KIR2DL5A

KIR2DL5A encodes an inhibitory surface receptor expressed on CD56dim peripheral blood NK cells and a subset of T lymphocytes that suppresses NK cell cytotoxicity: upon tyrosine phosphorylation it recruits the phosphatases SHP-2 and, to a lesser extent, SHP-1, and antibody-mediated cross-linking inhibits killing of target cells (PMID:17371997). The gene is one of two paralogous KIR2DL5 loci (KIR2DL5A and KIR2DL5B) within the KIR cluster on chromosome 19q13.4, with the paralogs arising through duplication and recombination and showing differential expression — KIR2DL5A alleles are predominantly transcriptionally active, whereas KIR2DL5B is epigenetically silenced by DNA methylation at a RUNX-binding promoter site (PMID:12185535, PMID:23060877). Allelic polymorphism further tunes receptor display: the common KIR2DL5A*001 allele traffics to the cell surface, while the *005 allele is largely retained intracellularly owing principally to a Gly174Ser substitution (PMID:28144240). Receptor expression is also compartment-specific, present on peripheral blood NK cells but absent from uterine NK cells (PMID:27815424). The cognate ligand of KIR2DL5A has not been identified in the available corpus.

1. 2002 Medium

   Whether KIR2DL5 was a single gene or multiple loci was unresolved; mapping defined two distinct paralogs, establishing the genomic architecture underlying expression variability.

   Evidence Genomic mapping, DNA sequencing, and haplotype segregation in family cohorts

   PMID:12185535

   Open questions at the time

   • Does not establish functional differences between the paralogs
   • Mechanism driving differential expression not addressed
2. 2007 High

   The signaling function of the receptor was undefined; this work showed KIR2DL5A is a surface inhibitory receptor that recruits SHP-2/SHP-1 and dampens NK cytotoxicity, defining it as an ITIM-type inhibitory receptor.

   Evidence Monoclonal antibody generation, flow cytometry, co-IP of SHP-1/SHP-2, and redirected NK cytotoxicity assay

   PMID:17371997

   Open questions at the time

   • Cognate physiological ligand not identified
   • Cross-linking is antibody-mediated, not by a natural ligand
3. 2012 Medium

   The basis for divergent expression of the two paralogs was unknown; integration of methylation data attributed KIR2DL5B silencing to DNA methylation at a RUNX-binding promoter site, contrasting with active KIR2DL5A.

   Evidence Review integrating DNA methylation and promoter studies

   PMID:23060877

   Open questions at the time

   • Review-level synthesis rather than new primary data
   • Does not address allelic surface expression variation within KIR2DL5A
4. 2016 Medium

   Whether KIR2DL5A is uniformly expressed across NK populations was unknown; flow cytometry showed it is present on peripheral blood NK cells but absent from uterine NK cells, revealing tissue-specific repertoire differences.

   Evidence Flow cytometry of decidual uNK vs. peripheral blood NK cells with KIR2DL5A-specific mAb

   PMID:27815424

   Open questions at the time

   • Single method, single study
   • Functional consequence of compartment-specific absence not determined
5. 2017 High

   The cause of variable surface expression among individuals was unclear; mutagenesis assigned the intracellular retention of the *005 allele primarily to a Gly174Ser substitution, defining a molecular determinant of trafficking.

   Evidence Transient transfection of tagged constructs, site-directed mutagenesis, Western blot, flow cytometry, confocal microscopy

   PMID:28144240

   Open questions at the time

   • Mechanism by which Gly174Ser causes retention not resolved
   • Trafficking studied in transfected cells, not primary NK cells

• The cognate ligand of KIR2DL5A and the physiological context in which it delivers inhibitory signals remain unidentified.
• No ligand identified
• No structural model of receptor-ligand engagement
• Physiological triggering of SHP recruitment uncharacterized