Programmed Death 1 (PD-1) and PD-1 Ligand (PD-L1) Expression in Chronic Apical Periodontitis

OBJECTIVE: This study aimed to examine programmed death protein 1 (PD-1) and programmed death lig-and 1 (PD-L1) expression on leukocytes from chronic apical periodontitis, and to determine the levels of cytokines in the apical periodontitis lesions. METHODS: Leukocytes from healthy gingival tissue (n=16) and chronic apical periodontitis (n=10) were eval-uated using flow cytometry. The PD-1 and PDL-1 expressions were evaluated using flow cytometry. The cy-tokine levels were evaluated by enzyme-linked immunosorbent assay. Data were analyzed using one-way ANOVA. The statistical significance level was set at P<0.05. RESULTS: Results showed that the apical periodontitis lesions are more infiltrated by PD-1(+) and PDL1(+) lym-phocytes than the control samples. In addition, the PDL-1 expression was detected on macrophages in the apical periodontitis lesions, and was significantly higher compared to leukocytes from healthy gingival tis-sue. The IFN-γ, TGF-β, IL-10, and TNF-α levels were significantly higher in the apical periodontitis lesions com-pared to control samples. CONCLUSION: The PD-1, PD-L1, and CTLA-4 molecules are evident in apical periodontitis, and can be an impor-tant immune checkpoint in chronic periapical periodontitis.