Enhanced expression of Toll-like receptor 2 in lesional tissues and peripheral blood monocytes of patients with oral lichen planus

Some members of the Toll‐like receptor (TLR) family, which plays key roles in both innate and adaptive immune responses, are involved in the pathogenesis of autoimmune, chronic inflammatory and infectious diseases. However, the role of TLR in the pathogenesis of oral lichen planus (OLP) has not been investigated. The aim of this study was to understand the roles of TLR in OLP. The expression of TLR genes in OLP tissues was analyzed by cDNA microarray and reverse transcription polymerase chain reaction, and TLR protein expression in OLP tissues and peripheral blood monocytes was examined by immunohistochemical analysis and flow cytometry, respectively. Furthermore, TLR ligand‐induced cytokine production from peripheral blood monocytes was measured by enzyme‐linked immunosorbent assay. Among 10 TLR genes, the average expression ratio of the genes for TLR1, 2, 3, 5, 6 and 10 in OLP tissues compared to that in the normal buccal mucosae was more than 1.0. In contrast, the average ratio of the genes for TLR7, 8 and 9 was less than 1.0. TLR2 but not TLR4 was highly expressed in the cells of the spinous layer and infiltrating monocytes in OLP tissues, and the mean fluorescence intensity of TLR2 on peripheral blood monocytes was significantly higher in OLP patients than in healthy controls. Furthermore, the peripheral blood monocytes from OLP patients produced considerably higher amounts of interleukin (IL)‐12 and lower amounts of IL‐10 than those from healthy controls. In OLP, the T‐helper cell (Th)1/Th2 balance appears to shift toward Th1 dominance, probably depending on the upregulation of TLR2 expression and these alterations in TLR2‐mediated immunity may be involved in the pathogenesis and maintenance of OLP.