Interleukin-9 (IL-9) is known to regulate many cell types involved in T-helper type 2 responses classically associated with asthma, including B- and T-lymphocytes, mast cells, eosinophils and epithelial cells. Growing evidence obtained from human genomic analysis and antigen-challenged transgenic mice suggests that interleukin-9 (IL-9) is a candidate factor in immunoglobulin E (IgE) production and thus is thought to be associated with bronchial inflammation and bronchial hyperresponsiveness (BHR). Recombinant Mouse IL-9 produced in E. coli is a non-glycosylated single polypeptide chain containing 127 amino acids with a MW of 14,298 Da.