ObjectiveTo investigate the expression of programmed death‐ligands 1 and 2 (PD‐L1, PD‐L2), programmed death‐1 (PD‐1), CD8 and granzyme B (GrB), as well as its correlation with the severity of oral lichen planus (OLP).Materials and MethodsIn a collaborative study, 33 cases of OLP were evaluated according to the latest criteria proposed by the American Academy of Oral and Maxillofacial Pathology (AAOMP/2016) and were submitted to immunohistochemistry. Positivity was measured semiquantitatively (PD‐L1, PD‐L2) and quantitatively (PD‐1, CD8, GrB). The severity of OLP was assessed according to clinical subtype, symptomatology and response to corticosteroid therapy.ResultsMost OLPs were considered to be negative for PD‐L1 (66.6%), but high expression of PD‐L2 (96.9%) by keratinocytes and immunoinflammatory cells was observed. PD‐1+ cell density/mm2 was reduced compared to CD8+ cells. A low cytotoxic immune response (CD8:GrB ratio) was also demonstrated. Interestingly, there were fewer GrB+ cells in the intraepithelial region in reticular OLP compared to erosive/bullous OLP.ConclusionsPD‐L1/PD‐1 pathways appear to be compromised in OLP due to low PD‐L1 expression in most samples. In contrast, PD‐L2 overexpression associated with a possible regulation of the cytotoxic immune response suggests an immune tolerance that may contribute to the chronic profile of OLP.

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