IL17A and chronic rhinosinusitis: Th1, Th2 and also Th17 cells were reported to be implicated in chronic diseases of the paranasal sinuses, Th1-related cytokine IFN-γ and Th2-related cytokines IL-4 and IL-5 in chronic rhinosinusitis without and with nasal polyps, respectively, and more recently Th17-cell-related IL-17 in nasal polyps [44–46].