Abstract
Fine particulate matter 2.5 (PM2.5) is a harmful air pollutant currently threatening public health. Although many studies have been performed on the general negative effects of PM2.5 in mice and humans, the migration patterns of various immune cells in response to PM2.5 exposure remain unclear. In this study, we aimed to investigate the immune cell migratory response in the lung and the liver of intratracheally PM2.5-inoculated mice. To investigate the migration trajectory of immune cells in the lung and the liver tissues of mice, we employed microscopic tools including two-photon intravital imaging, histological analysis, and transmission electron microscopy. Our data from two-photon intravital imaging showed that there was no significant difference in the number of infiltrated neutrophils in the lung and the liver of PM2.5-treated mice, compared to the nontreated condition. However, from the histological analysis and the transmission electron microscopy after vascular perfusion to remove intravascular leukocytes, we observed that some leukocytes were frequently observed in the lung and the liver of PM2.5-treated mice. Interestingly, quantification of leukocyte population using flow cytometry showed significant increase of neutrophils and macrophages in the lung, but not much in the liver, 24 h post-PM2.5 treatment. These data imply that two-photon intravital imaging of the lung and the liver actually visualized neutrophils, which were adherent to the luminal side of the vasculature. We then conducted mRNA microarray analysis to further observe how PM2.5 affects gene expression patterns in the lung and the liver. PM2.5 treatment changed the mRNA expression associated with the IL-17 signaling pathway in the lung and changed the mRNA expression associated with metabolic pathways in the liver. In summary, these results suggest that the immune response in the lung is distinctly regulated from that in the liver under acute PM2.5-induced inflammation and that these organs consequently are regulated via distinct signaling pathways.
Highlights
Particulate matter (PM2.5) has been a focus of interest among various artificial pollutants in recent years worldwide because of its biohazardous effects
To investigate the effect of PM2.5 treatment on neutrophil migration, mice were divided into three groups: (1) a control group, (2) a group assessed 24 h postPM2.5 treatment, and (3) a group assessed 48 h post-PM2.5 treatment
According to the twophoton intravital imaging analysis of both lung and liver tissues, there was no significant difference in the number of neutrophils of the three groups in these two organs (Figures 1(d) and 1(e))
Summary
Particulate matter (PM2.5) has been a focus of interest among various artificial pollutants in recent years worldwide because of its biohazardous effects. Unlike naturally occurring “dust,” PM mostly comprises chemicals that are emitted from diesel, construction factories, and power plants [1]. PM can be classified into two groups according to size: PM10 and PM2.5. PM10 refers to particulate matter that has a diameter smaller than 10 μm, whereas. PM2.5 has a diameter smaller than 2.5 μm. The components of PM differ depending on its sources, such as heavy metals and acidic substances, it is mainly composed of black carbon. PM can be inhaled into the trachea and the lung as it is extremely small and deposited into the alveoli and even the bloodstream, resulting in an inflammatory response. Exposure to PM2.5 leads to poor reproductive ability [2] and/or decreased brain functions [3]
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