**2.4 TNF-α**

It is a proinflammatory cytokine produced by macrophages. Gene localized at 6p21.3. A meta-analysis by Nikolopoulos et al., which based on 17 studies showed that there was no association of the TNF-α promoter −308G/A polymorphism with periodontitis while another meta-analysis by Song et al. which also included 17 studies found that TNF-α −308 A allele was associated with periodontitis in Brazilian, Asian, and Turkish populations [13]. Ding et al. in their meta-analysis based on 15 studies found an association between TNF-α SNP and periodontitis in Asian and Caucasian population [16]. Thus, the role of TNF-α SNP in the etiopathogenesis of periodontitis has to be explored with further studies.
