Background: The respiratory system is exposed to various allergens via inhaled and intranasal routes. Murine models of allergic lung disease have been developed to clarify the mechanisms underlying inflammatory responses and evaluate the efficacy of novel therapeutics. However, there have been no comparative studies on differences in allergic phenotypes following inhaled vs. intranasal allergen challenge. In this study, we compared the asthmatic features of mice challenged via different routes following allergen sensitization and investigated the underlying mechanisms. Methods: To establish ovalbumin (OVA)-induced allergic asthma models, BALB/c mice were sensitized to 20 μg OVA with 1 mg aluminum hydroxide by the intraperitoneal route and then challenged by inhalation or intranasal administration with 5% OVA for 3 consecutive days. Cellular changes and immunoglobulin (Ig) E levels in bronchoalveolar lavage fluid (BALF) and serum, respectively, were assessed. Histological changes in the lungs were examined by hematoxylin and eosin (H&E) and periodic acid Schiff (PAS) staining. Levels of T helper (Th)2 cytokines including interleukin (IL)-4, -5, and -13 in BALF and epithelial cytokines including IL-25 and -33 in BALF and lung tissues were measured by enzyme-linked immunosorbent assay and western blotting. Airway hyperresponsiveness (AHR) was evaluated by assessing airway resistance (Rrs) and elastance (E) via an invasive method. Results: OVA-sensitized and challenged mice showed typical asthma features such as airway inflammation, elevated IgE level, and AHR regardless of the challenge route. However, H&E staining showed that inflammation of pulmonary vessels, alveolar ducts, and alveoli were enhanced by inhaled as compared to intranasal OVA challenge. PAS staining showed that intranasal OVA challenge induced severe mucus production accompanied by inflammation in bronchial regions. In addition, Th2 cytokine levels in BALF and AHR in lung were increased to a greater extent by inhalation than by intranasal administration of OVA. Epithelial cytokine expression, especially IL-25, was increased in the lungs of mice in the inhaled OVA challenge group. Conclusion: OVA-sensitized mice exhibit different pathophysiological patterns of asthma including expression of epithelial cell-derived cytokines depending on the OVA challenge route. Thus, some heterogeneous phenotypes of human asthma can be replicated by varying the mode of delivery after OVA sensitization.

Diesel exhaust particulates (DEP) have adverse effects on the respiratory system. Endoplasmic reticulum (ER) abnormalities contribute to lung inflammation. However, the relationship between DEP exposure and ER stress in the respiratory immune system and especially the alveolar macrophages (AM) is poorly understood. Here, we examined ER stress and inflammatory responses using both in vivo and in vitro study. For in vivo study, mice were intratracheally instilled with 25, 50, and 100 μg DEP and in vitro AM were stimulated with DEP at 1, 2, and 3 mg/mL. DEP increased lung weight and the number of inflammatory cells, especially neutrophils, and inflammatory cytokines in bronchoalveolar lavage fluid of mice. DEP also increased the number of DEP-pigmented AM and ER stress markers including bound immunoglobulin protein (BiP) and CCAAT/enhancer binding protein-homologous protein (CHOP) were upregulated in the lungs of DEP-treated mice. In an in vitro study, DEP caused cell damage, increased intracellular reactive oxygen species, and upregulated inflammatory genes and ER stress-related BiP, CHOP, splicing X-box binding protein 1, and activating transcription factor 4 expressions in AM. Furthermore, DEP released the C-X-C Motif Chemokine Ligand 1 (CXCL1/KC) in AM. In conclusion, DEP may contribute to neutrophilic lung inflammation pathogenesis by modulating ER stress-mediated CXCL1/KC expression in AM.

Currently available toxicity data on humidifier disinfectants are primarily limited to polyhexamethylene guanidine phosphate-induced lung fibrosis. We, therefore, investigated whether the sterilizer component Kathon, which is a mixture of chloromethylisothiazolinone and methylisothiazolinone, induces fibrotic lung injury following direct lung exposure in an animal model. Mice were intratracheally instilled with either the vehicle or Kathon. Differential cell counts, cytokine analysis, and histological analysis of lung tissue were then performed to characterize the injury features, and we investigated whether Kathon altered fibrosis-related gene expression in lung tissues via RNA-Seq and bioinformatics. Cell counting showed that Kathon exposure increased the proportion of macrophages, eosinophils, and neutrophils. Moreover, T helper 2 (Th2) cytokine levels in the bronchoalveolar lavage were significantly increased in the Kathon groups. Histopathological analysis revealed increased perivascular/alveolar inflammation, eosinophilic cells, mucous cell hyperplasia, and pulmonary fibrosis following Kathon exposure. Additionally, Kathon exposure modulated the expression of genes related to fibrotic inflammation, including the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway, extracellular signal regulated kinase (ERK)1 and ERK2 cascade, extracellular matrix (ECM)-receptor interaction pathway, transforming growth factor beta receptor signaling pathway, cellular response to tumor necrosis factor, and collagen fibril organization. Our results suggest that Kathon exposure is associated with fibrotic lung injury via a Th2-dependent pathway and is thus a possible risk factor for fibrosis.

Diesel exhaust particulates (DEP) adversely affect the respiratory system and exacerbate lung diseases, resulting in high mortality rates. However, its pathogenesis is complicated, and the mechanisms involved are incompletely understood. We investigated the effects of DEP pre-exposure on lipopolysaccharide (LPS)-induced acute lung injury (ALI) and identified the roles of interleukin (IL)-17 in mice. Mice were divided into vehicle control, DEP, LPS, and DEP pre-exposed and LPS-instilled groups. Pre-exposure to DEP enhanced the number of total cells, neutrophils, and lymphocytes in the BAL fluid of LPS-instilled mice. Pre-exposure to DEP synergistically exacerbated pulmonary acute lung inflammation and granulomatous inflammation/pulmonary fibrosis, concomitant with the enhanced expression of inflammatory cytokines in the BAL fluid and of collagen I and TGF-β₁ in the lungs of LPS-instilled mice. The number of TGF-β₁-positive cells in the DEP pre-exposed and LPS-instilled group was higher than that in the LPS group. The expression of NLR family pyrin domain containing 3 (NLRP3) inflammasome components was markedly increased in the DEP pre-exposed and LPS-instilled group. IL-17 levels in the BAL fluid and IL-17-positive cells in the lungs were significantly increased by pre-exposure to DEP in the LPS-induced group compared to that in the DEP or LPS group. These results suggest that DEP predominantly contributes to fibrotic lung disease in LPS-related acute lung injury by upregulating IL-17 cytokine-mediated collagen I and TGF-β₁ and, at least in part, by activating LPS-induced NLRP3 inflammasome signaling. The study should be useful in devising better strategies for prevention and management of ALI.

This study evaluates the behavioral characteristics of components (methylisothiazolinone (MIT) and chloromethylisothiazolinone (CMIT)) contained in disinfectant solutions when they convert to liquid aerosols. The analytical method for MIT and CMIT quantitation was established and optimized using sorbent tube/thermal desorber-gas chromatography-mass spectrometry system; their behavioral characteristics are discussed using the quantitative results of these aerosols under different liquid aerosol generation conditions. MIT and CMIT showed different behavioral characteristics depending on the aerosol mass concentration and sampling time (sampling volume). When the disinfectant solution was initially aerosolized, MIT and CMIT were primarily collected on glass filter (MIT = 91.8 ± 10.6% and CMIT = 90.6 ± 5.18%), although when the generation and filter sampling volumes of the aerosols increased to 30 L, the relative proportions collected on the filter decreased (MIT = 79.0 ± 12.0% and CMIT = 39.7 ± 8.35%). Although MIT and CMIT had relatively high vapor pressure, in liquid aerosolized state, they primarily accumulated on the filter and exhibited particulate behavior. Their relative proportions in the aerosol were different from those in disinfectant solution. In the aerosol with mass concentration of ≤5 mg m⁻³, the relative proportion deviations of MIT and CMIT were large; when the mass concentration of the aerosol increased, their relative proportions constantly converged at a lower level than those in the disinfectant solution. Hence, it can be concluded that the behavioral characteristics and relative proportions need to be considered to perform the quantitative analysis of the liquid aerosols and evaluate various toxic effects using the quantitative data.