libitum ovalbumin 2% in sterile drinking water starting with the 1st ovalbumin inhalation (OT1 group) or after the 4th (OT2 group). The induction of OT in sensitized animals decreased the elastance of respiratory system (Ers) response after both antigen and methacholine challenges, peribronchial edema formation, eosinophilic airway infiltration, eosinophilopoiesis, and airways collagen and elastic fiber content compared to OVA group (P<0.05). The number of mononuclear cells and resistance of respiratory system (Rrs) responses after antigen and methacholine challenges were decreased only in OT2 group compared to OVA group (P<0.05). Concluding, our results show that inducing OT attenuates airway remodeling as well as eosinophilic inflammation and respiratory system mechanics.

Effects of nebulized ketamine on allergen-induced airway hyperresponsiveness and inflammation in actively sensitized Brown-Norway rats

Since airway hyperresponsiveness (AHR) and allergic inflammatory changes are regarded as the primary manifestations of asthma, the main goals of asthma treatment are to decrease inflammation and maximize bronchodilation. These goals can be achieved with aerosol therapy. Intravenous administration of the anesthetic, ketamine, has been shown to trigger bronchial smooth muscle relaxation. Furthermore, increasing evidence suggests that the anti-inflammatory properties of ketamine may protect against lung injury. However, ketamine inhalation might yield the same or better results at higher airway and lower ketamine plasma concentrations for the treatment of asthma. Here, we studied the effect of ketamine inhalation on bronchial hyperresponsiveness and airway inflammation in a Brown-Norway rat model of ovalbumin(OVA)-induced allergic asthma. Animals were actively sensitized by subcutaneous injection of OVA and challenged by repeated intermittent (thrice weekly) exposure to aerosolized OVA for two weeks. Before challenge, the sensitizened rats received inhalation of aerosol of phosphate-buffered saline (PBS) or aerosol of ketamine or injection of ketamine respectivity. Airway reactivity to acetylcholine (Ach) was measured in vivo, and various inflammatory markers, including Th2 cytokines in bronchoalveolar lavage fluid (BALF), as well as induciable nitric oxide synthase (iNOS) and nitric oxide (NO) in lungs were examined. Our results revealed that delivery of aerosolized ketamine using an ultrasonic nebulizer markedly suppressed allergen-mediated airway hyperreactivity, airway inflammation and airway inflammatory cell infiltration into the BALF, and significantly decreased the levels of interleukin-4 (IL-4) in the BALF and expression of iNOS and the concentration of NO in the inflamed airways from OVA-treated rats. These findings collectively indicate that nebulized ketamine attenuated many of the central components of inflammatory changes and AHR in OVA-provoked experimental asthma, potentially providing a new therapeutic approach against asthma.

Loss of pro-apoptotic Bim promotes accumulation of pulmonary T lymphocytes and enhances allergen-induced goblet cell metaplasia

Immunological tolerance during prolonged exposure to allergen is accompanied by a shift in the lymphocyte content and a reduction of goblet cell metaplasia (GCM). Bim initiates negative selection of autoreactive T and B cells and shut down of T cell immune responses in vivo. The present study investigated whether Bim plays a role in the resolution of GCM during prolonged exposure to allergen. Loss of Bim increased T lymphocyte numbers in the bronchoalveolar lavage at 4 and 15 days of allergen exposure. The numbers of pulmonary CD4(+)8(-), CD4(-)8(+), and gammadelta T cells were significantly higher in naive and allergen-challenged bim(-/-) mice compared with wild-type (WT) littermates. When activated, pulmonary bim(-/-) T cells produced increased levels of IFNgamma compared with bim(+/+) T cells. No differences were noted in the total numbers of epithelial cells per millimeter of basal lamina between bim(+/+) and bim(-/-) mice, and the rate of resolution over 15 days of exposure was similar in both groups of mice. However, GCM was significantly enhanced and expression of IL-13Ralpha2 was reduced in bim(-/-) mice compared with WT mice at 4 days. Furthermore, treatment of bronchiolar explant cultures with increasing IFNgamma levels reduced immunostaining for IL-13Ralpha2. Collectively, these studies suggest that, during prolonged exposure to allergen, Bim plays no role in the resolution of GCM, but increased IFNgamma levels in bim(-/-) mice may be responsible for reduced expression of IL-13Ralpha2 and enhanced GCM despite similar levels of IL-13 in bim(+/+) and bim(-/-) mice.

Modulation of citric acid-induced cough following lipopolysaccharide-mediated neutrophilia in the guinea pig

This investigation examined a possible correlation between lipopolysaccharide (LPS)-induced pulmonary neutrophilia and cough. Conscious male guinea pigs were acutely exposed to aerosolized LPS and thereafter at various times challenged with citric acid aerosol (CA; 250mM) to induce cough followed by bronchoalveolar lavage (BAL) to quantitate inflammatory cell accumulation. LPS caused a hyporesponsive cough at 24h post-LPS with neutrophilia apparent from 2h post-LPS. By 96h post-LPS both cough and neutrophilia had returned towards normal. Dexamethasone (DEX, 2mgkg(-1)/day for 3 days prior) did not affect the cough hyporesponsiveness at 24h; however it attenuated LPS-induced BAL fluid neutrophilia. Since LPS can stimulate inducible nitric oxide synthase (iNOS) we hypothesized that the cough hyporesponsiveness may involve nitric oxide. To investigate this we treated animals with an aerosolized iNOS inhibitor 1400W (1mM) immediately prior to LPS. 1400W had no significant effect on either cough hyporesponsiveness or BAL fluid neutrophilia at 24h post-LPS. Despite differing effects on neutrophilia, these findings clearly indicate that neither DEX nor iNOS inhibition had any direct effect on LPS-induced cough hyporesponsiveness. The mechanism underlying the LPS-induced cough hyporesponsiveness does not appear to be directly linked to LPS-induced neutrophilic inflammation.

Comparison of early and late responses to antigen of sensitized guinea pig parenchymal lung strips

The peripheral lung parenchyma has been studied as a component of the asthmatic inflammatory response. During induced constriction, tissue resistance increases in different asthma models. Approximately 60% of the asthmatic patients show early and late responses. The late response is characterized by more severe airway obstruction. In the present study, we evaluated lung parenchymal strips mechanics in ovalbumin-sensitized guinea pigs, trying to reproduce both early and late inflammatory responses. Oscillatory mechanics of lung strips were performed in a control group (C), in an early response group (ER), and in two late response groups: 17 h (L1) and 72 h (L2) after the last ovalbumin challenge. Measurements of resistance and elastance were obtained before and after ovalbumin challenge in C and ER groups and before and after acetylcholine challenge in all groups. Using morphometry, we assessed the density of eosinophils and smooth muscle cells, as well as collagen and elastin content in lung strips. The baseline and postagonist values of resistance and elastance were increased in ER, L1, and L2 groups compared with C (P < or = 0.001). The morphometric analysis showed an increase in alveolar eosinophil density in ER and L2 groups compared with C (P < 0.05). There was a significant correlation between eosinophil density in parenchymal strips of C, L1, and L2 groups and values of resistance and elastance postacetylcholine (r = 0.71, P = 0.001 and r = 0.74, P < 0.001, respectively). The results show that the lung parenchyma is involved in the late response, and the constriction response in this phase is related to the eosinophilic inflammation.

Neurokinins and inflammatory cell iNOS expression in guinea pigs with chronic allergic airway inflammation

In the present study we evaluated the role of neurokinins in the modulation of inducible nitric oxide synthase (iNOS) inflammatory cell expression in guinea pigs with chronic allergic airway inflammation. In addition, we studied the acute effects of nitric oxide inhibition on this response. Animals were anesthetized and pretreated with capsaicin (50 mg/kg sc) or vehicle 10 days before receiving aerosolized ovalbumin or normal saline twice weekly for 4 wk. Animals were then anesthetized, mechanically ventilated, given normal saline or N(G)-nitro-l-arginine methyl ester (l-NAME, 50 mg/kg ic), and challenged with ovalbumin. Prechallenge exhaled NO increased in ovalbumin-exposed guinea pigs (P < 0.05 compared with controls), and capsaicin reduced this response (P < 0.001). Compared with animals inhaled with normal saline, ovalbumin-exposed animals presented increases in respiratory system resistance and elastance and numbers of total mononuclear cells and eosinophils, including those expressing iNOS (P < 0.001). Capsaicin reduced all these responses (P < 0.05) except for iNOS expression in eosinophils. Treatment with l-NAME increased postantigen challenge elastance and restored both resistance and elastance previously attenuated by capsaicin treatment. Isolated l-NAME administration also reduced total eosinophils and mononuclear cells, as well as those cells expressing iNOS (P < 0.05 compared with ovalbumin alone). Because l-NAME treatment restored lung mechanical alterations previously attenuated by capsaicin, NO and neurokinins may interact in controlling airway tone. In this experimental model, NO and neurokinins modulate eosinophil and lymphocyte infiltration in the airways.

Comparison of glucocorticoid and cysteinyl leukotriene receptor antagonist treatments in an experimental model of chronic airway inflammation in guinea-pigs

BACKGROUND

Leukotriene receptor antagonists have been demonstrated in several studies to possess bronchodilating and anti-inflammatory properties in asthma. However, there are few experimental studies performed to compare the effects of anti-leukotrienes and glucocorticoids, most used anti-inflammatory agents in asthma. In the present study, we evaluated the effects of treatment with dexamethasone or montelukast on eosinophil and mononuclear cell recruitment in an experimental model of allergen-induced chronic airway inflammation in guinea-pigs (GP).

METHODS

GP were submitted to increasing concentrations of aerosols of ovalbumin (OVA) twice a week for 4 weeks. After 2 weeks, animals were treated daily with dexamethasone, montelukast or saline solution. After this period, GP were anaesthetized, tracheostomized, mechanically ventilated and challenged with OVA aerosol.

RESULTS

Maximal changes of respiratory system resistance and elastance induced by OVA challenge were attenuated by dexamethasone (P<0.001), but not by montelukast treatment. Neither dexamethasone nor montelukast significantly influenced bronchial oedema formation. Dexamethasone but not montelukast induced a decrease in mononuclear cells in airways (P<0.001). Eosinophil infiltration in the bronchial wall was reduced by both dexamethasone and montelukast (P<0.005). Only dexamethasone treatment reduced the levels of exhaled nitric oxide (P<0.025).

CONCLUSION

Although leukotriene receptor antagonist treatment reduces eosinophil accumulation induced by multiple antigen challenges, glucocorticoid treatment attenuates both eosinophil and mononuclear cell infiltration.

Site of inflammation influences site of hyperresponsiveness in experimental asthma

BACKGROUND

Our recently developed murine asthma model is capable of inducing airway-specific chronic inflammatory changes and remodeling, features of human asthma commonly missing in conventional animal models.

OBJECTIVES

To validate this model by site-specific physiological evaluation of hyperresponsiveness.

METHODS

Non-sensitized and sensitized mice received either short-term uncontrolled or long-term controlled low-level exposures to aerosolized ovalbumin (OVA). Respiratory impedance (Zrs) was measured in response to increasing doses of methacholine (Mch). The constant-phase model was fitted to Zrs spectra to determine the specific site of hyperresponsiveness.

RESULTS

Sensitized acutely exposed mice had significantly increased tissue damping (G), tissue elastance (H) and hysteresivity (eta) in response to Mch, but no significant increase in airway resistance (Raw), indicating tissue-specific hyperresponsiveness. In contrast, sensitized chronically exposed mice had significantly elevated Raw at all concentrations of Mch but no increases in G, H or eta indicating airway-specific hyperresponsiveness.

CONCLUSIONS

Chronic inhalational exposure of sensitized mice to low-mass concentrations of OVA induces airway-specific hyperresponsiveness.

Effect of SCH55700, a humanized anti-human interleukin-5 antibody, in severe persistent asthma: a pilot study

Antagonizing the effect of interleukin (IL)-5 is a potential new treatment strategy in allergic disorders. We evaluated the safety, biological activity, and pharmacokinetics of SCH55700, a humanized anti-human IL-5 antibody, in subjects with severe persistent asthma treated with oral or high doses of inhaled steroids. In a double-blind, randomized, multicenter trial, a rising single dose of SCH55700 (0.03 mg/kg [n = 2], 0.1 mg/kg [n = 4], 0.3 mg/kg [n = 6], or 1.0 mg/kg [n = 12]) or placebo (n = 8) was administered intravenously. SCH55700 dose dependently reduced circulating eosinophil counts. At a dose of 1.0 mg/kg, the decrease remained significant up to Day 30 [(0.07 +/- 0.01) x 10(9)/L versus (0.23 +/- 0.04) x 10(9)/L at baseline] (mean +/- SEM) (p = 0.05). After administration of SCH55700 at 0.3 and 1.0 mg/kg, a trend toward improvement in baseline FEV1 was observed, which reached significance 24 hours after the 0.3-mg/kg dose (p = 0.019 versus placebo). No significant changes occurred in other clinical indices of disease activity. Adverse events were not different between active treatment and placebo. We conclude that SCH55700 is a biologically active anti-human IL-5 antibody that can be safely used in severe steroid-treated asthma. Its therapeutic potential needs to be addressed in specifically designed efficacy trials.

Chronic bronchial allergic inflammation increases alveolar liquid clearance by TNF-alpha -dependent mechanism

Bronchial inflammation in allergic asthma is associated with active exudation from the bronchial tree into the interstitial space of both mucosa and submucosa. The aim of this study was to evaluate epithelial and endothelial permeability as well as alveolar fluid movement in a model of chronic allergic inflammation in Brown-Norway rats sensitized and challenged with ovalbumin (OA). Control groups were challenged with saline solution (C), and rats were immunized by OA but not challenged (Se). Lung sections showed a marked inflammatory infiltrate associated with perivascular and peribronchiolar edema in OA. To measure alveolar liquid clearance, a 5% bovine albumin solution with 1 microCi of (125)I-labeled human albumin was instilled into the air spaces. Alveolar-capillary barrier permeability was evaluated by intravascular injection of 1 microCi of (131)I-labeled albumin. Endothelial permeability was significantly increased in OA, from 0.08 +/- 0.01 in the C group to 0.19 +/- 0.03 in OA group (P < 0.05). Final-to-initial protein ratio was also statistically higher in OA (1.6 +/- 0.05) compared with C (1.38 +/- 0.03, P = 0.01) and Se groups (1.42 +/- 0.03, P = 0.04). Administration of anti-tumor necrosis factor-alpha antibodies within the instillate significantly decreased this ratio (1.32 +/- 0.08, P = 0.003 vs. OA). To conclude, we demonstrated a tumor necrosis factor-alpha-dependent increase in alveolar fluid movement in a model of severe bronchial allergic inflammation associated with endothelial and epithelial leakage.

Chronic exposure to innocuous antigen in sensitized mice leads to suppressed airway eosinophilia that is reversed by granulocyte macrophage colony-stimulating factor

In this study we investigated the impact of chronic allergen exposure on airway inflammation and humoral responses in sensitized mice. We observed marked eosinophilia in the bronchoalveolar lavage, lung tissue, and peripheral blood after 2 wk of exposure. In contrast, eosinophilia was markedly reduced by 3 wk and completely resolved by 4 wk of exposure, despite the continued presence of Ag. Decreases in airway eosinophilia were associated with a robust humoral response. We observed that levels of OVA-specific IgE, IgG1, and IgG2a increased during the course of exposure. To assess whether continuous exposure to Ag impacts the ability of the lung to respond to subsequent Ag challenge, mice were exposed to either 2 or 4 wk of OVA in the context of GM-CSF. All groups were then rested for 28 days and exposed to OVA on three consecutive days. We observed a significant decrease in airway eosinophilia and IL-5 expression in the bronchoalveolar lavage and serum in mice initially exposed to 4 wk of OVA, compared with animals exposed to 2 wk only. However, in both groups expression of B7.2 on dendritic cells as well as CD25, CD69, and T1/ST2 on CD4(+) T cells was enhanced, suggesting immune activation. Delivery of rGM-CSF fully restored airway eosinophilia. This study shows that exposure to innocuous Ag alone does not lead to persistent eosinophilic airway inflammation, but rather to abrogated eosinophilia. This suppression can be reversed by GM-CSF.

Antigen-induced airway inflammation in the Brown Norway rat results in airway smooth muscle hyperplasia

Asthma is characterized by chronic airways inflammation, airway wall remodeling, and airway hyperresponsiveness (AHR). An increase in airway smooth muscle has been proposed to explain a major part of AHR in asthma. We have used unbiased stereological methods to determine whether airway smooth muscle hyperplasia and AHR occurred in sensitized, antigen-challenged Brown Norway (BN) rats. Ovalbumin (OA)-sensitized BN rats chronically exposed to OA aerosol displayed airway inflammation and a modest level of AHR to intravenously administered ACh 24 h after the last antigen challenge. However, these animals did not show an increase in smooth muscle cell (SMC) number in the left main bronchus, suggesting that short-lived inflammatory mechanisms caused the acute AHR. In contrast, 7 days after the last aerosol challenge, there was a modest increase in SMC number, but no AHR to ACh. Addition of FCS to the chronic OA challenge protocol had no effect on the degree of inflammation but resulted in a marked increase in both SMC number and a persistent (7-day) AHR. These results raise the possibility that increases in airway SMC number rather than, or in addition to, chronic inflammation contribute to the persistent AHR detected in this model.

Modeling allergic asthma in mice: pitfalls and opportunities

Studies in murine experimental models have contributed greatly to understanding the mechanisms of allergic inflammation underlying asthma. However, models involving short-term high-level exposure of sensitized animals to antigen have significant limitations for investigating the pathogenesis of the lesions of chronic asthma. Modeling chronic asthma is problematic, because long-term antigenic challenge often triggers widespread pulmonary parenchymal inflammation or leads to eventual downregulation of inflammation and airway hyperreactivity. We have developed an improved murine model in which animals are exposed to low mass concentrations of aerosolized antigen for 6-8 wk. The mice exhibit airway-specific acute-on-chronic inflammation and changes of airway wall remodeling as seen in human asthma, together with hyperreactivity to a cholinergic agonist which can be specifically attributed to airway disease. This more realistic model of asthma offers a number of opportunities for investigation of pathogenetic mechanisms and novel therapeutic agents.

Ozone differentially modulates airway responsiveness in atopic versus nonatopic guinea pigs

While acute exposures to ozone (O(3)) can alter airway responsiveness, effects from long-term exposures at low concentrations are less clear. This study assessed whether such exposures could induce nonspecific hyperresponsiveness in nonatopic (nonsensitized) guinea pigs and/or could exacerbate the pre-existing hyperresponsive state in atopic (sensitized) animals, and whether gender was a factor modulating any effect of O(3). Responsiveness was measured during and following exposures to 0.1 and 0.3 ppm O(3) for 4 h/day, 4 days/wk for 24 wk in male and female nonsensitized animals, those sensitized to allergen (ovalbumin) prior to initiation of O(3) exposures, and those sensitized concurrently with exposures. Ozone did not produce hyperresponsiveness in nonsensitized animals, but did exacerbate hyperresponsiveness to both specific and nonspecific bronchoprovocation challenges in sensitized animals, an effect that persisted through at least 4 wk after exposures ended. Gender was not a factor modulating response to O(3). Induced effects on responsiveness were not associated with numbers of eosinophils in the lungs nor with any chronic pulmonary inflammatory response, but were correlated with antigen-specific antibodies in blood. This study supports a role for chronic O(3) exposure in the exacerbation of airways dysfunction in a certain segment of the general population, namely, those demonstrating atopy.

IFN-gamma, but not Fas, mediates reduction of allergen-induced mucous cell metaplasia by inducing apoptosis

Inflammatory responses induced by allergen exposure cause mucous cell metaplasia (MCM) by differentiation of existing and proliferating epithelial cells into mucus-storing cells. Airway epithelia have various mechanisms that resolve these changes to form normal airway epithelia. In this report, we first investigated the state of mucous cell metaplasia and the mechanisms by which MCM is reduced despite continued exposures to allergen. After 5 days of allergen exposure, extensive MCM had developed but was reduced when allergen challenge was continued for 15 days. During this exposure period, IL-13 levels decreased and IFN-gamma levels increased in the bronchoalveolar lavage fluid. In contrast, IL-13 levels decreased but IFN-gamma was not detected at any time point during the resolution of MCM following cessation of allergen exposure. Instillation of IFN-gamma but not anti-Fas caused accelerated resolution of MCM and MCM was not resolved in Stat1-deficient mice exposed to allergen for 15 days, confirming that IFN-gamma is crucial for reducing MCM during prolonged exposures to allergen. IFN-gamma but not anti-Fas induced apoptotic cell death in proliferating normal human bronchial epithelial cells and in human bronchial epithelial cells from subjects with asthma. The apoptotic effect of IFN-gamma was caspase dependent and was inhibited by IL-13, indicating that the Th2 milieu in asthmatics may maintain MCM by preventing cell death in metaplastic mucous cells. These studies could be useful in the understanding of deficiencies leading to chronicity in airway changes and designing novel therapies to reverse MCM and airway obstruction in asthmatics.

Airway hyperresponsiveness to adenosine induced by lipopolysaccharide in Brown Norway rats

We have explored the effects of bacterial endotoxin (lipopolysaccharide; LPS) on the response of the airways of Brown Norway (BN) rats to adenosine. Comparisons have been drawn with the effects on responses to methacholine and 5-hydroxytryptamine. In vehicle-challenged animals, adenosine, given i.v. was only a weak bronchoconstrictor. In contrast, 1 h following intratracheal administration of LPS, 0.3 mg kg-1, bronchoconstrictor responses to adenosine were markedly and selectively enhanced. At this time point, there were no significant changes in leukocyte numbers, eosinophil peroxidase and myeloperoxidase activities or protein concentrations in bronchoalveolar lavage (BAL) fluid. Twenty-four hours after challenge, the sensitivity of the airways to both adenosine and methacholine was reduced relative to the earlier time point and there were substantial increases in each marker of inflammation in BAL fluid. The bronchoconstrictor response to adenosine was blocked selectively by methysergide, disodium cromoglycate and the broad-spectrum adenosine receptor antagonist, 8-SPT, but not by DPCPX or ZM 243185, selective antagonists for the A1 and A2A receptors, respectively. Thus, the response to adenosine augmented following LPS is mast cell mediated and involves a receptor which can be blocked by 8-SPT but not by selective A1 or A2A receptor antagonists. It thus bears similarity to the augmented response to adenosine induced by allergen challenge in actively sensitized BN rats. Exposure to LPS could be a factor along with allergen in determining the increased sensitivity of the airways of asthmatics to adenosine.

Understanding airway wall remodeling in asthma: a basis for improvements in therapy?

Current strategies for the management of asthma focus on suppressing airway inflammation. Other characteristic features of human asthma, such as airway hyperreactivity and the structural changes collectively referred to as airway remodeling, are largely ignored in existing guidelines for monitoring the effectiveness of treatment. Evidence is accumulating that pharmacologic therapy targeting airway wall remodeling may be valuable in treating asthma. However, development of appropriate therapeutic agents will require a better understanding of the pathogenesis of remodeling, which appears to be regulated by a variety of cytokines and growth factors produced by inflammatory, epithelial, and stromal cells. Furthermore, testing the effectiveness of novel agents that specifically target the process of remodeling will require appropriate experimental models, but most currently available animal models of asthma have major limitations. A recently described murine model of chronic human asthma offers considerable potential for dissection of the mechanisms of airway wall remodeling, as well as for investigation of the therapeutic potential of drugs that can modulate chronic inflammation and remodeling.

Murine model of chronic human asthma

Human asthma is associated with acute and chronic inflammation of the airway mucosa, accompanied by airway wall remodelling. Experimental models of acute allergic bronchopulmonary inflammation in mice are useful for investigation of immunological mechanisms and of cellular recruitment, but have significant limitations because they fail to reproduce a number of characteristic lesions of human asthma, while usually being associated with marked alveolitis. We have developed an improved murine model of asthma that exhibits almost all of the morphological and functional changes that typify the human disease, without any confounding alveolitis. This model has considerable potential for the investigation of pathogenetic mechanisms and potential treatments of chronic human asthma.

New anti-asthma therapies: suppression of the effect of interleukin (IL)-4 and IL-5

Asthma is currently defined as a chronic inflammatory disorder of the airways. The central role of allergen-specific Th2 cells in the regulation of this mucosal airway inflammation has been highlighted. Hence, there is large interest in the therapeutic potential of an anti-Th2 cell approach. One of the strategies which has been developed, is to inhibit the effect of interleukin (IL)-4 or IL-5, two main Th2 cell derived cytokines. Interleukin-4 is pivotal in the pathogenesis of allergic disorders through its wide range of effects. An important observation, especially during secondary antigen exposure, is the possible redundancy with IL-13. Both cytokines share common elements in their receptor and intracellular signalling pathway. As a result, compounds can be developed that selectively inhibit the effect of either IL-4 or IL-13, or alternatively, by interfering with the common pathway, inhibit the effect of both cytokines. Eosinophils are generally seen as a particularly harmful element in the allergic inflammation. The importance of IL-5 on eosinophil biology has clearly been established. Conversely, in man, the biological effects of IL-5 are largely limited to eosinophil function. Therefore, IL-5 antagonists offer the unique opportunity of selectively neutralizing the effect of eosinophils. Several strategies have now been developed that successfully inhibit the biological effect of interleukin-4 or interleukin-5. Some of these compounds have proven to be biologically active in man. The challenge now is to establish their therapeutic role in asthma.

Mediator involvement in antigen-induced bronchospasm and microvascular leakage in the airways of ovalbumin sensitized Brown Norway rats

1. To determine which mediators are involved in antigen-induced bronchospasm and microvascular leakage in the airways of ovalbumin sensitised Brown Norway rats we investigated the effect of a histamine H(1) receptor antagonist, mepyramine, a 5-HT receptor antagonist, methysergide, and a cys-leukotriene-1 receptor antagonist, montelukast. 2. Ovalbumin at 1 mg kg(-1) i.v. caused a significant increase in microvascular leakage in the airways and at 3 mg kg(-1) i.v. caused a significant increase in airways resistance. 3. Histamine (1 mg kg(-1) i.v.), 5-HT (0.1 mg kg(-1) i.v.) and leukotriene D(4) (LTD(4), 50 microg kg(-1) i.v.) caused a significant increase in microvascular leakage in the airways. 4. Mepyramine (1 mg kg(-1) i.v.), methysergide (0.1 mg kg(-1) i.v.), or montelukast (30 mg kg(-1) i.v.) inhibited histamine, 5-HT or LTD(4) -induced microvascular leakage respectively. 5. Methysergide (0.1 mg kg(-1) i.v.) reduced ovalbumin-induced microvascular leakage in the trachea and at 0.3 mg kg(-1) i.v. inhibited bronchospasm (38 and 58%, respectively). Montelukast (30 mg kg(-1) p.o.) reduced ovalbumin-induced microvascular leakage in airway tissue to basal levels (78%) and inhibited ovalbumin-induced bronchospasm (50%). Mepyramine (3 mg kg(-1) i.v.) had no effect on ovalbumin-induced leakage or bronchospasm. 6. A combination of all three compounds (mepyramine, methysergide and montelukast) reduced ovalbumin-induced microvascular leakage in airway tissue to basal levels (70 - 78%) and almost completely inhibited bronchospasm (92%). 7. Antigen-induced bronchospasm appears to equally involve the activation of 5-HT and cys-leukotriene-1 receptors whereas ovalbumin-induced microvascular leakage appears to be predominantly mediated by cys-leukotriene-1 receptors.

Animal models of asthma: potential usefulness for studying health effects of inhaled particles

Asthma is now recognized to be a chronic inflammatory disease that affects the whole lung. Incidence appears to be increasing despite improved treatment regimens. There is substantial epidemiological evidence suggesting a relationship between the incidence and severity of asthma (e.g., hospitalizations) and exposure to increased levels of air pollution, especially fine and ultrafine particulate material, in susceptible individuals. There have been a few studies in animal models that support this concept, but additional animal studies to test this hypothesis are needed. However, such studies must be performed with awareness of the strengths and weaknesses of the currently available animal models. For studies in mice, the most commonly used animal, a broad spectrum of molecular and immunological tools is available, particularly to study the balance between Th1 and Th2 responses, and inbred strains may be useful for genetic dissection of susceptibility to the disease. However, the mouse is a poor model for bronchoconstriction or localized immune responses that characterize the human disease. In contrast, allergic lung diseases in dogs and cats may more accurately model the human condition, but fewer tools are available for characterization of the mechanisms. Finally, economic issues as well as reagent availability limit the utility of horses, sheep, and primates.

Ovalbumin aeroallergen exposure-response in Brown Norway rats

A major route of exposure to allergens is through the respiratory tract. Comparatively few animal studies have used aerosolized high-molecular-weight allergens for sensitization, and in these studies, proper characterization of the aeroallergen exposure was usually missing. The purpose of this study was to profile the exposure-response relationship in Brown Norway rats (BNR) to well-characterized ovalbumin (OVA) aerosols. Rats were exposed 30 min/wk x 6 wk to respirable OVA aerosols from <1 mg/m(3) to 64 mg/m(3) air. Ovalbumin-specific circulating immunoglobulin (Ig)E, IgG, and IgA were measured throughout the study period. Rats were sacrificed 1 day after the last exposure. Pulmonary tissue was processed for histopathological and histochemical analysis. Tracheas were isolated, perfused, and assessed for in vitro responsiveness to methacholine. Serum concentrations of OVA-specific antibodies increased with both exposure concentration and number of exposures. The number of BNR with measurable titers also increased with both dose and time. Pulmonary inflammatory changes were noted only in BNR exposed to higher OVA concentrations (15 and 64 mg/m(3) air). Increased tracheal reactivity to methacholine was not found in any of the sensitized BNR. In summary, sustained aeroallergen concentration-dependent changes in specific antibody responses and pulmonary inflammation have been demonstrated.

Prolonged allergen exposure induces structural airway changes in sensitized rats

The pathogenesis and functional consequences of airway remodeling in asthma remain to be fully established. In the present study we evaluated the effect of prolonged allergen exposure on airway function and structure in rats. Sensitized Brown Norway rats were repeatedly exposed for periods of 2, 4, or 12 wk to aerosolized ovalbumin (OA) or phosphate-buffered saline (PBS). OA exposure induced a persistent increase in OA-specific serum IgE and in the number of peribronchial eosinophils. After 2 wk of OA exposure, airway histology revealed goblet-cell hyperplasia, an increase in bromodeoxyuridine-positive cells in airway epithelium, increased fibronectin deposition, and a thickening of the airway inner wall area. This coincided with airway hyperresponsiveness (AHR) to aerosolized carbachol. After OA exposure for 12 wk, increased fibronectin (p < 0.05 versus PBS) and collagen deposition (p < 0.05 versus PBS) were observed in the submucosa. After 12 wk of exposure, neither total nor inner wall area or airway responsiveness to carbachol were any longer significantly different from those of PBS-exposed animals. In conclusion, prolonged OA exposure in rats induces structural airway changes that bear similarities to airway remodeling in asthma. The study data further indicate that depending on the extent and distribution of remodeling, changes in the extracellular matrix can enhance or protect against AHR.

Sensitization to inhaled antigen by intratracheal instillation of dendritic cells

BACKGROUND

Airway dendritic cells (DCs) capture and present inhaled antigen. It is not known whether antigen presentation by DCs in the airways is sufficient to induce sensitization to inhaled antigen in vivo.

METHODS

Rats were immunized by intratracheal instillation of ovalbumin (OVA) -pulsed bone marrow-derived DCs or macrophages and exposed 10 days later to a 30-min aerosol of OVA on 3 consecutive days. Total and differential cell counts and flow cytometry on bronchoalveolar lavage (BAL) fluid, airway histology and serum OVA-immunoglobulin (Ig) E levels were analysed 24 h after the last exposure.

RESULTS

As few as 2 x 104 OVA-DC induced sensitization to inhaled OVA. The secondary response to OVA-aerosol consisted of an antigen-specific increase in the number of bronchoalveolar mononuclear cells, activated CD4-positive alphabeta-TCR T lymphocytes, neutrophils and few eosinophils. Peribronchial and perivascular mononuclear cell infiltrates were seen on histological analysis. There was no production of systemic OVA-IgE. Bone marrow-derived macrophages did not induce sensitization.

CONCLUSION

Delivering antigen to the respiratory tract via professional antigen-presenting DCs sensitizes for a secondary response to inhaled antigen leading to airway inflammation. This model will prove very useful for studying the early events of sensitization to inhaled antigen using the respiratory route.

Allergen-induced changes in bone-marrow progenitor and airway dendritic cells in sensitized rats

Eosinophilic airway inflammation is orchestrated by T-helper (Th)-2 lymphocytes. We have previously demonstrated that dendritic cells (DC) are essential for the presentation of antigen to these Th2 cells leading to airway inflammation. Here, we have examined the presence of DC in the lungs, the kinetics of appearance, and the possible involvement of the bone-marrow progenitor for DC in a rat model of ovalbumin (OVA)-induced airway inflammation. Sensitized rats were exposed to 0, 1, 3, or 7 consecutive daily OVA aerosols. Control rats were sham sensitized and/or exposed to phosphate-buffered saline (PBS), and bronchoalveolar lavage (BAL) was performed 24 h after the last challenge. DC were identified in BAL fluid as low-density, low-autofluorescence, CD3(-), CD45RA-, OX62(+), OX6(+) cells that had long surface extensions and strong costimulatory activity. Low but detectable amounts of BAL DC were seen in sensitized, unexposed animals. After three OVA exposures, the inflammatory infiltrate consisted of CD4(+)-activated T cells, eosinophils, and monocytes. The number of BAL DC was significantly increased in OVA-sensitized/OVA-exposed animals compared with sham-sensitized or PBS-exposed animals. The kinetics of DC increase closely parallelled those in other inflammatory cells. Bone-marrow cells taken from the OVA-sensitized and -exposed group were grown in the DC growth factor granulocyte macrophage colony-stimulating factor for 6 d and the yield of OX62(+)OX6(+) DC was 60% higher compared with PBS-exposed or sham-sensitized animals. We conclude that allergen exposition in sensitized rats increases the number of DC in the airways and the production of progenitors for DC in the bone marrow.

CD4+ T cells can induce airway hyperresponsiveness to allergen challenge in the brown norway rat

Airway hyperresponsiveness to inhalational challenge with methacholine (MCh) develops by 32 h after allergen challenge of actively sensitized BN rats. To test the hypothesis that CD4+ T cells mediate allergen-induced hyperresponsiveness independent of IgE-mediated mechanisms, we administered CD4+ T cells, CD8+ T cells, and a mixture of CD4+ and CD8+ T cells (total T cells) isolated from the cervical lymph nodes of rats sensitized with ovalbumin (OA) to naive BN rats that underwent aerosol challenge with either OA or bovine serum albumin (BSA) 2 d later. Responsiveness to MCh was measured 2 d before transfer of T cells and 32 h after challenge with OA or BSA. Airway responsiveness increased significantly in recipients of CD4+ T cells after OA challenge, but not in any other of the treatment groups. Analysis of bronchoalveolar lavage (BAL) cells for major basic protein expression by immunostaining showed eosinophilia in OA-challenged CD4+ and total T-cell recipients. Cells retrieved by bronchoalveolar lavage showed increased expression of IL-5 mRNA (in situ hybridization) in CD4+ T cell recipients after OA challenge compared with other groups. Interferon-gamma mRNA was expressed to the greatest extent in CD8+ recipients, but it was elevated in both OA- and BSA-challenged animals. We conclude that CD4+ T cells can induce airway hyperresponsiveness after inhalational challenge with allergen and this is associated with IL-5 production and eosinophilia. CD8+ T cells may have a negative regulatory effect on responsiveness, possibly mediated by interferon-gamma.

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.

Effect of chronic antigen inhalation in guinea pigs

To examine the role of airway inflammation in airway hyperresponsiveness (AHR), we examined the effect of chronic antigen inhalation in sensitized guinea pigs. Guinea pigs were actively sensitized with dinitrophenylated Ascaris suum extract (DNP-As) and repeatedly exposed to aerosolized DNP-As antigen once a day for 4 or 10 days. Twenty-four hours after the last antigen exposure, airway responsiveness to inhaled acetylcholine (ACh) and bronchoalveolar lavage (BAL) were studied. The guinea pigs receiving 4 days of exposure to antigen demonstrated an increase in airway responsiveness to inhaled ACh (p < 0.05). On the other hand, the guinea pigs receiving 10 days of exposure to antigen showed no significant change in airway responsiveness to inhaled ACh. BAL fluid analysis indicated that a significant increase in the number of eosinophils and neutrophils was observed in both groups of guinea pigs. A significant increase in the number of lymphocytes in BAL fluid was observed in guinea pigs exposed for 10 days, but not in those exposed for 4 days. We conclude that repeated exposure to antigen induced both development and suppression of AHR. Our results suggest that airway inflammation may play a role in both the development and suppression of AHR.

CD23 deficient mice develop allergic airway hyperresponsiveness following sensitization with ovalbumin

The low affinity receptor for IgE (CD23) is reported to regulate immune and inflammatory events and as a result, it may have a role in the development of allergic airway inflammation and hyperresponsiveness (AHR). To test this hypothesis CD23-deficient mice were studied following different modes of allergic sensitization. Mice were actively sensitized either intraperitoneally with ovalbumin (OA)/alum or via the airways (10 days exposure to OA aerosol with no adjuvant). Passive sensitization was performed by intravenous injections of OA-specific IgE. Airway responsiveness, serum IgE and IgG levels were assessed together with airway inflammation. Passive sensitization followed by airway challenges resulted in increased OA-specific lgG and IgE in the serum of wild-type mice only, while both the CD23+/+ and CD23-/- groups developed tracheal smooth muscle hyperresponsiveness to electrical field stimulation, indicating that IgE/CD23-mediated immune functions may not be necessary for the development of allergic changes. Active sensitization of both CD23-/- and CD23+/+ mice resulted in increased serum levels of OA-specific IgE and lgG, airway eosinophilia and significant AHR when compared with nonsensitized mice. The genetic deficiency of CD23-/- mice not only failed to prevent but was associated with a significant increase of these responses. These results indicate that CD23 may not be essential for the development of allergen-induced AHR and further, that its presence may have some inhibitory effects on the allergic response.

Bronchial hyperresponsiveness, epithelial damage, and airway eosinophilia after single and repeated allergen exposure in a rat model of anhydride-induced asthma

Bronchial hyperresponsiveness (BHR) and damage of the epithelium, as well as eosinophilia in the airway wall, induced by trimellitic anhydride (TMA) in sensitized brown Norway rats were studied. Rats were challenged once or seven times with aerosol of TMA conjugated to rat serum albumin (TMA-RSA) 3 weeks after intradermal TMA sensitization. Airway responsiveness (-log PC300 of acetylcholine i.v.) was measured 24 h after allergen challenge. Epithelial lesion and eosinophil infiltration in the airway walls were quantified under light microscopy, and TMA-specific IgE and IgG in serum were evaluated with ELISA. High levels of TMA-specific IgE and IgG were found in all rats in the sensitized groups compared to nonsensitized groups (P < 0.001). Repeated allergen challenges of 0.03% TMA-RSA for 7 consecutive days enhanced the level of TMA-specific IgG, compared to single challenge (P < or = 0.05). Single allergen challenge of 0.3% TMA-RSA had a nonsignificant tendency to produce BHR in sensitized rats compared to nonsensitized rats (P = 0.06). However, repeated allergen challenges (0.003% and 0.03% TMA-RSA for 7 consecutive days) produced significant BHR in sensitized rats (P < 0.05). Furthermore, repeated low-dose (0.003%) TMA-RSA challenge produced more BHR than a 10 times higher single dose (0.03%) (P < 0.05). Slight damage of the airway epithelium was seen in sensitized and repeat-challenged groups. However, bronchial eosinophilia was found in the sensitized and single-challenged groups, but not in nonsensitized nonchallenged, and sensitized repeat-challenged groups (P < 0.005). We conclude that the brown Norway rat can be sensitized with TMA, and that repeated low-dose allergen challenges produce slight epithelial damage and BHR which is independent of ongoing eosinophilia in the airway wall.

Airway hyper- or hyporeactivity to inhaled spasmogens 24 h after ovalbumin challenge of sensitized guinea-pigs

1. The aim of this study was to determine whether an inhalation of ovalbumin (OA, 10 or 20 mg ml-1) by conscious OA-sensitized guinea-pigs leads to airway hyperreactivity to spasmogens 24 h later. In contrast to most previous studies, the spasmogens (5-HT, methacholine (MCh), U-46619 and adenosine) were administered by inhalation and airway function was measured in conscious guinea-pigs. 2. Guinea-pigs were sensitized by i.p. injection of 10 micrograms OA and 100 mg aluminium hydroxide in 1 ml normal saline; 14-21 days later they were exposed to an inhalation of 5-HT, MCh, U-46619 or adenosine. Specific airway conductance (sGaw) was measured in conscious animals by whole body plethysmography. The spasmogens caused bronchoconstriction, measured as a reduction in sGaw from the pre-inhalation basal values. Dose-related bronchoconstrictions were observed with 5-HT, MCh and U-46619. 3. The effect of an ovalbumin macroshock challenge upon the responses to each spasmogen were examined by giving an inhalation of aerosolized OA at 24 h (or 7 days in the cause of adenosine) after an initial spasmogen challenge. Eighteen to twenty-four hours after the OA macroshock, the same guinea-pigs were exposed to a repeated inhalation of 5-HT, MCh, U-46619 or adenosine. 4. U-46619 was the only spasmogen to demonstrate hyperresponsiveness, the peak change in sGaw being increased from -12.3 +/- 9.9 to -38.8 +/- 5.0% by 10 mg ml-1 OA challenge. In contrast, the ovalbumin challenge (20 mg ml-1) inhibited the bronchoconstrictions to 5-HT (50 micrograms ml-1) and MCh (100 micrograms ml-1). Adenosine demonstrated bronchoconstriction in sensitized guinea-pigs but no significant change in the response was observed after an OA challenge. 5. All results were compared with a control group of sensitized guinea-pigs receiving a NaCl challenge. The bronchoconstrictor responses to 5-HT, MCh, U-46619 or adenosine did not differ significantly before and after the saline challenge, indicating reproducibility of the responses. 6. In further experiments, guinea-pigs were exposed to inhalation of 5-HT (50 micrograms ml-1) or MCh (300 micrograms ml-1) 24 h before atropine (10 micrograms, 100 micrograms or 1 mg ml-1) and again at 0.5 to 1.5 h afterwards. Atropine, antagonized the 5-HT- and MCh-induced bronchoconstrictions over the same antagonist dose-range. This suggests that the bronchoconstriction induced in the conscious guinea-pig by 5-HT is mediated primarily via muscarinic receptors, possibly by a vagal reflex. The inhibition of the responses to 5-HT and MCh by OA challenge would therefore appear to be related to interference with a common cholinergic pathway for these spasmogens. 7. In summary, airway hyperresponsiveness was evident at 24 h after OA challenge as measured by an enhanced bronchoconstrictor response to inhaled U-46619. When 5-HT or MCh were used as the spasmogens, an opposing decrease in responsiveness was observed. This was presumed to be due to an inhibition of cholinergic pathways by the OA challenge. Adenosine caused a bronchoconstriction in the sensitized animals but this was not enhanced by the OA challenge.

The effect of psychological stress on neutrophil superoxide release

Stress has long been suggested to exacerbate symptom expression in people with chronic inflammatory disorders. The release of oxidative metabolites from activated PMN plays a significant role in the pathophysiology of inflammation. Thus, we examined the effects of psychological stress on release of superoxide anions from PMN of rats with or without an inflammation induced by injection of shellfish glycogen (SFG). Psychological stress was found to significantly increase PMN superoxide release in both healthy and SFG-injected animals. Total amounts of superoxide release were similar between the two groups, suggesting that PMN from animals with a mild inflammatory condition were not more susceptible to the effects of stress than PMN from healthy animals. However, this study should be repeated using an animal model of chronic inflammation, such as airway hyperactivity or rheumatoid arthritis.

Attenuation of allergic airway inflammation in IL-4 deficient mice

To investigate the role of IL-4 in vivo in allergic asthma, we developed a murine model of allergen-induced airway inflammation. Repeated daily exposures of actively immunized C57BL/6 mice to aerosolized ovalbumin (OVA) induced a peribronchial inflammation and an increase in eosinophils and lymphocytes in bronchoalveolar-lavage (BAL) fluid. In IL-4 deficient (IL4-/-) mice, treated in the same way, there were substantially fewer eosinophils in BAL and much less peribronchial inflammation compared with wild type mice. In this model, mast cell deficient (W/Wv) mice developed a similar degree of BAL eosinophilia and peribronchial inflammation as wild type mice, demonstrating that the mast cell is not required for the induction of chronic airway inflammation. In contrast, BAL eosinophilia and airway inflammation were absent in OVA-treated MHC ClassII deficient (B6.Aa-/-) mice which lack mature CD4+ T lymphocytes. In conclusion, these results indicate that IL-4 is a central mediator of allergic airway inflammation, regulating antigen-induced eosinophil recruitment into the airways by a T cell dependent mechanism.

Effect of dexamethasone on airway inflammation and responsiveness after antigen challenge of the rat

The purpose of this study was to examine the effects of dexamethasone on airway responsiveness and lung inflammation of rats at 8 h, 32 h, and 7 d after allergen challenge. Brown-Norway male rats, 7 to 8 wk old, were actively sensitized to ovalbumin (OA) and challenged 14 d later. The rats were divided into a control group (n = 31) and a test group (n = 34) that received dexamethasone (DEXA) (0.3 mg/kg intraperitoneally) 14 h and 2 h before saline or OA challenge. For challenge, rats were anesthetized with pentobarbital and intubated endotracheally. Aerosols of OA (5% wt/vol in saline) were administered for 5 min. Responsiveness to inhaled aerosols of methacholine and the total and differential leukocyte counts in the large airways (generations 0 to 5), small airways, and parenchyma isolated by tissue mincing and digestion were measured at 8 h, 32 h, and 7 d after OA challenge. The cellular influx into the airways and parenchyma was highest at 8 h and decreased progressively over 7 d. DEXA significantly inhibited the cellular influx after allergen challenge. At 8 h, cellular return from the large airways was 3.61 +/- 0.5 x 10(6) (controls) versus 1.0 +/- 0.2 x 10(6) (DEXA), and from the small airways and parenchyma was 31.7 +/- 2.8 x 10(6) (controls) versus 21.9 +/- 2.9 x 10(6) (DEXA) (p < 0.05). The differences were attributable mostly to decreases in neutrophils in DEXA-treated animals. In control animals, neutrophil yield fell between 8 and 32 h, whereas eosinophils and 32 h, whereas eosinophil and lymphocyte counts increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Interference of a neutrophil recruitment inhibitory factor upon the accumulation of inflammatory cells and airway hyperreactivity in sensitized guinea-pigs after intranasal antigen challenge

1. A neutrophil recruitment inhibitory factor (NRIF) recovered from the crude supernatant of lipopolysaccharide (LPS)-stimulated macrophages inhibited neutrophil migration following both intratracheal and intravenous administration of LPS, but did not alter the pattern of leukopenia/leucocytosis induced by intravenous LPS. 2. The correlation between airway infiltration by inflammatory cells and hyperreactivity in lungs from actively sensitized and challenged guinea-pigs was investigated by use of NRIF. 3. Increased eosinophil counts were found in the bronchoalveolar lavage fluid from guinea-pigs sensitized with 10 micrograms ovalbumin and challenged at day 14 by the intranasal administration of the antigen. The increase was evident 5 h after challenge and persisted at 24 h. Neutrophil numbers were also increased at this time. Pretreatment with NRIF suppressed the leucocyte increase in the bronchoalveolar lavage fluid. 4. Bronchoconstriction and histamine release induced by 3 ng PAF injected into the isolated lungs were increased in challenged guinea-pigs as compared to sensitized but unchallenged controls. Pretreatment of the animals with NRIF did not interfere with this response, but significantly reduced the bronchoconstriction induced by ovalbumin injection. 5. Even though the increased number of inflammatory cells in bronchoalveolar lavage and airway hyperresponsiveness were concomitant, NRIF inhibited cellular infiltration but failed to alter airway hyperreactivity to PAF, demonstrating that these events may occur independently. Conversely, the inhibition of antigen-induced bronchoconstriction by NRIF suggests that this response is dependent upon the emigration of granulocytes.