CD8A and oral lichen planus: Then, CD8+ T lesion cells cause apoptosis when in contact with diseased keratinocytes with the corresponding antigens, which may be due to FAS-FAS ligand interactions between keratinocytes and cytotoxic T cells, cytotoxic T cells producing granzyme B into keratinocytes through perforin-induced membrane pores, and TNF-α secreted by cytotoxic T cells binding to the TNF-α receptor on the keratinocyte surface, leading to the occurrence of OLP (13).