HLA-F and MHC Class I Open Conformers Are Ligands for NK Cell Ig-like Receptors

Killer Ig-like receptors (KIRs) are innate immune receptors expressed by NK and T cells classically associated with the detection of missing self through loss of their respective MHC ligand. Some KIR specificities for allelic classical class I MHC (MHC-I) have been described, whereas other KIR receptor-ligand relationships, including those associated with nonclassical MHC-I, have yet to be clearly defined. We report in this article that KIR3DL2 and KIR2DS4 and the nonclassical Ag HLA-F, expressed as a free form devoid of peptide, physically and functionally interact. These interactions extend to include classical MHC-I open conformers as ligands, defining new relationships between KIR receptors and MHC-I. The data collectively suggest a broader, previously unrecognized interaction between MHC-I open conformers--including prototypical HLA-F--and KIR receptors, acting in an immunoregulatory capacity centered on the inflammatory response.