Figure 4. PM2.5 aggravated the HDM-induced airway inflammation. Male C57BL/6 mice (N = 8 for each group) were instilled intratracheally with NS, HDM, PM, or HDM+PM. Total inflammatory cells, cell differentiation of inflammatory cells, and the percentage of eosinophils in BALF were assessed (A–C). Protein levels of IL-33 (D) and IL-25 (E) in the lung tissues were measured using ELISA. Representative images of lung tissues stained with H&E (F) and PAS (H) were showed under the microscope (10 × 20 magnification). Inflammatory score (G) and mucus production (I) with semi-quantification (score: 0–4) was analyzed (N = 10 images for each group). Data were presented as Means ± SEM (*, P < 0.05; **, P < 0.01; ***, P < 0.001; ****P < 0.0001).