Feline interferons (FeIFNs) are cytokines with antiviral, antitumor and immunomodulatory functions used as therapeutic agents in a variety of veterinary diseases. In this work, FeIFN-alpha 7 and FeIFN-alpha 7xArg containing eight residues of arginine were expressed in Sf9 cells and insect larvae. At 4 days post-infection (dpi), the concentrations of FeIFN-alpha 7 and FeIFN-alpha 7xArg in suspension culture were (1.28 +/- 0.15) X 10(6) U ml(-1) and (1.3 +/- 0.2) x 10(6) U ml(-1) respectively. The maximum expression levels of FeIFN-alpha 7 and FeIFN-alpha 7xArg were (3.7 +/- 0.2) x 106 U ml(-1) and (3.5 +/- 0.4) x 10(6) U ml(-1) at 2 dpi in Rachiplusia nu larvae and (1.1 +/- 0.2) x 10(6) U ml(-1) and (1.0 +/- 0.15) x 10(6) U ml(-1) at 5 dpi in Spodoptera frugiperda larvae respectively. R. nu was a better host for FeIFN-alpha 7 and FeIFN-alpha 7xArg expression. The 8xArg tag did not affect the biological activity of FeIFN-alpha 7 and was useful to promote the FeIFN-alpha 7xArg adsorption on ion exchange chromatography (IEC), allowing its purification in a single step from supernatant culture and R. nu larvae. FelFN-alpha 7xArg was purified from the larval extract with a yield of 70% and a purification factor of 25 free of viruses. We conclude that R. nu larvae are new low-cost hosts for the expression of recombinant FeIFN-alpha 7. (C) 2014 Elsevier Ltd. All rights reserved.