Growing evidence obtained from human genomic analysis and antigen-challenged transgenic mice suggests that 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 Human IL-9 produced in E.coli is a single, non-glycosylated single polypeptide chain containing 127 amino acids and having a molecular mass of 14 kDa.