APRIL (A proliferation-inducing ligand) is a newly-identified member of the tumor necrosis factor family that induces pleiotropic biological responses, including immunological responses, IgA class switch and cell growth. It is associated with multiple diseases such as cancer and autoimmune diseases. High levels of APRIL mRNA can be detected in transformed cell lines and several malignant tumors; heparin sulfate proteoglycans (HSPG) are also involved in the APRIL tumor cell proliferation induction response. The interaction of APRIL and HSPG occurs through an N-terminal basic region on APRIL We successfully expressed recombinant APRIL using an auto-induction system in Escherichia coli. By using in situ cleavage. we generated the mature form of APRIL, comprising its N-terminal basic region, which has full biological activity: receptor binding capability and proliferation induction activity. (C) 2009 Elsevier Inc. All rights reserved.