Effect of Oral Peritumoral Tissue on Infiltration and Differentiation of Tumor-Associated Macrophages in Oral Squamous Cell Carcinoma

The recruitment of tumor-associated macrophages (TAMs) in the tumor microenvironment (TME) of oral squamous carcinoma (OSCC) affects significant cancer invasion; however, in the normal host tissue that is located in the cancer's surrounding area, this is poorly investigated. In this study, we examined the impact of gingival connective tissue cells (GCTCs) and periodontal ligament cells (PDLCs), which are involved in the invasive pathway of OSCC, on oral cancer invasion via TAMs recruitment. Transwell (migration) assays were used to examine the effects of GCTCs and PDLCs on the migration of macrophages, which indicated that the interaction between GCTCs and HSC-2/HSC-3 (human oral squamous cell carcinoma cell line) promoted the recruitment of macrophages, whereas the interaction between PDLCs was inhibited. An indirect co-culture was then used to examine the effects of GCTCs and PDLCs on the differentiation of macrophages, which indicated that the interaction between GCTCs enhanced their ability to transform into M2-type macrophages. Furthermore, the effects of GCTCs and PDLCs on the recruitment of CD45(+) monocytes, F4/80(+) M0 macrophages, iNOS(+) M1 macrophages, and CD163(+) M2 TAMs were assayed by immunohistochemistry. The results revealed that the interaction between GCTCs and HSC-2/HSC-3 promoted the infiltration of CD45(+) monocytes, F4/80(+) M0 macrophages, and CD163(+) M2 TAMs, whereas the PDLCs inhibited it, while their effect on iNOS(+) M1 macrophages was limited. Collectively, the GCTCs contributed to the infiltration of TAMs into the TME of OSCC cells, whereas the PDLCs exerted an inhibitory effect. These findings suggest a potential regulatory mechanism underlying the progression of OSCC.