Project Summary - Innate immunity to enteric virus infection by IFNλ-stimulated-gene expression Antiviral immunity in the intestine and other mucosal surfaces faces a distinct challenge: clearance of viral infection while maintaining barrier function and tolerance of the bacterial microbiome. To maintain this balance, immune mechanisms with specificity to mucosal surfaces have evolved. Interferon lambda (IFNλ) stimulates antiviral responses in intestinal epithelial cells (IECs) and is a critical component of intestinal immunity in mouse models of norovirus (MNV) and rotavirus (MRV) infection; this requirement for IFNλ in control of these enteric virus infections distinguishes it from other interferon types. Additionally, the bacterial microbiome promotes MNV infection in an IFNλ receptor- (IFNLR) dependent manner, suggesting that the microbiome alters the IFNλ-stimulated antiviral response. This proposal aims to close the gap in our understanding regarding transcriptional programs unique to IFNλ, the effect of the bacterial microbiome on those transcriptional programs, and the specific interferon stimulated genes (ISGs) required for viral control. Specific Aim 1 will comprehensively characterize the transcriptional response in IECs and identify the genes necessary for cell-intrinsic control of rotavirus infection. Specific Aim 2 will use novel intestinal macrophage and IEC co- culture system to identify mechanisms by which IFNλ stimulates cell-extrinsic clearance of MNV. Specific Aim 3 will determine the role of the commensal microbiome in regulation of IFNλ-stimulated antiviral responses. The long-term goal of this work is to discover novel aspects of IFN biology and its regulation in the intestine that will aid in rational development of antivirals and immunotherapies.