Regulation of immune cells in oral lichen planus

Oral lichen planus (OLP) is an immunological disease and while it is understood that the T cell subsets, FoxP3(+) Tregs and IL17(+) Th17 cells are involved in immune regulation, little is known about their presence in OLP. The aims of this study were to compare the number of cells expressing FoxP3 or IL-17 in OLP with non-specifically inflamed oral mucosa and to determine which cell types expressed FoxP3 and/or IL-17 and their distribution. Immunohistochemistry was used to investigate the presence of FoxP3(+) or IL-17(+) cells in 12 control cases and 17 cases of OLP. These results were analysed quantitatively and qualitatively. Double-labelling immunofluorescence (IF) was used to determine the type of cell expressing FoxP3/IL-17 and these results were analysed qualitatively. OLP displayed significantly more FoxP3(+) cells (mean 79.3 vs. 20.6 cells/defined area, p < 0.0001) and fewer IL-17(+) cells (mean 1.05 vs. 3.30 cells/defined area, p = 0.0003) than non-specific inflammatory cases. The majority of FoxP3(+) cells were in the sub-epithelial infiltrate, while IL-17(+) cells were deeper in the stromal tissues. IF showed that FoxP3(+) cells co-localised with T cells, while the IL-17(+) cells did not. These results show that the balance between Tregs and IL-17(+) cells is altered in OLP, thus supporting the proposition that disturbance in local immune regulation is important in the pathogenesis of OLP. The observation that the IL-17(+) cells were mast cells has not previously been reported in OLP and again raises questions about the role of mast cells in this condition.