IMGT Lexique

KIR and LILR/ILT receptors

KIR: Killer cell Immunoglobulin-like Receptor, MHC class I receptors expressed by NK cells and a subpopulation of T cells.

The human leukocyte receptor complex (LCR) is a genetic region of at least 1MB on chromosome 19 at 19q13.4 which contains genes encoding the KIR responsible for inhibiting the innate cytotoxic activity of NK lymphocytes.

The LILR/ILT/LIR [1] which have

homology to the KIRs but with a more widespread cellular distribution and are expressed on a variety of hematopoietic cell types including NK, T and B lymphocytes as well as myelomonocytic cells such as macrophages, mast cells, and dendritic cells
additional proteins with related structure, function, and expression, such as LAIR-1 and FcαR.

The KIR and LILR/ILT/LIR protein families are structurally and functionally comparable. Both:

have similar extracellular regions comprising C-LIKE-DOMAINs: two or three for KIR, two or four for LILR/ILT/LIR.
possess isoforms with different cytoplasmic signalling functions. KIR and LILR/ILT/LIR receptors with long cytoplasmic tails inhibit cellular activation through recruitment of SHP-1 phosphatase to the ITIM motifs. KIR and LILR/ILT/LIR receptors with short cytoplasmic tails transmit activation signals via a charged residue in their transmembrane region associated with signalling adaptor proteins possessing ITAM motifs (TYROBP/DAP-12).

Despite these similarities, the KIR and LILR/ILT/LIR receptors have distinct functional characteristics. Whereas most KIR recognize discrete polymorphic epitopes within the G-ALPHA-1 of HLA class I, only the LILR1/ILT2 and LILR2/ILT4 receptors have been demonstrated to bind to a variety of HLA class I ligands. The binding of LILR1/ILT2 is probably mediated via a site in the conserved C-LIKE-DOMAIN of the HLA class I.

Mice do not possess KIR genes, but a locus on mouse chromosome 7 (syntenic to human 19q13) contains PIR genes with sequence homology to the human ILT/LIR genes.