The difference between the mean values for the controls and the OLP patients, −1.10, corresponds to approximately a doubling in PTGS2 expression relative to NAPEPLD. A similar change in the balance between PTGS2 and NAPEPLD was seen in three human cell lines treated with TNF-α, a cytokine known to be involved in the pathogenesis of OLP (Figure 2). This evidence concerns the gene TNF and oral lichen planus.