Alteration of lung defense mechanisms after exposure to urban coarse PM leads to infection by Streptococcus pneumoniae

Abstract

<b>Background:</b> Ambient particulate matter (PM) exposure has been shown to increase the risks of respiratory diseases and to contribute to the substantial worldwide burden of respiratory infections. However, the immune response to inhaled PM remains largely unexplored. <b>Aim:</b> We studied the effects of urban coarse PM on the pulmonary immunologic homeostasis and susceptibility to Streptococcus pneumoniae. <b>Methods:</b> Male mice were exposed to urban coarse PM in a ventilated inhalation chamber for 3 at a concentration relevant to episodic elevation peak of air pollution. Then the characteristics of PM-induced inflammation were assessed by flow cytometry and real-time PCR. Mice were then challenged intranasally to Streptococcus pneumoniae. Survival and lung immune responses were investigated. <b>Results:</b> Exposure to urban coarse PM led to the recruitment of immune cells to the lung compartment, including neutrophils and activated alveolar macrophages. Moreover, genes involved in anti-microbial responses, such as Reg3g, Lcn-2, Lyz and Slpi were downregulated in the lungs after PM exposure. Exposure to PM leads to a decrease in IL-1b expression. This results in a higher mortality of PM mice after Streptococcus pneumoniae infection. <b>Conclusion:</b> This study provided a characterization of immunologic profiles in lungs following exposure to a realistic dose of PM. It suggested new mechanistic insights which should be further explored, in pulmonary response to PM inhalation and the effects of PM exposure on the susceptibility to pulmonary infections.