The periodontium of rats submitted to experimental periodontitis and received no treatment (EPD) showed marked immune-staining for both TNF- α (Figure 4B, 4E) and iNOS (Figure 4H, 4K) when compared to the periodontium of the sham group (Figures 4A, 4D, and 4G, 4J, respectively). This evidence concerns the gene NOS2 and periodontitis.