Human interferon-λ3 is a potent member of the type III interferon family

Type III interferon (IFN) or IFN-λ is a recently discovered family of IFNs that signal through the same downstream transcription factors as type I IFN but use a separate receptor complex composed of the IL-10R2 and the unique IFN-λR1 receptor chains. We have established a simple and efficient expression system to produce highly pure and active IFN-λ of the three human IFN-λ isoforms (IFN-λ1, -λ2 and -λ3) and used this to compare the biological activity of the different IFN-λ subtypes. Surprisingly, we found IFN-λ3 to possess the highest specific activity of the human IFN-λ subtypes, exhibiting a twofold higher activity than IFN-λ1 and a 16-fold higher activity than IFN-λ2. Furthermore, in comparison with the commercially available preparations of IFN-λ1 and -λ2, we found our IFN-λ preparation to be superior in activity.