Immunohistochemical study of Toll-like receptors 1 and 2 expression in cutaneous lichen planus lesions

Lichen planus (LP) is a chronic inflammatory, T cell-mediated autoimmune skin disease. Innate immunity could explain the interplay between environmental triggers and the autoimmune cascade leading to disease development. Toll-like receptors (TLRs) are important components of the innate immune system, with no previous evaluation of TLRs 1 and 2 in cutaneous LP. This work aims to investigate TLRs 1 and 2 expression in cutaneous LP. This case-control study included 30 patients with LP and 15 healthy controls. Biopsies from the patients' lesional skin and from the controls' normal skin were examined immunohistochemically for TLR 1 and 2 expression. A significant re-localization was found in TLR1 expression with a higher percentage of basal and a significantly lower percentage of homogenous epidermal expression in patients (73.3 and 0 %, respectively) compared with controls (13.3 and 73.3 %, respectively) (P < 0.001). TLR2 showed a significantly higher percentage of epidermal expression (more in the upper spinous layer) and significantly lower percentage of epidermal but more basal expression in patients (66.6 and 10 %, respectively) compared with controls (0 and 73.3 %, respectively) (P < 0.001). The median (IQR) of TLR1 [1 (0.75-1)] and TLR2 [1 (1-1)] staining score in patients was significantly lower than that of the controls [2 (1-2) and 1 (1-2), respectively] (P < 0.05). This work thus shows a re-localization of TLR 1 and 2 expression sites with decreased grade of expression in LP lesions. Targeting TLR signaling is expected to be a novel treatment strategy for cutaneous LP.