Biological impact of sequential exposures to allergens and ultrafine particle-rich combustion aerosol on human bronchial epithelial BEAS-2B cells at the air liquid interface

The prevalence of allergic diseases is constantly increasing since few decades. Anthropogenic ultrafine particles (UFPs) and allergenic aerosols is highly involved in this increase; however, the underlying cellular mechanisms are not yet understood. Studies observing these effects focused mainly on singular in vivo or in vitro exposures of single particle sources, while there is only limited evidence on their subsequent or combined effects. Our study aimed at evaluating the effect of subsequent exposures to allergy-related anthropogenic and biogenic aerosols on cellular mechanism exposed at air-liquid interface (ALI) conditions. Bronchial epithelial BEAS-2B cells were exposed to UFP-rich combustion aerosols for 2 h with or without allergen pre-exposure to birch pollen extract (BPE) or house dust mite extract (HDME). The physicochemical properties of the generated particles were characterized by state-of-the-art analytical instrumentation. We evaluated the cellular response in terms of cytotoxicity, oxidative stress, genotoxicity, and in-depth gene expression profiling. We observed that single exposures with UFP, BPE, and HDME cause genotoxicity. Exposure to UFP induced pro-inflammatory canonical pathways, shifting to a more xenobiotic-related response with longer preincubation time. With additional allergen exposure, the modulation of pro-inflammatory and xenobiotic signaling was more pronounced and appeared faster. Moreover, aryl hydrocarbon receptor (AhR) signaling activation showed to be an important feature of UFP toxicity, which was especially pronounced upon pre-exposure. In summary, we were able to demonstrate the importance of subsequent exposure studies to understand realistic exposure situations and to identify possible adjuvant allergic effects and the underlying molecular mechanisms.

Automated summary

The prevalence of allergic diseases is increasing, and the role of anthropogenic ultrafine particles (UFPs) and allergenic aerosols in this increase is not well understood. This study aimed to evaluate the effect of subsequent exposures to allergenic and biogenic aerosols on cellular mechanisms. Bronchial epithelial cells were exposed to UFP-rich combustion aerosols with or without allergen pre-exposure. Genotoxicity, oxidative stress, and gene expression profiling were evaluated. The results showed that single exposures to UFP, allergens, and UFP with allergen pre-exposure caused genotoxicity. UFP exposure induced pro-inflammatory pathways and xenobiotic-related responses, which were amplified with allergen pre-exposure. The activation of aryl hydrocarbon receptor (AhR) signaling was found to be an important feature of UFP toxicity, especially with pre-exposure. Overall, this study highlights the importance of subsequent exposure studies for understanding realistic exposure situations and identifying molecular mechanisms underlying allergic effects.