Occurence of mucus producing cells in bronchioles. Periodic acid-Schiff (PAS) -stained mouse lung tissue, where mucus producing goblet cells can be seen in colour red around the bronchioles. Tissue samples from unexposed healthy (A) and asthmatic (B) mice and asthmatic mice exposed to nanosized (C; nTiO2) or fine (D; fTiO2) TiO2. (E) Effects of titanium dioxide exposure on the amount of mucus-producing cells around the bronchioles. Results are indicated as the average of PAS+ cells/100 μm of bronchus counted from three bronchioles per mouse (n = 8 mice per group) for healthy (PBS) and allergic (OVA) mice exposed to nanosized (nTiO2) or fine (fTiO2) TiO2 or left unexposed (-). N = 8 mice per group. The bars represent mean ± SEM; * P < 0.05 significantly different from unexposed control; Mann-Whitney U test.