Morphometrical analysis of volume density of PAS positive material. NS/UFP, S/OVA, S/UFP/OVA and S/NAC/UFP/OVA lungs were retrieved 7 days after OVA challenge/EC-UFP inhalation and stained with PAS. (A) Small airways (circumference ≤ 800 μm); (B) Large airways (circumference >800 μm), n = 6-12/group. **p < 0.01 vs NS/UFP; ##p < 0.01 vs S/UFP/OVA. Representative samples of lungs stained with PAS showing small airways in: (C) Non sensitized mice exposed EC-UFP (NS/UFP); (D) Sensitized and challenged mice exposed to filtered air (S/OVA); (E) Sensitized mice exposed to EC-UFP 24 h prior to OVA challenge (S/UFP/OVA); (F) Sensitized mice exposed to EC-UFP 24 h prior to OVA challenge and treated with NAC (S/NAC/UFP/OVA). Arrows, mucus hypersecretion; scale bar, 50 μm.