B10 cell-induced PD-L1/PD-1-linked macrophage polarization in periodontitis

Periodontitis is a chronic multifactorial inflammatory disease caused by the excessive host immune response to bacterial infection, leading to periodontal tissue destruction. Owing to their plasticity, macrophages are key players in this process, and B10 cells, with their immunosuppressive efects, are vital for periodontal immunity. We propose that, in periodontitis, B10 cells transmit immunosuppressive signals via programmed cell death ligand-1 (PD-L1) /programmed cell death protein 1 (PD-1) signalling, stimulating macrophage diferentiation, alleviating inflammation, restoring homeostasis, and reducing alveolar bone resorption. The aim of this study was to investigate the efect of B10 cells on the polarization of macrophages in the context of periodontitis and the related molecular mechanism.

B10 cells were cocultured with RAW264.7 cells in the presence or absence of a Transwell insert. The M2 macrophage proportion and PD-1 expression in macrophages were assessed by flow cytometry and quantitative polymerase chain reaction (qPCR). PD-L1 knockout (KO) B10 cells and wild-type B10 cells were subsequently cocultured with macrophages separately. For in vivo experiments, we injected phosphate-buffered saline (PBS), B10 cells, or PD-L1 KO B10 cells into periodontitis model mice. We evaluated outcomes via microcomputed tomography, histological analysis, and tartrate-resistant acid phosphatase (TRAP) staining and measured the messenger ribonucleic acid (mRNA) expression levels of tumor necrosis factor-α (TNF-α), receptor activator of nuclear factor kappa-B ligand (RANKL), interferon-γ (IFN-γ), interleukin 10 (IL-10), and osteoprotegerin (OPG) in gingival tissue surrounding the maxillary second molar via qPCR.

Compared with the indirect coculture, the direct coculture of macrophages with B10 cells led to a greater proportion of M2 macrophages and increased PD-1 expression levels in macrophages. Coculturing macrophages with PD-L1 KO B10 cells confirmed that B10 cells induced the M2 polarization of macrophages and upregulated PD-L1 expression in macrophages via PD-L1/PD-1 signalling. Compared with the groups injected with PBS or PD-L1 KO B10 cells, the B10 cell group exhibited significant decreases in local inflammatory factor levels, alveolar bone resorption, and the number of bone-resorbed cells within the alveolar bone area in vivo.

B10 cells can regulate macrophage polarization via the PD-L1/PD-1 signalling pathway, thereby suppressing the inflammatory response and reducing alveolar bone resorption during periodontitis. This novel concept can guide future treatment strategies for periodontitis.