Association of KIR2DL2 polymorphism rs2756923 with type 1 diabetes and preliminary evidence for lack of inhibition through HLA-C1 ligand binding

Significance of KIR like natural killer cell receptors in autoimmune disorders

Killer cell immunoglobulin-like receptors (KIRs), act as the regulators for the cytolytic activity of natural killer and certain T cells by interacting with the HLA class I ligands. KIRs have been shown to contribute to the pathogenesis of several autoimmune diseases. However, their specific roles are still not very clear. Autoimmune diseases are multifactorial in nature, highlighting the influence of both genetic and environmental factors. The innate immune response plays an important role in autoimmunity as it alters the self-glycans that mimic molecular patterns found on different intracellular pathogens. Natural killer (NK) cells have an important position in the innate immune response. NK cell receptors are encoded by the leukocyte receptor complex located on the chromosome 19q13.4 and lectin-like receptors on chromosome 12p13. This review focuses on the role of KIRs and their relationship with different autoimmune diseases.

Killer Cell Immunoglobulin-Like Receptor (KIR) Genotype Distribution in Familial Mediterranean Fever (FMF) Patients

BACKGROUND Familial Mediterranean fever (FMF) is an autosomal recessive autoinflammatory disease predominantly affecting Mediterranean populations. The gene associated with FMF is the MEFV gene, which encodes for a protein called pyrin. Mutations of pyrin lead to uncontrolled attacks of inflammation, and subclinical inflammation continues during attack-free intervals. Killer cell immunoglobulin-like receptor (KIR) genes encode HLA class I receptors expressed by NK cells. The aim this study was to look for immunogenetic determinants in the pathogenesis of FMF and find out if KIR are related to susceptibility to disease or complications like renal amyloidosis. MATERIAL AND METHODS One hundred and five patients with FMF and 100 healthy individuals were involved in the study. Isolated DNA from peripheral blood was amplified by sequence specific PCR probes and analyzed by Luminex for KIR genotypes. Fisher Exact test was used to evaluate the variation of KIR gene distribution. RESULTS All patients and healthy controls expressed the framework genes. An activator KIR gene, KIR2DS2, was significantly more frequent in FMF patients (p=0.036). Renal amyloidosis and presence of arthritis were not associated with KIR genes and genotype. KIR3DL1 gene was more common in patients with high serum CRP (p=0.016). CONCLUSIONS According to our findings, we suggest that presence of KIR2DS2, which is an activator gene for NK cell functions, might be related to the autoinflammation in FMF. The potential effect of KIR genes on amyloidosis and other clinical features requires studies with larger sample sizes.

Immunogenetics of type 1 diabetes: A comprehensive review

Type 1 diabetes (T1D) results from the autoimmune destruction of insulin-producing beta cells in the pancreas. Prevention of T1D will require the ability to detect and modulate the autoimmune process before the clinical onset of disease. Genetic screening is a logical first step in identification of future patients to test prevention strategies. Susceptibility to T1D includes a strong genetic component, with the strongest risk attributable to genes that encode the classical Human Leukocyte Antigens (HLA). Other genetic loci, both immune and non-immune genes, contribute to T1D risk; however, the results of decades of small and large genetic linkage and association studies show clearly that the HLA genes confer the most disease risk and protection and can be used as part of a prediction strategy for T1D. Current predictive genetic models, based on HLA and other susceptibility loci, are effective in identifying the highest-risk individuals in populations of European descent. These models generally include screening for the HLA haplotypes "DR3" and "DR4." However, genetic variation among racial and ethnic groups reduces the predictive value of current models that are based on low resolution HLA genotyping. Not all DR3 and DR4 haplotypes are high T1D risk; some versions, rare in Europeans but high frequency in other populations, are even T1D protective. More information is needed to create predictive models for non-European populations. Comparative studies among different populations are needed to complete the knowledge base for the genetics of T1D risk to enable the eventual development of screening and intervention strategies applicable to all individuals, tailored to their individual genetic background. This review summarizes the current understanding of the genetic basis of T1D susceptibility, focusing on genes of the immune system, with particular emphasis on the HLA genes.

High prevalence of HHV8 infection and specific killer cell immunoglobulin-like receptors allotypes in Sardinian patients with type 2 diabetes mellitus

The development of type 2 diabetes is thought to involve both environmental, possibly infectious, and genetic factors. Recently, a high prevalence of human herpesvirus 8 (HHV8) infection was observed in type 2 diabetes patients, and specific killer cell immunoglobulin-like receptors (KIR) allotypes were associated to both increased susceptibility to herpesvirus infection and risk to develop diabetes. However, no clear gene-disease or virus-disease associations have been established. To investigate the possible interplay between HHV8 infection, KIR allotype and type 2 diabetes, virus prevalence and KIR genotype were analyzed by PCR in 168 patients affected by type 2 diabetes and 108 control individuals belonging to the Sardinian population. Results showed a significant increase of HHV8 prevalence in type 2 diabetes patients versus controls (57% vs. 17%, P < 0.001), and a significant increase of KIR2DL2/DS2 homozygosity in diabetes patients infected with HHV8 compared to uninfected ones (64% vs. 14%, P < 0.0001), resulting in a significant OR of 11.31. In addition, the analysis of the frequency of the KIR2DL2/DS2 receptor and its HLA-C1 ligand, accordingly to the status of HHV8 infection, showed a significant increased correlation between KIR2DL2/DS2, type 2 diabetes and HLA-C1C1 genotype in the type 2 diabetes patients infected with HHV8 compared to uninfected ones (62% vs. 15%, P < 0.0001, OR = 8.64). These findings provide preliminary evidence that HHV8 infection might be a cofactor for type 2 diabetes in a specific subset of genetically susceptible individuals, and suggest the possibility that such patients might have an impaired immune-mediated component contributing to the development of type 2 diabetes.

Killer Immunoglobulin-like Receptors (KIR) haplogroups A and B track with Natural Killer Cells and Cytokine Profile in Aged Subjects: Observations from Octo/Nonagenarians in the Belfast Elderly Longitudinal Free-living Aging STudy (BELFAST)

BACKGROUND

Natural Killer Cells (NK) play an important role in detection and elimination of virus-infected, damaged or cancer cells. NK cell function is guided by expression of Killer Immunoglobulin-like Receptors (KIRs) and contributed to by the cytokine milieu. KIR molecules are grouped on NK cells into stimulatory and inhibitory KIR haplotypes A and B, through which NKs sense and tolerate HLA self-antigens or up-regulate the NK-cytotoxic response to cells with altered HLA self-antigens, damaged by viruses or tumours. We have previously described increased numbers of NK and NK-related subsets in association with sIL-2R cytokine serum levels in BELFAST octo/nonagenarians. We hypothesised that changes in KIR A and B haplotype gene frequencies could explain the increased cytokine profiles and NK compartments previously described in Belfast Elderly Longitudinal Free-living Aging STudy (BELFAST) octo/nonagenarians, who show evidence of ageing well.

RESULTS

In the BELFAST study, 24% of octo/nonagenarians carried the KIR A haplotype and 76% KIR B haplotype with no differences for KIR A haplogroup frequency between male or female subjects (23% v 24%; p=0.88) or for KIR B haplogroup (77% v 76%; p=0.99). Octo/nonagenarian KIR A haplotype carriers showed increased NK numbers and percentage compared to Group B KIR subjects (p=0.003; p=0.016 respectively). There were no KIR A/ B haplogroup-associated changes for related CD57+CD8 (high or low) subsets. Using logistic regression, KIR B carriers were predicted to have higher IL-12 cytokine levels compared to KIR A carriers by about 3% (OR 1.03, confidence limits CI 0.99-1.09; p=0.027) and 14% higher levels for TGF-β (active), a cytokine with an anti-inflammatory role, (OR 1.14, confidence limits CI 0.99-1.09; p=0.002).

CONCLUSION

In this observational study, BELFAST octo/nonagenarians carrying KIR A haplotype showed higher NK cell numbers and percentage compared to KIR B carriers. Conversely, KIR B haplotype carriers, with genes encoding for activating KIRs, showed a tendency for higher serum pro-inflammatory cytokines compared to KIR A carriers. While the findings in this study should be considered exploratory they may serve to stimulate debate about the immune signatures of those who appear to age slowly and who represent a model for good quality survivor-hood.

Regulatory T cells control NK cells in an insulitic lesion by depriving them of IL-2

Pancreatic T reg cells control the availability of CD4⁺ T cell–secreted IL-2 to limit NK cell function.

Regulatory T (T reg) cells control progression to autoimmune diabetes in the BDC2.5/NOD mouse model by reining in natural killer (NK) cells that infiltrate the pancreatic islets, inhibiting both their proliferation and production of diabetogenic interferon-γ. In this study, we have explored the molecular mechanisms underlying this NK–T reg cell axis, following leads from a kinetic exploration of gene expression changes early after punctual perturbation of T reg cells in BDC2.5/NOD mice. Results from gene signature analyses, quantification of STAT5 phosphorylation levels, cytokine neutralization experiments, cytokine supplementation studies, and evaluations of intracellular cytokine levels collectively argue for a scenario in which T reg cells regulate NK cell functions by controlling the bioavailability of limiting amounts of IL-2 in the islets, generated mainly by infiltrating CD4⁺ T cells. This scenario represents a previously unappreciated intertwining of the innate and adaptive immune systems: CD4⁺ T cells priming NK cells to provoke a destructive T effector cell response. Our findings highlight the need to consider potential effects on NK cells when designing therapeutic strategies based on manipulation of IL-2 levels or targets.

Diverse functionality among human NK cell receptors for the C1 epitope of HLA-C: KIR2DS2, KIR2DL2, and KIR2DL3

Interactions between killer immunoglobulin-like receptors (KIRs) and their HLA-A, -B, and -C ligands diversify the functions of human natural killer cells. Consequently, combinations of KIR and HLA genotypes affect resistance to infection and autoimmunity, success of reproduction and outcome of hematopoietic cell transplantation. HLA-C, with its C1 and C2 epitopes, evolved in hominids to be specialized KIR ligands. The system’s foundation was the C1 epitope, with C2 a later addition, by several million years. The human inhibitory receptor for C1 is encoded by KIR2DL2/3, a gene having two divergent allelic lineages: KIR2DL2 is a B KIR haplotype component and KIR2DL3 an A KIR haplotype component. Although KIR2DL2 and KIR2DL3 exhibit quantitative differences in specificity and avidity for HLA-C, they qualitatively differ in their genetics, functional effect, and clinical influence. This is due to linkage disequilibrium between KIR2DL2 and KIR2DS2, a closely related activating receptor that was selected for lost recognition of HLA-C.

Killer-cell immunoglobulin-like receptor genotyping and HLA killer-cell immunoglobulin-like receptor-ligand identification by real-time polymerase chain reaction

The effector function of natural killer (NK) cells is modulated by surface expression of a range of killer-cell immunoglobulin-like receptors (KIRs) that interact with human leukocyte antigen (HLA) class I ligands. We describe the use of real-time polymerase chain reaction (PCR) assays that allow easy and quick detection of 16 KIR genes and the presence/absence of KIR-ligands based on allelic discrimination at codon 80 in the HLA-A/B Bw4 and HLA-C C1/C2 genes. These methods overcome the tedious and expensive nature of conventional KIR genotyping and HLA class I typing using sequence-specific primer (SSP) PCR, sequence-specific oligonucleotide (SSO) hybridization or sequence-based typing (SBT). Using these two cost-effective assays, we measured the frequencies of KIRs, KIR-ligands and KIR/KIR-ligand pairs in a cohort of Black women recruited in South Africa.

An increased frequency of NK cell receptor and HLA-C group 1 combinations in early-onset type 1 diabetes

AIMS/HYPOTHESIS

Natural killer (NK) cells serve as primary immune surveillance and are partially regulated by combinations of killer immunoglobulin-like receptor (KIR) genes and their HLA class I ligands. Alterations in NK cell activity have been associated with type 1 diabetes. The aim of this study was to determine whether KIR-HLA class I gene frequency: (1) is altered in a current population with type 1 diabetes compared with healthy controls; and (2) has changed over the half century in which the incidence of type 1 diabetes has increased rapidly.

METHODS

KIR-HLA class I gene frequencies were compared in 551 individuals diagnosed with type 1 diabetes ≤ 15 years of age (394 in a current cohort and 157 from the historical 'Golden Years' cohort) and 168 healthy controls. The overall balance of activation and inhibition was analysed using KIR-HLA genotype models.

RESULTS

Children with type 1 diabetes who were positive for KIR2DS2/KIR2DL2 and KIR2DL3 were more often homozygous for HLA-C group 1 and this effect was strongest in children diagnosed with diabetes before the age of 5 years (p = 0.003, corrected p [p (corr)] = 0.012) and (p = 0.001, p (corr) = 0.004), respectively. Children with type 1 diabetes have fewer inhibitory KIRs with their corresponding ligands compared with healthy controls (p = 1.9 × 10(-4)). This pattern of NK activation has not changed significantly in individuals with type 1 diabetes over the last half century.

CONCLUSIONS/INTERPRETATION

Activating combinations of KIR-HLA genes are more frequent in young children with type 1 diabetes diagnosed in the first 5 years of life, suggesting that NK cell responses may be altered in this group.