Interferon-lambda1 (IFN-lambda 1) is a member of the recently discovered type III IFNs (IFN-lambda), which possesses antiviral, antitumor, and immunomodulatory activities. In this study, the recombinant human IFN-lambda 1 containing a hexahistidine tag was expressed in Escherichia coli. IFN-lambda 1 was overexpressed under the control of T7 promoter and most of the protein existed in the form of inclusion bodies. The expressed insoluble protein was solubilized with urea, purified and refolded by one-step immobilized metal-ion affinity chromatography using Ni2+-nitrilotriacetic acid agarose. The purified IFN-lambda 1 appeared as a single band on SDS-PAGE and the purity was more than 95%. The yield was 86 mg IFN-lambda 1 from 1L of bacterial culture. Western blotting and N-terminal sequencing confirmed the identity of the purified protein. The purified IFN-lambda 1 exhibited specific antiviral activity as demonstrated by a cytopathic effect reduction assay. Thus, this on-column refolding method provides an efficient way to obtain an active IFN-lambda 1 with high yield and high purity. (c) 2006 Elsevier Inc. All rights reserved.