*4.1.5 Tumour necrosis factor-*α

Study to explore 4 polymorphisms in TNF- α gene which are all transitions from G to A, 3 in the promoter positions: – 376, − 308, − 238 and at position +489, failed to be identified as susceptibility or severity factors in periodontitis.

### *4.1.6 Interleukin-10*

Three SNPs in the promoter regions of IL10 genes, a G to A transition, at position – 1087, C to T transition at 819, and a C to A transition at 592 have been linked with altered synthesis of IL10.

#### *4.1.7 Interleukin 18*

Six different IL-18 gene polymorphism (−656, −607, −137, +113, +127, and codon 35/3) were investigated and none of the polymorphisms were linked to destructive periodontal disease [38, 44].

#### **4.2 Immunoreceptor related polymorphism**
