Potential role of INTERLEUKIN‐17 in the pathogenesis of oral lichen planus: a systematic review with META‐analysis

Oral lichen planus (OLP) is a chronic inflammatory mucocutaneous disease of unknown aetiology, which may evolve into squamous cell carcinoma. Recent advances on OLP pathogenesis suggest the presence of Th17 cells and the up-regulation of interleukin-17 (IL-17) expression are crucial events. Our aim was to test the hypothesis in the literature about an important role of IL-17 in OLP by systematically investigating the overexpression of IL-17 in the lesional tissue and blood from OLP patients and healthy controls. A total of 22 studies comprising 658 OLP patients and 362 control subjects fulfilled inclusion criteria were subjected to meta-analysis. The assessment of IL-17 in the lesional tissue by quantitative real-time polymerase chain reaction (PCR) revealed a significant elevation in the OLP group (RR:1.35 95%CI: 0.20-2.50, I2 = 92%). There was a statistical overexpression of IL-17 in the serum of OLP group detected by ELISA (RR:2.47 95%CI: 1.17-3.77, I2 = 97%) and flow cytometry (RR:3.04 95%CI: 0.69-5.39, I2 = 97%). In the erosive OLP group, the tissue IL-17 assessed by PCR was higher than in reticular OLP patients (RR:0.78 95%CI: 0.21-1.36, I2 = 0%). Peripheral assessment of IL-17 by ELISA (RR:1.43 95%CI: 0.01-2.85, I2 = 94%) and flow cytometry (RR:1.55 95%CI: 0.29-2.81, I2 = 89%) revealed significant elevation in erosive OLP group. The dominating overexpression of IL-17 and Th17 cells in the local inflammatory infíltrate and serum of OLP patients confirms its role, probably in the interaction between T cells and keratinocytes. Notably, the upregulation of IL-17 is more intense in erosive than in reticular OLP suggesting a positive correlation between IL-17 levels and disease severity. Further research is warranted to investigate the potential role of anti-IL-17 drugs to manage this chronic condition.