Interleukin-15 (IL-15) is a recently discovered cytokine that shares with interleukin-2 (IL-2) the beta and gamma subunits of the receptor complex, therefore, both of them display similar biological effects. Moreover, IL-15 induces B and T cell proliferation, natural killer cell cytolytic activity and cytokine generation as well as protects T cell from apoptosis. The IL-15 synthesis and secretion are controlled both at transcriptional and post-transcriptional levels. This fine regulation poses a serious difficulty for its expression in eukaryotic systems. Here, the cDNA of human IL-15 was cloned into a prokaryotic vector under control of the tryptophan promoter for its expression in
Escherichia coli
. The recombinant IL-15 was obtained as an insoluble product, which represented 10% of the total protein. An extraction step in 8 M urea followed by a renaturalization process by diluting urea to 0.08 M was performed. The biological activity of this protein was 2.3 x 10
5 IU/mg in a CTLL-2 proliferation assay. The IL-15 proliferative activity on these cells was neutralized by a monoclonal antibody specific to IL-15, showing that the displayed activity was dependent on this cytokine. These simple and fast procedures allowed us to obtain a recombinant human IL-15 in
E. coli, making this cytokine easily available for
in vitro and therapeutic studies.