Abstract
BackgroundExposure to soybean allergens has been linked to asthma outbreaks. Exposure to diesel exhaust particles (DEP) has been associated with an increase in the risk of asthma and asthma exacerbation; however, in both cases the underlying mechanisms remain poorly understood, as does the possible interaction between the two entities.ObjectiveTo investigate how the combination of soybean allergens and DEP can affect the induction or exacerbation of asthma in a murine model.MethodsBALB/c mice received intranasal instillations of saline, 3 or 5 mg protein/ml soybean hull extract (SHE), or a combination of one of these three solutions with DEP. Airway hyperresponsiveness (AHR), pulmonary inflammation in bronchoalveolar lavage, total serum immunoglobulin E and histological studies were assessed.ResultsA 5 mg protein/ml SHE solution was able by itself to enhance AHR (p = 0.0033), increase eosinophilic inflammation (p = 0.0003), increase levels of IL-4, IL-5, IL-13, IL-17A, IL-17F and CCL20, and reduce levels of IFN-γ. The combination of 5 mg protein/ml SHE with DEP also produced an increase in AHR and eosinophilic inflammation, but presented a slightly different cytokine profile with higher levels of Th17-related cytokines. However, while the 3 mg protein/ml SHE solution did not induce asthma, co-exposure with DEP resulted in a markedly enhanced AHR (p = 0.002) and eosinophilic inflammation (p = 0.004), with increased levels of IL-5, IL-17F and CCL20 and decreased levels of IFN-γ.Conclusions & clinical relevanceThe combination of soybean allergens and DEP is capable of triggering an asthmatic response through a Th17-related mechanism when the soybean allergen concentration is too low to promote a response by itself. DEP monitoring may be a useful addition to allergen monitoring in order to prevent new asthma outbreaks.
Highlights
Several asthma epidemics due to soybean dust inhalation have been described in Spain and elsewhere [1,2,3]
The combination of 5 mg protein/ml soybean hull extract (SHE) with Diesel exhaust particles (DEP) produced an increase in Airway hyperresponsiveness (AHR) and eosinophilic inflammation, but presented a slightly different cytokine profile with higher levels of Th17-related cytokines
The combination of soybean allergens and DEP is capable of triggering an asthmatic response through a Th17-related mechanism when the soybean allergen concentration is too low to promote a response by itself
Summary
Several asthma epidemics due to soybean dust inhalation have been described in Spain and elsewhere [1,2,3]. The first reported epidemics occurred in Barcelona where soybean dust released during the unloading of these legumes from ships to silos caused asthma epidemics among residents of the neighborhoods closest to the harbor [1,2,4] In this city, the control measures adopted to avoid these outbreaks included the reduction of allergen emission levels by the installation of filter bags, the establishment of threshold values compatible with health, and the daily assessment of the emission and dispersion of the allergen to keep levels below these thresholds [5]. Diesel exhaust particles (DEP), the main contributor to traffic PM [6], have a potential enhancing effect on responses to inhaled allergen exposure, and may induce sensitization to neoallergens in human and animal models [8]. Attempts to explain the participation of DEP in the pathogenesis of asthma have suggested a role for oxidative stress and immune dysregulation, but at present the mechanisms involved remain poorly understood
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