The IFNL1 gene encodes Interferon-Lambda 1, a type III interferon belonging to the helical cytokine family. As an interferon, IFNL1 has antiviral, antitumor and immunomodulatory activities. Specifically, the interferon acts as a ligand for a cytokine receptor thereby activating the JAK/STAT signal cascade and promoting the expression of IFN-stimulated genes. It promotes the production of MHC class I antigens and interferon-gamma, and inhibits the production of interleukin-5 and interleukin-13.
However, the activities of IFNL1 are limited to certain targets due to the restricted distribution of its receptor IFNLR1. The IFNLR1 receptor is expressed specifically in epithelial cells and hence IFNL1 activity is primarily seen in these cells.