IFNLR1

IFNLR1 (IL28RA/CRF2-12) is the ligand-binding subunit of the type III interferon receptor, a class II cytokine receptor that pairs with IL10RB to transduce signals from IFN-λ1/λ2/λ3 and drive JAK-STAT activation (PMID:15120645). The cytoplasmic box1 and box2 motifs of IFNLR1 simultaneously engage the FERM and SH2-like domains of JAK1, with a glutamate adjacent to box2 mimicking the phosphotyrosine normally read by SH2 domains; deletion within box1 abolishes stable JAK1 binding (PMID:27725180). Through this receptor, IFN-λ signaling is required in intestinal epithelial cells for control of enteric viruses in vivo, where IEC-specific loss of Ifnlr1 recapitulates the global-null phenotype of elevated tissue titers and fecal shedding (PMID:28077655). Distinct IFNLR1 isoforms differentially tune the response: the full-length receptor supports broad ISG induction together with proinflammatory gene programs and undergoes rapid receptor internalization, whereas a noncanonical variant lacking part of the box1/box2 JAK1-binding domain retains antiviral ISG induction but fails to drive proinflammatory genes, and these isoforms also reset the TYK2-dependence of downstream signaling (PMID:36992341, PMID:39929255, PMID:42213608). A heterozygous IFNLR1 missense mutation (p.Arg99His) co-segregates with autosomal dominant nonsyndromic sensorineural hearing loss, and ifnlr1 knockdown in zebrafish reduces hair cells in a manner rescued by wild-type mRNA (PMID:29453195).

1. 2004 Medium

   Established the receptor architecture: which subunits and ligands define the type III interferon receptor, framing IFNLR1 as the ligand-specific chain.

   Evidence Genomic and functional characterization of the CRF2 receptor family identifying IFNLR1 (CRF2-12)/IL10RB heterodimerization for IFN-λ1/λ2/λ3

   PMID:15120645

   Open questions at the time

   • Does not define the cytoplasmic signaling contacts
   • Subunit assignment from binding/signaling data in a single review-level study
2. 2016 High

   Resolved how IFNLR1 physically couples to the JAK machinery at atomic resolution, defining the box1/box2 motifs as the JAK1-binding interface.

   Evidence 2.1 Å crystal structure of JAK1 FERM/SH2-like domains bound to the IFNLR1 intracellular fragment plus box1 deletion mutagenesis

   PMID:27725180

   Open questions at the time

   • Structure of a complete receptor-JAK signaling complex not resolved
   • Does not address how isoform differences alter this interface in cells
3. 2017 High

   Pinpointed the cell type where IFNLR1 function matters in vivo, showing intestinal epithelial receptor expression is sufficient for IFN-λ antiviral protection.

   Evidence IEC-specific conditional Ifnlr1 knockout mice challenged with MNoV and reovirus, including Rag1-deficient background

   PMID:28077655

   Open questions at the time

   • Downstream effector ISGs mediating protection not dissected
   • Restricted to enteric viruses in gut epithelium
4. 2018 Medium

   Linked IFNLR1 to a Mendelian phenotype and a developmental role beyond antiviral immunity, implicating it in inner-ear hair cell biology.

   Evidence Human family co-segregation of p.Arg99His with hearing loss; zebrafish ifnlr1 morpholino knockdown with wild-type mRNA rescue and JAK/STAT pathway qRT-PCR

   PMID:29453195

   Open questions at the time

   • Mechanism connecting IFNLR1 to hair cell development unknown
   • Morpholino-based, single family and single lab
5. 2023 Medium

   Revealed that IFNLR1 isoforms are not equivalent, separating antiviral from proinflammatory output and uncovering cross-pathway regulation of type-I IFN.

   Evidence Doxycycline-inducible FLAG-tagged IFNLR1 isoforms in HEK293T with IFNL3 stimulation and gene expression profiling

   PMID:36992341

   Open questions at the time

   • Mechanism by which truncated isoforms restrict proinflammatory genes not defined
   • Overexpression in a non-physiological cell line
6. 2025 Medium

   Mapped the isoform functional split to the JAK1-binding domain in a disease-relevant cell type, showing the box1/box2 region gates proinflammatory and HBV-control responses.

   Evidence FLAG-tagged IFNLR1 variant complementation in CRISPR KO stem cell-derived hepatocytes with antiviral/proinflammatory gene profiling and HBV replication assay

   PMID:39929255

   Open questions at the time

   • Whether secreted variant has decoy function elsewhere untested
   • Single lab
7. 2025 Medium

   Connected isoform differences to receptor trafficking and STAT phosphorylation dynamics, showing full-length IFNLR1 internalizes faster and reshapes TYK2-dependence.

   Evidence Proximity ligation assay, ImageStream flow cytometry, JAK-STAT western blotting, and JAK1/TYK2 inhibitors in WT and KO iHeps

   PMID:42213608

   Open questions at the time

   • Causal link between internalization rate and gene-program selectivity not established
   • Single lab
8. 2025 Low

   Proposed a JAK-STAT-independent arm in which IFN-λ through IFNLR1 promotes death of infected cells to limit spread.

   Evidence IFNLR1 knockout epithelial cells with IAV and RSV infection, cell death quantification, STAT1/2 phosphorylation, viral RNA/protein measurement (preprint)

   PMID:bio_10.1101_2024.09.09.612051

   Open questions at the time

   • Preprint, single lab, no independent replication
   • Death pathway and its mechanistic link to IFNLR1 undefined
   • Virus-specific (IAV not RSV) and unexplained

• How IFNLR1 receptor internalization, isoform composition, and the TYK2/JAK1 balance are mechanistically wired to select between antiviral, proinflammatory, and cell-death programs remains unresolved.
• No structure of a full receptor-JAK complex showing isoform-dependent assembly
• Effector mechanism of infected-cell death not defined
• Mechanism of IFNLR1 in hair cell development unknown