Evaluation of PD-L1, PD-L2, PD-1 and cytotoxic immune response in oral lichen planus

Objective To 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 Methods In 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. Results Most 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/mm(2) 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. Conclusions PD-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.