IFNLR1

IFNLR1 is the ligand-specific subunit of the heterodimeric IFN-λ receptor that restricts type III interferon signaling predominantly to epithelial surfaces, coupling cytokine recognition to JAK1/TYK2–STAT1/STAT2 activation and antiviral gene expression. The intracellular domain engages JAK1 through box1 and box2 motifs, with a crystal structure revealing simultaneous binding of both motifs to the JAK1 FERM and SH2-like domains and a glutamate residue that mimics phosphotyrosine recognition (PMID:27725180). Lineage-specific deletion of Ifnlr1 in intestinal epithelial cells recapitulates the global knockout phenotype of impaired antiviral defense against norovirus and reovirus, establishing that IEC-restricted expression is necessary and sufficient for IFN-λ–mediated mucosal immunity (PMID:28077655). Distinct IFNLR1 splice isoforms differentially control receptor internalization kinetics, the balance of JAK1/TYK2 versus STAT1/STAT2 phosphorylation, and the selective induction of antiviral versus pro-inflammatory gene programs, with the full-length isoform uniquely supporting both antiviral and pro-inflammatory responses and augmented inhibition of HBV replication (PMID:36992341, PMID:39929255).

1. 2004 Medium

   Establishing that IFNLR1 (IL28RA) is a CRF2-family receptor subunit that heterodimerizes to transduce signals for all three IFN-λ ligands defined the gene's core identity as the ligand-binding chain of the type III IFN receptor.

   Evidence Genomic and receptor family characterization

   PMID:15120645

   Open questions at the time

   • No direct binding data or structural information in this study
   • Second subunit (IL10RB) requirement not experimentally dissected here
2. 2016 High

   Determination of the JAK1–IFNLR1 intracellular domain crystal structure resolved how the receptor recruits its cognate kinase, showing that box1 and box2 motifs bind simultaneously to JAK1 FERM and SH2-like domains through a glutamate-based phosphotyrosine mimicry mechanism.

   Evidence X-ray crystallography at 2.1 Å resolution with deletion mutagenesis validation

   PMID:27725180

   Open questions at the time

   • Structure captures only the JAK1 interaction; TYK2 recruitment mechanism via IL10RB not resolved
   • No kinetic or thermodynamic binding data reported
3. 2017 High

   Conditional knockout of Ifnlr1 specifically in intestinal epithelial cells demonstrated that IFNLR1-restricted epithelial expression is the critical determinant of IFN-λ antiviral protection in the gut, independent of adaptive immunity.

   Evidence Lineage-specific conditional knockout mice; viral titer assays with norovirus and reovirus; Rag1-deficient background

   PMID:28077655

   Open questions at the time

   • Whether IFNLR1 on other epithelial surfaces (e.g., respiratory) is similarly necessary was not tested
   • Downstream signaling mediators in IECs not dissected
4. 2018 Medium

   Identification of an IFNLR1 missense mutation (p.Arg99His) segregating with autosomal dominant sensorineural hearing loss, combined with zebrafish knockdown/rescue, expanded the receptor's physiological roles beyond antiviral immunity to sensory organ development.

   Evidence Whole-exome sequencing and linkage analysis in a family; morpholino knockdown with mRNA rescue in zebrafish; immunostaining in mouse inner ear

   PMID:29453195

   Open questions at the time

   • Mechanism linking IFN-λ signaling to hair cell maintenance is unknown
   • No knock-in of the human mutation in a mammalian model
   • Single family reported
5. 2023 Medium

   Functional dissection of IFNLR1 splice isoforms revealed that the full-length isoform uniquely supports both antiviral and pro-inflammatory gene programs, while a signaling-defective isoform selectively induces antiviral genes at low expression, demonstrating that isoform usage tunes the downstream transcriptional output of IFN-λ signaling.

   Evidence Doxycycline-inducible FLAG-tagged isoform expression in HEK293T; antiviral and pro-inflammatory gene expression assays

   PMID:36992341

   Open questions at the time

   • Isoform-specific signaling intermediates not fully mapped
   • Relative isoform expression in primary tissues not quantified
   • Cross-talk with type I IFN pathway only partially characterized
6. 2024 Medium

   IFNLR1 knockout in epithelial cells showed that IFN-λ signaling restricts influenza virus spread by promoting rapid death of infected cells, suggesting a cell-death-promoting function distinct from classical ISG induction.

   Evidence IFNLR1 KO cell lines infected with IAV; flow cytometry for infection and cell death (preprint)

   PMID:bio_10.1101_2024.09.09.612051

   Open questions at the time

   • Cell death mechanism (apoptosis versus other forms) not molecularly defined
   • Not yet peer-reviewed
   • Whether this death-promoting function operates in vivo is untested
7. 2025 Medium

   Comparative analysis of IFNLR1 variants in knockout hepatocytes and with proximity ligation/internalization assays established that differences in the box1/box2 region alter receptor internalization rate, the ratio of JAK1/TYK2 to STAT1/STAT2 phosphorylation, and the dependence on TYK2, mechanistically explaining isoform-specific gene expression patterns.

   Evidence IFNLR1 KO iHeps with re-expression of individual variants; Duolink PLA; ImageStream internalization assay; JAK/TYK2 inhibitors; HBV replication assays; western blot and gene expression profiling

   PMID:39929255 PMID:41256602

   Open questions at the time

   • Preprint component (PMID:41256602) not yet peer-reviewed
   • Structural basis for differential internalization not determined
   • How isoform ratios are regulated at the splicing level is unknown

• How IFNLR1 isoform expression is regulated in different tissues, the structural basis of isoform-specific receptor trafficking, and the mechanism linking IFNLR1 to hearing remain major open questions.
• No structural data for full ectodomain–IFN-λ–IL10RB ternary complex
• Splicing regulation of IFNLR1 isoforms uncharacterized
• Mechanism of IFNLR1 in inner ear hair cell biology unknown