PD-L1⁺ Senescent Macrophages Reshape the Immune Microenvironment of Periodontitis via PI3K/AKT Pathway Activation

OBJECTIVE: To investigate the senescence/apoptosis phenotype of PD-L1⁺ macrophages in gingival tissues with periodontitis and their relationship with the PI3K/AKT pathway. METHODS: Immunohistochemistry and multiplex immunofluorescence were used to assess PD-L1 expression and its colocalization with CD68/CD163 and p21 in human periodontitis gingival tissues. Public single-cell and bulk transcriptomic datasets were integrated to characterize PD-L1⁺ macrophages. RAW264.7 senescence models were induced separately with Porphyromonas gingivalis LPS or H₂O₂, followed by lentiviral shRNA knockdown of PD-L1 to evaluate SASP, apoptosis-related markers, and PI3K/AKT signaling. RESULTS: PD-L1 was markedly upregulated in periodontitis gingiva and enriched in p21⁺ macrophages. Single-cell and bulk analyses showed expansion of PD-L1⁺ macrophages accompanied by upregulation of CDKN1A/CDKN2A and SASP factors such as IL-6 and IL-1β, increased expression of BCL2 family members, and activation of PI3K/AKT signaling. In the in vitro senescence model, PD-L1, p-PI3K, and p-AKT were elevated, and cells exhibited resistance to apoptosis. PD-L1 knockdown reduced PI3K/AKT activity, alleviated senescence and SASP, and promoted apoptosis. CONCLUSION: In periodontitis, PD-L1⁺ senescent macrophages maintain inflammatory amplification and resistance to apoptosis through activation of the PI3K/AKT pathway. The PD-L1/PI3K/AKT axis may represent a potential immunomodulatory target for periodontitis treatment.