Particular genetic variants of ligands for natural killer cell receptors may contribute to the HLA associated risk of primary sclerosing cholangitis

Primary sclerosing cholangitis

Primary sclerosing cholangitis (PSC) is a chronic bile duct disease leading to fibrotic biliary strictures and liver cirrhosis. The patient population is heterogeneous with regard to disease progression and the presence of co-morbidities, complicating the practical handling of patients as well as studies of pathogenetic mechanisms. The aetiology of PSC is unknown, but the recent findings of several robust susceptibility genes emphasise the importance of genetic risk factors. There is no effective medical treatment available to delay the disease progression, but endoscopic therapy of biliary stenoses may be indicated. Follow-up of patients includes management of the inflammatory bowel disease that is found in the majority of cases along with investigations aimed at the early detection of cholangiocarcinoma and colorectal cancer, which also occur at increased frequencies. In the present review, we aim to summarise the present knowledge of PSC with a particular emphasis on the possible basis of disease variability.

Update on primary sclerosing cholangitis

Early studies in primary sclerosing cholangitis (PSC) were concerned with disease characterization, and were followed by epidemiological studies of PSC and clinical subsets of PSC as well as a large number of treatment trials. Recently, the molecular pathogenesis and the practical handling of the patients have received increasing attention. In the present review we aim to give an update on the pathogenesis of PSC and cholangiocarcinoma in PSC, as well as to discuss the current opinion on diagnosis and treatment of PSC in light of the recent European Association for the Study of the Liver and the American Association for the Study of Liver Diseases practice guidelines.

Unique features of primary sclerosing cholangitis in children

PURPOSE OF REVIEW

To summarize publications on juvenile primary sclerosing cholangitis (PSC) published over the past 5 years. These studies contribute to the understanding of the clinical features, diagnostic pathways, genetic aspects, treatment and outcome of this condition.

RECENT FINDINGS

Sclerosing cholangitis with strong autoimmune features is particularly frequent in paediatric age, where it is more common in girls, responds to immunosuppressive treatment and has a better prognosis than classical PSC. Modern-day magnetic resonance cholangiography allows accurate diagnosis of bile duct disease in most cases. Prolonged oral vancomycin treatment may be beneficial in difficult-to-treat PSC associated with inflammatory bowel disease. Juvenile PSC has a high recurrence rate after liver transplantation. PSC susceptibility and resistance are associated with both human leucocyte antigen-related and unrelated genetic factors.

SUMMARY

Studies on large cohorts of children with PSC are needed for a better understanding of pathogenic mechanisms, response to treatment and outcome of this serious condition.

Genetic associations in Italian primary sclerosing cholangitis: heterogeneity across Europe defines a critical role for HLA-C

BACKGROUND & AIMS

The HLA complex on chromosome 6p21 is firmly established as a risk locus for primary sclerosing cholangitis (PSC). We aimed to exploit genetic differences between Northern Europe and Italy in an attempt to define a causative locus in this genetic region.

METHODS

Seventy-eight North-Italian PSC patients and 79 controls were included. We performed sequencing-based genotyping of HLA-C, HLA-B, and HLA-DRB1. The major histocompatibility chain-related A (MICA) transmembrane microsatellite was analysed using PCR fragment length determination. The tumour necrosis factor-alpha (TNF-alpha)-308G-->A polymorphism was genotyped with TaqMan. Allele frequencies were compared with Chi-square tests. Uncorrected p-values <0.05 were considered statistically significant when replicating findings in previous studies. The p-values of novel associations were corrected for multiple comparisons (Bonferroni).

RESULTS

The frequency of the strong inhibitory HLA-C2 killer-immunoglobulin receptor (KIR) ligand variant was significantly reduced in PSC vs. controls (0.39 vs. 0.58, p=0.0006). Consequently, HLA-C1 homozygosity was associated with an increased risk of PSC (OR 3.1; 95% CI 1.4-6.7, p=0.004). Importantly, there were no significant associations with the HLA-Bw4 KIR ligand variant, at the neighbouring MICA locus or with TNF-alpha-308G-->A. At HLA-DRB1, we confirmed positive and negative associations with DRB1*15 and DRB1*07, respectively, while there were no associations with the DRB1*03, *04 or *1301 alleles typically detected in PSC in Northern Europe.

CONCLUSIONS

The strong inhibitory of the KIR ligand HLA-C2 protects against PSC development in all populations hitherto studied. Further studies on the role of natural killer cells and T-lymphocytes expressing KIRs in PSC pathogenesis are warranted.

Genetics of cholestatic liver disease in 2010

PURPOSE OF REVIEW

Many of the cholestatic diseases show similar clinical features, despite underlying differences in the genetic etiology. The present review aims to present recent insight into this etiological heterogeneity.

RECENT FINDINGS

Mutations in the genes causing progressive familial intrahepatic cholestasis are also involved in less severe phenotypes like benign recurrent intrahepatic cholestasis, gallstone disease, intrahepatic cholestasis of pregnancy and drug-induced cholestasis. This probably represents a continuum of severity of the mutations involved, but also complex patterns of inheritance ranging from monogenic autosomal recessive disorders to heterozygosity only conferring a moderate increase in disease risk, where additional genetic or environmental factors are needed to acquire a disease phenotype. Recent genome-wide association studies in the inflammatory cholestatic diseases primary biliary cirrhosis and primary sclerosing cholangitis have revealed susceptibility genes involved in autoimmunity and inflammatory bowel disease, whereas the genetic risk factors for the biliary preference of these diseases remain unknown.

SUMMARY

The complexity of the genetic contribution to cholestatic liver disease needs to be accounted for to fully understand the pathogenesis of these conditions.

Genome-wide association analysis in primary sclerosing cholangitis

BACKGROUND & AIMS

We aimed to characterize the genetic susceptibility to primary sclerosing cholangitis (PSC) by means of a genome-wide association analysis of single nucleotide polymorphism (SNP) markers.

METHODS

A total of 443,816 SNPs on the Affymetrix SNP Array 5.0 (Affymetrix, Santa Clara, CA) were genotyped in 285 Norwegian PSC patients and 298 healthy controls. Associations detected in this discovery panel were re-examined in independent case-control panels from Scandinavia (137 PSC cases and 368 controls), Belgium/The Netherlands (229 PSC cases and 735 controls), and Germany (400 cases and 1832 controls).

RESULTS

The strongest associations were detected near HLA-B at chromosome 6p21 (rs3099844: odds ratio [OR], 4.8; 95% confidence interval [CI], 3.6-6.5; P = 2.6 x 10(-26); and rs2844559: OR, 4.7; 95% CI, 3.5-6.4; P = 4.2 x 10(-26) in the discovery panel). Outside the HLA complex, rs9524260 at chromosome 13q31 showed significant associations in 3 of 4 study panels. Lentiviral silencing of glypican 6, encoded at this locus, led to the up-regulation of proinflammatory markers in a cholangiocyte cell line. Of 15 established ulcerative colitis susceptibility loci, significant replication was obtained at chromosomes 2q35 and 3p21 (rs12612347: OR, 1.26; 95% CI, 1.06-1.50; and rs3197999: OR, 1.22; 95% CI, 1.02-1.47, respectively), with circumstantial evidence supporting the G-protein-coupled bile acid receptor 1 and macrophage-stimulating 1, respectively, as the likely disease genes.

CONCLUSIONS

Strong HLA associations and a subset of genes involved in bile homeostasis and other inflammatory conditions constitute key components of the genetic architecture of PSC.

The immunobiology of primary sclerosing cholangitis

Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease histologically characterized by the presence of intrahepatic and/or extrahepatic biliary duct concentric, obliterative fibrosis, eventually leading to cirrhosis. Approximately 75% of patients with PSC have inflammatory bowel disease. The male predominance of PSC, the lack of a defined, pathogenic autoantigen, and the potential role of the innate immune system suggest that it may be due to dysregulation of immunity rather than a classic autoimmune disease. However, PSC is associated with several classic autoimmune diseases, and the strongest genetic link to PSC identified to date is with the human leukocyte antigen DRB01*03 haplotype. The precise immunopathogenesis of PSC is largely unknown but likely involves activation of the innate immune system by bacterial components delivered to the liver via the portal vein. Induction of adhesion molecules and chemokines leads to the recruitment of intestinal lymphocytes. Bile duct injury results from the sustained inflammation and production of inflammatory cytokines. Biliary strictures may cause further damage as a result of bile stasis and recurrent secondary bacterial cholangitis. Currently, there is no effective therapy for PSC and developing a rational therapeutic strategy demands a better understanding of the disease.

Natural killer cell receptors and their ligands in liver diseases

The liver is a distinctive immune organ with predominant innate immunity, being rich in innate immune cells such as natural killer (NK) cells. In humans, NK cells comprise about 30%-50% of intrahepatic lymphocytes, whereas peripheral blood lymphocytes contain about 5%-20% NK cells. Accumulating evidence suggests that NK cells play an important role not only in host defense against invading microorganisms and tumor transformation in the liver but also in liver injury and repair. In recent years, significant progress has been made in terms of understanding how NK cells recognize their target cells and carry out their effector functions. It is now clear that NK cells are strictly regulated by numerous activating and inhibitory NK cell receptors that recognize various classes of cell surface ligands, some of which are expressed by normal healthy cells. Therefore, to further elucidate the involvement of NK cells in the pathogenesis of liver diseases, an understanding of recent advances in NK cell biology is crucial. This review provides an overview of recent advances in our knowledge of human NK cell receptors and their ligands in the context of liver diseases.

The Yin and Yang of HLA and KIR in human disease

Killer cell immunoglobulin-like receptors (KIR) are expressed on natural killer (NK) cells and subsets of T cells. The KIR genes are polymorphic and the KIR gene complex is polygenic with varying numbers of inhibitory and activating receptors. HLA class I molecules serve as ligands for the KIR. Interactions of the independently segregating KIR and HLA loci are important for recognition of targets by NK cells as well as NK cell 'licensing'. Several disease association studies indicate a role for interactions between these loci in infectious diseases, autoimmune/inflammatory disorders, cancer and reproduction. Emerging functional data supports a mechanism based on a continuum of inhibition to activation through various compound KIR-HLA genotypes in diseases.

NK and NKT cells in liver injury and fibrosis

The innate immune mechanisms of the liver represent an important first line of defense against bacterial products, toxins, and food antigens coming from the intestine. Natural Killer (NK) and Natural Killer T cells (NKT) are components of the innate immune system with increased presence in the liver compared to other organs and have been reported to participate in the inflammatory processes during hepatic diseases. However significant confusion has been noted in this field mainly due to changes in the characterization of these cells as new knowledge accumulates and due to differences in the approaches used for their study. Both cell types can mediate hepatic injury in several models but studies in human liver diseases have not managed to fully explain their functions. However accumulating evidence supports an antifibrotic role of NK cells mainly via an inhibitory effect on hepatic stellate cells by inducing apoptosis and via production of interferon-gamma. Therefore, downregulation of NK cells during most types of liver injury may facilitate liver fibrosis. Data about the role of NKT cells in liver fibrosis are limited. This review will summarize the studies about the role of NK and NKT cells in liver diseases with a special interest in hepatic injury and liver fibrosis.

An update on primary sclerosing cholangitis

PURPOSE OF REVIEW

Primary sclerosing cholangitis is a chronic cholestatic liver disease characterized by strictures of the biliary tree complicated by cirrhosis and cholangiocarcinoma. It is immune mediated, although the precise aetiology remains unknown.

RECENT FINDINGS

The research into aetiology, genetic associations, pathogenesis, epidemiology, diagnosis of cholangiocarcinoma and medical treatments are discussed.

SUMMARY

Multiple gene polymorphisms and human leucocyte antigen haplotype associations with primary sclerosing cholangitis have been investigated. Common inflammatory bowel disease associated polymorphisms and ulcerative colitis associated human leucocyte antigen haplotypes are not associated with primary sclerosing cholangitis. Biliary epithelial cells may mediate their own destruction by exaggerating innate and adaptive immune responses to bacterial products in the liver. The natural history of large and small duct primary sclerosing cholangitis has been reviewed. Positron emission tomography may be a useful adjunct to current imaging modalities in the pretransplant assessment of patients to exclude cholangiocarcinoma. Ursodeoxycholic acid remains the most studied medical treatment for primary sclerosing cholangitis; pilot studies suggest a possible role for tacrolimus and silymarin, however further studies are required.

Polymorphisms of KIRs gene and HLA-C alleles in patients with ankylosing spondylitis: possible association with susceptibility to the disease

INTRODUCTION

An emerging body of evidence is accumulating to suggest that killer cell immunoglobulin-like receptors (KIRs) and human leukocyte antigen (HLA) class I ligands contribute to the pathogenesis of diverse kinds of autoimmune diseases. However, the functional effects of their polymorphism remain largely unknown to date. Thus, the present study was undertaken to determine the association of the polymorphisms KIRs gene and HLA-C alleles with the susceptibility to ankylosing spondylitis (AS) by means of polymerase chain reaction/sequence-specific primers for genotyping KIRs from genomic DNA of 119 patients with AS together with 128 healthy donors as a control group.

RESULTS AND DISCUSSION

We found that the frequencies of KIR3DS1 and KIR2DL5 were statistically significantly higher in the patient group than those in the control group (P = 0.016 and P = 0.003, respectively). Meanwhile, the percentage of patients, who were carrying two or more of the activating KIRs, was higher than that of control group. With respect to HLA-C alleles, individuals with AS showed an increased frequency of HLA-Cw02. If HLA-C was divided into group 1 or group 2 based on whether there was an asparagine or lysine present at position 80 of the alpha-chain, HLA-C group 2 was more common in subjects with AS compared to control subjects. The genotype 2DS1+/HLA-C lys(80)+ was more common in subjects with AS. Moreover, the CD69 expression, a NK activation marker, remarkably increased in patient with AS.

CONCLUSION

In conclusions, this study suggests that KIR3DS1 may severe as AS susceptive genes to trigger continuous injury of arthrosis. The imbalance of activating and inhibitory KIR as well as HLA-C group 1 and group 2 may be the key factor, which influences the pathogenesis of AS. Moreover, KIR2DS1 might associate with the susceptibility of AS by influencing NK cell activity once group 2 HLA-C ligands are present.

Cholangiocarcinoma in primary sclerosing cholangitis is associated with NKG2D polymorphisms

Primary sclerosing cholangitis (PSC) is often complicated by the development of cholangiocarcinoma (CCA). Genetic variation of natural killer cell receptor G2D (NKG2D) has been associated with cancer susceptibility. An important ligand for NKG2D, major histocompatibility complex class I chain-related molecule A (MICA), serves as a marker of cellular stress. The 5.1 allele of the gene encoding MICA has been associated with PSC. In this study, we aimed to investigate the influence of genetic variations in the NKG2D-MICA receptor-ligand pair on the risk of CCA in patients with PSC. Seven single nucleotide polymorphisms (SNPs) covering the NKG2D gene were genotyped in 365 Scandinavian PSC patients and 368 healthy controls with TaqMan technology. Genotype data on the MICA 5.1 variant were available from previous studies. Forty-nine of the PSC patients (13.6%) had developed CCA at the time of study. Two of the NKG2D SNPs were associated with an increased risk of CCA: rs11053781 [odds ratio (OR) = 2.08, 95% confidence interval (CI) = 1.31-3.29, corrected P (P(c)) = 0.011] and rs2617167 (OR = 2.32, 95% CI = 1.47-3.66, P(c) = 0.0020). Carriership of the MICA 5.1 allele was associated with resistance against CCA (OR = 0.43, 95% CI = 0.20-0.95, not corrected P = 0.032).

CONCLUSION

Our results show that genetic variants of the NKG2D receptor are associated with development of CCA in PSC patients. This suggests that interaction between NKG2D and MICA is involved in protection against CCA in PSC. Patients who are homozygous for the nonrisk alleles are unlikely to develop CCA; this finding could be helpful in identifying PSC patients with a low CCA risk.

Genetic epidemiology of primary sclerosing cholangitis

The aetiology of primary sclerosing cholangitis (PSC) is not known. A more than 80-fold increased risk of PSC among first-degree relatives emphasizes the importance of genetic factors. Genetic associations within the human leukocyte antigen (HLA) complex on chromosome 6p21 were detected in PSC 25 years ago. Subsequent studies have substantiated beyond doubt that one or more genetic variants located within this genetic region are important. The true identities of these variants, however, remain to be identified. Several candidate genes at other chromosomal loci have also been investigated. However, according to strict criteria for what may be denominated a susceptibility gene in complex diseases, no such gene exists for PSC today. This review summarises present knowledge on the genetic susceptibility to PSC, as well as genetic associations with disease progression and clinical subsets of particular interest (inflammatory bowel disease and cholangiocarcinoma).