Abstract:

Objective To investigate the effect of Enterococcus faecalis (E. faecalis) lipoteichoic acid (LTA) on the expression of the macrophage immune checkpoint-programmed cell death protein ligand 1 (PD-L1) and explore the possible regulatory mechanisms. Methods In vitro model was established by stimulating mouse monocyte macrophage cell line (RAW264.7) with different concentrations of E. faecalis LTA. PD-L1 expression and nuclear factor kappa-B (NF-κB) p65 phosphorylation level were detected using flow cytometry, quantitative real-time polymerase chain reaction (qRT-PCR), Western blot and cellular immunofluorescence. Macrophages were pretreated with the NF-κB signaling pathway inhibitor BAY 11-7082, then the expression of PD-L1 and p65 phosphorylation level were detected by the above methods. Results LTA induced PD-L1 expression in RAW264.7 cells, and p65 phosphorylation level increased (P<0.05). Inhibition of the NF-κB signaling pathway could reduce p65 phosphorylation level, simultaneously reducing the expression of PD-L1 on LTA-stimulated RAW264.7 cells (P<0.05). Conclusion E. faecalis LTA can promote the PD-L1 expression of macrophages and this process is regulated by the NF-κB signaling pathway, which provides further insights into the occurrence and treatment of chronic periapical inflammation.

Key words: Enterococcus faecalis, lipoteichoic acid, immune checkpoint, NF-κB