Mouse interferon lambda 3 (IFN-λ3), also known as interleukin-28B (IL-28B), is a member of the type III interferon family and functions as a critical antiviral cytokine that signals through the IFNLR1 (IL-28Rα)/IL-10R2 receptor complex, activating JAK/STAT pathways and inducing interferon-stimulated genes (ISGs) that suppress viral replication primarily at epithelial barriers. In mice, IFN-λ3 plays a central role in mucosal antiviral immunity within the respiratory and gastrointestinal tracts, contributing to host defense against pathogens such as influenza virus, respiratory syncytial virus, norovirus, rotavirus, and SARS-like coronaviruses in experimental models. Unlike type I interferons, type III interferons act predominantly on epithelial cells and produce localized antiviral responses with limited systemic inflammation, making murine IFN-λ3 essential for studying barrier-specific immunity, viral transmission dynamics, and immune-mediated tissue protection. As mice are foundational models for immunology and infectious disease research, murine IFN-λ3 (IL-28B) is widely used in mechanistic studies of interferon signaling, antiviral therapeutics, and vaccine development relevant to human respiratory and enteric viral infections.