Priming of allergic immune responses by repeated ozone exposure in mice

Air pollution mixture associated with oxidative stress exacerbation and symptoms deterioration in allergic rhinitis patients: Evidence from a panel study

With allergic rhinitis (AR) on the rise globally, there has been a growing focus on the role of environmental pollutants in the onset of AR. However, the potential mechanisms by how and which these pollutants exacerbate AR conditions remain unknown. This panel study of 49 patients diagnosed with AR over one year aimed to assess the individual and combined effects of short-term exposure to multiple ambient pollutants on oxidative stress, symptoms, and quality of life among patients with AR. All participants underwent four repeated assessments of health conditions and personal environmental exposures (PM2.5, O3, SO2, and NO2) over warm and cold seasons during 2017-2018. We evaluated two oxidative stress biomarkers (malondialdehyde [MDA], and superoxide dismutase [SOD]) via nasal lavage. We collected information on self-reported symptoms and quality of life using the Rhinitis Symptom Scale (SRS), the Visual Analog Scale (VAS), and the Rhinoconjunctivitis Quality of Life Questionnaire (RQLQ) through in-person interviews. Bayesian kernel machine regression (BKMR) was used to evaluate the joint effects of pollutant mixture and identify key contributors. The results revealed a significant association of the pollutant mixture when all four pollutants were at or above their median levels, with increased oxidative stress. This was evidenced by elevated MDA and reduced SOD. We found a joint detrimental effect of the pollutant mixture on AR symptoms with a strong association with increased SRS scores, but a non-significant positive association with VAS and RQLQ scores. PM2.5, O3, and SO2 presented as the potentially primary contributors to the adverse health effects associated with the pollutant mixture in Taiyuan city. Patients with AR exposed to short-term air pollutant mixture are more likely to have greater nasal symptoms and worse quality of life from increased oxidative stress and reduced antioxidant capacity. Further research is warranted to better elucidate the underlying mechanisms.

Exposure to ambient fine particulate matter components during pregnancy and early childhood and its association with asthma, allergies, and sensitization in school-age children

BACKGROUND

Exposure to fine particulate matter (PM2.5) has been associated with allergic diseases, including asthma. However, information about the effects of specific PM2.5 components is limited. This study aimed to investigate the relationship of exposure to chemical components of PM2.5 during pregnancy and early childhood with the development of asthma, allergies, and sensitization in school-age children.

METHODS

This study included 2,408 children in the second grade of elementary school. Questionnaire surveys of respiratory/allergic symptoms and measurements of serum total IgE and specific IgE levels to house dust mite (HDM) and animal proteins were conducted. Exposures to ambient PM2.5 mass, sulfate (SO42-), nitrate (NO3-), ammonium (NH4+), elemental carbon (EC), and organic carbon (OC) of PM2.5 in participants' residences from conception to age six were estimated using predictive models. Multiple logistic regression analysis was used to analyze the association of respiratory/allergic symptoms and allergen sensitization with estimated exposure concentrations, after adjustment for survey year, sex, season of birth, feeding method during infancy, presence of siblings, history of lower respiratory tract infection, use of childcare facilities, passive smoking, presence of pets, mother's age, history of allergic diseases, smoking during pregnancy, and annual household income.

RESULTS

No significant association was found between PM2.5 and its component concentrations and asthma. However, wheezing significantly increased with mean NO3- concentrations during pregnancy (odds ratio of 1.64 [95% confidence interval: 1.10, 2.47] for an interquartile range increase). Significant associations were also found between EC in the second trimester of pregnancy and PM2.5, NO3-, EC, and OC concentrations in early childhood. Higher PM2.5, SO4-, and NH4+ concentrations during the second trimester increased the risk of rhinitis. Sensitizations to HDM and animal proteins were significantly associated with exposure to components such as SO42- and NH4+ during pregnancy but not with postnatal exposure.

CONCLUSIONS

Exposures to NO3-, EC, and OC during pregnancy and early childhood were associated with wheezing. SO42- and NH4+ exposures during pregnancy were associated with sensitization to HDM and animal proteins. Asthma was not associated with exposure to PM2.5 and its main components at any period.

Association between exposure to air pollution and risk of allergic rhinitis: A systematic review and meta-analysis

BACKGROUND

Allergic rhinitis (AR) is one of the most common allergic diseases in the world, and usually persists throughout the activity. Epidemiological studies have shown a positive association between air pollution and allergic rhinitis. However, we could not find any meta-analysis of the risk of air pollutants (PM_2.5, PM₁₀, NO₂, SO₂, O₃ and CO) on the prevalence of AR in people of all ages.

OBJECTIVES

Carry out a meta-analysis on the results of recent studies (up to 2020) to present valid information about exposure to air pollution and risk of prevalence of AR.

METHODS

We systematically searched three databases for studies up to December 17, 2020, including air pollution and AR. Random effect models were conducted to estimate the pooled odds ratios (ORs) and 95% confidence intervals (95% CIs). Subgroup analysis, funnel plot, Egger's test, and the trim-and-fill method were also conducted.

RESULTS

Thirty-five studies across 12 countries, including a total of 453,470 participants, were included. The OR per 10 μg/m³ increase of pollutants was 1.13 (1.04-1.22) for PM₁₀ and 1.12 (1.05-1.20) for PM_2.5. The OR per 10 μg/m³ increment of gaseous pollutants were 1.13 (1.07-1.20) for NO₂, 1.13 (1.04-1.22) for SO₂ and 1.07 (1.01-1.12) for O₃. No significant association was observed between CO and AR. Children or adolescents are more sensitive to air pollution than adults. The effects of PM₁₀ and SO₂ were significantly stronger in Europe than Asia. The effects of air pollutants were more significant and higher in developing countries than in developed countries, except for PM₁₀. A significant difference of subgroup test was found between developed and developing countries of NO₂.

CONCLUSION

This meta-analysis showed a positive association between air pollution and the prevalence of allergic rhinitis, and identified geographic area and economic level as the potential modifiers for the association.

The effects of ozone exposure and associated injury mechanisms on the central nervous system

Ozone (O3) is a component of photochemical smog, which is a major air pollutant and demonstrates properties that are harmful to health because of the toxic properties that are inherent to its powerful oxidizing capabilities. Environmental O3 exposure is associated with many symptoms related to respiratory disorders, which include loss of lung function, exacerbation of asthma, airway damage, and lung inflammation. The effects of O3 are not restricted to the respiratory system or function - adverse effects within the central nervous system (CNS) such as decreased cognitive response, decrease in motor activity, headaches, disturbances in the sleep-wake cycle, neuronal dysfunctions, cell degeneration, and neurochemical alterations have also been described; furthermore, it has also been proposed that O3 could have epigenetic effects. O3 exposure induces the reactive chemical species in the lungs, but the short half-life of these chemical species has led some authors to attribute the injurious mechanisms observed within the lungs to inflammatory processes. However, the damage to the CNS induced by O3 exposure is not well understood. In this review, the basic mechanisms of inflammation and activation of the immune system by O3 exposure are described and the potential mechanisms of damage, which include neuroinflammation and oxidative stress, and the signs and symptoms of disturbances within the CNS caused by environmental O3 exposure are discussed.

Adjuvant and inflammatory effects in mice after subchronic inhalation of allergen and ozone-initiated limonene reaction products

Inhalation of ozone (O3), a highly toxic environmental pollutant, produces airway inflammation and exacerbates asthma. However, in indoor air, O3 reacts with terpenes (cyclic alkenes), leading to formation of airway irritating pollutants. The aim of the study was to examine whether inhalation of the reaction products of O3 and the terpene, limonene, as well as limonene and low-level O3 by themselves, induced allergic sensitization (formation of specific immunoglobulin [Ig] E) and airway inflammation in a subchronic mouse inhalation model in combination with the model allergen ovalbumin (OVA). BALB/cJ mice were exposed exclusively by inhalation for 5 d/wk for 2 wk and thereafter once weekly for 12 wk. Exposures were low-dose OVA in combination with O3, limonene, or limonene/O3 reaction products. OVA alone and OVA + Al(OH)3 served as control groups. Subsequently, all groups were exposed to a high-dose OVA solution on three consecutive days. Serum and bronchoalveolar lavage fluid were collected 24 h later. Limonene by itself did not promote neither OVA-specific IgE nor leukocyte inflammation. Low-level O3 promoted eosinophilic airway inflammation, but not OVA-specific IgE formation. The reaction products of limonene/O3 promoted allergic (OVA-specific IgE) sensitization, but lung inflammation, which is a characteristic of allergic asthma, was not observed. In conclusion, the study does not support an allergic inflammatory effect attributed to O3-initiated limonene reaction products in the indoor environment.

Genes of innate immunity and the biological response to inhaled ozone

Ambient ozone has a significant impact on human health. We have made considerable progress in understanding the fundamental mechanisms that regulate the biological response to ozone. It is increasingly clear that genes of innate immunity play a central role in both infectious and noninfectious lung disease. The biological response to ambient ozone provides a clinically relevant environmental exposure that allows us to better understand the role of innate immunity in noninfectious airways disease. In this brief review, we focus on (1) specific cell types in the lung modified by ozone, (2) ozone and oxidative stress, (3) the relationship between genes of innate immunity and ozone, (4) the role of extracellular matrix in reactive airways disease, and (5) the effect of ozone on the adaptive immune system. We summarize recent advances in understanding the mechanisms that ozone contributes to environmental airways disease.

Ambient ozone and pulmonary innate immunity

Ambient ozone is a criteria air pollutant that impacts both human morbidity and mortality. The effect of ozone inhalation includes both toxicity to lung tissue and alteration of the host immunologic response. The innate immune system facilitates immediate recognition of both foreign pathogens and tissue damage. Emerging evidence supports that ozone can modify the host innate immune response and that this response to inhaled ozone is dependent on genes of innate immunity. Improved understanding of the complex interaction between environmental ozone and host innate immunity will provide fundamental insight into the pathogenesis of inflammatory airways disease. We review the current evidence supporting that environmental ozone inhalation: (1) modifies cell types required for intact innate immunity, (2) is partially dependent on genes of innate immunity, (3) primes pulmonary innate immune responses to LPS, and (4) contributes to innate-adaptive immune system cross-talk.

Inflammation-induced airway smooth muscle responsiveness is strain dependent in mice

Different mouse strains display different degrees of inflammation-induced airway hyperresponsiveness in vivo. It is not known whether these variations are attributable to distinct properties of the airway smooth muscle. Therefore, tracheal ring segments from C57BL/6 and BALB/c mice were exposed to three different pro-inflammatory stimuli for 4 days while maintained under tissue-culture conditions: tumour necrosis factor α (100 ng/ml), the Toll-like receptor (TLR) 3 agonist polyI:C (10 μg/ml), and the TLR4 agonist LPS (10 μg/ml). The contractile responses to carbachol, 5-hydroxytryptamine (5-HT) and bradykinin were assessed after culture. In addition, gene expression of TLR1-TLR9, pivotal inflammatory signal transduction proteins (jun-kinase, p38 and p65) and critical negative regulators of inflammation (A20, Itch, Tax1bp1 and RNF11) were studied in tracheal smooth muscle strips, fresh and following treatment for 4 days with LPS, from both strains. No differences between the strains were detected regarding the response of freshly isolated preparations to carbachol, 5-HT and bradykinin. After stimulation with pro-inflammatory mediators, contractions in response to 5-HT and bradykinin, but not to carbachol, were up-regulated. This up-regulation was markedly larger in BALB/c than in C57BL/6 segments and depended on the type of inflammatory stimulus. Expression of the genes investigated did not differ between the two strains. These findings indicate that strain differences in airway hyperresponsiveness can be linked to differences in the responsiveness of airway smooth muscle to pro-inflammatory mediators per se. The differences do not appear to be due to differential expression of TLR or common inflammatory transduction and repressor proteins.

Protective role of interleukin-10 in ozone-induced pulmonary inflammation

BACKGROUND

The mechanisms underlying ozone (O₃)-induced pulmonary inflammation remain unclear. Interleukin-10 (IL-10) is an anti-inflammatory cytokine that is known to inhibit inflammatory mediators.

OBJECTIVES

We investigated the molecular mechanisms underlying interleuken-10 (IL-10)-mediated attenuation of O₃-induced pulmonary inflammation in mice.

METHODS

Il10-deficient (Il10(-/-)) and wild-type (Il10(+/+)) mice were exposed to 0.3 ppm O₃ or filtered air for 24, 48, or 72 hr. Immediately after exposure, differential cell counts and total protein (a marker of lung permeability) were assessed from bronchoalveolar lavage fluid (BALF). mRNA and protein levels of cellular mediators were determined from lung homogenates. We also used global mRNA expression analyses of lung tissue with Ingenuity Pathway Analysis to identify patterns of gene expression through which IL-10 modifies O₃-induced inflammation.

RESULTS

Mean numbers of BALF polymorphonuclear leukocytes (PMNs) were significantly greater in Il10(-/-) mice than in Il10(+/+) mice after exposure to O₃ at all time points tested. O₃-enhanced nuclear NF-κB translocation was elevated in the lungs of Il10(-/-) compared with Il10(+/+) mice. Gene expression analyses revealed several IL-10-dependent and O₃-dependent mediators, including macrophage inflammatory protein 2, cathepsin E, and serum amyloid A3.

CONCLUSIONS

Results indicate that IL-10 protects against O₃-induced pulmonary neutrophilic inflammation and cell proliferation. Moreover, gene expression analyses identified three response pathways and several genetic targets through which IL-10 may modulate the innate and adaptive immune response. These novel mechanisms of protection against the pathogenesis of O₃-induced pulmonary inflammation may also provide potential therapeutic targets to protect susceptible individuals.

The effects of oxidative stress induced by prolonged low-dose diesel exhaust particle exposure on the generation of allergic airway inflammation differ between BALB/c and C57BL/6 mice

We have recently reported that airway inflammatory responses to the oxidative stress induced by prolonged low-dose diesel exhaust particle (DEP) exposure differ markedly between BALB/c and C57BL/6 mice. In the present study, the effects of genetic differences in the response to prolonged low-dose DEP exposure on the generation of ovalbumin-induced allergic airway inflammation were further explored using the same mouse strains. In BALB/c mice, eosinophils and mucous goblet cells in histopathological pulmonary specimens increased significantly after DEP exposure, and were more marked than in C57BL/6 mice. Interleukin (IL)-5 and IL-13 levels in bronchoalveolar lavage (BAL) fluid were increased significantly by DEP exposure only in BALB/c mice. The DEP-induced increases in peribronchial eosinophils and mucous goblet cells in the lung tissues, and of IL-5 and IL-13 in the BAL fluid, were significantly attenuated by the antioxidant N-acetylcysteine. Thus, the effects of prolonged low-dose DEP exposure on the generation of allergic airway inflammation differed markedly between the mouse strains. These differences may be caused by different antioxidant responses to the oxidative stress induced by DEP exposure. Our results contribute more information to the search for genetic susceptibility factors in the response to DEP, and may thus assist in the discovery of new biomarkers for DEP-related disease.

Ozone Uptake During Inspiratory Flow in a Model of the Larynx, Trachea and Primary Bronchial Bifurcation

Three-dimensional simulations of the transport and uptake of a reactive gas such as O(3) were compared between an idealized model of the larynx, trachea, and first bifurcation and a second "control" model in which the larynx was replaced by an equivalent, cylindrical, tube segment. The Navier-Stokes equations, Spalart-Allmaras turbulence equation, and convection-diffusion equation were implemented at conditions reflecting inhalation into an adult human lung. Simulation results were used to analyze axial velocity, turbulent viscosity, local fractional uptake, and regional uptake. Axial velocity data revealed a strong laryngeal jet with a reattachment point in the proximal trachea. Turbulent viscosity data indicated that jet turbulence occurred only at high Reynolds numbers and was attenuated by the first bifurcation. Local fractional uptake data affirmed hotspots previously reported at the first carina, and suggested additional hotspots at the glottal constriction and jet reattachment point in the proximal trachea. These laryngeal effects strongly depended on inlet Reynolds number, with maximal effects (approaching 15%) occurring at maximal inlet flow rates. While the increase in the regional uptake caused by the larynx subsided by the end of the model, the effect of the larynx on cumulative uptake persisted further downstream. These results suggest that with prolonged exposure to a reactive gas, entire regions of the larynx and proximal trachea could show signs of tissue injury.

AIRWAY INFLAMMATORY RESPONSES TO OXIDATIVE STRESS INDUCED BY LOW-DOSE DIESEL EXHAUST PARTICLE EXPOSURE DIFFER BETWEEN MOUSE STRAINS

Low-dose diesel exhaust particle (DEP) exposure induces airway inflammation and exaggerates asthmatic responses in mice, but it is unclear whether strains differ in their susceptibility to adverse effects from low-dose DEP exposure. The authors used BALB/c and C57BL/6 mouse strains to search for genetically based differences in response to low-dose DEP (100 microg/m(3)) exposure in terms of airway inflammatory response. The macrophage count in bronchoalveolar lavage (BAL) fluid soon after DE exposure began was significantly greater in C57BL/6 mice (P < .05) than that in BALB/c mice. The count did not increase significantly in BALB/c mice until later. Heme oxygenase-1 (HO-1) mRNA expression and protein production in lung tissues soon after exposure began were more marked in BALB/c mice than in C57BL/6 mice, but the reverse was true later on. The increases in interleukin (IL)-1beta and interferon (IFN)-gamma levels in BAL fluid after DE exposure were significant only in BALB/c mice; there were significantly increases in monocyte chemoattractant protein (MCP)-1, IL-12, IL-10, IL-4, and IL-13 in both strains, but these were more marked in C57BL/6 mice. These interstrain differences in airway inflammatory response after DE exposure were significantly attenuated by antioxidant N-acetylcysteine (NAC) treatment. Changes in airway hyperresponsiveness were independent of the airway inflammation induced by low-dose DEP. Thus, in BALB/c mice, innate immunity may play a central role in DE exposure response, whereas in C57BL/6 mice Th2-dominant responses play a central role. Low-dose DEP exposure induces airway inflammatory responses that differ among strains, and these differences may be caused by differences in sensitivity to oxidative stress.

Ozone and allergen exposure during postnatal development alters the frequency and airway distribution of CD25+ cells in infant rhesus monkeys

The epidemiologic link between air pollutant exposure and asthma has been supported by experimental findings, but the mechanisms are not understood. In this study, we evaluated the impact of combined ozone and house dust mite (HDM) exposure on the immunophenotype of peripheral blood and airway lymphocytes from rhesus macaque monkeys during the postnatal period of development. Starting at 30 days of age, monkeys were exposed to 11 cycles of filtered air, ozone, HDM aerosol, or ozone+HDM aerosol. Each cycle consisted of ozone delivered at 0.5 ppm for 5 days (8 h/day), followed by 9 days of filtered air; animals received HDM aerosol during the last 3 days of each ozone exposure period. Between 2-3 months of age, animals co-exposed to ozone+HDM exhibited a decline in total circulating leukocyte numbers and increased total circulating lymphocyte frequency. At 3 months of age, blood CD4+/CD25+ lymphocytes were increased with ozone+HDM. At 6 months of age, CD4+/CD25+ and CD8+/CD25+ lymphocyte populations increased in both blood and lavage of ozone+HDM animals. Overall volume of CD25+ cells within airway mucosa increased with HDM exposure. Ozone did not have an additive effect on volume of mucosal CD25+ cells in HDM-exposed animals, but did alter the anatomical distribution of this cell type throughout the proximal and distal airways. We conclude that a window of postnatal development is sensitive to air pollutant and allergen exposure, resulting in immunomodulation of peripheral blood and airway lymphocyte frequency and trafficking.

Air pollution and asthma severity in adults

BACKGROUND/OBJECTIVES

There is evidence that exposure to air pollution affects asthma, but the effect of air pollution on asthma severity has not been addressed. The aim was to assess the relation between asthma severity during the past 12 months and home outdoor concentrations of air pollution.

METHODS

Asthma severity over the past 12 months was assessed in two complementary ways among 328 adult asthmatics from the French Epidemiological study on the Genetics and Environment of Asthma (EGEA) examined between 1991 and 1995. The four-class severity score integrated clinical events and type of treatment. The five-level asthma score is based only on the occurrence of symptoms. Nitrogen dioxide (NO(2)), sulphur dioxide (SO(2)) and ozone (O(3)) concentrations were assigned to each residence using two different methods. The first was based on the closest monitor data from 1991 to 1995. The second consisted of spatial models that used geostatistical interpolations and then assigned air pollutants to the geo-coded residences (1998).

RESULTS

Higher asthma severity score was significantly related to the 8-hour average of ozone during April-September (O(3)-8 h) and the number of days (O(3)-days) with 8-hour ozone averages above 110 microg.m(-3) (for a 36-day increase, equivalent to the interquartile range, in O(3)-days, odds ratio 2.22 (95% confidence interval 1.61 to 3.07) for one class difference in score). Adjustment for age, sex, smoking habits, occupational exposure, and educational level did not alter results. Asthma severity was unrelated to NO(2). Both exposure assessment methods and severity scores resulted in very similar findings. SO(2) correlated with severity but reached statistical significance only for the model-based assignment of exposure.

CONCLUSIONS

The observed associations between asthma severity and air pollution, in particular O(3), support the hypothesis that air pollution at levels far below current standards increases asthma severity.

Sensitivity to Ozone, Diesel Exhaust Particles, and Standardized Ambient Particulate Matter in Rats with aListeria Monocytogenes-Induced Respiratory Infection

Ambient particulate matter may increase respiratory allergic skewing of the T-cell-mediated immune response toward a T-helper-2 (Th2) response, with the consequence that the Th1 response develops less well. Successful clearing of a respiratory bacterial infection depends on an adequate Th1 immune response; therefore, the subject would not control the infection as well if exposed to particulate matter. To substantiate this hypothesis, we examined the effect of exposure to diesel exhaust particles (DEP) and urban particulate matter (EHC-93, Ottawa dust) on rats with a Listeria monocytogenes respiratory infection. Since this hypothesis has been confirmed for ozone, we used it as a positive control. Wistar rats were exposed to ozone (2 mg/m3 for 24 h/day for 7 days) and to DEP or to EHC-93 (50 microg/rat intranasally daily for 7 consecutive days). Twenty-four hours after the last exposure, the rats were infected intratracheally with 1 x 10(6) L. monocytogenes bacteria. The number of L. monocytogenes was determined after 3, 4 and 5 days. Statistically significant increases of the number of L. monocytogenes in rats exposed to ozone were observed in the lungs and spleen at all three times. However, we found no significant differences in the numbers of bacteria that were found in rats exposed to DEP or EHC-93 compared to the saline-treated group at any of the three times. In conclusion, the results of this study do not support the hypothesis that exposure to DEP or EHC-93 reduces subsequent resistance to a respiratory infection in rats.

Airway inflammatory responses to oxidative stress induced by prolonged low-dose diesel exhaust particle exposure from birth differ between mouse BALB/c and C57BL/6 strains

The authors used BALB/c and C57BL/6 mouse strains to search for genetically based differences in response to prolonged (6 months) low-dose (100 microg/m3) diesel exhaust particle (DEP) exposure from birth in terms of airway inflammatory responses. Histopathological assessment showed that inflammatory cells infiltrated the perivascular areas only in C57BL/6 mice. The count of DEP-laden alveolar macrophages in bronchoalveolar lavage (BAL) fluid was significantly greater in BALB/c mice (P < .05) than in C57BL/6 mice. The lymphocyte and eosinophil count in BAL fluid was significantly greater in C57BL/6 mice (P < .05) than in BALB/c mice. Immunoglobulin (Ig) IgG1 and IgG2 levels in serum, and the monocyte chemoattractant protein (MCP)-1 level in BAL fluid were significantly greater in BALB/c mice than in C57BL/6 mice. The interleukin (IL)-12 level in BAL fluid was significantly greater in C57BL/6 mice than in BALB/c mice, but the IL-13 level in BAL fluid was significantly less in BALB/c mice than in C57BL/6 mice. Glutathione S-transferase (GST) mRNA expression and protein production in lung tissues were significantly lower in C57BL/6 mice than in BALB/c mice, and 8-hydroxy-2'-deoxyguanosine (8-OHdG) level in the lung tissues were significantly greater in C57BL/6 mice than in BALB/c mice. In conclusion, prolonged low-dose DEP exposure induces airway inflammatory responses that differ remarkably among mouse strains; these differences are caused by differences in the host defense response to the oxidative stress induced by DEP exposure and may be useful in the development of biomarkers.

The IL-4Ralpha pathway in macrophages and its potential role in silica-induced pulmonary fibrosis

Crystalline silica exposure can result in pulmonary fibrosis, where the pulmonary macrophage is key as a result of its ability to react to silica particles. In the mouse silicosis model, there is initial Th1-type inflammation, characterized by TNF-alpha and IFN-gamma. Previous studies determined that Th2 mediators (i.e., IL-13) are vital to development of pulmonary fibrosis. The present study, using in vivo and in vitro techniques, compares silica exposures between Balb/c and Th2-deficient mice in an effort to determine the link between Th2 immunity and silicosis. In long-term experiments, a significant increase in fibrosis and activated interstitial macrophages was observed in Balb/c but not IL-4Ralpha(-/-) mice. Additionally, a significant increase in Ym1 mRNA levels, a promoter of Th2 immunity, was determined in the interstitial leukocyte population of silica-exposed Balb/c mice. To elucidate the effects of silica on macrophage function, bone marrow-derived macrophages (BMdM) were exposed to particles and assayed for T cell (TC) stimulation activity. As a control, Ym1 mRNA expression in Balb/c BMdM was determined using IL-4 stimulation. In the in vitro assay, a significant increase in TC activation, as defined by surface markers and cytokines, was observed in the cultures containing the silica-exposed macrophages in wild-type and IL-4Ralpha(-/-) mice, with one exception: IL-4Ralpha(-/-) BMdM were unable to induce an increase in IL-13. These results suggest that crystalline silica alters cellular functions of macrophages, including activation of TC, and that the increase in Th2 immunity associated with silicosis is via the IL-4Ralpha-Ym1 pathway.

CD4+ T cells from mice with intestinal immediate-type hypersensitivity induce airway hyperreactivity

BACKGROUND

A subset of food-allergic patients does not only respond clinically with symptoms in the gastro-intestinal tract but also with asthmatic reactions.

OBJECTIVE

The aim of this study was to analyse whether CD4+ T cells from mice with intestinal immediate-hypersensitivity reactions to food allergen are involved in the development of experimental asthma.

METHODS

BALB/c mice were intraperitoneally sensitized to ovalbumin (OVA), followed by repeated intra-gastric (i.g.) OVA challenges. Control animals were either sham-sensitized or sham-challenged with phosphate-buffered saline (PBS). Duodenum, jejunum, ileum and colon were histologically examined. CD4+ T cells from mesenteric lymph nodes were transferred from various donor groups into recipient mice that received either OVA or PBS aerosol challenges. Recipients were analysed by measurements of lung function using head-out body-plethysmography and examination of broncho-alveolar lavage and lung histology.

RESULTS

The highest levels of OVA-specific IgE antibody levels were detected in OVA-sensitized and OVA-challenged mice. Throughout the lower intestinal tract, a marked infiltration with eosinophils was observed, and goblet cell numbers as well as goblet cell area were significantly increased. The villus/crypt ratio was decreased compared with controls. The transfer of CD4+ T cells from mesenteric lymph nodes of OVA-sensitized and OVA-challenged mice triggered airway hyperreactivity and eosinophilic airway inflammation in recipients aerosol challenged with OVA, but not with PBS.

CONCLUSION

We conclude that CD4+ T cells from mesenteric lymph nodes of mice with allergen-induced immediate-type hypersensitivity reactions in the gut are able to transfer the phenotype of experimental asthma.

The impact of aluminium in acid-suppressing drugs on the immune response of BALB/c mice

BACKGROUND

Recently we have shown that anti-acid drugs lead to an enhanced risk of food allergy. This may be due to hindered peptic digestion, caused by an elevation of the gastric pH. Additionally, it is known that aluminium-linked antigens lead to an increased probability of sensitization.

OBJECTIVE

Our aim in this study was to show whether sucralfate promotes sensitization not only by preventing peptic digestion but also by acting as a T-helper type 2 (Th2) adjuvant.

METHODS

To avoid the effect of sucralfate on the gastric pH and to show only the adjuvant effect, BALB/c mice were immunized on the parenteral route with codfish extract plus sucralfate, and control groups with aluminium hydroxide (alum) (Th2 adjuvant) or monophosphoryl lipid A (MPL) (Th1 adjuvant). Antigen-specific antibodies and cytokine levels were determined. The in vivo effect was investigated by intradermal skin tests.

RESULTS

Codfish-specific high IgG1 and IgE antibody levels as well as elevated IL-4 and IL-5 levels in alum- and MPL-treated mice, but more importantly also in sucralfate-treated mice, indicated a Th2 shift. Positive skin tests confirmed this Th2 response.

CONCLUSIONS

Our data show that parenterally applied sucralfate is able to induce a Th2 response probably due to the aluminium content. This indicates that orally applied sucralfate may lead to an enhanced risk of food allergy not only by inhibiting peptic digestion but also by acting as a Th2 adjuvant.

Immunomodulatory effects of viral TLR ligands on experimental asthma depend on the additive effects of IL-12 and IL-10

Based on epidemiological data, the hygiene hypothesis associates poor hygienic living conditions during childhood with a lower risk for the development of allergic diseases such as bronchial asthma. The role of viral infections, and especially of viral TLR ligands, within this context remains to be clarified. Viral TLR ligands involve dsRNA and ssRNA which are recognized by TLR-3 or TLR-7, respectively. In this study, we evaluated the impact of TLR-3 or TLR-7 activation on experimental asthma in mice. Systemic application of the synthetic TLR-3 or TLR-7 ligands polycytidylic-polyinosinic acid (p(I:C)) or R-848, respectively, during the sensitization phase prevented the production of OVA-specific IgE and IgG1 Abs and subsequently abolished all features of experimental asthma including airway hyperresponsiveness and allergic airway inflammation. Furthermore, administration of p(I:C) or R-848 to animals with already established primary allergic responses revealed a markedly reduced secondary response following allergen aerosol rechallenges. In contrast to wild-type animals, application of p(I:C) or R-848 to IL-12p35(-/-) mice had no effect on airway inflammation, goblet cell hyperplasia, and airway hyperresponsiveness. However, in the absence of IL-12, the numbers of eosinophils and lymphocytes in bronchoalveolar lavage fluids were still significantly reduced. These partial effects could also be abolished by neutralizing anti-IL-10 Abs in IL-12p35(-/-) mice. These data indicate that TLR-3 or TLR-7 activation by viral TLR ligands has both preventive as well as suppressive effects on experimental asthma which is mediated by the additive effects of IL-12 and IL-10.

Ozone exposure impairs antigen-specific immunity but activates IL-7-induced proliferation of CD4-CD8- thymocytes in BALB/c mice

It is well known that ozone (O3), a potent reactive oxidant and air pollutant, induces respiratory inflammation and hyperresponsiveness upon inhalation. It was previously shown that O3 exposure (0.6 ppm, 10 h/day for 15 days) not only results in local bronchial inflammation, but also affects the nervous system and thymocyte proliferation, and places mice under oxidative stress. In the present study, data showed that O3 exposure could impair both the natural killer (NK) cell activity and the proliferation potential of spleen T cells to a specific antigen stimulus. Immunological function assays indicated that O3 exposure attenuated the proliferation of spleen mononuclear cells induced by concanavalin A and decreased CD4+ and CD28+ lymphocyte subsets. However, supplementation with natural antioxidants protected mice from O3-induced dysfunction of splenocyte proliferation. Meanwhile, O3 exposure resulted in a decline of mitogen-induced IL-2 production in splenocytes. It was also found that O3 exposure dramatically enhanced the proliferation of CD4-CD8- thymocytes stimulated by recombinant mouse interleukin-7 (rmIL-7), which is usually observed during the mammal aging process. Taken together, data conclude that short-term repetitive O3 exposure damages both innate and acquired immunity via altering the lymphocyte subset and cytokine profile, and via impact on thymocyte early development. O3-induced oxidative damage is one of the key factors leading to immune dysfunction in this mouse model.

ROS generated by pollen NADPH oxidase provide a signal that augments antigen-induced allergic airway inflammation

Pollen exposure induces allergic airway inflammation in sensitized subjects. The role of antigenic pollen proteins in the induction of allergic airway inflammation is well characterized, but the contribution of other constituents in pollen grains to this process is unknown. Here we show that pollen grains and their extracts contain intrinsic NADPH oxidases. The pollen NADPH oxidases rapidly increased the levels of ROS in lung epithelium as well as the amount of oxidized glutathione (GSSG) and 4-hydroxynonenal (4-HNE) in airway-lining fluid. These oxidases, as well as products of oxidative stress (such as GSSG and 4-HNE) generated by these enzymes, induced neutrophil recruitment to the airways independent of the adaptive immune response. Removal of pollen NADPH oxidase activity from the challenge material reduced antigen-induced allergic airway inflammation, the number of mucin-containing cells in airway epithelium, and antigen-specific IgE levels in sensitized mice. Furthermore, challenge with Amb a 1, the major antigen in ragweed pollen extract that does not possess NADPH oxidase activity, induced low-grade allergic airway inflammation. Addition of GSSG or 4-HNE to Amb a 1 challenge material boosted allergic airway inflammation. We propose that oxidative stress generated by pollen NADPH oxidases (signal 1) augments allergic airway inflammation induced by pollen antigen (signal 2).

Disruption of Nrf2 enhances susceptibility to severe airway inflammation and asthma in mice

Oxidative stress has been postulated to play an important role in the pathogenesis of asthma; although a defect in antioxidant responses has been speculated to exacerbate asthma severity, this has been difficult to demonstrate with certainty. Nuclear erythroid 2 p45-related factor 2 (Nrf2) is a redox-sensitive basic leucine zipper transcription factor that is involved in the transcriptional regulation of many antioxidant genes. We show that disruption of the Nrf2 gene leads to severe allergen-driven airway inflammation and hyperresponsiveness in mice. Enhanced asthmatic response as a result of ovalbumin sensitization and challenge in Nrf2-disrupted mice was associated with more pronounced mucus cell hyperplasia and infiltration of eosinophils into the lungs than seen in wild-type littermates. Nrf2 disruption resulted in an increased expression of the T helper type 2 cytokines interleukin (IL)-4 and IL-13 in bronchoalveolar lavage fluid and in splenocytes after allergen challenge. The enhanced severity of the asthmatic response from disruption of the Nrf2 pathway was a result of a lowered antioxidant status of the lungs caused by lower basal expression, as well as marked attenuation, of the transcriptional induction of multiple antioxidant genes. Our studies suggest that the responsiveness of Nrf2-directed antioxidant pathways may act as a major determinant of susceptibility to allergen-mediated asthma.

Natural ozone scavenger prevents asthma in sensitized rats

The assumption that ozone is not only a strong oxidant, but also an important inflammatory mediator, is heavily supported by the ample literature on the pulmonary toxicity and biological effects of environmental ozone and by the recent discovery that antibodies, human neutrophils, and inflammatory lesions catalyze the formation of ozone in vivo. We hypothesized that the pulmonary inflammation in asthma involves a vicious circle of ozone production and recruitment of white blood cells, which produce more ozone. Accordingly, we predicted that electron-rich olefins, which are known ozone scavengers, could be used for prophylactic treatment of asthma. In particular, volatile, unsaturated monoterpenes, could saturate the pulmonary membranes and thereby equip the airways with local chemical protection against either exogenous or endogenous ozone. Here we present experimental evidence using a sensitized rat model to support this hypothesis. Examination of the pulmonary function of sensitized rats that inhaled either limonene (unsaturated, ozone scavenger) or eucalyptol (saturated, inert to ozone) showed that limonene inhalation significantly prevents bronchial obstruction while eucalyptol inhalation does not cause any effect. The anti-inflammatory effect of limonene was also evident from pathological parameters, such as diminished peribronchiolar and perivascular inflammatory infiltrates.

Protein nitration by polluted air

The effects of air pollution on allergic diseases are not yetwell-understood. Here, we show that proteins, in particular birch pollen proteins including the allergen Bet v 1, are efficiently nitrated by polluted air. This posttranslational modification of proteins is likely to trigger immune reactions and provides a molecular rationale for the promotion of allergies bytraffic-related air pollution. Enzyme immunoassays have been used to determine equivalent degrees of nitration (EDN) for protein samples exposed to urban outdoor air and synthetic gas mixtures. The observed rates of nitration were governed by the abundance of nitrogen oxides and ozone, and concentration levels typical for summer smog conditions led to substantial nitration within a few hours to days (EDN up to 20%). Moreover, nitrated proteins were detected in urban road dust, window dust, and fine air particulate matter (EDN up to 0.1%).

Genetic susceptibility to ozone-induced lung inflammation in animal models of asthma

PURPOSE OF REVIEW

Epidemiological associations between ozone exposure and allergic responsiveness are well-documented and have been corroborated in animal studies. The complex interaction between ozone and allergen has genetic and environmental components that affect atopic individuals and may increase the incidence of allergy in susceptible individuals. This review describes the advances that have been made in understanding mechanisms of genetic susceptibility to ozone-induced inflammation, and the interaction between ozone and allergen exposure in mice and a non-human primate model.

RECENT FINDINGS

Antioxidant and innate immune defense genes contribute to ozone-induced inflammation and hyperpermeability in mice and humans. Ozone exposure during the allergic challenge phase induces greater enhancement of allergic responsiveness than the sensitization stage. Ovalbumin-pulsed dendritic cells injected into naïve mice successfully sensitize the mouse to ovalbumin in the absence of adjuvant. Debate continues over the role of T helper 1-T helper 2 immune profile development in mediating the ozone-allergen interaction, and the potential confounding influence of the predominant T helper 2 system most commonly used to study these responses.

SUMMARY

The role of genetic background in susceptibility to ozone-induced lung inflammation has been confirmed, and promising candidate genes have been identified. Descriptive studies confirm that ozone exacerbates allergic responsiveness. Ozone administered during the challenge phase of ovalbumin allergen exposure induces greater responsiveness than during the sensitization phase. Allergen-induced responses enhanced by concurrent ozone exposure warrant further mechanistic research, particularly regarding the influence of susceptibility genes.

Nasal allergy-like symptoms aggravated by ozone exposure in a concentration-dependent manner in guinea pigs

Our previous study revealed that exposure to 0.4 ppm ozone (O(3)) enhanced nasal allergy-like reactions in guinea pigs. In the present study, we investigated the concentration-dependency of the effects of exposure to O(3) on the aggravation of nasal allergy-like reactions induced by repeated nasal administration of antigen. Guinea pigs were exposed to filtered air or 0.1-0.6 ppm O(3) for 5 weeks. After each weekly administration of ovalbumin (OVA), sneezes and nasal secretions were measured. The number of eosinophils infiltrating the nasal septum and the titers of OVA-specific antibody were measured 24h after the last administration. Ozone increased sneezing and nasal secretion induced by OVA, nasal responsiveness to physical stimuli, and the number of infiltrating eosinophils in a concentration-dependent manner. The titer of anti-OVA-IgG was increased in animals exposed to 0.6 ppm O(3). Thus, exposure to O(3) aggravated nasal allergy-like symptoms concentration dependently. The aggravation was caused by induction of nasal hyperresponsiveness, the infiltration of eosinophils, and the increase in the production of anti-OVA-IgG. The estimated maximum likelihood estimation concentrations (MLECs) and bench mark concentrations (BMCs) of O(3) for these indices were in the range of 0.09-0.18 and 0.02-0.06 ppm, respectively.

Exposure to ozone enhances antigen-presenting activity concentration dependently in rats

The effect of ozone (O(3)) on the symptoms of allergic asthma and the mechanisms underlying have not yet been fully elucidated. Antigen presentation is one of the factors contributing to the allergic reaction. Therefore, we investigated the effects of repeated exposure to O(3) on antigen-presenting (AP) activity, on the expression of cell-surface molecules associated with antigen presentation (Ia, B7.1, B7.2 and CD11b/c) in bronchoalveolar lavage cells (BAL cells), and on allergic asthma-like symptoms. Rats were exposed to 0.3, 0.56, 1ppm O(3) or filtered air for a 3-day period every 2 weeks, this was replicated three times. AP activity was assessed by measuring antigen-specific T-cell proliferation; and the expression of cell-surface molecules, by flow cytometry. Rats were also made to inhale aerosolized 1% ovalbumin (OVA) or saline for 10min post-exposure to O(3), and allergic asthma-like symptoms were measured by determining the increase in enhanced pause (Penh), which correlates well with lung resistance. O(3) increased both AP activity and expression of Ia and costimulatory molecules in BAL cells concentration dependently. It also increased lung resistance, and the increase in lung resistance after O(3) exposure was significantly higher in the OVA-inhaled group than in the saline-inhaled group. The present results show that O(3) increased AP activity concentration dependently and suggest that O(3) might aggravate allergy symptoms by enhancing AP activity.

Ovalbumin-induced airway inflammation and fibrosis in mice also exposed to ozone

A murine model of allergen-induced airway inflammation was used to examine the effects of exposure to ozone on airway inflammation and remodeling. Sensitized BALB/c mice were exposed to ovalbumin aerosol for 4 wk before and after 2 wk of exposure to either 0.2 ppm or 0.5 ppm ozone. Other groups of mice were exposed to ovalbumin aerosol for 6 wk with continuous concurrent exposure to ozone during wk 1-6, or during intermittent concurrent exposure to ozone. Lung inflammation was measured by quantitative differential evaluation of lung lavage cells and by histological evaluation of stained lung sections. Alterations in lung structure (airway fibrosis) were evaluated by quantitative biochemical analysis of microdissected airways. The same total number of cells was observed in lavage fluid from animals exposed for 4 wk to ovalbumin alone or to ovalbumin for 4 wk immediately before or after exposure to 2 wk of 0.2 or 0.5 ppm ozone. Mice exposed to ovalbumin for 6 wk with concurrent exposure to either 0.2 ppm or 0.5 ppm ozone during wk 3-6 had a significant decrease in the total number of cells recovered by lavage. Values as low as 7% of the cell number found in mice exposed to ovalbumin aerosol alone were observed in the mice exposed to ovalbumin plus 0.2 ppm ozone during wk 3-6. There were significant differences in the cell differential counts in the lavage fluid from mice exposed to ovalbumin alone as compared with values from mice exposed to ovalbumin and ozone under all of the protocols studied. When ozone was given for 2 wk prior to ovalbumin exposure (Experiment 1), there were a high percentage of macrophages and low percentages of lymphocytes and eosinophils in the lung lavage. When ozone was given for 2 wk after ovalbumin exposure (Experiment 2), there were a moderate percentage of macrophages, a low percentage of eosinophils, and a high percentage of lymphocytes in the lung lavage. When ozone and ovalbumin were given simultaneously (Experiments 3 and 4), there were a high percentage of macrophages in the lavage with 0.2 ppm ozone and a high percentage of eosinophils. Ozone appears to antagonize the specific inflammatory effects of ovalbumin exposure, especially when given before or during exposure to ovalbumin. Airway remodeling was examined by two different quantitative methods. None of the groups exposed concurrently to ovalbumin and ozone had a significant increase in airway collagen content as compared to the matched groups of mice exposed to ovalbumin alone. The findings were consistent with an additive response of mice to simultaneous exposure to ovalbumin and ozone. Ozone exposure alone for 6 wk did not affect the number of goblet cells in the airways, while mice exposed to ovalbumin aerosol alone for 6 wk had about 25% goblet cells in their conducting airways. Concurrent exposure to ovalbumin and 0.2 ppm ozone caused significant increases in goblet cells (to 43% of total cells) in the conducting airways of the exposed mice. We conclude that when mice with allergen-induced airway inflammation induced by ovalbumin are also exposed to ozone, the lung inflammatory response may be modified, but that this altered response is dependent on the sequence of exposure and the concentration of ozone to which they are exposed. At the concentrations of ozone tested, we did not see changes in airway fibrosis. However, goblet-cell hyperplasia appeared to be increased in mice exposed concurrently to ovalbumin and 0.2 ppm ozone.

Susceptibility to ovalbumin-induced airway inflammation and fibrosis in inducible nitric oxide synthetase-deficient mice: mechanisms and consequences

In a previous study, we showed that BALB/c mice demonstrate significant increases in accumulation of airway collagen after 4 weeks of exposure to ovalbumin aerosol. In the current study we examined the response to ovalbumin aerosol of a different strain of mice, C57BL/6, and compared this response to an otherwise isogenic C57BL strain (iNOS(-/-)) in which the gene for inducible nitric oxide synthetase (iNOS) had been knocked out. We hypothesized that C57BL mice, a Th-1-responsive strain, would be relatively resistant to ovalbumin exposure compared with our previous observations in the BALB/c strain, a Th-2 responder. Our results are consistent with this hypothesis, especially with respect to the accumulation of collagen in the airways of the mice exposed to ovalbumin and increased airway reactivity to challenge with methacholine, as measured by the Penh response. Since NO participates in multiple signal transduction pathways, there was no a priori reason to predict whether iNOS(-/-) mice would be more or less susceptible to allergen-induced airway inflammation than their parental wild-type strain. Responses to ovalbumin exposure of the Th-1-responsive C57BL animals were significantly less (or slower) than those we observed with the iNOS(-/-) mice. Significant increases in airway collagen content were seen only after 6 weeks of exposure of the C57BL mice, as contrasted with 4 weeks in the iNOS(-/-) animals. At each time point examined, Penh values for the iNOS(-/-) mice were significantly increased, while no increases were observed with the C57BL strain. Thus, the iNOS(-/-) mice are more susceptible to ovalbumin-induced airway inflammation and fibrosis than the C57BL strain, giving results intermediate between the previous observations in BALB/c mice and our current findings in C57BL animals with the various assays performed. We also asked whether the effects of knocking out the iNOS gene were exerted before or after the release of TGF-beta(1) by eosinophils and other effector cells in the lung. We measured the response of C57BL and iNOS(-/-) mice to direct intratracheal challenge with TGF-beta(1). There was no apparent response of C57BL mice to TGF-beta(1) at 4 or 11 days after TGF-beta(1) challenge, as evaluated by bronchoprovocation testing. On the other hand, the observed Penh values were significantly greater in iNOS(-/-) mice that had also received TGF-beta(1) 4 days previously. These results strongly support the hypothesis that the increased sensitivity of iNOS(-/-) mice to ovalbumin is at least partially dependent on pathways that come into play subsequent to the release of TGF-beta(1) by effector cells in the lungs of mice exposed to ovalbumin aerosol.

Repeated episodes of ozone inhalation amplifies the effects of allergen sensitization and inhalation on airway immune and structural development in Rhesus monkeys

Twenty-four infant rhesus monkeys (30 days old) were exposed to 11 episodes of filtered air (FA), house dust mite allergen aerosol (HDMA), ozone (O3), or HDMA + O3 (5 days each followed by 9 days of FA). Ozone was delivered for 8 h/day at 0.5 ppm. Twelve of the monkeys were sensitized to house dust mite allergen (Dermatophagoides farinae) at ages 14 and 28 days by subcutaneous inoculation (SQ) of HDMA in alum and intraperitoneal injection of heat-killed Bordetella pertussis cells. Sensitized monkeys were exposed to HDMA aerosol for 2 h/day on days 3-5 of either FA (n = 6) or O3 (n = 6) exposure. Nonsensitized monkeys were exposed to either FA (n = 6) or O3 (n = 6). During the exposure regimen, parameters of allergy (i.e., serum IgE, histamine, and eosinophilia), airways resistance, reactivity, and structural remodeling were evaluated. Eleven repeated 5-day cycles of inhaling 0.5 ppm ozone over a 6-month period had only mild effects on the airways of nonsensitized infant rhesus monkeys. Similarly, the repeated inhalation of HDMA by HDMA-sensitized infant monkeys resulted in only mild airway effects, with the exception of a marked increase in proximal airway and terminal bronchiole content of eosinophils. In contrast, the combined cyclic inhalation of ozone and HDMA by HDMA sensitized infants monkeys resulted in a marked increase in serum IgE, serum histamine, and airways eosinophilia. Furthermore, combined cyclic inhalation of ozone and HDMA resulted in even greater alterations in airway structure and content that were associated with a significant elevation in baseline airways resistance and reactivity. These results suggest that ozone can amplify the allergic and structural remodeling effects of HDMA sensitization and inhalation.

Airway obstruction after acute ozone exposure in BALB/c mice using barometric plethysmography

BACKGROUND

Airway responsiveness after acute inhalation of ozone is related to the concentration and duration of ozone exposure. Using barometric whole-body plethysmography and increase in enhanced pause (Penh) as an index of airway obstruction, we measured the response of BALB/c mice to acute ozone inhalation to study the time course change of pulmonary function after ozone exposure.

METHODS

Penh was measured before and after exposure to filtered air or 0.12, 0.5, 1, or 2 ppm ozone for 3 hr (n = 6/group). In addition, Penh was measured 24, 48 and 72 hr after ozone exposure. Bronchoalveolar lavage (BAL) and histopathologic examinations were performed.

RESULTS

The increase in Penh after ozone exposure was significantly higher in the 0.12, 0.5, 1 and 2 ppm groups compared with the control group (all p < 0.01). Increases in Penh 24 hr after ozone exposure were significantly lower than those immediately after acute ozone exposure; however, increases in Penh 72 hr after ozone exposure were significantly higher than those in the control group (each p < 0.01). The proportion of neutrophils in BAL fluid was significantly higher in the group exposed to 2 ppm ozone than in the groups exposed to filtered air or 0.12 ppm ozone (both p < 0.01).

CONCLUSION

These results indicate that airway obstruction is induced following ozone exposure in a concentration-dependent manner and persists for at least 72 hr.

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

BACKGROUND

Epidemiological studies suggest that ozone exposure is related to increased asthma symptoms. Dendritic cells (DCs) are the principal antigen-presenting cells in the airways.

OBJECTIVE

We have examined whether ambient doses of ozone (100 ppb for 2 h) enhance allergic sensitization and/or airway inflammation in a mouse model.

METHODS

C57BL/6 mice were sensitized to inhaled ovalbumin (OVA) by intratracheal instillation of OVA-pulsed DCs on day 0. Daily exposure to OVA aerosol on days 14-20 resulted in an eosinophilic airway inflammation, as reflected in bronchoalveolar lavage fluid and lung histology. In a first experiment, mice were exposed to ozone or room air immediately prior to and following sensitization. Subsequently, we tested the effect of ozone exposure during antigen challenge in DC-sensitized mice.

RESULTS

Exposure to ozone during sensitization did not influence airway inflammation after subsequent allergen challenge. In contrast, in sensitized mice, challenge with OVA together with ozone (days 14-20) resulted in enhanced airway eosinophilia and lymphocytosis, as compared with mice exposed to OVA and room air (1.91 x 106 +/- 0.46 x 106 vs. 0.16 x 106 +/- 0.06 x 106 eosinophils/mL lavage fluid; P = 0.015; 0.49 x 106 +/- 0.11 x 106 vs. 0.08 x 106 +/- 0.03 x 106 lymphocytes/mL lavage fluid; P = 0.004). Ozone exposure without subsequent OVA exposure did not cause airway inflammation.

CONCLUSION

Ozone exposure does not increase allergic sensitization but enhances antigen-induced airway inflammation in mice that are sensitized via the airways.

Modulation of inhaled antigen-induced IgE tolerance by ongoing Th2 responses in the lung

The normal response to inhaled Ag is the absence of Ag-specific IgE and cytokine production to later Ag challenges. Although the mechanism of this aerosol-induced IgE tolerance is not completely understood, it may prevent sensitization to inhaled Ags, which could otherwise lead to allergy and asthma. We examined the consequences of ongoing Th1 and Th2 responses in the lungs of mice during OVA inhalation to mimic conditions that may subvert tolerance and lead to sensitization. We found that concurrent, secondary Th2 lung responses to keyhole limpet hemocyanin or primary responses to Nippostrongylus larvae or Asperigillus fumagatus extract prevented establishment of IgE tolerance to aerosolized OVA. Intranasal rIL-4 given before OVA aerosolization also prevented establishment of tolerance, whereas concurrent Th1 responses to influenza virus or Mycobacterium bovis bacillus Calmette-Guérin had no effect. However, once established, aerosol tolerance to OVA could not be completely broken by OVA rechallenge concurrent with a secondary Th2 response to keyhole limpet hemocyanin or A. fumagatus extract, or by intranasal rIL-4. These data suggest that the immune status of the lung of an individual may profoundly influence the initial response to inhaled Ag, and that aerosol-induced IgE tolerance may not be appropriately established in individuals undergoing concurrent, Th2-mediated responses to Ags or pathogens.