Several studies have investigated the expression of cytokines, such as TNF- α, IFN-γ, TGF-β, IL-1, 2, 4, 5, 6, 8, 10, 12, 17, 18, and IL-22 in serum, saliva, and lesions in OLP patients [ 32- 36]. This evidence concerns the gene IFNG and oral lichen planus.