Exploring the Role of Killer Cell Immunoglobulin-Like Receptors and Their HLA Class I Ligands in Autoimmune Hepatitis

Background

Natural killer cells are involved in the complex mechanisms underlying autoimmune diseases but few studies have investigated their role in autoimmune hepatitis. Killer immunoglobulin-like receptors are key regulators of natural killer cell-mediated immune responses.

Methods and Findings

KIR gene frequencies, KIR haplotypes, KIR ligands and combinations of KIRs and their HLA Class I ligands were investigated in 114 patients diagnosed with type 1 autoimmune hepatitis and compared with a group of 221 healthy controls. HLA Class I and Class II antigen frequencies were compared to those of 551 healthy unrelated families representative of the Sardinian population. In our cohort, type 1 autoimmune hepatitis was strongly associated with the HLA-B18, Cw5, DR3 haplotype. The KIR2DS1 activating KIR gene and the high affinity HLA-C2 ligands were significantly higher in patients compared to controls. Patients also had a reduced frequency of HLA-Bw4 ligands for KIR3DL1 and HLA-C1 ligands for KIR2DL3. Age at onset was significantly associated with the KIR2DS1 activating gene but not with HLA-C1 or HLA-C2 ligand groups.

Conclusions

The activating KIR gene KIR2DS1 resulted to have an important predictive potential for early onset of type 1 autoimmune hepatitis. Additionally, the low frequency of the KIR-ligand combinations KIR3DL1/HLA-Bw4 and KIR2DL3/HLA-C1 coupled to the high frequency of the HLA-C2 high affinity ligands for KIR2DS1 could contribute to unwanted NK cell autoreactivity in AIH-1.     

Low CD4+ T cell counts among African HIV-1 infected subjects with group B KIR haplotypes in the absence of specific inhibitory KIR ligands

Natural killer (NK) cells are regulated by interactions between polymorphic killer immunoglobulin-like receptors (KIR) and human leukocyte antigens (HLA). Genotypic combinations of KIR3DS1/L1 and HLA Bw4-80I were previously shown to influence HIV-1 disease progression, however other KIR genes have not been well studied. In this study, we analyzed the influence of all activating and inhibitory KIR, in association with the known HLA inhibitory KIR ligands, on markers of disease progression in a West African population of therapy-naïve HIV-1 infected subjects. We observed a significant association between carriage of a group B KIR haplotype and lower CD4+ T cell counts, with an additional effect for KIR3DS1 within the frame of this haplotype. In contrast, we found that individuals carrying genes for the inhibitory KIR ligands HLA-Bw4 as well as HLA-C1 showed significantly higher CD4+ T cell counts. These associations were independent from the viral load and from individual HIV-1 protective HLA alleles. Our data suggest that group B KIR haplotypes and lack of specific inhibitory KIR ligand genes, genotypes considered to favor NK cell activation, are predictive of HIV-1 disease progression.     

Genetic Diversity of the KIR/HLA System and Outcome of Patients with Metastatic Colorectal Cancer Treated with Chemotherapy

Objective

To explore genes of the killer-cell immunoglobulin-like receptor (KIR) and of the HLA ligand and their relationship with the outcome of metastatic colorectal cancer (mCRC) patients treated with first-line 5-fluorouracil, leucovorin, and irinotecan (FOLFIRI).

Methods

A total of 224 mCRC patients were screened for KIR/HLA typing. The determination of the KIR/HLA combinations was based upon the gene content and variants. Genetic associations with complete response (CR), time to progression (TTP) and overall survival (OS) were evaluated by calculating odds and hazard ratios. Multivariate modeling with prognostic covariates was also performed.

Results

For CR, the presence of KIR2DL5A, 2DS5, 2DS1, 3DS1, and KIR3DS1/HLA-Bw4-I80 was associated with increased CR rates, with median ORs ranging from 2.1 to 4.3, while the absence of KIR2DS4 and 3DL1 was associated with increased CR rates (OR 3.1). After univariate analysis, patients that underwent resective surgery of tumor, absence of KIR2DS5, and presence of KIR3DL1/HLA-Bw4-I80 showed a significant better OS (HR 1.5 to 2.8). Multivariate analysis identified as parameters independently related to OS the type of treatment (surgery; HR 2.0) and KIR3DL1/HLA-Bw4-I80 genotype (HR for T-I80 2.7 and for no functional KIR/HLA interaction 1.8). For TTP, no association with KIR/HLA genes was observed.

Conclusion

This study, for the first time, evidences that the genotyping for KIR-HLA pairs are found predictive markers associated with complete response and improves overall survival prediction of FOLFIRI treatment response in metastatic colorectal cancer. These results suggest a role of the KIR/HLA system in patient outcome, and guide new research on the immunogenetics of mCRC through mechanistic studies and clinical validation.     

Analysis of binding of KIR3DS1*014 to HLA suggests distinct evolutionary history of KIR3DS1

NK cell activity is regulated by the integration of positive and negative signals. One important source of these signals for human NK cells is the killer Ig-like receptor (KIR) family, which includes both members that transduce positive and those that generate negative signals. KIR3DL1 inhibits NK cell activity upon engagement by its ligand HLA-Bw4. The highly homologous KIR3DS1 is an activating receptor, which is implicated in the outcome of a variety of pathological situations. However, unlike KIR3DL1, direct binding of KIR3DS1(+) cells to HLA has not been demonstrated. We analyzed four key amino acid differences between KIR3DL1*01502 and KIR3DS1*013 to determine their role in KIR binding to HLA. Single substitutions of these residues dramatically reduced binding by KIR3DL1. In the reciprocal experiment, we found that the rare KIR3DS1 allotype KIR3DS1*014 binds HLA-Bw4 even though it differs from KIR3DS1*013 at only one of these positions (position 138). This reactivity was unexpectedly dependent on residues at other variable positions, as HLA-Bw4 binding was lost in receptors with KIR3DL1-like residues at both positions 199 and 138. These data provide the first evidence, to our knowledge, for the direct binding of KIR3DS1(+) cells to HLA-Bw4 and highlight the key role for position 138 in determining ligand specificity of KIR3DS1. They also reveal that KIR3DS1 reactivity and specificity is dictated by complex interactions between the residues in this region, suggesting a unique functional evolution of KIR3DS1 within the activating KIR family.     

Cutting edge: susceptibility to psoriatic arthritis: influence of activating killer Ig-like receptor genes in the absence of specific HLA-C alleles

NK cell activity is partially controlled through interactions between killer Ig-like receptors (KIR) on NK cells and their respective HLA class I ligands. Independent segregation of HLA and KIR genes, along with KIR specificity for particular HLA allotypes, raises the possibility that any given individual may express KIR molecules for which no ligand is present. Inhibitory receptor genes KIR2DL2/3 and KIR2DL1 were present in nearly all subjects sampled in this study, whereas their respective activating homologs, KIR2DS2 and KIR2DS1, are each present in about half of the subjects. In this work we report that subjects with activating KIR2DS1 and/or KIR2DS2 genes are susceptible to developing psoriatic arthritis, but only when HLA ligands for their homologous inhibitory receptors, KIR2DL1 and KIR2DL2/3, are missing. Absence of ligands for inhibitory KIRs could potentially lower the threshold for NK (and/or T) cell activation mediated through activating receptors, thereby contributing to pathogenesis of psoriatic arthritis.     

Cutting Edge: KIR3DS1, a gene implicated in resistance to progression to AIDS, encodes a DAP12-associated receptor expressed on NK cells that triggers NK cell activation

The killer cell Ig-like receptor (KIR) gene, KIR3DS1, has been implicated in slowing disease progression in HIV infection; however, little is known about its expression, function, or ligand specificity. Using retrovirally transduced NKL cells and peripheral blood NK cells from KIR3DS1-positive donors we assessed expression of this gene by flow cytometry and its function by in vitro assays measuring KIR3DS1-induced cell-mediated cytotoxicity and cytokine production. In the present study, we demonstrate that KIR3DS1 is expressed on peripheral blood NK cells and triggers both cytotoxicity and IFN-gamma production. Using cotransfection and coimmunoprecipitation, we found that KIR3DS1 associates with the ITAM-bearing adaptor, DAP12. Soluble KIR3DS1-Ig fusion proteins did not bind to EBV-transformed B lymphoid cell lines transfected with HLA-Bw4 80I or 80T allotypes, suggesting that if KIR3DS1 does recognize HLA-Bw4 ligands, this may be peptide dependent.     

Cutting edge: resistance to HIV-1 infection among African female sex workers is associated with inhibitory KIR in the absence of their HLA ligands

NK cells are regulated in part by killer Ig-like receptors (KIR) that interact with HLA molecules on potential target cells. KIR and HLA loci are highly polymorphic and certain KIR/HLA combinations were found to protect against HIV disease progression. We show in this study that KIR/HLA interactions also influence resistance to HIV transmission. HIV-exposed but seronegative female sex workers in Abidjan, C?te d'Ivoire, frequently possessed inhibitory KIR genes in the absence of their cognate HLA genes: KIR2DL2/KIR2DL3 heterozygosity in the absence of HLA-C1 and KIR3DL1 homozygosity in the absence of HLA-Bw4. HIV-seropositive female sex workers were characterized by corresponding inhibitory KIR/HLA pairings: KIR2DL3 homozygosity together with HLA-C1 and a trend toward KIR3DL1/HLA-Bw4 homozygosity. Absence of ligands for inhibitory KIR could lower the threshold for NK cell activation. In addition, exposed seronegatives more frequently possessed AB KIR genotypes, which contain more activating KIR. The data support an important role for NK cells and KIR/HLA interactions in antiviral immunity.     

Contribution of KIR3DL1/3DS1 to ankylosing spondylitis in human leukocyte antigen-B27 Caucasian populations

Killer cell immunoglobulin-like receptors (KIRs) and human leukocyte antigen (HLA) loci are both highly polymorphic, and some HLA class I molecules bind and trigger cell-surface receptors specified by KIR genes. We examined whether the combination of KIR3DS1/3DL1 genes in concert with HLA-B27 genotypes is associated with susceptibility to ankylosing spondylitis (AS). Two HLA-B27-positive Caucasian populations were selected, one from Spain (71 patients and 105 controls) and another from the Azores (Portugal) (55 patients and 75 controls). All were typed for HLA-B and KIR (3DS1 and 3DL1) genes. Our results show that in addition to B27, the allele 3DS1 is associated with AS compared with B27 controls (p < 0.0001 and p < 0.003 in the Spanish population and Azoreans, respectively). We also observed that the association of KIR3DS1 to AS was found in combination with HLA-B alleles carrying Bw4-I80 in trans position in the Spanish population (30.9% in AS versus 15.2% in B27 controls, p = 0.02, odds ratio (OR) = 2.49) and in Azoreans (27.2% in AS versus 8.7% in B27 controls, p = 0.01, OR = 4.4 in Azoreans). On the other hand, 3DL1 was decreased in patients compared with B27 controls (p < 0.0001 in the Spanish population and p < 0.003 in Azoreans). The presence of this allele in combination with Bw4-I80 had a protective effect against the development of AS in the Spanish population (19.7% in AS, 35.2% in B27 controls; p = 0.03, OR = 0.45). The presence of KIR3DS1 or KIR3DL1 in combination with HLA-B*27s/HLA-B Bw4-I80 genotypes may modulate the development of AS. The susceptibility to AS could be determined by the overall balance of activating and inhibitory composite KIR-HLA genotypes.     

Genetic polymorphism of NK receptors and their ligands in melanoma patients: prevalence of inhibitory over activating signals

Antitumor cytotoxicity of NK cells and T cells expressing NK-associated receptors is regulated by interaction between their cell surface killer immunoglobulin-like receptors (KIRs) and CD94/NKG2 heterodimers with MHC class I ligands on target cells. To test the hypothesis that KIR and/or HLA polymorphisms, and KIR/HLA combinations could contribute to the tumorigenesis, association studies were performed in 50 patients with malignant melanoma (MM) in different stages of disease and 54 controls. Our data showed that the frequency of inhibitory and activating KIR genes and KIR genotypes did not differ significantly between healthy individuals and melanoma patients. HLA haplotype distribution showed statistically significant increased frequencies of A*01-B*35-Cw*04 (0.069 vs 0.000; pc<0.05; OR=19.9), A*01-B*08-DRB1*03 (0.079 vs 0.019; pc<0.05; OR=4.5), and A*24-B*40-DRB1*11 (0.026 vs 0.000; pc<0.05; OR=7.1) in melanoma patients compared with healthy controls. Individuals homozygous for group 2 HLA-C ligands were less frequent in the patient group compared with the control cohort (12% vs 31.5%; p<0.017). In addition, we observed an increased frequency (88.0% vs 68.5%; p=0.017; OR=2.80) of KIR2DL2/2DL3 in combination with their group 1 HLA-C ligands, while the presence of these KIRs in the absence of the putative ligands was decreased (12.0% vs 31.5%; p=0.017) in the patient group. Furthermore, an increased frequency of activating KIR2DS1 in the absence of the putative HLA-C^Lys80 ligands was found in melanoma patients (16.0% vs 9.2%). In contrast, KIR2DS2 was absent in patients more often (38.0% vs 25.9%) when the presumptive HLA-C^Asn80 ligands were present. A slightly higher incidence of KIR3DL1 in combination with the less effective Bw4^Thr80 ligands was seen in patients with primary (20.8%) compared with metastatic (4.2%) disease. The data obtained in this study imply that there may not be a direct association between KIR gene content in the genome and the presence of malignant melanoma, or melanoma progression. However, some HLA haplotypes could be predisposing to MM in the Bulgarian population. Furthermore, distinct KIR/HLA ligand combinations may be relevant to the development of malignancy whereby inhibition overrides activation of NK cells and T cells expressing NK-associated receptors, which in turn might facilitate tumor escape and progression.     

Changes in DNA methylation levels during seed development in <Emphasis Type="Italic">Jatropha curcas</Emphasis>

The antiviral action of natural killer (NK) cells is regulated by a wide repertoire of germ-line encoded membrane receptors which recognize the expression of certain self-molecules on target cells. Among the receptors, killer cell immunoglobulin-like receptor (KIR) which recognizes the expression of human leukocyte antigen (HLA) class I has a predominant role in regulating the effector functions of NK cells, particularly in viral infections. We studied a total of 128 hepatitis B virus (HBV) patients (15 acute, 43 asymptomatic, 27 chronic and 43 with other liver diseases) while attending the Department of Medical Gastroenterology, Government Rajaji Hospital, Madurai, India, and 128 ethnic matched control to find the association between the KIR : HLA genes and differential manifestations of HBV. KIR and its ligand HLA polymorphism were identified by DNA-PCR methods. The activatory receptor KIR-2DS1 was significantly elevated in various disease categories, namely asymptomatic, chronic and other HBV, except acute HBV infection. Whereas, KIR 2DS3 in acute and chronic patients and KIR 2DS5 and 3DS1 in asymptomatic individuals. Among various KIR–HLA combinations, homozygous 2DS2:C1 and individuals with 3DSI:BW4 (OR = 3.23, CI = 1.55–6.7, Pc = 0.02) are associated with HBV asymptomatism, while most of the two domain inhibitory receptors with their ligands showed significant risk in other liver diseases. Further, KIR3DL1 : HLA Bw4Iso80 (OR = 3.89, 95% CI = 1.58–9.55, Pc = 0.004) is related with higher risk for asymptomatic infection when compared with chronic HBV. Thus, the select KIR : HLA alleles and combinations seem to direct the NK cell activities and immune response in different directions resulting in varied symptoms and manifestations in the subgroups of HBV-infected patients studied.     

Conferral of enhanced natural killer cell function by KIR3DS1 in early human immunodeficiency virus type 1 infection

A flurry of recent reports on the role of activating and inhibitory forms of the killer cell immunoglobulin-like receptors (KIR) in natural killer (NK) cell activity against human immunodeficiency virus type 1 (HIV-1) have yielded widely divergent results. The role of the activating NK receptor encoded by the KIR3DS1 allele and its putative ligands, members of the HLA class I Bw4Ile80 cluster, in early HIV-1 disease is controversial. We selected 60 treatment-naïve adults for study from the OPTIONS cohort of individuals with early HIV-1 infection in San Francisco. We performed NK cell functional assays measuring gamma interferon (IFN-γ) and CD107a expression by NK cells in the unstimulated state and after stimulation by the major histocompatibility complex class I-deficient 721.221 B-lymphoblastoid cell line. In addition, we measured CD38 expression (a T-cell activation marker) on T and NK cells. Persons who have at least one copy of the KIR3DS1 gene had higher IFN-γ and CD107a expression in the unstimulated state compared to those who do not possess this gene. After stimulation, both groups experienced a large induction of IFN-γ and CD107a, with KIR3DS1 carriers achieving a greater amount of IFN-γ expression. Differences in effector activity correlating with KIR3DS1 were not attributable to joint carriage of HLA Bw4Ile80 and KIR3DS1. We detected a partial but not complete dependence of KIR3DS1 on the members of B*58 supertype (B*57 and B*58) leading to higher NK cell function. Possessing KIR3DS1 was associated with lower expression of CD38 on both CD8⁺ T and NK cells and with a loss or weakening of the known strong associations between CD8⁺ T-cell expression of CD38 mean fluorescence intensity and the HIV-1 viral load. We observed that possessing KIR3DS1 was associated with higher NK cell effector functions in early HIV-1 disease, despite the absence of HLA Bw4Ile80, a putative ligand of KIR3DS1. Carriage of KIR3DS1 was associated with diminished CD8⁺ T-cell activation, as determined by expression of CD38, and a disruption of the traditional relationship between viral load and activation in HIV-1 disease, which may lead to better clinical outcomes for these individuals.NK cell function is regulated by a family of receptors encoded by the killer cell immunoglobulin-like receptor (KIR) genes (18, 33). Within the KIR family, certain genes encode inhibitory receptors that recognize HLA class I ligands (i.e., HLA-Bw4 or HLA-C), whereas other KIR genes encode activating receptors which are not completely known. Studies on the role of KIRs in human immunodeficiency virus (HIV) disease have focused on the activating receptor encoded by the KIR3DS1 allele. However, recent genetic association and functional studies of KIR and HIV disease have yielded widely disparate results on the role of KIR3DS1 and its putative ligands, a subset of HLA class I-B alleles referred to as Bw4Ile80. The Bw4Ile80 cluster is a subset of HLA-B alleles that bear an isoleucine at position 80 in the α-1 helix, on the rim of the peptide-binding cleft. The inhibitory receptors encoded by KIR3DL1 alleles, which are highly related in the extracellular domains to the activating receptor encoded by KIR3DS1, specifically recognize HLA-Bw4 ligands (5). Because of this similarity, KIR3DS1 has been assumed to also recognize Bw4Ile80 ligands. In 2002, Martin et al. reported that HIV-infected individuals in the Multicenter AIDS Cohort Study possessing the KIR3DS1 allele demonstrated significantly delayed progression to AIDS, provided that the individuals also expressed a Bw4Ile80 allele (20).In 2005, Gaudieri et al. reported on the association of the entire KIR gene cluster and HLA class I in HIV disease progression in an Australian HIV cohort (8, 9). These authors observed a trend toward slowed CD4⁺ T-cell percent loss among those who carried both Bw4Ile80 and KIR3DS1 (8). However, this trend was not statistically significant, and Gaudieri et al. simultaneously observed an acceleration of time to AIDS (1987 definition) among joint KIR3DS1 and Bw4Ile80 carriers. In 2006, Qi et al. published a follow-up report from the Multicenter AIDS Cohort Study cohort documenting an association between the coexpression of KIR3DS1 and Bw4Ile80 and enhanced protection against certain opportunistic infections in HIV-infected individuals (26), an effect partially attributed to very modest differences in viral load. In 2007, our group observed that KIR3DS1 gene carriage was associated with higher CD4⁺ T-cell counts and hence protection against HIV type 1 (HIV-1) progression in early disease (4); however, we observed that this effect was not attributable to differences in the viral load and further was independent of Bw4Ile80. In other words, our analyses suggested that the KIR3DS1 and Bw4Ile80 genes were each associated with protection against HIV disease but via different mechanisms.Until recently, it was not clear if KIR3DS1 was expressed on the surface of NK cells; however, two recent reports have conclusively established that KIR3DS1 is expressed on NK cells (6, 24) and that expression is dose dependent, with higher expression for homozygotes. These studies also demonstrated that KIR3DS1 recognizes neither HLA-Bw4 nor HLA-Bw6 ligands, at least when these major histocompatibility complex (MHC) class I molecules are expressed on Epstein-Barr virus-transformed B-lymphoblastoid cell lines. Similarly, an independent study by another group reported that KIR3DS1 fails to bind to soluble Bw4Ile80 tetrameric complexes (10). In contrast, Alter et al. have presented results from in vitro cytotoxicity assays suggesting that target cells possessing HLA-Bw4Ile80 are better targets for NK cells possessing KIR3DS1 (1); however, no evidence was provided to confirm a physical interaction between the KIR3DS1 and HLA-Bw4 proteins.Here, we present a study of the NK cell phenotype and function in 60 treatment-naïve, recently HIV-1-infected persons with defined HLA-B and KIR3DS1/KIR3DL1 allotypes. We also measured the expression of CD38 on NK cells and CD8⁺ T cells, a widely used marker of disease progression and virulence in HIV research and a marker of immune activation. The expression of CD38, as measured by flow cytometry, is known to be elevated on CD8⁺ T cells in HIV disease, reaching steady-state levels in early HIV-1 infection (7), and predicts disease progression independently of the viral load (19). The individuals studied were selected from our recent genetic association study of KIR and HLA among 255 recently HIV-1-infected persons (4), in which KIR3DS1 carriage alone was associated with higher CD4⁺ T-cell counts, despite the absence of a difference in the viral loads. On the basis of these clinical findings, we performed this study to determine whether persons who carried the KIR3DS1 gene had enhanced NK cell phenotypic and functional profiles and if these profiles were further enhanced by carriage of the putative KIR3DS1 ligands encoded by HLA-Bw4Ile80 alleles. Flow cytometry-based detection of KIR3DS1 has been hampered by the absence of a monoclonal antibody that can bind to KIR3DS1 specifically and not cross-react with the related KIR3DL1 proteins (25). Hence, we used genotypic KIR assignments for our analyses rather than flow cytometry-based methods.     

Association of killer cell immunoglobulin-like receptor polymorphisms with chronic hepatitis C and responses to therapy in Brazil

Soroprevalence for Hepatitis C virus is reported as 2.12% in Northern Brazil, with about 50% of the patients exhibiting a sustained virological response (SVR). Aiming to associate polymorphisms in Killer Cell Immunoglobulin-like Receptors (KIR) with chronic hepatitis C and therapy responses we investigated 125 chronic patients and 345 controls. Additionally, 48 ancestry markers were genotyped to control for population stratification. The frequency of the KIR2DL2 and KIR2DL2+HLA-C^Asp80 gene and ligand was higher in chronic infected patients than in controls (p < 0.0009, OR = 3.4; p = 0.001, OR = 3.45). In fact, KIR2DL3 is a weaker inhibitor of NK activity than KIR2DL2, which could explain the association of KIR2DL2 with chronic infection. Moreover, KIR2DS2 and KIR2DS2+HLA-C^Asp80 (p < 0.0001, OR = 2.51; p = 0.0084, OR = 2.62) and KIR2DS3 (p < 0.0001; OR = 2.57) were associated with chronic infection, independently from KIR2DL2. No differences in ancestry composition were observed between control and patients, even with respect to therapy response groups. The allelic profile KIR2DL2/KIR2DS2/KIR2DS3 was associated with the chronic hepatitis C (p < 0.0001; OR = 3). Furthermore, the patients also showed a higher mean number of activating genes and a lower frequency of the homozygous AA profile, which is likely secondary to the association with non-AA and/or activating genes. In addition, the KIR2DS5 allele was associated with SVR (p = 0.0261; OR = 0.184).The ancestry analysis of samples ruled out any effects of population substructuring and did not evidence interethnic differences in therapy response, as suggested in previous studies.     

Functional polymorphism of the KIR3DL1/S1 receptor on human NK cells

NK cells express both inhibitory and activatory receptors that allow them to recognize target cells through HLA class I Ag expression. KIR3DL1 is a receptor that recognizes the HLA-Bw4 public epitope of HLA-B alleles. We demonstrate that polymorphism within the KIR3DL1 receptor has functional consequences in terms of NK cell recognition of target. Inhibitory alleles of KIR3DL1 differ in their ability to recognize HLA-Bw4 ligand, and a consistent hierarchy of ligand reactivity can be defined. KIR3DS1, which segregates as an allele of KIR3DL1, has a short cytoplasmic tail characteristic of activatory receptors. Because it is very similar to KIR3DL1 in the extracellular domains, it has been assumed that KIR3DS1 will recognize a HLA-Bw4 ligand. In this study, we demonstrate that KIR3DS1 is expressed as a protein at the cell surface of NK cells, where it is recognized by the Z27 Ab. Using this Ab, we found that KIR3DS1 is expressed on a higher percentage of NK cells in KIR3DS1 homozygous compared with heterozygous donors. In contrast to the inhibitory KIR3DL1 allotypes, KIR3DS1 did not recognize HLA-Bw4 on EBV-transformed cell lines.     

Copy number variation of KIR genes influences HIV-1 control

A genome-wide screen for large structural variants showed that a copy number variant (CNV) in the region encoding killer cell immunoglobulin-like receptors (KIR) associates with HIV-1 control as measured by plasma viral load at set point in individuals of European ancestry. This CNV encompasses the KIR3DL1-KIR3DS1 locus, encoding receptors that interact with specific HLA-Bw4 molecules to regulate the activation of lymphocyte subsets including natural killer (NK) cells. We quantified the number of copies of KIR3DS1 and KIR3DL1 in a large HIV-1 positive cohort, and showed that an increase in KIR3DS1 count associates with a lower viral set point if its putative ligand is present (p = 0.00028), as does an increase in KIR3DL1 count in the presence of KIR3DS1 and appropriate ligands for both receptors (p = 0.0015). We further provide functional data that demonstrate that NK cells from individuals with multiple copies of KIR3DL1, in the presence of KIR3DS1 and the appropriate ligands, inhibit HIV-1 replication more robustly, and associated with a significant expansion in the frequency of KIR3DS1+, but not KIR3DL1+, NK cells in their peripheral blood. Our results suggest that the relative amounts of these activating and inhibitory KIR play a role in regulating the peripheral expansion of highly antiviral KIR3DS1+ NK cells, which may determine differences in HIV-1 control following infection.     

KIR,HLA, and IL28B Variant Predict Response to Antiviral Therapy in Genotype 1 Chronic Hepatitis C Patients in Japan

Natural killer cell responses play a crucial role in virus clearance by the innate immune system. Although the killer immunoglobulin-like receptor (KIR) in combination with its cognate human leukocyte antigen (HLA) ligand, especially KIR2DL3-HLA-C1, is associated with both treatment-induced and spontaneous clearance of hepatitis C virus (HCV) infection in Caucasians, these innate immunity genes have not been fully clarified in Japanese patients. We therefore investigated 16 KIR genotypes along with HLA-B and -C ligands and a genetic variant of interleukin (IL) 28B (rs8099917) in 115 chronic hepatitis C genotype 1 patients who underwent pegylated-interferon-α2b (PEG-IFN) and ribavirin therapy. HLA-Bw4 was significantly associated with a sustained virological response (SVR) to treatment (P = 0.017; odds ratio [OR] = 2.50, ), as was the centromeric A/A haplotype of KIR (P = 0.015; OR 3.37). In contrast, SVR rates were significantly decreased in patients with KIR2DL2 or KIR2DS2 (P = 0.015; OR = 0.30, and P = 0.025; OR = 0.32, respectively). Multivariate logistic regression analysis subsequently identified the IL28B TT genotype (P = 0.00009; OR = 6.87, 95% confidence interval [CI] = 2.62 - 18.01), KIR2DL2/HLA-C1 (P = 0.014; OR = 0.24, 95% CI = 0.08 - 0.75), KIR3DL1/HLA-Bw4 (P = 0.008, OR = 3.32, 95% CI = 1.37 - 8.05), and white blood cell count at baseline (P = 0.009; OR = 3.32, 95% CI = 1.35 - 8.16) as independent predictive factors of an SVR. We observed a significant association between the combination of IL28B TT genotype and KIR3DL1-HLA-Bw4 in responders (P = 0.0019), whereas IL28B TT along with KIR2DL2-HLA-C1 was related to a non-response (P = 0.0067). In conclusion, combinations of KIR3DL1/HLA-Bw4, KIR2DL2/HLA-C1, and a genetic variant of the IL28B gene are predictive of the response to PEG-IFN and ribavirin therapy in Japanese patients infected with genotype 1b HCV.     

Increased activating killer immunoglobulin-like receptor genes and decreased specific HLA-C alleles in couples with recurrent spontaneous abortion

Accumulating evidence indicates natural killer (NK) cells play crucial roles in successful pregnancy. To investigate whether the killer cell immunoglobulin-like receptor (KIR) gene polymorphism and the corresponding specific HLA ligands in parent couples possessing a susceptibility to unexplained recurrent spontaneous abortion (RSA), we searched 73 pairs of childless couples with three or more abortions characterized as unexplained RSA and 68 pairs of healthy control couples. Peripheral blood was drawn to obtain genomic DNA which was used for a polymerase chain reaction using sequence-specific primers (PCR-SSP) in order to determine whether 15 selected KIR genes and two groups of HLA-C alleles were present. Our result showed that gene frequency of KIR2DS1 was higher in patients with RSA compared to that of control subjects (P =0.029). Increased numbers of activating KIR genes was observed in patients (P =0.041). Women who possessed more than two activating KIR genes were found more frequently in patients than those in control subjects (P =0.018). From a cohort of husband and wife couples, the women with a KIR2DS1 gene, and with a decreased group 2 HLA-C allele for the homologous inhibitory receptor KIR2DL1, had a tendency to fall into the RSA group (P =0.004). The results suggest that a genetic variation at the KIR locus influences the susceptibility to unexplained RSA in the Chinese Han population. Moreover, decreased ligands for inhibitory KIRs could potentially lower the threshold for NK cell activation, mediated through activating receptors, thereby contributing to pathogenesis of RSA.     

Genotypic diversity of the Killer Cell Immunoglobulin-like Receptors (KIR) and their HLA class I Ligands in a Saudi population

Killer Cell Immunoglobulin-like Receptors (KIR) have been used as good markers for the study of genetic predisposition in many diseases and in human genetic population dynamics. In this context, we have investigated the genetic diversity of KIR genes and their main HLA class I ligands in Saudi population and compared the data with other studies of neighboring populations. One hundred and fourteen randomly selected healthy Saudi subjects were genotyped for the presence or absence of 16 KIR genes and their HLA-C1, -C2, -Bw4^Thr80 and Bw4^Ile80 groups, using a PCR-SSP technique. The results show the occurrence of the framework genes (3DL2, 3DL3 and 2DL4) and the pseudogenes (2DP1 and 3DP1) at highest frequencies. All inhibitory KIR (iKIR) genes appeared at higher frequencies than activating genes (aKIR), except for 2DS4 with a frequency of 90.35%. A total of 55 different genotypes were observed appearing at different frequencies, where 12 are considered novel. Two haplotypes were characterized, AA and Bx (BB and AB), which were observed in 24.5% and 75.5% respectively of the studied group. The frequencies of iKIR + HLA associations were found to be much higher than aKIR + HLA. KIR genes frequencies in the Saudi population are comparable with other Middle Eastern and North African populations.     

Killer Cell Immunoglobulin-like Receptors and Their HLA Ligands are Related with the Immunopathology of Chagas Disease

The aim of this study was to investigate the influence of killer cell immunoglobulin-like receptor (KIR) genes and their human leucocyte antigen (HLA) ligands in the susceptibility of chronic Chagas disease. This case-control study enrolled 131 serologically-diagnosed Chagas disease patients (59 men and 72 women, mean age of 60.4 ± 9.8 years) treated at the University Hospital of Londrina and the Chagas Disease Laboratory of the State University of Maringa. A control group was formed of 165 healthy individuals - spouses of patients or blood donors from the Regional Blood Bank in Maringa (84 men and 81 women, with a mean age of 59.0 ± 11.4 years). Genotyping of HLA and KIR was performed by PCR-SSOP. KIR2DS2-C1 in the absence of KIR2DL2 (KIR2DS2⁺/2DL2^-/C1⁺) was more frequent in Chagas patients (P = 0.020; Pc = 0.040; OR = 2.14) and, in particular, those who manifested chronic chagasic cardiopathy—CCC (P = 0.0002; Pc = 0.0004; OR = 6.64; 95% CI = 2.30–18.60) when compared to the control group, and when CCC group was compared to the patients without heart involvement (P = 0.010; Pc = 0.020; OR = 3.97). The combination pair KIR2DS2⁺/2DL2^-/KIR2DL3⁺/C1⁺ was also positively associated with chronic chagasic cardiopathy. KIR2DL2 and KIR2DS2 were related to immunopathogenesis in Chagas disease. The combination of KIR2DS2 activating receptor with C1 ligand, in the absence of KIR2DL2, may be related to a risk factor in the chronic Chagas disease and chronic chagasic cardiopathy.     

Common HIV-1 peptide variants mediate differential binding of KIR3DL1 to HLA-Bw4 molecules

Epidemiological studies have shown the protective effect of KIR3DL1/HLA-Bw4 genotypes in human immunodeficiency virus type 1 (HIV-1) infection; however, the functional correlates for the protective effect remain unknown. We investigated whether human leukocyte antigen (HLA)-Bw4-presented HIV-1 peptides could affect the interaction between the inhibitory natural killer (NK) cell receptor KIR3DL1 and its ligand HLA-Bw4. Distinct HIV-1 epitopes differentially modulated the binding of KIR3DL1 to HLA-Bw4. Furthermore, cytotoxic T lymphocyte (CTL) escape mutations within the immunodominant HLA-B57 (Bw4)-restricted Gag epitope TSTLQEQIGW abrogated KIR3DL1 binding to HLA-B57, suggesting that sensing of CTL escape variants by NK cells can contribute to the protective effect of the KIR3DL1/HLA-Bw4 compound genotype.     

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.