IL17A and oral lichen planus: Given that cytotoxic CD8+ T cells are thought to be the main lymphocytes in OLP, the KEGG analysis of top 20 differentially expressed genes in NEOLP and EOLP cytotoxic CD8+ T cells revealed enrichment in antigen processing and presentation, IL-17 signaling pathway and Th17 cell differentiation compared with healthy control (Supplementary Figure S1D, E).