Type III IFNs: new layers of complexity in innate antiviral immunity.

Cytokines are small secreted molecules, which mediate cross-talk between cells involved in the immune response. Interferons (IFN)s, constitute a class of cytokines with antiviral activities, and the type I IFNs have been ascribed particularly important roles in the innate antiviral response. Type III IFNs (also known as IFN-lambda or interleukin 28/29) represent a class of novel cytokines with biological activities similar to the type I IFNs, but seem to have a more specialized role in antiviral defense by exerting host-protection primarily at epithelial surfaces. In this review, we describe the current knowledge on the role of type III IFNs in antiviral defense. (c) 2009 International Union of Biochemistry and Molecular Biology, Inc.