Radiation is a crucial component of head and neck squamous cell carcinoma (HNSC) treatment. Human papillomavirus-positive (HPV+) HNSC is significantly more radiosensitive than HPV- HNSC, but the mechanism underlying this increased sensitivity is unknown. We investigated the possible involvement of macrophage subpopulations as key mediators of HNSC radiosensitivity linked to HPV status. We collected forty-one clinical HNSC specimens and determined HPV status and radiosensitivity of each sample. We investigated cytokine mediated induction of macrophage polarization by HPV+ and HPV- HNSC cells. Radiosensitive HNSC tissues exhibited greater numbers of infiltrating M1 macrophages than radioresistant tumor tissue samples. Moreover, M1 macrophage numbers were positively correlated with HNSC radiosensitivity. HPV+ and HPV- tumor cells induced macrophage polarization to M1 and M2 type, respectively. HPV+ HNSC cells secreted more IL-6 than HPV- cells. HPV promoted tumor cell secretion of IL-6, thereby increasing radiosensitivity through M1 polarization of macrophages. M1 macrophages represent an important tissue microenvironment factor with implications for HNSC treatment efficacy and may prove valuable as a biomarker of radiation sensitivity.
