Up-regulation of HMGB1 and TLR4 in skin lesions of lichen planus.

Lichen planus (LP) is a chronic, mucocutaneous inflammatory disease of an unknown aetiology. The disease has been associated with certain viruses, and the factors such as DAMPs (damage-associated molecular patterns) and PAMPs (pathogen-associated molecular patterns) may also contribute to the inflammatory response in LP. HMGB1 (high mobility group box 1 protein) is one of the major DAMPs that induces inflammation and could trigger LP disease. The present study was aimed to examine TLR4, RAGE and HMGB1 production in epidermis or dermis by immunohistochemistry and the respective expression of these targets in the skin lesions of patients with LP. Moreover, we measured HMGB1 serum levels by ELISA. The results showed similar profile of expression by HMGB1 and TLR4, which are decreased at epidermis and up-regulated at dermis of skin lesions of LP patients that was sustained by intense cellular infiltration. RAGE expression was also increased in dermis of LP. Although there is increased RAGE protein levels, a decreased RAGE transcript levels was detected. Similar HMGB1 serum levels were detected in the LP and control groups. This study demonstrates that HMGB1 and TLR4 could contribute to the inflammatory LP process in skin.