Functions of IFN?s in Anti-Bacterial Immunity at Mucosal Barriers

Type III interferons (IFNs), or IFN lambda s, are cytokines produced in response to microbial ligands. They signal through the IFN lambda receptor complex (IFNLR), which is located on epithelial cells and select immune cells at barrier sites. As well as being induced during bacterial or viral infection, type III IFNs are produced in response to the microbiota in the lung and intestinal epithelium where they cultivate a resting antiviral state. While the multiple anti-viral activities of IFN lambda s have been extensively studied, their roles in immunity against bacteria are only recently emerging. Type III IFNs increase epithelial barrier integrity and protect from infection in the intestine but were shown to increase susceptibility to bacterial superinfections in the respiratory tract. Therefore, the effects of IFN lambda can be beneficial or detrimental to the host during bacterial infections, depending on timing and biological contexts. This duality will affect the potential benefits of IFN lambda s as therapeutic agents. In this review, we summarize the current knowledge on IFN lambda induction and signaling, as well as their roles at different barrier sites in the context of anti-bacterial immunity.