The analysis of alveolar bone resorption during P. gingivalis-induced experimental periodontitis in MHC-I or MHC-II deficient mice showed the destructive role for CD4+ T cells (52); yet effector-memory CD8+ T cells are present in normal gingival mucosa (43) suggesting a protective role for CD8+ T cells during periodontitis possibly due their ability to suppress osteoclastogenesis (53). This evidence concerns the gene CD4 and periodontitis.