PTGS2 and periodontitis: The periodontium of untreated rats with experimental periodontitis showed marked immune-staining for COX-2, MMP-2, MMP-9, RANK-L, and RANK (Figures 4B, 4E, 4H, 4K, and 4N), compared to normal rats treated with saline alone (Figures 4A, 4D, 4G, 4J, and 4M).