Recurrent aerosol antigen exposure induces distinct patterns of experimental allergic asthma in mice

The joint effect of cumulative doses for outdoor air pollutants exposure in early life on asthma and wheezing among young children

BACKGROUND

Constrained by no proper way to assess cumulative exposure, the joint effect of air pollution cumulative exposure doses on childhood asthma and wheezing (AW) was not understood.

OBJECTIVE

To assess the association between cumulative exposure to multiple air pollutants in early life and childhood AW.

METHODS

We designed a nested case-control study based on the birth cohort in Jinan City. Children with AW followed up within 2 years after birth were treated as cases, and non-cases in this cohort were treated as the control source population, and the propensity score matching method was used to match each case to 5 controls. We calculated the individual cumulative outdoor exposure doses for each period using an inverse distance weighted model, alongside the complex Simpson's formula, accounting for outdoor time and respiratory volume. The Least absolute shrinkage and selection operator (Lasso) regression was performed to screen for covariates. To analyze the joint effects of pollutants, we employed the weighted quantile sum (WQS) regression model in conjunction with conditional logistic regression.

RESULTS

84 cases and 420 controls were included in this study. The odds ratio (OR) with 95% confidence interval (CI) of the impact of cumulative exposure (mg/m3) after birth on childhood AW was 1.78 (1.15-2.74) for SO2, 1.69 (1.11-2.57) for NO2, and 1.65 (1.09-2.52) for PM2.5, respectively. Furthermore, with each 25th percentile increase in the WQS index, the overall risk of cumulative doses for six pollutants exposure after birth on AW increased by an adjusted OR of 1.10 (1.03, 1.18), and SO2, PM2.5, and NO2 contributed the most to the WQS index. However, no statistically significant association was found between cumulative exposure to all pollutants before birth and childhood AW.

CONCLUSIONS

There was a joint effect of the cumulative exposure dose of outdoor air pollutants after birth on AW in children aged 0-2 years. And traffic-related pollutants (SO2, PM2.5, and NO2) make a greater contribution to the joint effect.

β-Glucosylceramide From Allergic Mothers Enhances Offspring Responsiveness to Allergen

In animals and humans, offspring of allergic mothers have increased responsiveness to allergen and the allergen-specificity of the offspring can be different than that of the mother. In our preclinical models, the mother's allergic responses influence development of the fetus and offspring by elevating numbers of cells in dendritic cell subsets. A major question is the identity of maternal factors of allergic mothers that alter offspring development of responsiveness to allergen. Lipids are altered during allergic responses and lipids are transported to the fetus for growth and formation of fetal membranes. We hypothesized that pro-inflammatory lipids, that are elevated in allergic mothers, are transported to the fetus and regulate fetal immune development. We demonstrate in this report that there was a significant 2-fold increase in β-glucosylceramides (βGlcCer) in allergic mothers, the fetal liver and her offspring. The βGlcCer were transported from mother's plasma, across the placenta, to the fetus and in breastmilk to the offspring. Administration of βGlcCer to non-allergic mothers was sufficient for offspring responses to allergen. Importantly, maternal administration of a clinically relevant pharmacological inhibitor of βGlcCer synthase returned βGlcCer to normal levels in the allergic mothers and her offspring and blocked the offspring increase in dendritic cell subsets and offspring allergen responsiveness. In summary, allergic mothers had increased βGlcCer that was transported to offspring and mediated increases in offspring DCs and responsiveness to allergen. These data have a significant impact on our understanding of mechanisms for development of allergies in offspring of allergic mothers and have the potential to lead to novel interventions that significantly impact risk for allergic disease early in life.

The role of the γ δ T cell in allergic diseases

The predominant distribution of γδ T cells in the mucosal and epithelial tissues makes these unconventional lymphocytes the “guards” to contact external environment (like allergens) and to contribute to immune surveillance, as well as “vanguards” to participate in initiating mucosal inflammation. Therefore, γδ T cells have been considered to bridge the innate and adaptive immunity. The role these cells play in allergy seems to be complicated and meaningful, so it makes sense to review the characteristics and role of γδ T cells in allergic diseases.

The metalloporphyrin antioxidant, MnTE-2-PyP, inhibits Th2 cell immune responses in an asthma model

MnTE-2-PyP, a superoxide dismutase mimetic, inhibited OVA-induced airway inflammation in mice suggesting an effect on Th2 responsiveness. Thus, we hypothesized that MnTE-2-PyP may alter dendritic cell-Th2 interactions. Bone marrow derived dendritic cells (DC) and OVA(323-339)-specific Th2 cells were cultured separately in the presence or absence of MnTE-2-PyP for 3 days prior to the co-culturing of the two cell types in the presence of an OVA(323-339) peptide and in some cases stimulated with CD3/CD28. MnTE-2-PyP-pretreated DC inhibited IL-4, IL-5 and IFNγ production and inhibited Th2 cell proliferation in the DC-Th2 co-culturing system in the presence of the OVA(323-339) peptide. Similar results were obtained using the CD3/CD28 cell-activation system; the addition of MnTE-2-PyP inhibited Th2 cell proliferation. MnTE-2-PyP suppressed CD25 expression on OVA-specific Th2 cells, which implied that MnTE-2-PyP can inhibit the activation of Th2 cells. MnTE-2-PyP also down-regulated co-stimulatory molecules: CD40, CD80 and CD86 on immature DC. Our studies suggest that the major mechanism by which MnTE-2-PyP inhibits airway inflammation is by acting on the DC and suppressing Th2 cell proliferation and activation.

Isoforms of vitamin E differentially regulate inflammation

Vitamin E regulation of disease has been extensively studied in humans, animal models and cell systems. Most of these studies focus on the α-tocopherol isoform of vitamin E. These reports indicate contradictory outcomes for anti-inflammatory functions of the α-tocopherol isoform of vitamin E, especially with regards to clinical studies of asthma and atherosclerosis. These seemingly disparate clinical results are consistent with recently reported unrecognized properties of isoforms of vitamin E. Recently, it has been reported that physiological levels of purified natural forms of vitamin E have opposing regulatory functions during inflammation. These opposing regulatory functions by physiological levels of vitamin E isoforms impact interpretations of previous studies on vitamin E. Moreover, additional recent studies also indicate that the effects of vitamin E isoforms on inflammation are only partially reversible using physiological levels of a vitamin E isoform with opposing immunoregulatory function. Thus, this further influences interpretations of previous studies with vitamin E in which there was inflammation and substantial vitamin E isoforms present before the initiation of the study. In summary, this review will discuss regulation of inflammation by vitamin E, including alternative interpretations of previous studies in the literature with regards to vitamin E isoforms.

Supplemental and highly elevated tocopherol doses differentially regulate allergic inflammation: reversibility of α-tocopherol and γ-tocopherol's effects

We have reported that supplemental doses of the α- and γ-tocopherol isoforms of vitamin E decrease and increase, respectively, allergic lung inflammation. We have now assessed whether these effects of tocopherols are reversible. For these studies, mice were treated with Ag and supplemental tocopherols in a first phase of treatment followed by a 4-wk clearance phase, and then the mice received a second phase of Ag and tocopherol treatments. The proinflammatory effects of supplemental levels of γ-tocopherol in phase 1 were only partially reversed by supplemental α-tocopherol in phase 2, but were completely reversed by raising α-tocopherol levels 10-fold in phase 2. When γ-tocopherol levels were increased 10-fold (highly elevated tocopherol) so that the lung tissue γ-tocopherol levels were equal to the lung tissue levels of supplemental α-tocopherol, γ-tocopherol reduced leukocyte numbers in the lung lavage fluid. In contrast to the lung lavage fluid, highly elevated levels of γ-tocopherol increased inflammation in the lung tissue. These regulatory effects of highly elevated tocopherols on tissue inflammation and lung lavage fluid were reversible in a second phase of Ag challenge without tocopherols. In summary, the proinflammatory effects of supplemental γ-tocopherol on lung inflammation were partially reversed by supplemental levels of α-tocopherol but were completely reversed by highly elevated levels of α-tocopherol. Also, highly elevated levels of γ-tocopherol were inhibitory and reversible in lung lavage but, importantly, were proinflammatory in lung tissue sections. These results have implications for future studies with tocopherols and provide a new context in which to review vitamin E studies in the literature.

Conditional deletion of histone deacetylase 1 in T cells leads to enhanced airway inflammation and increased Th2 cytokine production

Chromatin modifications, such as reversible histone acetylation, play a key role in the regulation of T cell development and function. However, the role of individual histone deacetylases (HDACs) in T cells is less well understood. In this article, we show by conditional gene targeting that T cell-specific loss of HDAC1 led to an increased inflammatory response in an in vivo allergic airway inflammation model. Mice with HDAC1-deficient T cells displayed an increase in all critical parameters in this Th2-type asthma model, such as eosinophil recruitment into the lung, mucus hypersecretion, parenchymal lung inflammation, and enhanced airway resistance. This correlated with enhanced Th2 cytokine production in HDAC1-deficient T cells isolated from diseased mice. In vitro-polarized HDAC1-deficient Th2 cells showed a similar enhancement of IL-4 expression, which was evident already at day 3 of Th2 differentiation cultures and restricted to T cell subsets that underwent several rounds of cell divisions. HDAC1 was recruited to the Il4 gene locus in ex vivo isolated nonstimulated CD4(+) T cells, indicating a direct control of the Il4 gene locus. Our data provide genetic evidence that HDAC1 is an essential HDAC that controls the magnitude of an inflammatory response by modulating cytokine expression in effector T cells.

Are mouse models of allergic asthma useful for testing novel therapeutics?

Experimental mouse allergic asthma is a reliable, clinically relevant facsimile of human disease. The focus here is to demonstrate that antigen-induced mouse allergic asthma is a useful model for testing novel therapeutics. Furthermore, it is especially crucial to treat mice during established disease, either during ongoing clinically manifest disease or to prevent disease relapses. In addition, our results indicate that lung Th2 resting memory cells are important targets for the treatment of allergic asthma.

Targeting memory Th2 cells for the treatment of allergic asthma

Th2 memory cells play an important role in the pathogenesis of allergic asthma. Evidence from patients and experimental models indicates that memory Th2 cells reside in the lungs during disease remission and, upon allergen exposure, become activated effectors involved in disease exacerbation. The inhibition of memory Th2 cells or their effector functions in allergic asthma influence disease progression, suggesting their importance as therapeutic targets. They are allergen specific and can potentially be suppressed or eliminated using this specificity. They have distinct activation, differentiation, cell surface phenotype, migration capacity, and effector functions that can be targeted singularly or in combination. Furthermore, memory Th2 cells residing in the lungs can be treated locally. Capitalizing on these unique attributes is important for drug development for allergic asthma. The aim of this review is to present an overview of therapeutic strategies targeting Th2 memory cells in allergic asthma, emphasizing Th2 generation, differentiation, activation, migration, effector function, and survival.

Inhaled dexamethasone differentially attenuates disease relapse and established allergic asthma in mice

Inhaled glucocorticoids are effective in patients with chronic allergic asthma. We examined the effects of inhaled glucocorticoids on relapse (allergen challenge after disease remission) and established/overt allergic asthma (repeated allergen challenge in weekly intervals) in mice to establish a reference standard for novel treatments. BALB/c mice were treated before relapse or during overt disease with 1 h of nebulized PBS or 10 mg% dexamethasone twice daily for 5 days. Dexamethasone eliminated airway hyperresponsiveness before relapse and during overt disease. They more efficiently reduced airway inflammation, mucus production, and OVA-specific IgG1 and IgE during relapse compared to overt disease. However, during overt disease, parenchymal inflammatory infiltrates were more effectively eliminated compared to relapse, suggesting that activated infiltrating leukocytes have increased sensitivity to steroids. These data demonstrate that inhaled corticosteroids attenuate relapse and overt disease differentially and suggest that both airway and parenchymal inflammation need to be evaluated for treatment efficacy.

Reversal of allergic airway hyperreactivity after long-term allergen challenge depends on gammadelta T cells

Long-term allergen exposure can attenuate inflammation and revert airway hyperreactivity to normal responsiveness. A model of such reversal was established in which airway hyperreactivity and inflammation in ovalbumin-sensitized and challenged mice were decreased after multiple daily airway challenges. This change in responsiveness and inflammation was associated with a transition from a helper T cell Type 2 to a helper T cell Type 1 cytokine-biased profile in bronchoalveolar lavage fluid. Cell transfer from long-term exposed mice into hyperreactive mice also restored normal airway responsiveness, establishing the mechanism underlying the reversal of the hyperreactivity as active suppression, but did not affect eosinophilic airway inflammation. Conversely, airway hyperreactivity, suppressed as a result of long-term allergen exposure, could be reestablished by depleting gammadelta T cells, in particular Vgamma4+ cells. Antigen-specific tolerance of alphabeta T cells or suppression by non-gammadelta T cells did not play a role in the reversal to normal airway responsiveness and gammadelta T cells did not play a role in the regulation of the allergic inflammatory response. These findings show that normal responsiveness in previously hyperreactive mice, achieved after long-term allergen challenge, is based on several, apparently independent regulatory mechanisms. One of these, focused on airway responsiveness, involves active suppression and requires gammadelta T cells.

Long-lived Th2 memory in experimental allergic asthma

Although life-long immunity against pathogens is beneficial, immunological memory responses directed against allergens are potentially harmful. Because there is a paucity of information about Th2 memory cells in allergic disease, we established a model of allergic asthma in BALB/c mice to explore the generation and maintenance of Th2 memory. We induced disease without the use of adjuvants, thus avoiding Ag depots, and found that unlike allergic asthma in mice immunized with adjuvant, immunizing with soluble and aerosol OVA resulted in pathological lung lesions resembling human disease. To test memory responses we allowed mice with acute disease to recover and then re-exposed them to aerosol OVA a second time. Over 400 days later these mice developed OVA-dependent eosinophilic lung inflammation, airway hyperresponsiveness, mucus hypersecretion, and IgE. Over 1 year after recuperating from acute disease, mice had persistent lymphocytic lung infiltrates, Ag-specific production of IL-4 and IL-5 from spleen and lung cells in vitro, and elevated IgG1. Moreover, when recuperated mice were briefly aerosol challenged, we detected early expression of Th2 cytokine RNA in lungs. Taken together, these data demonstrate the presence of long-lived Th2 memory cells in spleen and lungs involved in the generation of allergic asthma upon Ag re-exposure.

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.