Introduction: Microorganism infection has been reported to associate with many cancers. Previous studies indicated that patients carrying oral premalignant lesion with Candida albicans infection have a higher risk of developing oral cancer. We aimed to investigate the role of Candida infection in the development of oral cancer using a carcinogeninduced oral cancer model in mice. Methods: C57BL/6 mice were exposed to two compounds, 4-Nitroquinoline 1-oxide and arecoline, in drinking water to induce oral squamous cell carcinoma (OSCC) in the tongue. Additional injury in the tongue was created and live Candida was applied to the lesion for the establishment of chronic infection, which was verified by the presence of mycelium in the tongue tissue. The incidence of OSCC was determined after 28 weeks and the tongues were harvested for pathology, gene, and cytokine expression analyses. Results: We have found that chronic Candida albicans infection increased the incidence and severity of OSCC. RNA analysis using Nanostring technology revealed that there is an elevated expression of Th17 signature and inflammatory cytokines in the tumor microenvironment. Immunohistochemistry analysis also demonstrated that there is a co-localization of Candida mycelium and expression of IL-1beta, IL-6, IL-17A, IL-17F, and IL-22. Exposure of Candida component such as Curdlan to mouse macrophage enhanced the production of arginase by M2 macrophage and strikingly skewed the differentiation of M2 macrophage to simultaneously display a M1 macrophage cytokine phenotype, characterized by high levels of TNFalpha and IL-6. Conclusions: We demonstrated that there is a close link between persistent activation of Th17 and M1 cytokine pathways and the development of oral cancer associated with Candida infection.
