NK (Natural Killer) cells are lymphocytes of the innate immune system that combat infections by producing cytokines and killing infected cells. Their functional activity is regulated by the interaction between Killer Immunoglobulin-like Receptors (KIR) and Class I HLA alleles expressed on target cells. NK cells express multiple types of KIR on their surface, which can have either inhibitory or activating effects on immunity.
Located within the leukocyte receptor complex (LRC) on chromosome 19q13.4, the human KIR gene family consists of 14 functional genes and two pseudogenes. Human NK cells express various combinations of these 16 KIR genes through two common haplotypes.
