Diversity of the p70 killer cell inhibitory receptor (KIR3DL) family members in a single individual

The killer cell immunoglobulin-like receptor (KIR) genomic region: gene-order, haplotypes and allelic polymorphism

Recent genetic studies have established that the killer cell immunoglobulin-like receptor (KIR) genomic region displays extensive diversity through variation in gene content and allelic polymorphism within individual KIR genes. It is demonstrated by family segregation analysis, genomic sequencing, and gene order determination that genomic diversity by gene content alone gives rise to more than 20 different KIR haplotypes and at least 40-50 KIR genotypes. In the most reductionist format, KIR haplotypes can be accommodated within one of 10 different prototypes, each with multiple permutations. Our haplotype model considers the KIR haplotype as two separate halves: the centromeric half bordered upstream by KIR3DL3 and downstream by 2DL4, and the telomeric half bordered upstream by 2DL4 and downstream by 3DL2. There are rare KIR haplotypes that do not fit into this model. Recombination, gene duplication, and inversion can however, readily explain these haplotypes. Additional allelic polymorphism imposes extensive individual variability. Accordingly, this segment of the human genome displays a level of diversity similar to the one observed for the human major histocompatibility complex. Recent application of immunogenetic analysis of KIR genes in patient populations implicates these genes as important genetic disease susceptibility factors.

KIR: diverse, rapidly evolving receptors of innate and adaptive immunity

KIR genes have evolved in primates to generate a diverse family of receptors with unique structures that enable them to recognize MHC-class I molecules with locus and allele-specificity. Their combinatorial expression creates a repertoire of NK cells that surveys the expression of almost every MHC molecule independently, thus antagonizing the spread of pathogens and tumors that subvert innate and adaptive defense by selectively downregulating certain MHC class I molecules. The genes encoding KIR that recognize classical MHC molecules have diversified rapidly in human and primates; this contrasts with conservation of immunoglobulin- and lectin-like receptors for nonclassical MHC molecules. As a result of the variable KIR-gene content in the genome and the polymorphism of the HLA system, dissimilar numbers and qualities of KIR:HLA pairs function in different humans. This diversity likely contributes variability to the function of NK cells and T-lymphocytes by modulating innate and adaptive immune responses to specific challenges.

Genotyping of human killer-cell immunoglobulin-like receptor genes by polymerase chain reaction with sequence-specific primers: an update

Killer-cell Immunoglobulin-like Receptors (KIR) help human natural killer (NK) cells counteract infections by pathogens that evade the immune system by inducing down-regulation of HLA class I molecules in infected cells. KIRs are structural and functionally diverse receptors encoded by a family of polymorphic genes. The most extreme aspect of KIR polymorphism is the varying content of KIR-genes in the genome of different individuals, as first demonstrated by KIR genotyping using the PCR-SSP method. Knowledge on the KIR-gene family has been recently expanded by the identification of new genes, pseudogenes and multiple gene variants, several of which escaped detection by the original genotyping technique. We present here an upgraded PCR-SSP method for KIR genotyping that integrates recent achievements in the research of the diversity of this gene family. Our method permits detection of all known KIR genes and pseudogenes in a 16-reaction set. Furthermore, an additional set of six reactions permits subtyping of KIR2DL5 variants, each of which shows well-differentiated functional and genetic features.

Structure and function of major histocompatibility complex (MHC) class I specific receptors expressed on human natural killer (NK) cells

Natural killer (NK) cells express receptors that are specific for MHC class I molecules. These receptors play a crucial role in regulating the lytic and cytokine expression capabilities of NK cells. In humans, three distinct families of genes have been defined that encode for receptors of HLA class I molecules. The first family identified consists of type I transmembrane molecules belonging to the immunoglobulin (Ig) superfamily and are called killer cell Ig-like receptors (KIR). A second group of receptors belonging to the Ig superfamily, named ILT (for immunoglobulin like transcripts), has more recently been described. ILTs are expressed mainly on B, T and myeloid cells, but some members of this group are also expressed on NK cells. They are also referred to as LIRs (for leukocyte Ig-like receptor) and MIRs (for macrophage Ig-like receptor). The ligands for the KIR and some of the ILT receptors include classical (class Ia) HLA class I molecules, as well as the nonclassical (class Ib) HLA-G molecule. The third family of HLA class I receptors are C-type lectin family members and are composed of heterodimers of CD94 covalently associated with a member of the NKG2 family of molecules. The ligand for most members is the nonclassical class I molecule HLA-E. NKG2D, a member of the NKG2 family, is expressed as a homodimer, along with the adaptor molecule DAP10. The ligands of NKG2D include the human class I like molecules MICA and MICB, and the recently described ULBPs. Each of these three families of receptors has individual members that can recognize identical or similar ligands yet signal for activation or inhibition of cellular functions. This dichotomy correlates with particular structural features present in the transmembrane and intracytoplasmic portions of these molecules. In this review we will discuss the molecular structure, specificity, cellular expression patterns, and function of these HLA class I receptors, as well as the chromosomal location and genetic organization.