PD-1, PD-L1 and PD-L2 Expression was Increased in Moderate-severe Periodontitis

Objectives: Programmed death 1 (PD-1) signaling has attracted extensive interests for its role in suppression of anti-tumor immunity. Programmed death ligand 1 (PD-L1) and PD-L2 are cell surface glycoproteins that interact with PD-1 to suppress host immune responses. The role of these molecules in periodontal diseases has not been elaborated yet. The aim of this pilot study was to compare the expression of PD-1 and its ligands between patients with moderate-severe periodontitis and controls.
Methods: Expression levels of PD-1, PD-L1 and PD-L2 of the gingival tissues were compared between 8 patients with moderate-severe periodontitis and 7 healthy controls. Real-time PCR and western were used to detect the gene and protein expression, respectively. Then, we further examined the mRNA expression levels of PD-L1 and PD-L2 in human gingival fibroblasts (HGFs) after 1 μg/ml and 10 μg/ml P. gingivalis LPS treatment for 2, 4, 6, 8, 12 and 24 h through real-time PCR.
Results: The gene and protein expression levels of PD-1, PD-L1 and PD-L2 of the gingival tissues were significantly increased in the patients with moderate-severe periodontitis compared with controls (p＜0.05). Furthermore, after 1 μg/ml and 10 μg/ml P. gingivalis LPS treatment, the mRNA expression of PD-L1 and PD-L2 in HGFs was significantly upregulated (p＜0.05), and reached peak level at 6 h.
Conclusions: In conclusion, the expression of PD-1 and its ligands (PD-L1 and PD-L2) was increased in patients with moderate-severe periodontitis, indicating that PD-1 signaling may play a role in the progression of periodontitis. The exact mechanisms need to be further clarified.