TNF and periodontitis: Inflamed tissues, such as gums in periodontitis, produce high levels of pro-inflammatory factors, including IL-1β, TNF-ɑ and IFN-γ, and low levels of anti-inflammatory factors.21 Several studies demonstrated the presence of T regulatory cells (Tregs) in periodontal tissues, which play an important role in controlling periodontal infection and protecting against tissue destruction.22,23 The expression of IFN-γ was excessive because of the restrained function of Tregs, which was associated with severe destructive periodontal tissues.