In contrast, asthmatics with refractory asthma symptoms present generally a significant infiltration of neutrophils in the airways, and detectable levels of Th-17-associated cytokines (IL-17A, IL-17F, IL-21) [4], [6], [10], [11], [13]; in these patients, a preferential infiltration of neutrophils over eosinophils is driven by IL-17-stimulated airway epithelial cells via p38 MAPK, and release the chemokine CXCL8 (IL-8) that promotes granulocyte recruitment, particularly neutrophils [5], [14]–[15]. Here, IL17F is linked to asthma.