mRNA expression of chemokines. mRNA expression of proinflammatory chemokine CCL3 (A) and neutrophil attracting chemokines CXCL5 and CXCL2 (B) in the lung tissue of mice. Results are shown in relative units (RU) for healthy (PBS) and allergic (OVA) mice exposed for 2 hours a day, three days a week, for four weeks at a concentration of 10 mg/m3 to nanosized (nTiO2) or fine (fTiO2) TiO2 or left unexposed (-). N = 8 mice per group. The bars represent mean ± SEM; * P < 0.05, ** P < 0.01, and *** P < 0.001 significantly different from unexposed control; Mann-Whitney U test.