The aim of this study was to investigate the effect of Porphyromonas gingivalis lipopolysaccharide (LPS)-induced macrophages on head and neck squamous cell carcinoma (HNSCC) cell line proliferation and invasion.

THP-1 monocytes were differentiated toward macrophages using 12.5 ng/ml phorbol 12-myristate 13-acetate treatment for 48 h. The expression of interleukin-6 (IL-6) mRNA and cytokine by monocytes and macrophages was determined using real time PCR and ELISA, respectively. The cells were analyzed for CD14 expression using immunofluorescent labeling. The macrophages were induced using 1 μg/ml P. gingivalis LPS for 24 h, and the conditioned medium (CM) was collected. The monocyte, macrophage, and LPS-induced macrophage CM were evaluated for IL-6 and tumor necrosis factor-alpha (TNF-α), and nitric oxide (NO) content using ELISA and the Griess Reagent System, respectively. Human primary (HN18, HN30, and HN4) and metastatic (HN17, HN31, and HN12) HNSCC cell lines were treated with the monocyte, macrophage, and LPS-induced macrophage CM. The proliferation and invasion of the HNSCC cell lines were evaluated using MTT and modified Boyden chamber assays, respectively.

Macrophages demonstrated increased IL-6 and CD14 expression. The P. gingivalis LPS significantly induced macrophage NO secretion, however, that of TNF-α decreased. The LPS-induced macrophages CM inhibited HN4 proliferation. Interestingly, the LPS-induced macrophage CM promoted invasion of all HNSCC cell lines.

Our data demonstrate that P. gingivalis LPS-induced macrophages increased NO secretion. The activated macrophage CM inhibited HN4 cell proliferation and promoted invasion of all HNSCC cell lines.