Fig. 4. Iron oxide nanoparticles (IONPs) induce inflammatory response. (a) Blood IL-1β, IL-6 and TNF-α after IONPs treatment; (b) IL-4 production in different treatment groups; (c) IFN-γ production in different treatment groups; (d) nitric oxide production in different treatment groups. All graphs present average ± SEM. n: 6. Rats were treated with IONPs intravenously for 28 days in a 7 days interval. **p < 0.01; and ***p < 0.001 versus saline control.