Association of short-term PM exposure with airway innate immune response, microbiota and metabolism alterations in human airways.

Exposure to fine particulate matter (PM) has been associated with impaired airway innate immunity, leading to diverse lung disorders. However, the mechanisms of the adverse effects of PM on the airway innate immune system has not been adequately elucidated. This study aimed to investigate the association between short-term exposure to ambient PM and airway innate immune responses. A panel study of 53 undergraduate students was conducted in November 2020 and April 2021. Levels of airway innate immune biomarkers including interleukin-1β (IL-1β), IL-4, IL-6, IL-8, IL-17, interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α), myeloperoxidase (MPO), and matrix metalloproteinase-9 (MMP-9) in induced sputum were measured, and airway microbiota and metabolites examined. Linear mixed-effect model was used to evaluate the effects of short-term exposure to PM on the above-listed airway immune biomarkers. The results indicated that for every 10 μg/m increase in PM concentration (at lag3), was associated with an increase of 21.3 % (5.4 %-37.1 %), 26.2 % (0.30 %-52.1 %), 22.4 % (0.70 %-44.2 %), 27.4 % (6.6 %-48.3 %), 18.3 % (4.6 %-31.9 %), 3.9 % (0.20 %-7.6 %) or 2.4 % (0.10 %-4.7 %) in IL-6, TNF-α, IL-17, IL-4, IFN-γ, MPO, or MMP-9 levels, respectively. Meanwhile, exposure to higher levels of ambient PM was found to significantly modulate airway microbiota and metabolite profile. Specifically, Prevotella and Fusobacterium, as well as 96 different metabolites were associated with PM levels. The metabolic pathways associated with these metabolites mainly included amino acid biosynthesis and metabolism. Notably, PM exposure-induced alterations of some airway microbiota were significantly correlated with specific airway metabolic change. Taken together, these results demonstrated that short-term exposure to PM was associated with alterations of airway immune response, microbial dysbiosis and changes of metabolites. This study provided insights into the mechanisms underlying PM-induced airway innate immune responses.