Killer Cell Immunoglobulin-like Receptor

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The killer cell immunoglobulin-like receptors ( KIR or KIR receptors for short ) are receptors that mainly occur in the plasma membrane of natural killer cells (NK cells), i.e. they are part of the immune system of mammals. With the help of the KIR, the NK cell recognizes pathological cells such as tumor cells or cells attacked by microorganisms. This is done with the help of short peptides , which each cell takes from its metabolism and presents on the plasma membrane (see main histocompatibility complex ). KIR can either bind to these or not and thus differentiate between sick and healthy cells.

The KIR genes form a gene family that is located on human chromosome 19 ( gene locus 19q13.4) and belongs to the immunoglobulin superfamily . The receptors encoded by these genes are almost exclusively expressed on NK cells; however, there is also a small subpopulation of T cells that also express KIR on the cell surface. The KIR are the most important NK cell receptors in humans and other primates , while the LY49 molecules assume the analogous function in mice.

A distinction is made in the KIR between activating and inhibiting receptors, which differ mainly in the transmembrane region and the cytoplasmic tail. Both the inhibiting and the activating MHC class I molecules serve as ligands.

There are 14 KIR genes in humans, but the number of KIR genes present in the genome of different people varies . The expression of the different combinations of KIR molecules on the cells also varies, with the respective expression pattern of the receptors being passed on to the daughter cell by methylation of the non-expressed KIR genes.

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