IFN-λ1, also known as IL-29, is a member of the type III interferon (IFN) family. Type III interferons, including IFN-λ1, IFN-λ2 and IFN-λ3, are produced upon virus infection and are functionally similar to type I interferon (IFN-α/β). IFN-λ binds to a heterodimeric receptor composed of the IFN-λ receptor 1 (IFNLR1) and the interleukin-10 receptor 2 (IL-10R2), subsequently tranducing signal through the JAK-STAT pathway and leading to transactivation of various IFN-stimulated genes (ISGs). ?IFN-λ has been demonstrated to mediate an antiviral immune response against several viruses, such as hepatitis B virus (HBV), hepatitis C virus (HCV), and human immunodeficiency virus (HIV). In contrast to type I or type II interferons, IFN-λ receptor is expressed preferentially on epithelial-like cells and some immune cells. Because the response to IFN-λ is highly restricted to certain cell types, IFN-λ is considered a potential therapuetic agent for the treatment of viral diseases with less side effects when compared with type I interferon.