IL17A and asthma: Of these, neutrophil infiltration is an important cause of AAS exacerbation and resistance to hormone therapy.208 Th17 lymphocytes are critical for neutrophilic asthma, and are the major producers of IL-17A, IL-17F and IL-22, whose amounts are elevated in the airways of severe steroid-refractory asthma cases.209 NF-κB signaling is associated with IL-17 and/or IL-22-related production of epithelial mucin and ASM cell proliferation.210–212 IL-33 promotes neutrophil polarization via c-Jun N-terminal kinase and NF-κB-related pathways.