IL9 and airway hyperresponsiveness: In humans, the IL-9 and IL-9R gene are located on chromosomal region where a linkage with asthma and its risk factors has been demonstrated[6], [7].Moreover, the development of transgenic mice over-expressing IL-9 has suggested a potential role for this cytokine in the development of airway eosinophilia, mast cell hyperplasia, mucus production and airway hyperresponsiveness[8], [9], [10].