In conclusion, we have found that IL-9 can elicit detrimental effects on epithelial tight junctions, ciliated cell differentiation and mucus hypersecretion, rather than on goblet cell hyperplasia, as was previously thought [15], [17], [19] which may be physiologically important in vivo, reinforcing IL-9 as a potential therapeutic target in asthma. This evidence concerns the gene IL9 and asthma.