Effect of PM on the expression of CYP1A1, NQO-1 and HO-1 biomarkers. Ultrafine PM (UF [0.03 μm-0.17 μm]), fine PM (F [0.17 μm-1 μm]) and coarse PM (C [1 μm-10 μm]) were used at 1 to 10 μg/cm2 for 24 h. mRNA of CYP1A1 (A), NQO-1 (B) and HO-1 (C) were assessed. CYP1A1 and NQO-1 are metabolizing enzymes and HO-1 is an antioxidant enzyme. These data are expressed comparatively to the control (=1). Results are mean of four replicates. * p < 0.05 compared with the control fixed to 1.