Assessment of PD-1 and PD-L1 tissue expression levels in lichen planus patients: a case-control study

Programmed cell death protein-1 (PD-1) is an immune checkpoint protein, PD-1 interaction with PD ligand-1 (PD-L1) is essential for maintaining immunological tolerance. The study aimed to study and compare the levels of PD-1 and PD-L1 in lesional and nonlesional skin of lichen planus (LP) patients and compare these levels to normal healthy controls to assess their role in the pathogenesis of LP. This case-control study involved 30 patients with LP and 30 healthy age-and sex-matched controls. After clinical assessment of the severity by LP severity index score (LPSI), skin biopsies were taken from lesional and nonlesional skin of LP patients and from normal skin in healthy controls for assessment of the tissue levels of PD-1 and PD-L1 by ELISA. The tissue levels of both PD-1 and PD-L1 were significantly higher in healthy controls than in both lesional and nonlesional skin of LP patients (P < 0.001). Also, significantly higher PD-l and PD-L1 levels in nonlesional skin than in lesional skin of LP patients were reported (P < 0.001). No significant correlations were found between lesional and nonlesional PD-1, PD-L1 levels, or LPSI score. Based on the fact that PD-1/PD-L1 interaction is important to maintain tolerance and protection against autoimmune diseases, in addition to our study results that revealed lower levels of PD-1/PD-L1 in LP skin than in healthy skin, we can conclude that PD-1/PDL-1 may be incriminated in the pathogenesis of LP. ClinicalTrials.govID: NCT04892381.