Interleukin 33 (IL-33) is a proimflammatory cytokine belonging to the IL-1 family. IL-33 is cleaved intracellularly, generating an N terminal and a C terminal fragment. The C terminal fragment corresponds to the mature IL-33 protein and mediates its biological effect by interacting with the IL-1 receptor, also known as ST2. Binding of mature IL-33 to this receptor activates NF-kappa-B and MAP kinases and induces the production of associated cytokines, in particular IL-4, IL-5 and IL-13, causing severe pathological changes in mucosal organs. Recombinant interleukin-33 comprises a 159 amino acid fragment (112-270) corresponding to C terminal Interleukin-33 fragment and is expressed in E. coli with an amino-terminal hexahistidine tag.