Objective  To investigate the role of periodontitis in the development of oral squamous cell carcinoma (OSCC) and to determine whether periodontitis microorganisms induce M2 macrophage (M2) polarization and promote tumor progression.

  Methods  The tumor tissues of OSCC patients with periodontitis and those without periodontitis were collected and immunohistochemistry tests were done to validate the trend of changes in M2 macrophages. A mouse model of OSCC accompanied by periodontitis was established by treating mice with drinking water containing four antibiotics for three consecutive days, applying in the mouths of the mice a coat of bacteria collected from the saliva of patients with periodontitis once every other day for five times, and injecting in their buccal mucosa OSCC cells (SCC7). We observed the effect of periodontitis on the development of OSCC, analyzed the M2 macrophage content in the tumor tissues, and analyzed salivary microbiota structure, and examined the pathological changes in the spleen and colon tissues of the mice. Finally, we collected saliva from patients with periodontitis, co-cultured it with mice peripheral blood mononuclear cells (PBMC) and SCC7 cells, and examined M2 macrophage percentage by flow cytometry.

  Results  Immunohistochemical findings from the clinical samples showed that M2-polarized macrophages in OSCC patients with periodontitis were more enriched (27.01%±2.12%) compared with those of OSCC patients without periodontitis (17.00%±3.66%). The OSCC mice with periodontitis (PO group) had tumors of larger size and lower survival rate than OSCC mice (O group) did. Furthermore, the expression rate of Ki67-positive cells (35.49%±5.00%) was significantly higher than that of O group (23.89%±4.13%) (P<0.05). According to the results of flow cytometry, M2 macrophage expression (24.97%±4.41%) in PO group was higher than that of O group (5.75%±0.52%) (P<0.05). In addition, qPCR results showed that gene expression of M2 macrophage-related factors, Arg1, IL-10, and CD206, showed an overall upward trend. Immunohistochemistry results showed that the positive expression of M2 macrophages was significantly increased in the PO group (21.82%±4.16%) compared to that of the O group (9.64%±0.60%) (P<0.05). Mice in the PO group showed changes in their oral flora structure, exhibiting increased bands and diversity. The white pulp in their spleen tissue decreased and the boundary of the red pulp became indistinct with severe bleeding. The morphology of the colon glands was abnormal and the U-shaped crypt was damaged rather seriously. According to the results of cell experiment, when co-culturing PBMC with SCC7 cells, the presence of periodontitis microorganisms increased the polarization of M2 macrophages (71.00%±0.66%).

  Conclusion  Periodontitis promotes the development of OSCC by inducing M2 polarization in tumor-associated macrophages. Hence, periodontitis treatment holds important values for OSCC patients.