Cutting edge: KIR antisense transcripts are processed into a 28-base PIWI-like RNA in human NK cells

Killer Ig-like receptors (KIRs) are expressed in a variegated, clonally restricted fashion on NK cells and are important determinants of NK cell function. Although silencing of individual KIR genes is strongly correlated with the presence of CpG dinucleotide methylation within the promoter, the mechanism responsible for silencing has not been identified. Our results show that antisense transcripts mediate KIR transcriptional silencing through a novel PIWI-like 28-base small RNA. Although PIWI RNA-mediated silencing of transposable elements within germ cells have been described, this is the first report that identifies a PIWI-like RNA in an immune somatic cell lineage and identifies a mechanism that may be broadly used in orchestrating immune development.