['To investigate whether programmed death ligand 1 (PD-L1) expressed in the periodontal tissue of chronic periodontitis and the correlativity of PD-L1 and different degrees of chronic periodontitis, provide experience for immunoregulation mechanism, clinical treatment and prognosis of chronic periodontitis.', 'Gingiva and periodontal tissue of healthy people and chronic periodontitis patients were collected. Based on clinical probing, periodontal tissue were classified into three groups: periodontal tissues of healthy people, periodontal tissue of mild chronic periodontitis, periodontal tissue of severe chronic periodontitis. Fluorescent quantitation polymerase chain reaction was applied to explore the expression of PD-L1 mRNA in the periodontal tissue of the different groups. Western blot and immunohistochemistry method were utilized to test the expression of PD-L1 protein in the periodontal tissue of the different groups. Combining with clinical image data, the relationship between differentially expressions of PD-L1 and different degrees of chronic periodontitis was analyzed.', 'The relative expression quantity of PD-L1 in the periodontal tissue of the mild chronic periodontitis was significantly higher that of the severe chronic periodontitis (P<0.01). The relative expression quantity of PD-L1 in the periodontal tissue of healthy subjects and severe chronic periodontitis had no statistical significance (P>0.05).'] Does [ Programmed death ligand 1 negatively regulate inflammatory response of chronic periodontitis ]?