Expression of antibodies. Levels of ovalbumin (OVA) specific antibodies IgE (A) and IgG2a (B). 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 < 0.01 significantly different from unexposed control; Mann-Whitney U test.