Biological activity of interleukins-28 and -29: Comparison with type I interferons

Despite binding to receptors distinct from those of type I interferons (IFNs), human interleukins-28A, -28B and -29 (IL-28A, IL-28B and IL-29; alternatively named IFN lambda-2 {IFN-λ2}, IFN-λ3 and IFN-λ1, respectively, or collectively, type III IFNs), a small family of three structurally-related cytokines, are, like IFNs, known to induce antiviral activity. To further biologically characterize IL-28A and IL-29, we compared their activities with those of IFNs in a range of human cell lines. We found that they induced antiviral activity in fewer cell lines and more weakly than IFNs; also IL-28A was less active than IL-29. Additionally, we showed IL-28A and IL-29 induced reporter genes - protein MxA promoter linked to luciferase, or interferon stimulated response element (ISRE) linked to secreted alkaline phosphatase (SEAP) - more weakly than IFN. Antiproliferative activity was induced by IFNs in most cell lines, but only in one human glioblastoma cell line, LN319, was dose-dependent IL-29-growth inhibition demonstrable. Polymerase chain reaction (PCR) quantification of messenger (m) RNA of IL-28/29 receptor subunits, IL-28Rα and IL-10Rβ, indicated variable expression levels; although their expression was highest in the responsive LN319 cell line, lower but significant expression of both mRNAs was found in relatively unresponsive cell lines. In conclusion, we found IL-28A and IL-29 act similarly to IFNs, but are less effective generally and have activity in a more limited range of cell lines.