Figure 3: Comparison of the effect of ZnO on proinflammatory and oxidative stress markers in A549 cells following exposure at the ALI and under submerged (SUB) conditions. (a) mRNA expression of proinflammatory cytokines (IL-8, GM-CSF, and IL-6) was measured with RT-PCR either directly after (0 h after incubation) or two hours after the exposure (2 h). (b) Same as (a), but for oxidative stress markers (HMOX1, SOD-2, and GCS). The postincubation of the cells after ALI exposure was also performed under submerged conditions. The mRNA values were normalized to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) levels and expressed as the fold increase over control (the control level was set to unity) which was filtered air and pure medium for ALI and SUB, respectively. The data show the geometric means and geometric standard error of the mean based on 4 to 7 independent experiments. Due to differences in the deposition kinetics described in the experimental section, the final dose was delivered to the cells after 3 h (ALI, open bars 0.7 μg/cm2 and solid bars 2.2 μg/cm2) or 1 h (submerged, open bars 0.7 μg/cm2 and solid bars 2.5 μg/cm²). The symbol (*) indicates significant differences from control levels at , and (**) at . The symbol (#) indicates mRNA values which are statistically different from the corresponding submerged mRNA levels (differences are 2.8 to 12-fold ()).