Alterations in macrophage polarization in injured murine vocal folds

Objectives: Macrophages are prominent inflammatory cells in wounds, and their phenotypes are altered during wound healing. They are reported to contribute to not only inflammatory responses but also tissue remodeling. However, few studies in vocal fold biology have focused on the function of macrophages. The purpose of this study was to investigate macrophage polarization and distribution in injured murine vocal folds. Study Design: Animal experiments with controls. Method: Unilateral vocal fold stripping was performed on C57BL/6 mice, and larynges were harvested 1, 3, 5, 7, and 14 days postinjury. Immunohistochemical analysis of the vocal fold lamina propria was performed to detect the expression of classically activated (M1) and alternatively activated (M2) macrophage markers (inducible nitric oxide synthase [iNOS] and CD206, respectively) in F4/80 ⁺ macrophages. Results: The proportion of F4/80 ⁺ iNOS ⁺ cells out of all F4/80 ⁺ cells tended to increase from day 1. F4/80 ⁺ iNOS ⁺ cell percentage tended to be high at days 1 through 7 and declined to close to a normal level by day 14. F4/80 ⁺ CD206 ⁺ cell percentage tended to decrease at day 1 and then to increase the rest of the time. In the normal vocal fold, the majority of F4/80 ⁺ macrophages were only positive for CD206. F4/80 ⁺ iNOS ⁺ CD206 ⁺ cells were observed at days 1 through 7. Conclusion: The main population of injured sites gradually shifted from M1 to M2 marker-positive macrophages in murine vocal folds. However, coexistence of M1 and M2 markers in the same macrophages was observed. Our results suggest that macrophage phenotypes are regulated by complex tissue-derived signals and exhibit dynamic changes during wound healing. Level of Evidence: NA Laryngoscope, 129:E135–E142, 2019.