Matrix-assisted refolding and purification of placenta-derived recombinant human interleukin-6 produced in Escherichia coli

Biological activity of human interleukin‐6 (IL‐6) is associated with a vast number of diseases such as rheumatoid arthritis, sepsis, and severe inflammatory diseases. In this study, human IL‐6 cDNA was isolated from a cDNA library that was constructed with mRNA derived from human placental tissues. Subsequently, the complete human IL‐6 cDNA was cloned and expressed in BL21DE3 cells. The recombinant human IL‐6 (rhIL‐6) protein was expressed in a form of an insoluble inclusion body. Inclusion bodies were solubilized under denaturing conditions and purified by immobilized metal affinity chromatography with gradual on‐column refolding by the gradient elution method (from 6 to 0 M urea). The protein was purified to apparent homogeneity of about 99% with a yield of 50 mg/L. The purity was assessed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS‐PAGE), size exclusion high‐performance liquid chromatography, and Western blotting analysis. The bioactivity was assessed by proliferation assay of TF‐1 cells in a dose‐dependent manner. The present study confirms the expression of the placenta‐derived IL‐6 gene in a prokaryotic expression system and matrix‐assisted on‐column refolding and purification of rhIL‐6 by immobilized metal affinity chromatography.