Expression, purification and characterization of recombinant interleukin-21

Interleukin-21 (IL-21) is a key regulator of the immune system. However, studies of this cytokine have so far been hampered by the limited availability of recombinant protein preparations. Here we describe a method based on refolding of inclusion bodies expressed in E. coli by rapid dilution. The method was applied to human and murine IL-21 proteins, which were further purified by affinity chromatography and gel-filtration. The proteins are pure and highly active as determined by endotoxin and cell proliferation assays. The availability of milligram quantities of protein enabled us to generate monoclonal antibody fragments against the cytokine and will aid in further structural, biochemical and physiological analyses.