In addition to allelic polymorphism, there is haplotypic variability due to the different number and kind of KIR genes. Because haplotypic diversity is a major contributor to the population diversity of KIR and of NK cell repertoires, there was agreement amongst the KIR Nomenclature committee that it would be useful to devise a robust and versatile nomenclature system that could be used to describe the gene content of different KIR haplotypes. It was suggested that each KIR haplotype be designated 'KH' followed by a hyphen and then a unique three-digit number, assigned sequentially indicating the different haplotypes. This system would allow 999 KIR haplotypes to be named.
Two kinds of KIR haplotype have been described based upon gene content, and are designated A and B. No single specific criterion distinguishes all A and B haplotypes, a current working definition being as follows. Group B haplotypes are characterised by one or more of the following genes: KIR2DL5, KIR2DS1, KIR2DS2, KIR2DS3, KIR2DS5 and KIR3DS1. Conversely, group A haplotypes are characterised by the absence of all these genes. As a consequence of these differences, the B haplotypes have more genes encoding activating KIR than A haplotypes. Different investigators have used different criteria to distinguish A and B haplotypes and certain haplotypes are assigned differently when using these different criteria (1,2). The KIR Nomenclature committee felt that the distinction between A and B haplotypes is a useful one, having potential biological and medical significance, and that efforts should be made to develop a consistent and logical set of criteria for distinguishing them. It was proposed that as part of the haplotype nomenclature the letter A or B would follow the three-digit number. So a haplotype may, for example, be named KH-001A or KH-022B.
To supplement the haplotype name and provide further information, it was suggested that following the haplotype designation a 17-digit binary code would indicate the presence or absence of the genes on the haplotype. Each digit in the code would represent a distinct gene: a '1' indicating presence of the gene, and a '0' its absence. Thus a full haplotype name could be given as KH-001A-11100010011011011. This system can readily accommodate the discovery of additional KIR genes by simple introduction of another digit. Wherever possible the order of the genes in the full haplotype designation will reflect their order in the genome. However, when digits are added to represent newly discovered genes, they will be placed at the end of the code, in the order of their discovery (3).
The nomenclature for KIR haplotypes has not yet been implemented.
Fully Sequenced KIR Haplotypes
There are a number of fully sequenced KIR haplotypes that have been reported. A graphic displaying the gene and allele content of these haplotypes is now available from here.
All references are linked to the PubMed abstract where possible.
- Human diversity in killer cell inhibitory receptor genes.Immunity (1997) 7:753-63 (Abstract)
- The killer cell immunoglobulin-like receptor (KIR) genomic region: gene-order, haplotypes and allelic polymorphism.Immunological Review (2002) 190:40-52 (Abstract)
Killer-cell Immunoglobulin-like Receptors (KIR) Nomenclature Report, 2002Tissue Antigens (2003) 62:79-86 (Abstract)Immunogenetics (2003) 55:220-226 (Abstract)Human Immunology (2003) 64:648-654 (Abstract)European Journal of Immunogenetics (2003) 30:229-234 (Abstract)Journal of Immunological Methods (2003) 281:1-8