Identification of gingipains in glioblastoma tumors and evidence that P. gingivalis infection drives IL-6 and PD-L1 expression in glioma cells

Glioblastoma multiforme (GBM), a highly aggressive brain tumor that accounts for approximately 60% of all gliomas and 48% of primary central nervous system malignancies, is incurable and poorly understood, with a median survival of only 15 months after diagnosis. Thus, there is an urgent need to understand GBM pathogenesis in order to develop an effective treatment. Recent research has revealed frequent Alzheimer’s disease (AD) pathology in the brains of patients with GBM, i.e. , amyloid beta (Aβ) and hyperphosphorylated tau (pTau), indicating that GBM and AD may share some unknown environmental risk. Since chronic periodontitis (CP), and specifically Porphyromonas gingivalis ( P. gingivalis) , a keystone bacterial pathogen in CP, have emerged as risk factors for both AD and GBM, we investigated whether P. gingivalis gingipain virulence factors could be identified in GBM tissue samples and whether P. gingivalis infection affects glioma cell behavior. Using immunohistochemistry on tissue microarrays (70 GBM cores from 35 patients; 34 cerebral tissue cores from 17 patients), we quantified the presence of arginine-gingipain B (RgpB) and lysine-gingipain (Kgp) antigens. Both gingipains showed significantly elevated staining in GBM samples compared to controls (**p < .01, ****p < .0001, respectively), with Kgp levels notably higher than RgpB within GBM tissue (****p < .0001). In functional assays using U251 glioma cells, P. gingivalis infection induced robust, dose-dependent IL-6 secretion (peaking at MOI 5), increased PD-L1 expression by 30% (*p = .036), and significantly enhanced cell invasiveness (**p < .01) in a viability-dependent manner. These findings demonstrate that P. gingivalis gingipains are present at elevated levels in GBM tissue and that P. gingivalis infection reprograms glioma cells to adopt an immunosuppressive, invasive phenotype through upregulation of the IL-6/PD-L1 axis, suggesting a potential microbial contribution to GBM pathogenesis and immune evasion.