Natural killer cell immunoglobulin-like receptor (KIR) locus profiles in African and South Asian populations

KIR ligands and prediction of relapse after unrelated donor hematopoietic cell transplantation for hematologic malignancy

Recurrent malignancy remains a significant complication after allogeneic hematopoietic cell transplantation (HCT). Efforts to decrease relapse have included donor lymphocyte infusion to stimulate donor anti-recipient T-cell allorecognition of major and minor histocompatibility differences. Recently, alloreactive effects of donor natural killer cell-mediated inhibitory killer immunoglobulin-like receptor (KIR) recognition of recipient HLA-C and -B ligands have been described. We examined KIR ligand effects on risk of relapse in 1770 patients undergoing myeloablative T-replete HCT from HLA-matched or -mismatched unrelated donors for the treatment of myeloid and lymphoid leukemias. KIR ligands defined by HLA-B and -C genotypes were used to determine donor-recipient ligand incompatibility or recipient lack of KIR ligand. Among HLA-mismatched transplantations, recipient homozygosity for HLA-B or -C KIR epitopes predicted lack of KIR ligand and was associated with a decreased hazard of relapse (hazard ratio, 0.61; 95% confidence interval, .043-0.85; P = .004). Absence of HLA-C group 2 or HLA-Bw4 KIR ligands was associated with lower hazards of relapse (hazard ratio, 0.47; 95% confidence interval, 0.28-0.79, P = .004; hazard ratio, 0.56; 95% confidence interval, 0.33-0.97; P = .04, respectively). The decrease in hazard of relapse in patients with acute myelogenous leukemia was similar to that in patients with chronic myelogenous leukemia and acute lymphoblastic leukemia (P = .95). Recipient homozygosity for HLA-B or -C epitopes that define KIR ligands is likely to be a predictive factor for leukemia relapse after myeloablative HCT from HLA-mismatched unrelated donors. This effect was not observed in HLA-identical unrelated transplants.

Receptor-ligand analyses define minimal killer cell Ig-like receptor (KIR) in humans

Interactions between inhibitory killer cell immunoglobulin-like receptors (iKIR) and human leukocyte antigen (HLA) class I molecules regulate natural killer (NK) cell responses to eliminate infected and transformed cells while maintaining tolerance to healthy cells. Unlinked polymorphic gene families encode KIR receptors and HLA class I ligands and their independent segregation results in a variable number and type of iKIR + HLA pairs inherited in individuals. The diversity in the co-inheritance of iKIR + HLA pairs and activating KIR (aKIR) genes in 759 unrelated individuals from four ethnic populations was analyzed. Every individual studied inherited a minimum of one iKIR + HLA pair; suggesting that major histocompatibility complex class I-dependent inhibitory KIR signaling is essential for human NK cell function. In contrast, 13.4% of the study group lacked all aKIR genes. Twenty percent of the study group carried only one of the four iKIR + HLA pairs. Interestingly, 3% of the study group carrying only KIR2DL3 + HLA-C1 as an iKIR + HLA pair lacked aKIR genes. These data suggest that a single iKIR can constitute the minimal KIR repertoire for human NK cells. Genotypes carrying an equal number of iKIR + HLA pairs and aKIR genes represented 20% of the study group. The remaining individuals had either a dominant inhibitory KIR genotype (iKIR + HLA > aKIR) or a dominant activating KIR genotype (iKIR + HLA < aKIR). Genotypes encoding these imbalanced inhibitory and activating interactions may contribute to susceptibility or resistance to human diseases.

Distribution of killer cell immunoglobulin-like receptors genotypes in the Lebanese population

This study represents the first report on the distribution of 16 Killer cell Immunoglobulin-like Receptors (KIR) genes in 120 unrelated healthy Lebanese individuals. We observed that 2DL2 frequency (61%) comes second highest after South Asians (64%) and 2DL5 frequency (58.3%) is the second highest reported so far after the South Asians (74%). Interestingly, a large number of AA1 genotype individuals with no loci for activating KIR and three completely new BB profiles not previously reported were found in our population with a group A : group B haplotypes ratio of 1.3:1. The frequency of the KIR loci suggests that the Lebanese population shares common general features with the Caucasoid populations studied before, but still has its own unique decreased or increased frequencies of several loci.

The killer immunoglobulin-like receptor gene cluster: tuning the genome for defense

Killer immunoglobulin-like receptors (KIRs) are molecules expressed on the surface of natural killer (NK) cells, which play an important role in innate immunity. KIR recognition of major histocompatability complex (MHC) class I allotypes represents one component of the complex interactions between NK cells and their targets in determining NK cell reactivity. KIRs are encoded by a gene cluster at human chromosome 19q13.4. Despite their high degree of sequence identity, KIR genes encode proteins that have diverse recognition patterns (specific HLA class I allotypes) and confer opposing signals (activating or inhibitory) to the NK cell. The KIR gene cluster is highly polymorphic, with individual genes exhibiting allelic variability and individual haplotypes differing in gene content. The polymorphism of the KIR locus parallels that of the MHC, facilitating the adaptation of the immune system to a dynamic, challenging environment. This variation is associated with a growing number of human diseases, which is likely to extend to levels observed for the HLA loci. Here we review current progress in understanding KIR biology and genetics.

Inhibitory and activatory KIR gene frequencies in the Polish population

Killer cell immunoglobulin-like receptors (KIRs) present on natural killer cells and minor subpopulations of T cells recognize class I human leukocyte antigen (HLA) molecules on the surface of target cells. Human individuals differ by the presence or absence of some KIR genes on their chromosomes (haplotypic polymorphism). As KIRs (especially two-immunoglobulin-domain-like containing, or KIR2D, molecules) are important for the outcome of tissue (particularly for haematopoietic stem cell) transplantation and possibly for pregnancy, the knowledge of KIR gene distribution in a given human population is of practical value. Therefore, we tested 175 healthy individuals from Poland for the presence or absence of these KIR genes which show haplotypic polymorphism and are expressed. Results were compared with those published for other human populations, showing close relations with other Caucasoids.

Diversity of killer cell immunoglobulin-like receptor genes in Pacific Islands populations

Killer immunoglobulin-like receptors (KIRs) regulate the activity of NK and T cells through interaction with specific HLA class I molecules on target cells. To date, 16 KIR genes and pseudogenes have been identified. Diversity in KIR gene content and KIR allelic and haplotype polymorphism has been observed between different ethnic groups. Here, we present data on the KIR gene distribution in Pacific Islands populations. Sixteen KIR genes were observed in Pacific Islands populations from the Cook Islands, Samoa, Tokelau, and Tonga. The majority of KIR genes were present at similar frequencies between the four populations with KIR2DL4, KIR3DL2, and KIR3DP1 genes observed in all individuals. Commonly observed KIR genes in Pacific Islands populations (pooled frequencies) were KIR2DL1 (0.77), KIR2DL3 (0.77), KIR3DL1 (0.65), KIR3DL3 (0.93), KIR2DS4/1D (0.78), and KIR2DP1 (0.82), compared to the less-frequently observed KIR2DL2 (0.27), KIR2DL5 (0.30), KIR2DS1 (0.19), KIR2DS2 (0.27), KIR2DS3 (0.16), KIR2DS5 (0.17), and KIR3DS1 (0.18) genes. Differences in KIR gene frequency distributions were observed between the Pacific Islands populations and when compared to other populations. Sixty-nine different genotypes were identified, with five genotypes accounting for more then 50% of all genotypes observed. The number of genotypes observed in each population was similar in the Cook Islands, Samoan, and Tokelauan populations (19, 18, and 19, respectively), but 26 different genotypes were observed in Tongans. The putative haplotype A was predominantly observed over haplotype B in all Pacific Islands populations. Significant linkage disequilibrium was observed for a number of KIR gene pairs.

High KIR diversity in Amerindians is maintained using few gene-content haplotypes

Interaction between killer cell immunoglobulin-like receptors (KIR) and cognate HLA class I ligands influences the innate and adaptive immune response to infection. The KIR family varies in gene content and allelic polymorphism, thereby, distinguishing individuals and populations. KIR gene content was determined for 230 individuals from three Amerindian tribes from Venezuela: the Yucpa, Bari and Warao. Gene-content haplotypes could be assigned to 212 individuals (92%) because only five different haplotypes were present-group A and four group B. Six different haplotype combinations accounted for >80% of individuals. Each tribe has distinctive genotype frequencies. Despite few haplotypes, all 14 KIR genes are at high frequency in the three tribes, with the exception of 2DS3. Each population has an even frequency of group A and B haplotypes. Allele-level analysis of 3DL1/S1 distinguished five group A haplotypes and six group B haplotypes. The high frequency and divergence of the KIR haplotypes in the Amerindian tribes provide greater KIR diversity than is present in many larger populations. An extreme case being the Yucpa, for whom two gene-content haplotypes account for >90% of the population. These comprise the group A haplotype and a group B haplotype containing all the KIR genes, except 2DS3, that typify the group B haplotypes. Here is clear evidence for balancing selection on the KIR system and the biological importance of both A and B haplotypes for the survival of human populations.

Distribution of killer-cell immunoglobulin-like receptor (KIR) in Comoros and Southeast France

Killer-cell immunoglobulin-like receptors (KIRs) expressed by natural killer cells are cell surface molecules able to recognize groups of HLA class I alleles. The number and distribution of KIR genes vary among individuals and populations. The aim of this study is to analyse the KIR gene content in a Comorian population in order to investigate genetic relationships with other populations and to reconstruct past migration events. The Comorian population consisted of 54 unrelated immigrants living in France and a control population consisted of 38 individuals from Southeast France. We investigated the presence or absence of 15 KIR genes, two pseudogenes expressed and non-expressed forms of KIR2DL5 and the two major subtype full-length and deleted forms of KIR2DS4. All individuals were typed positive for the framework genes, i.e. KIR2DL4, KIR3DL2 and KIR3DL3, and the two pseudogenes KIR3DP1 and KIR2DP1. The frequencies of full-length KIR2DS4 (*00101/00102/002) were lower in the French population (F = 29%) than in the Comorian population (F = 72%) (P(c) < 0.05). No significant differences were found for other KIR genes. A total of 11 genotypes were identified in the Southeast French population and 22 genotypes in the Comorian population. The most common genotype (2DL1, 2DL3, 2DL4, 3DL1, 3DL2, 3DL3 and 2DS4) accounted for 41% in the Comorian population and 34% in the Southeast French population. Principal component analysis using KIR gene data from 20 populations was performed to determine genetic differences and relations between populations. The Comorian population exhibited closest kinship with Africans and Asians. As KIR gene content is heterogeneous among ethnic groups, it can probably be used to assess the genetic relationships among populations from different geographic areas.

KIR gene in ethnic and Mestizo populations from Mexico

Killer cell immunoglobulin-like receptors are characterized by their great diversity of genes and alleles. Population studies have identified the presence of a broad variety of genotypes. In Mexico, there are diverse ethnic groups representing 9% of the total population and the rest is composed of Mestizos with a more varied biology. For the purpose of this study, genotyping was performed in Mestizos, in Mexico City inhabitants, and in three ethnic groups. The frequencies of genes KIR2DL2, 2DL5, 2DS1-3, 2DS5, and 3DS1 showed a greater variability in the groups studied. A total of 12 different genotypes were identified, the higher number for the Mestizos and the lower number for the Tarahumaras. Genotype 1 was found at a greater frequency in all the groups, except for the Tarahumaras, in which genotype 4 was more frequent. The frequency of genotypes 4 and 8 in Mexicans was higher than that for other populations analyzed. By subtyping of KIR3DL1, 3DL2, 2DL1, and 2DL3, two B haplotypes were identified in families; both were absent in Caucasian families. Our results indicated a greater diversity of genes in the Mestizos group than in the ethnic groups.

HLA-C and Killer Cell Immunoglobulin-like Receptor Genes in Idiopathic Bronchiectasis

RATIONALE

In idiopathic bronchiectasis, lung inflammation and chronic bacterial infection lead to progressive lung damage. A possible role for natural killer (NK) cells is suggested by the observation that familial bronchiectasis occurs in a rare group of individuals with impaired HLA class I expression and consequent NK cell dysfunction.

OBJECTIVE

Because the HLA-C locus and killer cell immunoglobulin-like receptors (KIRs) are of key importance for NK cell recognition, we analyzed HLA-C/KIR combinations by genotyping patients with idiopathic bronchiectasis.

METHODS

Genomic DNA from 96 individuals with idiopathic bronchiectasis and 101 control subjects was analyzed by polymerase chain reaction with sequence-specific primers. High-resolution HLA-C genotyping was performed in addition to KIR analysis.

RESULTS

HLA-Cw*03 alleles and, in particular, HLA-C group 1 homozygosity are associated with the presence of bronchiectasis. Analysis of the relationship between HLA-C and KIR genes suggests a shift to activatory NK cell function.

CONCLUSION

This is the first demonstration of genetic susceptibility in idiopathic bronchiectasis. The association with HLA-C group 1 homozygosity, and the interplay between HLA-C and KIR genes, argue for a role for NK cells in the progressive lung damage seen in this disease. This will require further investigation using functional studies.

Genetic diversity of KIR natural killer cell markers in populations from France, Guadeloupe, Finland, Senegal and Réunion

Killer cell immunoglobulin-like receptors (KIRs) belong to a diverse family of natural killer (NK) cell receptors recognizing human leukocyte antigen (HLA) class I molecules. Due to this functional link, KIR molecules are expected to display a high polymorphism, such as their HLA ligands. Moreover, many studies conducted in mouse and human models have shown that NK-KIR receptors play an important role in haematopoietic stem cell transplantation (HSCT). A beneficial impact of peculiar KIR ligand (HLA) mismatching has been reported suggesting a role to this combinatory HLA-KIR polymorphism. It is thus important to investigate KIR diversity in various human populations. To this end, we used polymerase chain reaction-sequence-specific primers to evaluate KIR gene in five selected populations (France, Guadeloupe, Senegal, Finland and Réunion). Genotypic and haplotypic frequencies were computed, as well as genetic distances and dendrogram (phylip package). These data illustrate the genetic relationship of these five populations through the KIR polymorphism. Results revealed a wide diversity in KIR gene frequencies in Guadeloupe and Réunion, and a high specificity in Senegal. The obtained dendrogram indicated small genetic distances between France, Guadeloupe and Réunion as well as between France and Finland. Senegal showed a distant genetic relationship with the other countries and, interestingly, an inverted ratio of coding/non-coding (KIR2DS4/1D) alleles compared with Caucasians. These data expose the broad diversity in KIR genes worldwide and show that KIR genes are pertinent tools in human population genetics. If the role of KIR donor-recipient incompatibilities is confirmed, KIR diversity according to ethnicity should be taken into account during the selection of HSCT donors.

A population-based cohort study of KIR genes and genotypes in relation to cervical intraepithelial neoplasia

Natural killer (NK) cells are involved both in control of virus infections and in elimination of tumor cells. Killer immunoglobulin-like receptors (KIRs) either activate or inhibit NK cell-mediated cytolysis, protecting healthy cells from destruction while enabling killing of abnormal cells. To investigate whether KIR genes or genotypes are associated with cervical carcinogenesis, a nested case-control study of 65 case women with cervical intraepithelial neoplasia (CIN) diagnosed during a 6-year follow-up of 15,234 women and 150 control women from the same cohort that remained healthy was performed. More than 70 different genotypes were observed, and 33 of which had not been described previously. An A-genotype including KIR2DL1, KIR2DL2, KIR2DL3, KIR2DL4, KIR3DL1, KIR3DL2, KIR3DL3, and KIR2DS4 was associated with increased risk of CIN (OR 6.7; 95% CI 1.7-26.3), and KIR2DL5B*002 appeared to have an inverse association with disease (OR 0.5; 95% CI 0.5-2.9). There was no association of CIN with the number of activating KIR genes. There was also no association between KIR genes and type of human papilloma virus or with other CIN-related immune response genes. It was concluded that certain KIR genes and genotypes may associate with cervical neoplasia.

Natural killer cell receptors: regulating innate immune responses to hematologic malignancy

Critical to innate immunity, the natural killer (NK) cell performs its function of immunosurveillance through its recognition of altered or missing self on damaged, infected, or transformed malignant cells. NK cell receptors responsible for detection of human leukocyte antigen (HLA) class I and class I-like proteins on potential target cells transmit inhibitory and activating signals that integrate to determine NK cell function. Advances in the fields of NK cell receptor biology and immunogenetics have enhanced our understanding of NK cell target recognition and may now guide studies to determine NK cell effects in the clinical setting. Analysis of NK cell receptor-ligand relationships, such as the inhibitory killer immunoglobulin-like receptors (KIRs) and their HLA class I ligands, has revealed the potential for NK cell-mediated benefit in allogeneic hematopoietic stem cell transplantation for hematologic malignancies.

KIR genes

This review updates the on-going investigations into KIR genes and their alleles with the main emphasis on what has taken place in this laboratory over the last 3 years.

Natural selection drives recurrent formation of activating killer cell immunoglobulin-like receptor and Ly49 from inhibitory homologues

Expression of killer cell Ig-like receptors (KIRs) diversifies human natural killer cell populations and T cell subpopulations. Whereas the major histocompatibility complex class I binding functions of inhibitory KIR are known, specificities for the activating receptors have resisted analysis. To understand better activating KIR and their relationship to inhibitory KIR, we took the approach of reconstructing their natural history and that of Ly49, the analogous system in rodents. A general principle is that inhibitory receptors are ancestral, the activating receptors having evolved from them by mutation. This evolutionary process of functional switch occurs independently in different species to yield activating KIR and Ly49 genes with similar signaling domains. Selecting such convergent evolution were the signaling adaptors, which are older and more conserved than any KIR or Ly49. After functional shift, further activating receptors form through recombination and gene duplication. Activating receptors are short lived and evolved recurrently, showing they are subject to conflicting selections, consistent with activating KIR's association with resistance to infection, reproductive success, and susceptibility to autoimmunity. Our analysis suggests a two-stage model in which activating KIR or Ly49 are initially subject to positive selection that rapidly increases their frequency, followed by negative selection that decreases their frequency and leads eventually to loss.

Complex interactions: The immunogenetics of human leukocyte antigen and killer cell immunoglobulin-like receptors

The killer cell immunoglobulin-like receptors (KIR) for human leukocyte antigen (HLA) modulate innate and adaptive immunity by controlling effector cells. HLA and KIR are encoded in genomic regions that have complex organization and exhibit exceptional diversity within and among human population groups. This diversity is likely to have arisen to combat a constantly evolving pathogen challenge. Numerous variations influence the expression level or function of KIR molecules and can affect their interaction with HLA, with important implications for the immune response. The functional variety of natural immune responses that are controlled by HLA and KIR interactions is genetically determined and maintained by natural selection.

Improved outcome in HLA-identical sibling hematopoietic stem-cell transplantation for acute myelogenous leukemia predicted by KIR and HLA genotypes

Inhibitory killer immunoglobulin (Ig)-like receptors (KIRs) recognize HLA-C and -B epitopes on target cells, thereby regulating natural killer (NK) cell activity. In 178 patients receiving T-cell-depleted HLA-identical sibling transplants for acute myelogenous leukemia (AML), chronic myelogenous leukemia (CML), acute lymphoblastic leukemia (ALL), or myelodysplastic syndrome (MDS), analysis of donor KIR genotype with HLA genotype demonstrated that 62.9% of the patients lacked an HLA ligand for donor-inhibitory KIR. Lack of HLA ligand for donor-inhibitory KIR (missing KIR ligand) had no effect on disease-free survival (DFS), overall survival (OS), or relapse in patients receiving transplants for CML and ALL. In patients with AML and MDS, however, there was a significant missing KIR ligand effect on DFS (P = .014; hazard ratio [HR], 0.53; 95% confidence interval [95% CI], 0.28-0.88) and OS (P = .03; HR, 0.53; 95% CI, 0.3-0.93). Incidence of relapse was also lower in patients with AML and MDS who lacked the HLA ligand for donor-inhibitory KIR (P = .04; HR, 0.41; 95% CI, 0.18-0.97). AML and MDS patients lacking 2 HLA ligands for donor-inhibitory KIR had the highest DFS (P = .002) and OS (P = .003). There was no significant contribution of donor-activating KIR to transplantation outcome in these patients. These data indicate that the absence of class I ligand in the recipient for donor-inhibitory KIR can be a prognostic factor for transplantation outcome in HLA-identical sibling transplantation and that the lack of HLA-C or -B ligands for donor-inhibitory KIR can contribute to improved outcomes for patients with AML and MDS.

The silent KIR3DP1 gene (CD158c) is transcribed and might encode a secreted receptor in a minority of humans, in whom the KIR3DP1, KIR2DL4 and KIR3DL1/KIR3DS1 genes are duplicated

Killer-cell Ig-like receptors (KIR) are structurally and functionally diverse, and enable human NK cells to survey the expression of individual HLA class I molecules, often altered in infections and tumors. Multiple events of non-reciprocal recombination have contributed to the rapid diversification of KIR. We show that approximately 4.5% of the individuals of a Caucasoid population bear a recombinant allele of KIR3DP1, officially designed KIR3DP1*004, that associates tightly with gene duplications of KIR3DP1, KIR2DL4 and KIR3DL1/KIR3DS1. The KIR3DP1 gene is normally silent, but the recombinant allele carries a novel promoter sequence and, as a consequence, is transcribed in all tested individuals. Messenger RNA of KIR3DP1*004 is made up of six exons; of these, exons 1-5 are similar to, and spliced like, those encoding the leader peptide and Ig-domains of KIR3D. By contrast, exon 6 is homologous to no other human KIR sequence, but only to possible homologs in chimpanzees and rhesus macaques, and encodes a short hydrophilic tail. The putative KIR3DP1*004 product, like those of the related genes LAIR-2 and LILRA3/ILT6/LIR4, is predicted to be secreted to the extracellular medium rather than anchored to the cell membrane.

Haplotype analysis of killer cell immunoglobulin-like receptor genes in 77 Korean families

Killer cell immunoglobulin-like receptor (KIR) genes constitute a multigene family whose genomic diversity is achieved through variation in gene content and allelic polymorphism within individual KIR genes. To date, 16 KIR genes and pseudogenes have been identified, and group A and group B haplotypes are characterized by a dominance of genes encoding inhibitory and activating receptors, respectively. In the present study, we have investigated the presence or absence of 16 KIR genes and pseudogenes and subtypes of four genes (3DP1, 3DP1 variant; 2DL1, 2DL1 variant; expressed and nonexpressed variant of 2DL5; full length and deleted form of 2DS4) in 352 members of 77 unrelated Korean families using a PCR-based sequence-specific priming method. KIR haplotypes were determined by segregation analysis. A total of 29 different KIR genotypes and 19 (two group A and 17 group B) haplotypes were identified in 154 parents. The distribution of genotypes, in terms of combination of haplotypes, was AA 55.2%, AB 36.4%, and BB 8.4%. Different from Caucasians, full-length 2DS4 (80.5%) was the predominant subtype of 2DS4 and group A (73.4%) outnumbered group B haplotypes (26.6%). The KIR gene frequencies and the predominance of A haplotypes in Koreans are similar to those in the Japanese.

The KIR gene family: life in the fast lane of evolution

A hallmark of human NK cells is the expression of HLA class I-specific killer-cell immunoglobulin-like receptors (KIR). An interesting facet of the KIR family is the unusual variability of the respective gene cluster, which is changing shape at an astonishing evolutionary pace. Not only do KIR genes come in different allelic variants, but the KIR locus has also gone through drastic contractions and expansions in recent evolutionary history, resulting in a wide variety of KIR haplotypes. A new study now reveals how an originally nonfunctional KIR pseudogene, KIR3DP1, is brought back to life in certain individuals via non-reciprocal recombination between two different KIR haplotypes. This Commentary outlines how the unique architecture of the KIR locus facilitates the generation of new KIR haplotypes and discusses the functional relevance of it.

Investigation of killer cell immunoglobulinlike receptor gene diversity: I. KIR2DL4

Polymerase chain reaction-sequence-specific oligonucleotide probes typing procedures identifying alleles of the killer immunoglobulin-like gene (KIR2DL4) have been established. The methods, designed around the specific amplification of the D0 and D2 domains of this gene, produce discrimination of KIR2DL4 alleles. The methods have been applied to a healthy Northern Irish control group, establishing frequencies for this Caucasian population. Additionally, the KIR2DL4 allele status of cell line DNA and CEPH families, from the 13th International Histocompatibility Workshop and local families, have also been investigated.

Investigation of KIR diversity in immunosenecence and longevity within the Irish population

Natural killer (NK) cells play a pivotal role in the innate immune response. During the ageing process, variations occur in NK cell number and function. The cytolytic activity of NK cells is controlled by an array of activating and inhibitory cell surface receptors, including the killer cell immunoglobulin-like receptors (KIRs). In the present study, genetic diversity of the KIR loci was analysed with respect to successful ageing in the Irish population. A PCR-SSOP KIR gene identification system was employed to determine the frequency of the named KIR genes/pseudogenes and KIR genotypes within a healthy aged cohort and young control group. Although, two KIR genes (2DS3, 2DL5) displayed an initial increased frequency in the aged group, the significance of this association was lost when repeated in a second cohort. In view of the lack of studies to date, investigating the role of the KIR gene system in healthy ageing, further analysis of KIR diversity is required to fully elucidate it's role in respect to age-related disease and longevity.

Immunobiology of Natural Killer Lymphocytes in Transplantation

Natural killer (NK) lymphocytes are powerful effector cells of the peripheral immune system. NK cell functions are controlled by the expression of a variety of cell surface receptors with either inhibitory or activating roles. The genetic and functional diversity of this repertoire of receptors and the role of human leukocyte antigen class I histocompatibility molecules as a major group of NK receptor ligands endows NK cells with an innate alloreactive capacity. Early studies of experimental bone marrow transplantation revealed an important role for NK cells in the rejection of allogeneic grafts and contributed significantly to our understanding of NK cell behavior. Both animal models and in vitro studies have since implicated NK cells as contributors to the pathology of clinical transplantation. However, recent clinical studies have demonstrated the potential benefits of exploiting NK cell alloreactivity in mismatched hematopoietic stem cell transplantation for particular types of acute leukemia. Future investigations of NK cell alloreactive functions will undoubtedly reveal additional roles and potential therapeutic applications of this fundamental cell type in clinical transplantation.

Distribution of killer cell immunoglobulin-like receptors in the Greek population

The interaction between killer cell immunoglobulin-like receptors (KIR) expressed on natural killer (NK) cells, and human leukocyt antigen (HLA) molecules expressed on target cells is known to regulate the cytolytic activity. A wide range of KIR genotypes is observed in the population, as the number of KIR loci can vary. In the present study we have determined the frequencies and combinations of 13 KIR genes and two CD94:NKG2 receptor genes and their distribution in the two haplotype groups in a panel of 233 unrelated healthy Greek Caucasians. We have typed genomic DNA for the presence of the putative KIR loci KIR2DL1, KIR2DL2, KIR2DL3, KIR2DL4, KIR3DL1, KIR3DL2, KIR3DL3, KIR2DS1, KIR2DS2, KIR2DS3, KIR2DS4, KIR2DS5, and KIR3DS1 using modified polymerase chain reaction sequence-specific primers. The frequency of KIR loci combined with the linkage disequilibrium values suggest that the Greek population shares several general features with other Caucasoid populations studied before, but still distinguishes itself by the increased or decreased frequency of several alleles. The majority of the 45 different KIR genotypes seen in Greeks have been observed in Caucasoid populations studied before. Nevertheless, two of these genotypes, although met in other populations, have not been found in Caucasians before. One individual possesses a novel profile with no KIR inhibitory gene. The A haplotypes remain the most prevalent, with AA1 being the most common genotype, and the number of inhibitory KIRs being more variable than the number of noninhibitory KIRs in most haplotypes.

Domain Shuffling Has Been the Main Mechanism Forming New Hominoid Killer Cell Ig-Like Receptors

The killer cell Ig-like receptor (KIR) gene family encodes MHC class I-specific receptors, which regulate NK cell responses and are also expressed on subpopulations of T cells. KIR haplotypes vary in gene content, which, in combination with allelic polymorphism, extensively diversifies the KIR genotype both within and between human populations. Species comparison indicates that formation of new KIR genes and loss of old ones are frequent events, so that few genes are conserved even between closely related species. In this regard, the hominoids define a time frame that is particularly informative for understanding the processes of KIR evolution and its potential impact on killer cell biology. KIR cDNA were characterized from PBMC of three gorillas, and genomic DNA were characterized for six additional individuals. Eleven gorilla KIR genes were defined. With attainment of these data, a set of 75 KIR sequences representing five hominoid species was assembled, which also included rhesus monkey, cattle, and rodent KIR. Searching this data set for recombination events, and phylogenetic analysis using Bayesian methods, demonstrated that new KIR were usually the result of recombination between loci in which complete protein domains were shuffled. Further phylogenetic analysis of the KIR sequences after removal of confounding recombined segments showed that only two KIR genes, KIR2DL4 and KIR2DL5, have been preserved throughout hominoid evolution, and one of them, KIR2DL4, is also common to rhesus monkey and hominoids. Other KIR genes represent recombinant forms present in a minority of species, often only one, as exemplified by 8 of the 11 gorilla KIR genes.

Natural killer-cell activity after human renal transplantation in relation to killer immunoglobulin-like receptors and human leukocyte antigen mismatch

BACKGROUND

Natural killer (NK) cells use killer immunoglobulin-like receptors (KIR) that bind to self-class I major histocompatibility complex (MHC) molecules to prevent killing of autologous cells. Mismatched allografts, which do not express recipient MHC class I molecules, can therefore be potential targets for NK-cell killing. In our living related-unrelated renal transplantation program, donor-recipient pairs vary in the amount of both HLA and KIR genes they share. This provides us with a unique opportunity to dissect the influence of KIR on NK-cell function after transplantation.

METHODS

Recipient NK cells were used in a cytotoxicity assay against donor peripheral blood mononuclear cells 2 days before, on the day of, and 3 days after transplantation. Results were correlated to HLA-KIR compatibility between donor and recipient.

RESULTS

NK killing, in a direct ex vivo setting, was demonstrated to be HLA mismatch dependent. Recipient NK antidonor cytotoxicity was unaltered despite having received 2 days' treatment with cyclosporine A before transplantation. However, cytotoxicity increased 3 days after transplantation in 71% of recipients. Recipients exhibiting increased NK cytotoxicity against their donors after transplantation were found to possess more activating KIR genes specific for donor class I MHC molecules than those in whom killing activity did not increase (P<0.04).

CONCLUSIONS

NK cells are activated after transplantation despite quadruple immunosuppression, suggesting that recipient NK-cell cytotoxicity against the donor may be a previously unrecognized area of the rejection process, especially in poorly matched donor-recipient pairs where the recipient may not express the correct repertoire of inhibitory receptors to prevent killing of donor cells.

The Protein Made from a Common Allele ofKIR3DL1(3DL1*004) Is Poorly Expressed at Cell Surfaces due to Substitution at Positions 86 in Ig Domain 0 and 182 in Ig Domain 1

KIR3DL1 is an inhibitory HLA-B receptor of human NK and T cells that exhibits genetic and phenotypic polymorphism. KIR3DL1*004, a common allotype, cannot be detected on the surface of PBLs using the KIR3DL1-specific Ab DX9. The nature of this phenotype was investigated through comparison of 3DL1*004 with 3DL1*002, an allele giving high DX9 binding to cell surfaces. Analysis of Jurkat T cell transfectants with 3DL1*004 cDNA showed that 3DL1*004 is poorly expressed at the cell surface, but detectable intracellularly. Analysis of recombinant mutants made between 3DL1*004 and 3DL1*002 showed that polymorphism in Ig domains 0 and 1 (D0 and D1) causes the intracellular retention of 3DL1*004. Reciprocal point mutations were introduced into 3DL1*004 and 3DL1*002 at positions 44 and 86 of the D0 domain, where 3DL1*004 has unique residues, and at position 182 of the D1 domain, where 3DL1*004 resembles 3DL1*005, an allotype giving low DX9-binding phenotype. Leucine 86 in 3DL1*004 is the principal cause of its intracellular retention, with a secondary and additive contribution from serine 182. By contrast, glycine 44, which is naturally present in 3DL1*004, slightly increased cell surface expression when introduced into 3DL1*002. In 3DL1*004, the presence of leucine at position 86 corrupts the WSXPS motif implicated in proper folding of the KIR D0 Ig-like domain. This study demonstrates how a difference between KIR3DL1 allotypes in the D0 domain profoundly affects cell surface expression and function.

Activation of a Subset of Human NK Cells upon Contact with Plasmodium falciparum-Infected Erythrocytes

Human NK cells are the earliest source of the protective cytokine IFN-gamma when PBMC from nonimmune donors are exposed to Plasmodium falciparum-infected RBC (iRBC) in vitro. In this study, we show that human NK cells form stable conjugates with iRBC but not with uninfected RBC and that induction of IFN-gamma synthesis is dependent on direct contact between the NK cell and the iRBC. NK cells respond to iRBC only in the presence of a source of IL-12/IL-18 and the subset of NK cells that preferentially respond to iRBC express high levels of the lectin-like receptor CD94/NKG2A. There is heterogeneity between donors in their ability to respond to iRBC. DNA analysis has revealed considerable heterogeneity of killer Ig-like receptor (KIR) genotype among the donor population and has identified 21 new KIR allelic variants in the donors of African and Asian descent. Importantly, we find evidence for significant associations between KIR genotype and NK responsiveness to iRBC. This emphasizes the need for large-scale population-based studies to address associations between KIR genotype and susceptibility to malaria.

Analysis of Fc gamma receptor II (CD32) polymorphism in populations of African and South Asian ancestry reveals east-west geographic gradients of allele frequencies

Analysis of FcgammaRIIA alleles in Pakistanis and in Trinidadians of South Asian, African and mixed ancestry revealed no significant differences between Trinidadian South Asians and Pakistanis. H131 homozygotes were more common among Trinidadian South Asians than among Africans and those of mixed ancestry. Comparison with other populations revealed east-west geographic gradients of allele frequencies.

The impact of donor KIR and patient HLA-C genotypes on outcome following HLA-identical sibling hematopoietic stem cell transplantation for myeloid leukemia

Killer immunoglobulin-like receptors (KIRs) regulate cell activity of natural killer (NK) cells and some T cells. The predominant ligand for inhibitory KIRs is HLA-C, which subdivides into 2 groups based on the specificity of inhibitory KIRs. The ligands for activatory KIRs are unknown. Following hematopoietic stem cell transplantation (HSCT), recipient tissues may not express a ligand for KIRs present within the graft, and the combination of donor KIR and recipient HLA-C types could influence outcome. HLA and KIR genotypes were determined in 220 donor-recipient pairs from HLA-matched sibling HSCTs performed for myeloid (n = 112) and lymphoid (n = 108) diseases. In HSCTs performed for myeloid disease, overall survival was worse in patients homozygous for group 2 HLA-C (C2) than in patients who carried a group 1 HLA-C (C1) allele (P <.005). Moreover, this effect is seen only when the donor additionally carries the activating KIR gene KIR2DS2 (P =.045). No effect was seen in patients with lymphoid disease. Thus, in HLA-matched sibling HSCT for myeloid leukemia, patients homozygous for C2 alleles receiving a graft from a donor carrying the KIR gene KIR2DS2 have a significantly reduced chance of survival.

Multiple copies of KIR 3DL/S1 and KIR 2DL4 genes identified in a number of individuals

Multiple copies of the killer immunoglobulin-like receptor gene, 3DL/S1, have been identified in certain individuals. Additionally, allele determination of the killer immunoglobulin-like receptor gene (KIR), 2DL4, has identified three alleles of this gene present in these same individuals. This event has been confirmed by isolating three distinct KIR2DL4 allele clones in each individual, which sequenced as the alleles identified by the allele identification technique. It is our assumption that an unequal crossover event has occurred between differing KIR haplotypes resulting in the duplication of the 2DL4, 3DS1/3DL1 genes on the newly formed haplotype(s).

The distribution of 13 killer-cell immunoglobulin-like receptor loci in UK blood donors from three ethnic groups

Killer-cell immunoglobulin-like receptors (KIRs) can inhibit the killing activity of natural killer (NK) cells if they interact with their ligand, class I HLA. Using a modified polymerase chain reaction-sequence-specific primers (PCR-SSP) method for typing KIRs using genomic DNA, we compared KIR frequencies in three ethnic populations drawn from UK blood donors. We found a significantly lower frequency of the inhibitory KIRs KIR2DS1 and 3DS1 in Afro-Caribbean blood donors. Despite this, there was a (non-significant) increase in the B haplotype in Afro-Caribbean and Indian Asian donors. Some donors from each group tested negative for all non-inhibitory KIRs. In addition, we describe several new KIR profiles. Analysis of linkage disequilibrium was consistent with previously published findings.

Natural killer receptor repertoires in transplantation

Natural killer (NK) lymphocytes are potent effector cells that are controlled by the expression of a variety of cell surface receptors with either inhibitory or activating functions. The genetic and functional diversity of this receptor repertoire and the role of HLA class I molecules as a major group of NK receptor ligands create an innate alloreactive capacity in this cell type. Both animal models and in vitro studies have implicated NK cells as contributors to the pathology of clinical transplantation. However, recent clinical studies have indicated the potential benefit of exploiting NK cell alloreactivity in mismatched haematopoietic stem cell transplantation. Further investigations of NK cell alloreactivity will undoubtedly reveal additional applications of this fundamental cell type in clinical transplantation.

A multi-laboratory characterization of the KIR genotypes of 10th International Histocompatibility Workshop cell lines

Killer immunoglobulinlike receptors (KIRs) are expressed on natural killer and T cells. Both inhibitory and noninhibitory forms have been described, leading to inhibition or continuation of cellular killing activity. The natural ligands identified so far of KIRs are class I human leukocyte antigens (HLA). In particular, the interaction of some KIRs with HLA-Cw has been well characterized. Recent work has implicated KIRs in affecting the outcome of hematopoietic stem-cell transplant (HSCT). This may well lead to a requirement for prospective KIR typing of donor and recipient. We have utilized different typing systems (two using polymerase chain reaction-sequence-specific primers, and one using polymerase chain reaction-sequence-specific oligonucleotide probes) in three separate laboratories to characterize the KIR gene complement of 25 cell lines from the 10th International Histocompatibility Workshop. There were consistent results in 22, and minor differences in 3. When compared with previous results for some of these cell lines, no further differences were found. The differences are due to typing of KIRs KIR2DL1 and KIR2DS5, and may be explained by technical differences or the inability to type new variants. Further improvements in typing may be required if population and clinical studies are to produce accurate results.

Assessment of killer cell immunoglobulinlike receptor expression and corresponding HLA class I phenotypes demonstrates heterogenous KIR expression independent of anticipated HLA class I ligands

Natural killer (NK) cell-mediated cytolysis is stimulated and downregulated through the interaction of distinct human leukocyte antigen (HLA) class I molecules on target cells with specific killer cell immunoglobulinlike receptors (KIRs) on NK cells. Killer cell immunoglobulinlike receptors are highly polymorphic and are clonally distributed on NK cell populations within individuals. However, the regulation of KIR expression by individual HLA class I phenotypes is not well understood. To examine a potential influence of the HLA class I phenotype on KIR expression patterns we studied the KIR expression in individuals that were subgrouped according to the major HLA-C encoded KIR-epitopes (group C1 versus C2). In these individuals, NK cells were analyzed for KIR expression using flow cytometry and RNA-based expression analysis. Our results demonstrate that KIR genes are transmitted very heterogeneously with two main patterns of KIR genotypes as previously described; group A and group B (with 21 different genotypes). There are distinct populations exhibiting different densities of CD158a and/or CD158b positive NK cells that coexist in all individuals. A clear correlation between KIR expression and the currently known HLA class I ligands was not observed. In conclusion, the surface expression of KIRs in individuals with different HLA class I genotypes indicates that other non-HLA class I encoded factors contribute to the shaping of the KIR repertoire.

Alloreactive killer cells: hindrance and help for haematopoietic transplants

Haematopoietic-cell transplantation is a treatment for leukaemia and lymphoma. To reduce the incidence of graft-versus-host disease (GVHD) caused by transplanted T cells, donors and recipients are HLA matched. For patients for whom a matched donor is not available, one option is transplantation from an HLA-mismatched relative who shares one HLA haplotype. This procedure is distinguished by the use of a stronger conditioning regimen for the patient and of a T-cell-depleted graft containing numerous stem cells. After transplantation, natural killer cells are prevalent, and they can include alloreactive cells that kill tumour cells and prevent GVHD. The alloreactions seem to be determined by the mismatched HLA class I ligands and their killer-cell immunoglobulin-like receptors.

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.

Killer Ig-like receptor haplotype analysis by gene content: evidence for genomic diversity with a minimum of six basic framework haplotypes, each with multiple subsets

Killer Ig-like receptor (KIR) genes constitute a multigene family whose genomic diversity is achieved through differences in gene content and allelic polymorphism. KIR haplotypes containing a single activating KIR gene (A-haplotypes), and KIR haplotypes with multiple activating receptor genes (B-haplotypes) have been described. We report the evaluation of KIR gene content in extended families, sibling pairs, and an unrelated Caucasian panel through identification of the presence or absence of 14 KIR genes and 2 pseudogenes. Haplotype definition included subtyping for the expressed and nonexpressed KIR2DL5 variants, for two alleles of pseudogene 3DP1, and for two alleles of 2DS4, including a novel 2DS4 allele, KIR1D. KIR1D appears functionally homologous to the rhesus monkey KIR1D and likely arose as a consequence of a 22 nucleotide deletion in the coding sequence of 2DS4, leading to disruption of Ig-domain 2D and a premature termination codon following the first amino acid in the putative transmembrane domain. Our investigations identified 11 haplotypes within 12 families. From 49 sibling pairs and 17 consanguineous DNA samples, an additional 12 haplotypes were predicted. Our studies support a model for KIR haplotype diversity based on six basic gene compositions. We suggest that the centromeric half of the KIR genomic region is comprised of three major combinations, while the telomeric half can assume a short form with either 2DS4 or KIR1D or a long form with multiple combinations of several stimulatory KIR genes. Additional rare haplotypes can be identified, and may have arisen by gene duplication, intergenic recombination, or deletions.

A comparison of HLA-DR and -DQ allele and haplotype frequencies in Trinidadian populations of African, South Asian, and mixed ancestry

Using polymerase chain reaction-sequence-specific primer (PCR-SSP) typing, this study determined the frequency of human leukocyte antigen (HLA) DR- and -DQ alleles and haplotypes in individuals of African (n = 75), South Asian (n = 98), and mixed (n = 102) ancestry from the Caribbean island of Trinidad. We detected 19 different haplotypes containing DRB3, 8 containing DRB4, 6 containing DRB5, and 6 different haplotypes without DRB3/4/5 genes. Twenty-nine haplotypes were identified in Africans, 24 in the South Asians, and 32 in the mixed group. We detected significant differences between the populations, principally at the DQA1 and DQB1 loci, although the allele frequency for DRB1*0901 was highest in the Africans (p(c) < 0.05). Trinidad African and mixed groups were generally more diverse than the South Asians and displayed a wider range of DRB1-DQB1 associations; DQB1*02 and DQB1*0301 each associated with five to six different DRB1 alleles in the Africans and mixed group but only two in South Asians. In the Africans and the mixed group, DQB1*04 was found with DRB1*0302 and DRB1*04, but only with DRB1*08 in the South Asians. Trinidad Africans revealed consistencies with populations in Western, Central, and Northern Africa, but differed considerably from individual populations on the African continent. Trinidad South Asians displayed similar allele frequencies and associations to other populations from Northern India.

Variable receptors controlling activation and inhibition of NK cells

NK cells are important effector lymphocytes of innate immunity; they kill infected cells and produce cytokines that stimulate other immune effects. Once considered relatively homogeneous, NK cells are now seen to be highly diverse. Within an individual, expression of different combinations of inhibitory and stimulatory receptors creates a diverse NK cell repertoire, which exhibits specificity in the immune response. Rapid evolution of NK cell receptor gene families distinguishes members of a species and causes substantial species-specific differences in NK cell receptor systems. All known ligands for these diverse receptors are MHC class I molecules, or molecules of host or pathogen origin that are homologous to MHC class I.