IFNG and periodontitis: In this study, there was no association between IFNg level and +874A/T polymorphism which in line with previous studies found no significant correlation for alleles and genotypes between periodontitis and controls.6, 8, 9, 13, 29On the contrary, Heidari et al showed a significant association for IFNg +874A/T polymorphism between patients with chronic periodontitis and controls.12The IFNg +874A/T polymorphism showed different distribution in Asia.