PM2.5 affects establishment of immune tolerance in newborn mice by reducing PD-L1 expression.

This study was conducted to determine whether exposure to particulate matter 2.5 (PM2.5) affects the immune tolerance of neonatal mice via the regulation of PD-L1 expression. One-week-old BALB/c mice were exposed to PM2.5 for 8 days. From day 8 to day 18, the mice were treated with 5 μg house dust mite (HDM) (i. n.) every two days. Adenovirus-carried PD-L1 overexpression vectors were infected into mice via nasal inhalation 6 days after exposure to PM2.5. Airway hyperresponsiveness (AHR) was examined in mice 19 days after exposure to PM2.5, and the related parameters of airway inflammation were studied on day 22. Co-exposure to PM2.5 and HDM reduced PD-L1 expression but greatly increased infiltration of inflammatory cells, which was reversed by PD-L1 overexpression. Co-exposure to PM2.5 and HDM also elevated serum IL-4, IL-5 and IL-13 levels and reduced TGF-β level. Exposure to PM2.5 alone slightly increased the numbers of dendritic cells (DCs) but reduced the numbers of antigen-presenting cells expressing PD-L1 and Treg cells. Therefore, early exposure to PM2.5 reduced PD-L1 expression in the lungs of neonatal mice, which interfered with immune tolerance establishment and subsequently resulted in allergic airway inflammation.