Disruption of Type III Interferon (IFN) Genes <i>Ifnl2</i> and <i>Ifnl3</i> Recapitulates Loss of the Type III IFN Receptor in the Mucosal Antiviral Response

Abstract

Type III interferon (IFN), or IFN lambda (IFN-λ), is an essential component of the innate immune response to mucosal viral infections. In both the intestine and the lung, signaling via the IFN-λ receptor (IFNLR) controls clinically important viral pathogens, including influenza virus, norovirus, and rotavirus. While it is thought that IFN-λ cytokines are the exclusive ligands for signaling through IFNLR, it is not known whether genetic ablation of these cytokines phenotypically recapitulates disruption of the receptor. Here, we report the serendipitous establishment of <i>Ifnl2^-</i>^/<i>^- Ifnl3^-</i>^/<i>^-</i> mice, which lack all known functional murine IFN-λ cytokines. We demonstrate that, like <i>Ifnlr1^-</i>^/<i>^-</i> mice lacking IFNLR signaling, these mice display defective control of murine norovirus, reovirus, and influenza virus and therefore genocopy <i>Ifnlr1^-</i>^/<i>^-</i> mice. Thus, for regulation of viral infections at mucosal sites of both the intestine and lung, signaling via IFNLR can be fully explained by the activity of known cytokines IFN-λ2 and IFN-λ3. Our results confirm the current understanding of ligand-receptor interactions for type III IFN signaling and highlight the importance of this pathway in regulation of mucosal viral pathogens.<b>IMPORTANCE</b> Type III interferons are potent antiviral cytokines important for regulation of viruses that infect at mucosal surfaces. Studies using mice lacking the <i>Ifnlr1</i> gene encoding the type III interferon receptor have demonstrated that signaling through this receptor is critical for protection against influenza virus, norovirus, and reovirus. Using a genetic approach to disrupt murine type III interferon cytokine genes <i>Ifnl2</i> and <i>Ifnl3</i>, we found that mice lacking these cytokines fully recapitulate the impaired control of viruses observed in mice lacking <i>Ifnlr1</i> Our results support the idea of an exclusive role for known type III interferon cytokines in signaling via IFNLR to mediate antiviral effects at mucosal surfaces. These findings emphasize the importance of type III interferons in regulation of a variety of viral pathogens and provide important genetic evidence to support our understanding of the ligand-receptor interactions in this pathway.