TNF and oral lichen planus: According to Janardhanan and Ramesh, on degranulation mast cells release a range of pro-inflammatory mediators such as histamines, TNF-α, chymase, and tryptase, and each of these mediators has specific functions in the pathogenesis of oral lichen planus.15 Histamine causes dilatation of the blood vessel and extravasation of the lymphocytes during the initial phase.