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Air pollution events frequently occur in China during the winter. Most investigations of pollution studies have focused on the physical and chemical properties of PM2.5. Many of these studies have indicated that PM2.5 exacerbates asthma or eosinophil inflammation. However, few studies have evaluated the relationship between bacterial loads in PM2.5, and especially pathogenic bacteria and childhood asthma. Airborne PM2.5 samples from heavily polluted air were collected in Hangzhou, China between December 2014 and January 2015. PM2.5 and ovalbumin (OVA) were intratracheally administered twice in 4-week intervals to induce the allergic pulmonary inflammation in adolescent C57/BL6 mice. PM2.5 exposure caused neutrophilic alveolitis and bronchitis. In the presence of OVA, the levels of the Th2 cytokines IL-4, IL-12, and IL-17 were significantly increased in bronchoalveolar lavage fluids (BALF) after PM2.5 exposure, while eosinophil infiltration and mucin secretion were also induced. In addition to adjuvant effects on OVA-induced allergic inflammation, PM2.5 exposure also led to the maturation of dendritic cells. These results suggest that PM2.5 exposure may aggravate lung eosinophilia and that PM2.5-bound microbial can exacerbate allergic and inflammatory lung diseases. [ABSTRACT FROM AUTHOR]