Interleukin 9, also known as IL-9, is a cytokine (cell signalling molecule) belonging to the group of interleukins. This protein produced by T-cells and specifically by CD4+ helper cells that acts as a regulator of a variety of hematopoietic cells and stimulates cell proliferation and prevents apoptosis. It functions through the interleukin-9 receptor (IL9R), which activates different signal transducer and activator (STAT) proteins and thus connects this cytokine to various biological processes. Recombinant human IL9, fused to His-tag at C-terminus, was expressed in Sf9 and purified by using conventional chromatography techniques.