Analysis of killer immunoglobulin-like receptor genes in ankylosing spondylitis

Functional genomics implicates natural killer cells in the pathogenesis of ankylosing spondylitis

Objective

Multiple lines of evidence indicate that ankylosing spondylitis (AS) is a lymphocyte-driven disease. However, which lymphocyte populations are critical in AS pathogenesis is not known. In this study, we aimed to identify the key cell types mediating the genetic risk in AS using an unbiased functional genomics approach.

Methods

We integrated genome-wide association study (GWAS) data with epigenomic and transcriptomic datasets of human immune cells. To quantify enrichment of cell type-specific open chromatin or gene expression in AS risk loci, we used three published methods that have successfully identified relevant cell types in other diseases. We performed co-localization analyses between GWAS risk loci and genetic variants associated with gene expression (eQTL) to find putative target genes.

Results

Natural killer (NK) cell-specific open chromatin regions are significantly enriched in heritability for AS, compared to other immune cell types such as T cells, B cells, and monocytes. This finding was consistent between two AS GWAS. Using RNA-seq data, we validated that genes in AS risk loci are enriched in NK cell-specific gene expression. Using the human Space-Time Gut Cell Atlas, we also found significant upregulation of AS-associated genes predominantly in NK cells. Co-localization analysis revealed four AS risk loci affecting regulation of candidate target genes in NK cells: two known loci, ERAP1 and TNFRSF1A, and two under-studied loci, ENTR1 (aka SDCCAG3) and B3GNT2.

Conclusion

Our findings suggest that NK cells may play a crucial role in AS development and highlight four putative target genes for functional follow-up in NK cells.

The Role of Natural Killer Cells in Autoimmune Diseases

Natural killer (NK) cells, the large granular lymphocytes differentiated from the common lymphoid progenitors, were discovered in early 1970’s. They are members of innate immunity and were initially defined by their strong cytotoxicity against virus-infected cells and by their important effector functions in anti-tumoral immune responses. Nowadays, NK cells are classified among the recently discovered innate lymphoid cell subsets and have capacity to influence both innate and adaptive immune responses. Therefore, they can be considered as innate immune cells that stands between the innate and adaptive arms of immunity. NK cells don’t express T or B cell receptors and are recognized by absence of CD3. There are two major subgroups of NK cells according to their differential expression of CD16 and CD56. While CD16⁺CD56^dim subset is best-known by their cytotoxic functions, CD16^-CD56^bright NK cell subset produces a bunch of cytokines comparable to CD4⁺ T helper cell subsets. Another subset of NK cells with production of interleukin (IL)-10 was named as NK regulatory cells, which has suppressive properties and could take part in immune-regulatory responses. Activation of NK cells is determined by a delicate balance of cell-surface receptors that have either activating or inhibitory properties. On the other hand, a variety of cytokines including IL-2, IL-12, IL-15, and IL-18 influence NK cell activity. NK-derived cytokines and their cytotoxic functions through induction of apoptosis take part in regulation of the immune responses and could contribute to the pathogenesis of many immune mediated diseases including ankylosing spondylitis, Behçet’s disease, multiple sclerosis, rheumatoid arthritis, psoriasis, systemic lupus erythematosus and type-1 diabetes. Dysregulation of NK cells in autoimmune disorders may occur through multiple mechanisms. Thanks to the rapid developments in biotechnology, progressive research in immunology enables better characterization of cells and their delicate roles in the complex network of immunity. As NK cells stand in between innate and adaptive arms of immunity and “bridge” them, their contribution in inflammation and immune regulation deserves intense investigations. Better understanding of NK-cell biology and their contribution in both exacerbation and regulation of inflammatory disorders is a requisite for possible utilization of these multi-faceted cells in novel therapeutic interventions.

The Genetics of Spondyloarthritis

The term spondyloarthritis (SpA) encompasses a group of chronic inflammatory diseases with common features in terms of clinical presentation and genetic predisposition. SpA is characterized by inflammation of the spine and peripheral joints, and is also be associated with extra-articular inflammatory manifestations such as psoriasis, uveitis, or inflammatory bowel disease (IBD). The etiology of SpA is not completely understood, but it is known to have a strong genetic component dominated by the human leukocyte antigen (HLA)-B27. In the last few years, our understanding of genetic susceptibility to SpA, particularly ankylosing spondylitis (AS), has greatly improved thanks to the findings derived from powered genome-wide association studies (GWAS) based on single nucleotide polymorphism (SNP) arrays. These studies have identified many candidate genes, therefore providing new potential directions in the exploration of disease mechanisms, especially with regard to the key role of the immune system in the pathogenesis of SpA. SpA is a complex disease where genetic variability, environmental factors, and random events interact to trigger pathological pathways. The aim of this review is to summarize current findings on the genetics of SpA, some of which might help to study new treatment approaches.

Epistatic interactions between killer immunoglobulin-like receptors and human leukocyte antigen ligands are associated with ankylosing spondylitis

The killer immunoglobulin-like receptors (KIRs), found predominantly on the surface of natural killer (NK) cells and some T-cells, are a collection of highly polymorphic activating and inhibitory receptors with variable specificity for class I human leukocyte antigen (HLA) ligands. Fifteen KIR genes are inherited in haplotypes of diverse gene content across the human population, and the repertoire of independently inherited KIR and HLA alleles is known to alter risk for immune-mediated and infectious disease by shifting the threshold of lymphocyte activation. We have conducted the largest disease-association study of KIR-HLA epistasis to date, enabled by the imputation of KIR gene and HLA allele dosages from genotype data for 12,214 healthy controls and 8,107 individuals with the HLA-B*27-associated immune-mediated arthritis, ankylosing spondylitis (AS). We identified epistatic interactions between KIR genes and their ligands (at both HLA subtype and allele resolution) that increase risk of disease, replicating analyses in a semi-independent cohort of 3,497 cases and 14,844 controls. We further confirmed that the strong AS-association with a pathogenic variant in the endoplasmic reticulum aminopeptidase gene ERAP1, known to alter the HLA-B*27 presented peptidome, is not modified by carriage of the canonical HLA-B receptor KIR3DL1/S1. Overall, our data suggests that AS risk is modified by the complement of KIRs and HLA ligands inherited, beyond the influence of HLA-B*27 alone, which collectively alter the proinflammatory capacity of KIR-expressing lymphocytes to contribute to disease immunopathogenesis.

Cells of the immune system utilise various cell-surface receptors to differentiate between healthy and infected or malignant cells, enabling targeted inflammatory responses while minimising damage to self-tissue. In instances where the immune system fails to correctly differentiate healthy from diseased tissue, or inflammatory activity is poorly regulated, autoimmune or autoinflammatory conditions can develop. Here we have investigated a possible role for a class of immune-cell activating and inhibitory receptors in the pathogenesis of ankylosing spondylitis (AS), a common but poorly understood inflammatory arthritis in which the immune system causes severe damage to the joints of the pelvis and spine. Using genetic information from 12,214 healthy controls and 8,107 individuals with AS we were able to identify combinations of independently inherited immune cell receptors and their ligands that increase or decrease an individual’s risk of disease. This research provides new insight into the nature of co-inherited genetic factors that may collectively alter the proinflammatory capacity of immune cells, contributing to the immunopathogenesis of immune-mediated diseases.

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.

Association study between killer immunoglobulin-like receptor polymorphisms and ankylosing spondylitis disease: An updated meta-analysis

BACKGROUND

Several genetic studies have assessed the association between polymorphisms in killer immunoglobulin-like receptors (KIR) genes and susceptibility of individuals to ankylosing spondylitis (AS), but the findings have been inconclusive and incongruous. Therefore, we conducted this meta-analysis of all case-control studies meeting the inclusion criteria for obtaining an exact conclusion of the effect of KIR polymorphisms on the risk of AS.

METHODS

A systematic literature search was conducted in electronic databases, including Scopus web of science, ScienceDirect, and PubMed to find all eligible studies exploring the association between KIR polymorphisms and the risk of AS, prior to June 2017. Pooled odds ratios (OR) and their corresponding 95% CIs were used to evaluate the strength of the association between KIR polymorphisms and the risk of AS.

RESULTS

A total of 16 case-control studies, encompassed in 12 papers, with 1770 cases and 2907 healthy subjects were included in the meta-analysis. This meta-analysis revealed three significant positive associations of 2DS1, 2DS5, and 3DS1 with susceptibility to AS, while two significant negative associations of 2DL2 and 2DS2 with susceptibility to AS were identified. In the subgroup analysis based on human leukocyte antigen (HLA)-B*27 positive patients and healthy subjects, results indicated that there were four significant positive associations between 2DL5, 2DS4, 2DS5, 3DS1 polymorphisms and susceptibility to AS in HLA-B*27-positive patients; a significant negative association of 3DL1 in HLA-B*27-positive patients was found.

CONCLUSIONS

While 2DS1, 2DS5, and 3DS1 polymorphisms increased AS risk, 2DL2 and 2DS2 polymorphisms were associated with reduced AS susceptibility.

Expression analysis of HLA-E and NKG2A and NKG2C receptors points at a role for natural killer function in ankylosing spondylitis

Background

Ankylosing spondylitis (AS) is a complex chronic inflammatory disease strongly associated with the majority of human leucocyte antigen (HLA)-B27 alleles. HLA-E molecules are non-classical major histocompatibility complex (MHC) class I molecules that specifically interact with the natural killer receptors NKG2A (inhibitory) and NKG2C (activating), and have been recently proposed to be involved in AS pathogenesis.''.

Objective

To analyse the expression of HLA-E and the CD94/NKG2 pair of receptors in HLA-B27-positive patients with AS and healthy controls (HC) bearing the AS-associated B*2705 and the non-AS-associated B*2709 alleles.

Methods

The level of surface expression of HLA-E molecules on CD14+ peripheral blood mononuclear cell was evaluated in 21 HLA-B*2705 patients with AS, 12 HLA-B*2705 HC, 12 HLA-B*2709 HC and 6 HLA-B27-negative HC using the monoclonal antibody MEM-E/08 by quantitative cytofluorimetric analysis. The percentage and density of expression of HLA-E ligands NKG2A and NKG2C were also measured on CD3-CD56+ NK cells.

Results

HLA-E expression in CD14+ cells was significantly higher in patients with AS (587.0, IQR 424-830) compared with B*2705 HC (389, IQR 251.3-440.5; p=0.0007), B*2709 HC (294.5, IQR 209.5-422; p=0.0004) and HLA-B27-negative HC (380, IQR 197.3-515.0; p=0.01). A higher number of NK cells expressing NKG2A compared with NKG2C were found in all cohorts analysed, as well as a higher cell surface density.

Conclusion

The higher surface level of HLA-E molecules in patients with AS compared with HC, concurrently with a prevalent expression of NKG2A, suggests that the crosstalk between these two molecules might play a role in AS pathogenesis, accounting for the previously reported association between HLA-E and AS.

Human Leukocyte Antigen C*12:02:02 and Killer Immunoglobulin-Like Receptor 2DL5 are Distinctly Associated with Ankylosing Spondylitis in the Taiwanese

Human leukocyte antigen (HLA) class I ligands and Killer immunoglobulin-like receptors (KIRs) regulate the cytolytic activity of natural killer (NK) cells and certain T cells. We examined their genetic predisposition to disease susceptibility and clinical phenotypes in Taiwanese ankylosing spondylitis (AS) patients. KIR genotyping and Human Leucocyte Antigen C (HLA-C) sequencing were performed in 653 Taiwanese AS patients and 952 healthy controls. KIR genotype distributions and HLA-C allele frequencies were compared in patients and controls and among patients with and without HLA-B27 positivity, early age onset and spinal syndesmophytes. HLA-C alleles were functionally characterized using 3D structural modelling with peptide simulation. This study discovered that the HLA-C*12:02:02 allele (43.42% vs. 3.31%; p < 0.00001 odds ratio (OR), 16.88; 95% confidence intervals (CI): 11.27-25.28) confers a strong risk for Taiwanese AS development. The 3D modelling results identified four unique amino acid polymorphisms, Ala73, Trp156, Arg219 and Met304, that may affect the function of the HLA-C*12:02:02 allele. KIR2DL5 (p = 0.0047; pFDR = 0.0423) and the KIR Bx haplotype (p = 0.0000275) were protective against Taiwanese AS, while KIR 2DS4/1D (22 base pair truncated deletion; p = 0.0044; pFDR = 0.1998) appeared to be a risk factor for it. KIR2DL5 combined with the HLA-C1/C2 heterozygous genotype showed a protective effect (AS 5.97% vs. normal 11.66%; p = 0.002; pFDR = 0.0127, OR, 0.48 95% CI: 0.33-0.70); in contrast, KIR 2DS4/1D combined with the HLA-C1C1 homozygous genotype (AS 45.33% vs. normal 35.92%; p = 0.002; pFDR = 0.0127, OR, 1.48 95% CI: 1.21-1.81) represented a risk factor for AS development. Our data suggested that interactions between KIRs and their cognate HLA-C ligands may contribute to the pathogenesis of AS.

Genetics and the Causes of Ankylosing Spondylitis

Ankylosing spondylitis (AS) is a common inflammatory arthritis in which genetic factors are the primary determinants of disease risk and severity. Substantial progress has been made in identifying genetic pathways involved in the disease, and in translating those discoveries to drug discovery programs. Recently discovered novel disease pathways include those involved in control of DNA methylation, bacterial sensing, and mucosal immunity. Additional pathways are likely to be identified as a higher proportion of the genetic risk of AS is determined.

Evaluation of KIR3DL1/KIR3DS1 polymorphism in Behçet's disease

The Behçet's disease (BD)-associated human leukocyte antigen (HLA) allele, HLA-B*51 (B*51), encodes a ligand for a pair of allelic killer immunoglobulin-like receptors (KIR) present on cytotoxic cells-KIR3DL1, which inhibits their cytotoxicity, and KIR3DS1, which activates their cytotoxic activity. We tested whether KIR-regulated mechanisms contribute to BD by testing for association of KIR3DL1/KIR3DS1 genotypes with disease in 1799 BD patients and 1710 healthy controls from Turkey, as well as in different subsets of individuals with HLA-type-defined ligands for the KIR3D receptors. HLA types were imputed from single nucleotide polymorphism genotypes determined with the Immunochip. The presence of inhibitory KIR3DL1 or activating KIR3DS1 alleles did not differ significantly between cases and controls (KIR3DL1: 92.9% vs 93.4%, P_dominant=0.55; KIR3DS1: 42.7% vs 41.0%, P_dominant=0.29). The KIR3DL1/KIR3DS1 alleles were also present at similar frequencies among cases and controls bearing HLA-B with a Bw4 motif; HLA-B with a Bw4 motif with isoleucine at position 80; and HLA-B*51. Our results suggest that pathogenic mechanisms associated with HLA-B*51 do not primarily involve differential interactions with KIR3DL1 and KIR3DS1 receptors. However, due to the complexity of this locus (that is, sequence variation and copy number variation), we cannot exclude a role for other types of KIR variation in the pathogenesis of BD.

Overexpression of KIR inhibitory ligands (HLA-I) determines that immunosurveillance of myeloma depends on diverse and strong NK cell licensing

Missing self recognition makes cancer sensitive to natural killer cell (NKc) reactivity. However, this model disregards the NKc licensing effect, which highly increases NKc reactivity through interactions of inhibitory killer cell immunoglobulin-like receptors (iKIR) with their cognate HLA-I ligands. The influence of iKIR/HLA-ligand (HLA-C1/C2) licensing interactions on the susceptibility to and progression of plasma cell (PC) dyscrasias was evaluated in 164 Caucasian patients and 286 controls. Compared to controls, myeloma accumulates KIR2DL1^-L2⁺L3^- genotypes (2.8% vs. 13.2%, p < 0.01, OR = 5.29) and less diverse peripheral repertoires of NKc clones. Less diverse and weaker-affinity repertoires of iKIR2D/HLA-C licensing interactions increased myeloma susceptibility. Thus, the complete absence of conventional iKIR2D/HLA-C licensing interactions (KIR2DL1^-L2⁺L3^-/C2C2, 2.56% vs. 0.35%; p < 0.05; OR = 15.014), single-KIR2DL3⁺/C1⁺ (20.51% vs. 10.84%; p < 0.05; OR = 2.795) and single-KIR2DL2⁺/C1⁺ (12.82% vs. 4.9%; p < 0.01; OR = 5.18) interactions were over-represented in myeloma, compared to controls. Additionally, KIR2DL1^-L2⁺L3^- (20% vs. 83%, p < 0.00001) as well as KIR3DL1^- (23% vs. 82%, p < 0.00001) genotypes had a dramatic negative impact on the 3-y progression-free survival (PFS), particularly in patients with low-tumor burden. Remarkably, myeloma-PCs, compared to K562 and other hematological cancers, showed substantial over-expression of HLA-I ("increasing-self" instead of missing-self), including HLA-C, and mild expression of ligands for NKc activating receptors (aRec) CD112, CD155, ULBP-1 and MICA/B, which apparently renders myeloma-PCs susceptible to lysis mainly by licensed NKc. KIR2DL1^-L2⁺L3^-/C2C2 patients (with no conventional iKIR2D/HLA-C licensing interactions) lyse K562 but barely lyse myeloma-PCs (4% vs. 15%; p < 0.05, compared to controls). These results support a model where immunosurveillance of no-missing-self cancers, e.g., myeloma, mainly depends on NKc licensing.

Activating killer immunoglobulin-like receptors genes are associated with increased susceptibility to ankylosing spondylitis

The aim of this study was to analyse the association of specific killer cell immunoglobulin-like receptors (KIR) genes and haplotypes with susceptibility to ankylosing spondylitis (AS) and its different clinical manifestations in a Spanish population. The presence or absence of all KIR genes was studied for their association with AS. A total of 176 patients with AS and 435 healthy control subjects were selected for this study based on clinical criteria. The commercial KIR-sequence-specific oligonucleotides (SSO) typing kit was used to investigate KIR typing. Frequencies of KIR2DS1 and KIR3DS1 genes were increased significantly in patients compared with healthy controls [52·8 versus 38·2%, PBonf < 0·01, odds ratio (OR) = 1·81 (1·28-2·59); 51·7 versus 37·5%, PBonf < 0·01, OR = 1·79 (1·25-2·54)]. Moreover, the frequency of activating genotypes in the AS patient group was significantly higher than in the healthy control group (P < 0·05). KIR2DS1 and KIR3DS1, in addition to human leucocyte antigen (HLA)-B27, may play an important role in the pathogenesis of AS. However, we show that the contribution of the KIR genes to AS susceptibility extends beyond the association with individual KIRs, with an imbalance between activating and inhibitory KIR genes seeming to influence the susceptibility to AS.

Genetic variations in the KIR gene family may contribute to susceptibility to ankylosing spondylitis: a meta-analysis

The present meta-analysis of relevant case-control studies was conducted to investigate the possible relationships between genetic variations in the killer cell immunoglobulin-like receptor (KIR) gene clusters of the human KIR gene family and susceptibility to ankylosing spondylitis (AS). The following electronic databases were searched for relevant articles without language restrictions: the Web of Science, the Cochrane Library Database, PubMed, EMBASE, CINAHL, the Chinese Biomedical Database (CBM) and Chinese National Knowledge Infrastructure (CNKI) databases, covering all papers published until 2013. STATA statistical software was adopted in this meta-analysis as well. We also calculated the crude odds ratios (OR) and its 95% confidence intervals (95 % CI). Seven case-control studies with 1,004 patients diagnosed with AS and 2,138 healthy cases were implicated in our meta-analysis, and 15 genes in the KIR gene family were also evaluated. The results of our meta-analysis show statistical significance between the genetic variations in the KIR2DL1, KIR2DS4, KIR2DS5 and KIR3DS1 genes and an increased susceptibility to AS (KIR2DL1: OR 7.82, 95% CI 3.87-15.81, P< 0.001; KIR2DS4: OR 1.91, 95% CI 1.16-3.13, P = 0.010; KIR2DS5: OR1.51, 95% CI 1.14-2.01, P = 0.004; KIR3DS1: OR 1.58, 95% CI 1.34-1.86, P< 0.001; respectively). However, we failed to found positive correlations between other genes and susceptibility to AS (all P >0.05). The current meta-analysis provides reliable evidence that genetic variations in the KIR gene family may contribute to susceptibility to AS, especially for the KIR2DL1, KIR2DS4, KIR2DS5 and KIR3DS1 genes.

Association between KIR polymorphisms and ankylosing spondylitis in populations: a meta-analysis

OBJECTIVES

Published association studies of killer cell immunoglobulin-like receptors (KIRs) and ankylosing spondylitis (AS) in populations are inconsistent. The aim of this study is to determine whether the KIR polymorphisms confer susceptibility to AS in populations by conducting a meta-analysis.

METHODS

A computer search was carried out up to August 2013 for literature pertaining to AS and KIR polymorphisms. Publications addressing the association between the KIR polymorphisms and susceptibility to AS in populations were selected from the Pubmed, Elsevier Science Direct, China National Knowledge Infrastructure (CNKI) and Chinese Biomedical Literature Database (CBM) databases. The odds ratio (OR) with 95% confidence interval (95%CI) was calculated.

RESULTS

A total of 13 case-control studies in 9 articles were included in this meta-analysis. Meta-analysis results identified two positive associations of 2DS4 and 3DS1 with susceptibility to AS in populations. In subgroup analysis, there was a positive association between 2DS4 and susceptibility to AS in Asians, but not in Caucasians. And there were associations between 3DL1, 3DS1 and susceptibility to AS in Caucasians, but not in Asians. Results of subgroup analysis also showed that there were associations between 2DL5, 2DS4, 2DS5, 3DL1, 3DS1 and susceptibility to AS in HLA-B*27-positive patients and HLA-B*27-positive healthy controls.

CONCLUSIONS

This meta-analysis confirms that 2DS4 and 3DS1 might be potential risk factors for AS in populations.

Ankylosing spondylitis: from cells to genes

Ankylosing spondylitis (AS) is a chronic inflammatory disease of unknown etiology, though it is considered an autoimmune disease. HLA-B27 is the risk factor most often associated with AS, and although the mechanism of involvement is unclear, the subtypes and other features of the relationship between HLA-B27 and AS have been studied for years. Additionally, the key role of IL-17 and Th17 cells in autoimmunity and inflammation suggests that the latter and the cytokines involved in their generation could play a role in the pathogenesis of this disease. Recent studies have described the sources of IL-17 and IL-23, as well as the characterization of Th17 cells in autoimmune diseases. Other cells, such as NK and regulatory T cells, have been implicated in autoimmunity and have been evaluated to ascertain their possible role in AS. Moreover, several polymorphisms, mutations and deletions in the regulatory proteins, protein-coding regions, and promoter regions of different genes involved in immune responses have been discovered and evaluated for possible genetic linkages to AS. In this review, we analyze the features of HLA-B27 and the suggested mechanisms of its involvement in AS while also focusing on the characterization of the immune response and the identification of genes associated with AS.

New perspectives on the ligands and function of the killer cell immunoglobulin-like receptor KIR3DL2 in health and disease

KIR3DL2/CD158k/p140 is a three domain killer cell immunoglobulin-like receptor incorporating cytoplasmic immunoreceptor tyrosine inhibitory motifs, expressed as a disulphide-bonded dimer. KIR3DL2 is a framework gene within the KIR locus and is highly polymorphic, with 62 allelic variants possibly coding for protein reported. KIR3DL2 binds to HLA-A3 and -A11 in a peptide-dependent fashion and to B27 free heavy chain forms. In addition, KIR3DL2 can also function as an innate immune receptor for delivery of CpG DNA to TLR9 in NK cells. The increased levels of expression of KIR3DL2 compared with other KIR expressed by T cell subsets in healthy individuals suggest it may function as a default KIR receptor. KIR3DL2-expressing natural killer (NK) cells and IL17 secreting CD4 T cells have been implicated in the pathogenesis of ankylosing spondylitis. Moreover, KIR3DL2 expression delineates circulating and cutaneous lymphoma T cells in Sézary's syndrome. Here we discuss how the unique molecular attributes of KIR3DL2 impact on its function on NK and T cells and how this may relate to its role in disease.

Role of KIR3DS1 in human diseases

The function of natural killer (NK) cells is controlled by several activating and inhibitory receptors, including the family of killer-immunoglobulin-like receptors (KIRs). One distinctive feature of KIRs is the extensive number of various haplotypes generated by the gene content within the KIR gene locus as well as by highly polymorphic members of the KIR gene family, namely KIR3DL1/S1. Within the KIR3DL1/S1 gene locus, KIR3DS1 represents a conserved allelic variant and displays other unique features in comparison to the highly polymorphic KIR3DL1 allele. KIR3DS1 is present in all human populations and belongs to the KIR haplotype group B. KIR3DS1 encodes for an activating receptor featuring the characteristic short cytoplasmic tail and a positively charged residue within the transmembrane domain, which allows recruitment of the ITAM-bearing adaptor molecule DAP12. Although HLA class I molecules are thought to represent natural KIR ligands, and HLA-Bw4 molecules serve as ligands for KIR3DL1, the ligand for KIR3DS1 still needs to be identified. Despite the lack of formal evidence for an interaction of KIR3DS1 with HLA-Bw4-I80 or any other HLA class I subtype to date, a growing number of associations between the presence of KIR3DS1 and the outcome of viral infections have been described. Especially, the potential protective role of KIR3DS1 in combination with HLA-Bw4-I80 in the context of HIV-1 infection has been studied intensively. In addition, a number of recent studies have associated the presence or absence of KIR3DS1 with the occurrence and outcome of some malignancies, autoimmune diseases, and graft-versus-host disease (GVHD). In this review, we summarize the present knowledge regarding the characteristics of KIRD3S1 and discuss its role in various human diseases.

Association of KIR genotype with susceptibility to HLA-B27-positive ankylosing spondylitis

OBJECTIVE

Recent studies have explored the role of killer cell immunoglobulin-like receptors (KIRs) in chronic autoimmune diseases. The purpose of this study was to demonstrate whether KIR genes contribute to the pathogenesis of ankylosing spondylitis (AS) in Chinese populations.

METHODS

Sixteen KIR genes were genotyped from 60 unrelated patients with AS and 60 HLA-B27-positive matched healthy controls by PCR-SSP. The frequencies of the KIR alleles and genotypes in the AS and control groups were assessed by the χ(2) test.

RESULTS

Our results showed that the frequency of the activator receptor KIR3DS1 gene in the AS group was significantly increased compared to the controls (χ(2) = 5.263, P = 0.006, OR = 3.059, 95 % CI = 1.357-6.896). Moreover, the frequency of the KIR3DL1/3DS1 genotype was greater in the AS group than in the control group (P = 0.039, OR = 3.059, 95 % CI = 1.357-6.896). In contrast, the frequency of the no KIR3DL1/no 3DS1 genotype was lower in patients with AS compared with the controls (P = 0.032, OR = 0.110, 95 % CI = 0.013-0.911).

CONCLUSION

KIR3DS1, in addition to HLA-B27, may play an important independent role in the pathogenesis of AS in the Chinese population.

KIR3DL1+HLA-B Bw4Ile80 and KIR2DS1+HLA-C2 combinations are both associated with ankylosing spondylitis in the Iranian population

Contribution of killer cell immunoglobulin-like receptors (KIR) and their human leucocyte antigen (HLA) class I ligands in the pathogenesis of autoimmune diseases has been shown in several studies. In this study, the possible association of KIR genes, their known HLA ligands and compound KIR/HLA genotypes with ankylosing spondylitis (AS) was assessed. Combined KIR/HLA ligand genotyping was performed by a polymerase chain reaction-sequence-specific primers assay in 35 Iranian patients with AS, and genotypes were compared to those in 200 healthy individuals. The frequencies of telomeric cluster genes KIR2DL5A, KIR2DS1 and KIR3DS1 were significantly increased in AS patient group (P(c) = 0.0082, P(c) = 0.0195 and P(c) = 0.0328, respectively). Conversely, HLA-Bw4 ligand (the presence of one or more -B Bw4(Ile80) , -B Bw4(Thr80) and -A Bw4 epitopes) (P(c) = 0.0004) and HLA-B Bw4(Ile80) (P(c) = 0.053) were less frequent in these patients. Meanwhile, compound KIR/HLA genotype analyses revealed lower frequency of KIR3DL1+HLA-B Bw4(Ile80) (P(c)  = 0.0343) and higher frequency of KIR2DS1+HLA-C2 (P(c) = 0.0308) combinations in patients with AS than in controls. In addition, the genotypes iKIR+HLA > aKIR+HLA (P(c) = .0308) and iKIR+HLA > aKIR (P(c) = 0.0258) were statistically less common, and genotypes iKIR+HLA = aKIR+HLA (P(c) = 0.0081) and iKIR+HLA < aKIR (P(c) = 0.077) were more common in patient group. Our findings suggest a role for excessive or inappropriate NK cell activation through 'KIR/HLA' system in AS disease.

An update on the genetics of HLA B27-associated acute anterior uveitis

The discovery of the association of HLA B27 with spondyloarthropathy led to more questions than answers about the role of this gene in disease susceptibility. The realization that HLA B27 was not responsible for all of the genetic effects helped to lay a foundation for further investigation into the genetics of uveitis. Over several decades, genetic findings have provided clues to advance the understanding of mechanisms of uveitis and to catalyze new research on diagnostics, animal models, and therapies. From the early candidate gene studies on immune mediators to the recent genome-wide investigations, much has been discovered. However, these discoveries have come with the caveat that a genetic finding does not automatically reveal the disease-relevant functional effect of the associated variant.

Contribution of functional KIR3DL1 to ankylosing spondylitis

Increasing evidence points to a role for killer immunoglobulin-like receptors (KIRs) in the development of autoimmune diseases. In particular, a positive association of KIR3DS1 (activating receptor) and a negative association of KIR3DL1 (inhibitory receptor) alleles with ankylosing spondylitis (AS) have been reported by several groups. However, none of the studies analyzed these associations in the context of functionality of polymorphic KIR3DL1. To better understand how the KIR3DL1/3DS1 genes determine susceptibility to AS, we analyzed the frequencies of alleles and genotypes encoding functional (KIR3DL1*F) and non-functional (KIR3DL1*004) receptors. We genotyped 83 AS patients and 107 human leukocyte antigen (HLA)-B27-positive healthy controls from the Russian Caucasian population using a two-stage sequence-specific primer PCR, which distinguishes KIR3DS1, KIR3DL1*F and KIR3DL1*004 alleles. For the patients carrying two functional KIR3DL1 alleles, those alleles were additionally genotyped to identify KIR3DL1*005 and KIR3DL1*007 alleles, which are functional but are expressed at low levels. KIR3DL1 was negatively associated with AS at the expense of KIR3DL1*F but not of KIR3DL1*004. This finding indicates that the inhibitory KIR3DL1 receptor protects against the development of AS and is not simply a passive counterpart of the segregating KIR3DS1 allele encoding the activating receptor. However, analysis of genotype frequencies indicates that the presence of KIR3DS1 is a more important factor for AS susceptibility than the absence of KIR3DL1*F. The activation of either natural killer (NK) or T cells via the KIR3DS1 receptor can be one of the critical events in AS development, while the presence of the functional KIR3DL1 receptor has a protective effect. Nevertheless, even individuals with a genotype that carried two inhibitory KIR3DL1 alleles expressed at high levels could develop AS.

Association of the KIR3DS1*013 and KIR3DL1*004 alleles with susceptibility to ankylosing spondylitis

OBJECTIVE

The killer cell immunoglobulin-like receptors (KIRs) form a group of regulatory molecules that specifically recognize HLA class I molecules. The aim of this study was to analyze the possible contribution of the KIR3DL1 and KIR3DS1 alleles, in addition to HLA-B27, in the susceptibility to ankylosing spondylitis (AS) in a population of individuals from Spain.

METHODS

We genotyped the KIR3DS1 and KIR3DL1 alleles in 2 cohorts of patients with AS and healthy control subjects. In total, 270 patients with AS and 435 healthy, HLA-B27-positive matched control subjects from Spain were enrolled. The KIR3DS1 and KIR3DL1 alleles were genotyped by sequence-specific oligonucleotide probe-polymerase chain reaction, and their association with AS was analyzed. All individuals were typed for HLA-B.

RESULTS

The KIR3DS1*013 allele was solely responsible for the increased frequency of the activator receptor KIR3DS1 in patients with AS compared with healthy HLA-B27-positive control subjects (35.7% versus 22.6% [P = 10(-6)], odds ratio 1.90, 95% confidence interval 1.50-2.40). The increased frequency of the KIR3DS1*013 allele in patients with AS was independent of the presence or absence of the HLA-Bw4I80 epitope. Moreover, the null allele KIR3DL1*004 was a unique inhibitory KIR3DL1 allele that showed a negative association with AS in the presence of HLA-Bw4I80.

CONCLUSION

The increased frequency of the KIR3DS1*013 allele in patients with AS is clearly independent of the presence of the HLA-Bw4I80 epitope, whereas the presence of inhibitory allotypes such as KIR3DL1*004 demonstrated a negative association in patients with AS in the presence of HLA-Bw4I80. As a consequence, the influence of KIR genotypes on AS susceptibility would be mediated by a general imbalance between protective/inhibitory and risk/activating allotypes.

HLA-E gene polymorphism associates with ankylosing spondylitis in Sardinia

INTRODUCTION

Ankylosing spondylitis (AS) is a severe, chronic inflammatory disease strongly associated with HLA-B27. The presence of additional HLA risk factors has been suggested by several studies. The aim of the current study is to assess the occurrence of an additional HLA susceptibility locus in the region between HLA-E and HLA-C in the Sardinian population.

METHODS

200 random controls, 120 patients with AS and 175 HLA-B27 positive controls were genotyped for six single nucleotide polymorphisms (SNPs) spanning the HLA region between HLA-E and HLA-C loci previously shown to harbour an additional susceptibility locus for AS. Allele, genotype and haplotype frequencies were compared.

RESULTS

The data confirm our previous finding of a significant increase in patients with AS of allele A at SNP rs1264457 encoding for an Arg at the functional HLA-E polymorphism (Arg128/Gly128). This was due to a remarkable increase in the frequency of genotype A/A in patients vs HLA-B27-matched controls (51% vs 29%; P for trend: 5 x 10-5). Genotype distribution of three other SNPs mapping in genes (GNL1, PRR3 and ABCF-1) close to HLA-E and showing high LD with it, was also significantly skewed. Accordingly, haplotype distribution was also remarkably different. The frequency of the haplotype AAGA, is 42% in random controls, increases to 53% in the HLA-B27-positive controls, and reaches 68% in patients with AS (P values: 2 x 10-11 vs random and 3 x 10-4 vs HLA-B27 controls).

CONCLUSIONS

There is a strong association between the presence of a haplotype in genes mapping between HLA-E and HLA-C and AS due to an increase of homozygous markers in patients. The strongest association however, is with the HLA-E functional polymorphism rs1264457. Since HLA-E is the ligand for the NKG2A receptor, these data point to the natural killer (NK) activity as possible player in the pathogenesis of AS.

Killer cell immunoglobulin-like receptors in HLA-B27-associated acute anterior uveitis, with and without axial spondyloarthropathy

PURPOSE

To determine associations between polymorphic genes that encode KIRs and their HLA class I ligands in patients with HLA-B27-associated acute anterior uveitis (AAU), with and without axial spondyloarthropathy (axial SpA).

METHODS

Molecular DNA typing methods were used to define the frequencies of variable KIR genes and their relevant HLA class I ligands in HLA-B27(+) (B27(+)) Caucasian subjects with AAU and 429 healthy Caucasian control subjects. The patients were evaluated for axial SpA based on their histories using published criteria.

RESULTS

Of 143 Caucasian subjects with AAU, 71 (49.6%) had features of axial SpA. The only difference between cases and controls in KIR gene frequencies was a trend toward fewer activating KIRs in subjects with AAU with axial SpA, which reached statistical significance for 2DS5 (P = 0.025, corrected P [P(c)] = 0.05; odds ratio [OR], 0.48; 95% CI, 0.25-0.90). The 3DL1+Bw4(T80) combination implicated in weak inhibition was more frequent in subjects with AAU than in control subjects (P = 2.73 x 10(-28), P(c) = 8.2 x 10(-27); OR, 13.5; 95% CI, 7.73-23.68). The 2DL1+HLA-C2 combination was decreased in subjects with axial SpA compared with subjects with AAU without axial SpA (P = 0.022; P(c) = NS; OR, 0.43; 95% CI, 0.21-0.88).

CONCLUSIONS

Evidence was found of a role for KIR-HLA combinations that trigger weaker inhibition in subjects with AAU. Furthermore, there was a trend toward fewer KIR3DS1, -2DS1, and -2DS5 in AAU patients with axial SpA, which have been implicated in NK cell activation. HLA-B27(+) without KIR2DS3 (and -2DS1 and -3DS1) may fail to trigger an early NK cell response to clear antigenic stimuli, which may in part contribute to disease pathogenesis.

Genetics and the pathogenesis of ankylosing spondylitis

PURPOSE OF REVIEW

The field of genetic research in ankylosing spondylitis (AS) is advancing rapidly. The purpose of this review is to outline recent findings, particularly, in regard to genetic studies of the major histocompatibility complex (MHC) and the non-MHC genes IL23R, ERAP1, and killer cell immunologlobulin-like receptor (KIR) complex, in AS.

RECENT FINDINGS

Convincing evidence has been reported for the existence of further non-B27 MHC genes involved in AS. Strong, replicated association has been reported with IL23R and ERAP1 and AS. The IL23R finding strongly implicates the TH17 lymphocyte system in AS aetiopathogenesis. Suggestive evidence of a role for KIR gene polymorphism in AS exists, but definitive findings are awaited.

SUMMARY

The findings suggest that further genome-wide studies in large case-control cohorts are likely to be very productive in this disease. The IL23R findings and subsequent immunological investigations suggest that targeted intervention in the TH17 system is likely to have major therapeutic benefit, as it does in the genetically related diseases, inflammatory bowel disease and psoriasis.