CTLA-4 polymorphisms and systemic lupus erythematosus (SLE): a meta-analysis

Associations between interleukin-23R polymorphisms and ankylosing spondylitis susceptibility: a meta-analysis

OBJECTIVE

The aim of this study was to determine whether interleukin-23R (IL-23R) polymorphisms confer susceptibility to ankylosing spondylitis (AS).

METHODS

The authors conducted meta-analyses on associations between IL-23R polymorphisms and AS susceptibility, using fixed and random effects models.

RESULTS

A total of 10 studies (14 separate comparisons) were included in this meta-analysis, which included European and Asian populations. Meta-analysis revealed a significant association between AS and the two alleles of rs11209032 polymorphism in all study subjects (OR = 1.182, 95% CI 1.120-1.249, P = 0.000). Stratification by ethnicity identified a significant association between this polymorphism and AS in the European (OR = 1.234, 95% CI 1.159-1.313, P = 0.000), but not in the Asian populations (OR = 1.030, 95% CI 0.921-1.152, P = 0.608). Meta-analyses of rs1004819, rs10489629, rs1343151, rs1495965, and rs2201841 polymorphisms showed the same pattern as that shown by rs11209032 meta-analysis. Meta-analysis also revealed a significant association between the two alleles of the rs11209026 and the rs11465804 polymorphisms and the risk of developing AS in Europeans. Interestingly, the rs7517847 polymorphism was found to be significantly associated with AS susceptibility in both Europeans and Asians.

CONCLUSIONS

This meta-analysis shows that the IL-23R polymorphisms are associated with the development of AS in Europeans.

The association between interleukin-6 polymorphisms and systemic lupus erythematosus: a meta-analysis

The aim of this study was to determine whether the functional interleukin-6 (IL-6) promoter -174 G/C and -572 G/C polymorphisms confer susceptibility to systemic lupus erythematosus (SLE) in ethnically different populations. Meta-analysis was conducted on the associations between the IL-6 polymorphisms and SLE using; 1) allele contrast, 2) the recessive model, 3) the dominant model, and 4) the additive model. A total of 11 studies were considered in this study, and ethnicity-specific meta-analysis was performed on European and Asian populations. Meta-analysis of the IL-6 -174 G/C polymorphism showed an association between SLE and the IL-6 -174 G allele in all study subjects (odds ratio (OR) = 1.344, 95% confidence interval (CI) = 1.052-1.718, p = 0.018). Furthermore, stratification by ethnicity indicated an association between the IL-6 -174 G allele and SLE in Europeans (OR = 1.264, 95% CI = 1.037-1.541, p = 0.020). Meta-analysis of the IL-6 -572 G/C polymorphism revealed that an association was found between SLE and the IL-6 -572 G/C polymorphism using the recessive model, but ethnicity-specific meta-analysis revealed no association between SLE and the IL-6 -572 G/C polymorphism in Asians. In conclusion, this meta-analysis demonstrates that the IL-6 -174 G/C polymorphism may confer susceptibility to SLE in Europeans, but that the IL-6 -572 G/C polymorphism is not associated with susceptibility to SLE in Asians.

Genetic risk factors of systemic lupus erythematosus in the Malaysian population: a minireview

SLE is an autoimmune disease that is not uncommon in Malaysia. In contrast to Malays and Indians, the Chinese seem to be most affected. SLE is characterized by deficiency of body's immune response that leads to production of autoantibodies and failure of immune complex clearance. This minireview attempts to summarize the association of several candidate genes with risk for SLE in the Malaysian population and discuss the genetic heterogeneity that exists locally in Asians and in comparison with SLE in Caucasians. Several groups of researchers have been actively investigating genes that are associated with SLE susceptibility in the Malaysian population by screening possible reported candidate genes across the SLE patients and healthy controls. These candidate genes include MHC genes and genes encoding complement components, TNF, FcγR, T-cell receptors, and interleukins. However, most of the polymorphisms investigated in these genes did not show significant associations with susceptibility to SLE in the Malaysian scenario, except for those occurring in MHC genes and genes coding for TNF-α, IL-1β, IL-1RN, and IL-6.

CTLA-4 gene polymorphism and the risk of systemic lupus erythematosus in the Chinese population

Several variants of CTLA-4 have been reported to be associated with susceptibility systemic lupus erythematosus (SLE); however, findings have been inconsistent across different populations. Using a case-control study design, we have investigated the role of CTLA-4 polymorphism at positions −1661 and −1722 on SLE susceptibility in our Chinese SLE population in central China's Hubei province. Samples were collected from 148 SLE patients and 170 healthy controls. Polymerase chain reaction restriction fragments length polymorphism (PCR-RFLP) was used to analyze the genotypes of the two sites. Statistically significant difference was observed in genotypes for −1722, but not for −1661. The frequency of the T allele on the −1722 SNP was significantly increased in SLE patients: 57.8% versus 40.6% in controls (P < 0.001, OR = 2.002). While the detected C allele frequency in the controls was significantly elevated in comparison to that in the SLE patients (59.4% versus 42.2%). On the contrary, no association was found between SLE and CTLA-4 polymorphism at position −1661.

Ipilimumab (Yervoy) and the TGN1412 catastrophe

The development of the anti-CTLA-4 antibody (ipilimumab; marketed as Yervoy) immune regulatory therapy was based on the premise that "Abrogation of the function of CTLA-4 would permit CD28 to function unopposed and might swing the balance in favor of immune stimulation, tolerance breakdown and tumor eradication…" (Weber, 2009). By now, the vast majority of data collected from more than 4000 patients proves that this prediction was entirely correct. Paradoxically, the successful blockade of immune checkpoints raises the question whether an anti-CTLA-4 antibody could ever become an important therapy against cancer. T cells lost their ability to discriminate between self and non-self. Thus, tolerance to self tissues was broken in ∼70% of the patients. In the recent industry-sponsored phase III clinical trial of ipilimumab, 147 (38.7%) of the patients experienced severe adverse events and 6.8% suffered dose-limiting events (8.4%, in the ipilimumab-alone group). There were 14 deaths related to the study drugs and 7 of these were associated with immune-related adverse events. In contrast, the complete response rate was only 0.2%, in one patient out of 403 who received ipilimumab plus a peptide vaccine. Promoters of ipilimumab appear to be unmindful of the clinical trial catastrophe in London. Then, a humanized "superagonist" anti-CD28 monoclonal antibody, TGN1412, which "preferentially" activated regulatory T cells, at a higher dose, also activated all CD28 positive T cells. This precipitated a "cytokine storm" leading to life-threatening multiple organ failure in the six healthy human volunteers. Neither anti-CD28 nor anti-CTLA-4 therapies rely on antigen-specificity. Both release free antibody into the body against common molecular targets that are expressed on the targeted as well as on the non-targeted T cells. At lower antibody doses specific T cells are preferentially activated. With increasing antibody dose, however, the kinetics of the interaction is pushed in favor of widespread non-specific T cell expansion. Using the law of mass action we calculated that the vast majority of the CTLA-4 receptors on all activated T cells (including melanoma specific T cells) in the phase III clinical trial of ipilimumab will have been saturated. This would explain the runaway immune response observed. The conclusions drawn by the authors of the ipilimumab trial paper could bear an independent inspection and reassessment concerning the validation of the blockade of immune checkpoints as an important therapeutic strategy against cancer.

Current advances in lupus genetic and genomic studies in Asia

The genetic components in systemic lupus erythematosus (SLE) have long been established, however, it has been unclear for many years whether the same genetic risk factors for SLE are shared across different ethnic groups. Over the past few years, a number of genetic and genomic studies have been conducted in Asian populations to address this question. These studies have demonstrated that genetic heterogeneity does exist in SLE across different ethnic groups. With these studies, it has been established that a number of genes associated with SLE in Caucasians are also risk factors in Asians: HLA class II genes, STAT4, BANK1, BLK, IRF5, TNFSF4, ITGAM, etc., while there are also novel genetic risk factors identified by these studies in Asians, for instance, the ETS1 and WDFY4 in Chinese. For the genomic studies, the interferon signature has been confirmed as a major lupus molecular phenotype in Asians the same as in Caucasians; microRNA expression profiling and its novel role in regulating the interferon pathway has been first revealed in Asians. Further understanding of the function of lupus disease genes and delineating the key molecular pathway(s) will enhance the development of novel therapeutic targets and biomarkers for individualized clinical management for lupus patients.

+49A/G polymorphism of cytotoxic T-lymphocyte antigen 4 gene in type 1 autoimmune hepatitis and primary biliary cirrhosis: A meta-analysis

AIM

  Recently, the associations of +49A/G polymorphisms of cytotoxic T-lymphocyte antigen 4 (CTLA-4) gene with the susceptibility to type 1 autoimmune hepatitis (AIH) and primary biliary cirrhosis (PBC) have been reported; however these associations are yet to be fully elucidated. This study aimed to identify the associations of CTLA-4 gene +49A/G polymorphisms with the susceptibility to type 1 AIH and PBC by using a meta-analysis.

METHODS

  PubMed was searched by using the following keywords: "autoimmune hepatitis AND (polymorphism OR polymorphisms)" or "primary biliary cirrhosis AND (polymorphism OR polymorphisms)". Meta-analyses of five studies including 526 patients with type 1 AIH and 631 controls and seven studies including 1500 patients with PBC and 2345 controls were performed.

RESULTS

  For type 1 AIH, the odds ratio (OR) of G allele was 1.26 [95% confidence interval (CI) 1.06-1.51] although G/G homozygosity was not associated with the susceptibility to type 1 AIH. On the other hand, the OR of A/A homozygosity for type 1 AIH was 0.66 (95% CI 0.50-0.86). For PBC, the OR of G allele was 1.20 (95% CI 1.06-1.34). Furthermore, G/G homozygosity was significantly associated with the susceptibility to PBC (OR 1.29, 95% CI 1.01-1.66). The OR of A/A homozygosity for PBC was 0.81 (95% CI 0.70-0.94).

CONCLUSIONS

  This study suggests that CTLA-4 gene +49A/G polymorphisms may be associated with the susceptibility to type 1 AIH and PBC. Especially, while G/G genotype may be associated with the susceptibility to PBC, A/A genotype may be protective against type 1 AIH and PBC.

Cytotoxic T-lymphocyte antigen 4 haplotype correlates with relapse and survival after allogeneic hematopoietic SCT

CTLA-4 is a negative regulator of activated T cells and the association of CTLA-4 polymorphisms with autoimmune diseases and transplant outcome has been reported. We evaluated the effect of donor CTLA-4 polymorphisms on outcome after allogeneic hematopoietic SCT (HSCT). We analyzed 147 Japanese HLA-matched sibling recipients and their donors who had undergone allogeneic HSCT. Genotyping of three single-nucleotide polymorphisms in CTLA-4 (-318, +49, CT60) was performed using TaqMan-PCR. According to the international HapMap database, only these three CTLA-4 haplotypes, classified as C-G-G, C-A-A and T-A-G, are present in the Japanese population. In this study, percentage expression of the C-G-G, C-A-A and T-A-G haplotypes was 59.5, 30.6 and 9.9%, respectively. Recipients of the C-A-A haplotype donor showed a significantly lower risk of relapse (HR: 0.54, 95% CI: 0.30-0.97, P=0.040) and a trend toward higher OS (HR: 0.61, 95% CI: 0.36-1.0, P=0.054) than did recipients of a donor without the C-A-A haplotype. The presence or absence of the C-A-A haplotype did not affect GVHD or non-relapse mortality. As the presence of the C-A-A haplotype reduced relapse risk and improved survival after allogeneic HSCT, this CTLA-4 haplotype may provide useful information for donor selection.

Abnormal CTLA-4 function in T cells from patients with systemic lupus erythematosus

CTLA-4 is a critical gatekeeper of T-cell activation and immunological tolerance and has been implicated in patients with a variety of autoimmune diseases through genetic association. Since T cells from patients with the autoimmune disease systemic lupus erythematosus (SLE) display a characteristic hyperactive phenotype, we investigated the function of CTLA-4 in SLE. Our results reveal increased CTLA-4 expression in FOXP3(-) responder T cells from patients with SLE compared with other autoimmune rheumatic diseases and healthy controls. However, CTLA-4 was unable to regulate T-cell proliferation, lipid microdomain formation and phosphorylation of TCR-zeta following CD3/CD28 co-stimulation, in contrast to healthy T cells. Although lupus T cells responded in vitro to CD3/CD28 co-stimulation, there was no parallel increase in CTLA-4 expression, which would normally provide a break on T-cell proliferation. These defects were associated with exclusion of CTLA-4 from lipid microdomains providing an anatomical basis for its loss of function. Collectively our data identify CTLA-4 dysfunction as a potential cause for abnormal T-cell activation in patients with SLE, which could be targeted for therapy.

+49G > A polymorphism in the cytotoxic T-lymphocyte antigen-4 gene increases susceptibility to hepatitis B-related hepatocellular carcinoma in a male Chinese population

Cytotoxic T-lymphocyte antigen 4 (CTLA-4) is an important regulator and functions negatively in immune response. Its nonsynonymous polymorphism +49G > A (dbSNP: rs231775) has been linked to an elevated risk of T-cell-mediated autoimmune diseases, infectious diseases, and even carcinomas. Here, we examined the genotypes at rs231775 of 1003 subjects in a Han Chinese population to detect the association between this single-nucleotide polymorphism (SNP) and hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC) susceptibility, including 375 HBV-related HCC patients, 209 non-HCC patients with HBV infection, and 419 healthy controls. Our results indicated a weak trend for the relationship between rs231775 and HBV-related HCC susceptibility, although the statistical level was not significant. However, a significant difference was identified in males between HBV-related HCC patients and healthy controls. The data revealed that the frequency of the A/A genotype was higher in patients compared with healthy controls (odds ratio [OR] = 1.79, 95% confidence interval [95% CI] 1.05-3.08). The G allele appeared to have a protective effect in developing HBV-related HCC. Subjects with the A allele had higher HCC susceptibility than those with the G allele (OR = 1.31, 95% CI 1.03-1.66). These results suggested that the A/A genotype and A allele of rs231775 increased the risk of developing HBV-related HCC in a male Chinese population.

Tyrosine kinase 2 and interferon regulatory factor 5 polymorphisms are associated with discoid and subacute cutaneous lupus erythematosus

Lupus erythematosus (LE) is a heterogeneous disease ranging from skin-restricted manifestations to a progressive multisystem disease. The specific skin lesions include chronic cutaneous, subacute cutaneous and acute cutaneous LE. Both genetic and environmental factors are involved in the development of LE. However, reports on the genetic background of cutaneous lupus erythematosus (CLE) forms, namely discoid (DLE) and subacute cutaneous lupus erythematosus (SCLE), are sparse. We investigated whether the known systemic LE (SLE) susceptibility genes also predispose to CLE. Altogether, 219 Finnish patients with DLE or SCLE and 356 healthy controls were recruited. Single nucleotide polymorphisms tagging reported risk genes were genotyped. Tyrosine kinase 2 (TYK2) rs2304256 was associated with increased risk of DLE (P = 0.012, OR = 1.47, 95% CI = 1.01-1.98). Expression of TYK2 was demonstrated by immunohistochemistry in macrophage-like cells and neutrophils and interferon regulatory factor 5 (IRF5) in macrophage- and fibroblast-like cells of DLE, SCLE and SLE skin. IRF5 rs10954213 showed association with DLE (P = 0.017, OR = 1.40, 95% CI = 1.06-1.86) and SCLE (P = 0.022, OR = 1.87, 95% CI = 1.09-3.21). A haplotype of cytotoxic T-lymphocyte-associated protein 4 (CTLA4) showed association with DLE (P = 0.0065, OR = 2.51, 95% CI = 1.25-5.04). Our results show that the TYK2, IRF5 and CTLA4 genes previously associated with SLE also confer risk for DLE and SCLE, suggesting that different LE subphenotypes may share pathogenetic pathways.

Genetic polymorphisms in cytotoxic T-lymphocyte antigen 4 and cancer: the dialectical nature of subtle human immune dysregulation

Genetic polymorphisms in the human genome are an important component of genotypic variability including one's immune status. Single nucleotide polymorphisms (SNPs) in the cytotoxic T-lymphocyte antigen 4 (CTLA-4) gene have been linked to susceptibility to autoimmune disease. Interestingly, we have recently shown that an SNP in the CTLA-4 coding region (49A > G) is also associated with susceptibility to human cancer, but the risk allele for susceptibility to cancer (allele A) is the opposite of that found for susceptibility to autoimmune disease (allele G), which has been confirmed by a meta-analysis of reported studies. These findings indicate an important role of the dialectical nature of T-cell immune dysregulation in human disorders, such as autoimmune disease and cancer. The requisites of CTLA-4 polymorphisms for susceptibility to cancer and response to targeted therapy are discussed in this review.

Joint genetic susceptibility to type 1 diabetes and autoimmune thyroiditis: from epidemiology to mechanisms

Type 1 diabetes (T1D) and autoimmune thyroid diseases (AITD) frequently occur together within families and in the same individual. The co-occurrence of T1D and AITD in the same patient is one of the variants of the autoimmune polyglandular syndrome type 3 [APS3 variant (APS3v)]. Epidemiological data point to a strong genetic influence on the shared susceptibility to T1D and AITD. Recently, significant progress has been made in our understanding of the genetic association between T1D and AITD. At least three genes have been confirmed as major joint susceptibility genes for T1D and AITD: human leukocyte antigen class II, cytotoxic T-lymphocyte antigen 4 (CTLA-4), and protein tyrosine phosphatase non-receptor type 22. Moreover, the first whole genome linkage study has been recently completed, and additional genes will soon be identified. Not unexpectedly, all the joint genes for T1D and AITD identified so far are involved in immune regulation, specifically in the presentation of antigenic peptides to T cells. One of the lessons learned from the analysis of the joint susceptibility genes for T1D and AITD is that subset analysis is a key to dissecting the etiology of complex diseases. One of the best demonstrations of the power of subset analysis is the CTLA-4 gene in T1D. Although CTLA-4 showed very weak association with T1D, when analyzed in the subset of patients with both T1D and AITD, the genetic effect of CTLA-4 was significantly stronger. Gene-gene and genetic-epigenetic interactions most likely play a role in the shared genetic susceptibility to T1D and AITD. Dissecting these mechanisms will lead to a better understanding of the etiology of T1D and AITD, as well as autoimmunity in general.

Functional genetic variations in cytotoxic T-lymphocyte antigen 4 and susceptibility to multiple types of cancer

Antitumor T lymphocytes play a pivotal role in immunosurveillance of malignancy. The CTL antigen 4 (CTLA-4) is a vital negative regulator of T-cell activation and proliferation. This study examined whether genetic polymorphisms in CTLA-4 are associated with cancer susceptibility. A two-stage investigation using haplotype-tagging single nucleotide polymorphism approach and multiple independent case-control analyses was performed to assess the association between CTLA-4 genotypes and cancer risk. Functional relevance of the polymorphisms was examined by biochemical assays. We found that the 49G>A polymorphism in the CTLA-4 leading sequence causing (17)Ala to (17)Thr amino acid substitution is associated with increased susceptibility to multiple cancers, including lung, breast, esophagus, and gastric cardia cancers. Genotyping in 5,832 individuals with cancer and 5,831 control subjects in northern and southern Chinese populations showed that the CTLA-4 49AA genotype had an odds ratio of 1.72 (95% confidence interval, 1.50-2.10; P = 3.4 x 10(-7)) for developing cancer compared with the 49GG genotype. Biochemical analyses showed that CTLA-4-(17)Thr had higher capability to bind B7.1 and stronger inhibitory effect on T-cell activation compared with CTLA-4-(17)Ala. T cells carrying the 49AA genotype had significantly lower activation and proliferation rates compared with T cells carrying the 49GG genotype upon stimulation. These results are consistent with our hypothesis and indicate that genetic polymorphisms influencing T-cell activation modify cancer susceptibility.

CTLA-4 +49 A/G genotype and HLA-DRB1 polymorphisms in Turkish patients with Henoch-Schönlein purpura

The pathogenesis of Henoch-Schönlein purpura (HSP) remains unknown; however, it is generally considered to be an immune complex-mediated disease. Cytotoxic T lymphocyte-associated protein 4 (CTLA-4) is expressed on activated T cells, and, thus, it is critically involved in the immune response. We aimed to investigate the possible influence of CTLA-4 polymorphisms for susceptibility to HSP and determine if there were associations with human leukocyte antigen (HLA)-DRB1 genotypes. Using polymerase chain reaction-based DNA genotyping, we investigated the polymorphisms located in the genes encoding CTLA-4 in 100 patients with HSP and 156 ethnically matched healthy controls. When CTLA-4 +49 A/G polymorphism of HSP patients and control group was compared, no associations with joint, gastrointestinal or renal manifestations, or susceptibility to HSP, were observed. However, patients with nephrotic proteinuria had higher HLA-DRB1*13 positivity [odds ratio (OR) = 3.76, 95% confidence interval (95%CI) = 1.25-11.23, P = 0.025]. When the patients were stratified according to CTLA-4 polymorphism, a significant association between nephrotic proteinuria patients and carriage of the AG genotype was also found (OR = 15.42, 95%CI = 1.59-148.82, P = 0.008). These results suggested that CTLA-4 +49 A/G polymorphism does not contribute to susceptibility to HSP; however, the presence of CTLA-4 AG genotype and HLA-DRB1*13 could be a risk factor for developing nephrotic-range proteinuria in these patients.

Global T cell dysregulation in non-autoimmune-prone mice promotes rapid development of BAFF-independent, systemic lupus erythematosus-like autoimmunity

In otherwise non-autoimmune-prone C57BL/6 (B6) mice rendered genetically deficient in CD152 (CTLA-4), polyclonal hypergammaglobulinemia with increased levels of systemic lupus erythematosus (SLE)-associated IgG autoantibodies, glomerular IgG and C3 deposition, and interstitial nephritis all developed by 3-5 wk of age. Remarkably, superimposing genetic deficiency of BAFF (B cell-activating factor belonging to the TNF family) onto CD152 deficiency did not substantially attenuate humoral autoimmunity and immunopathology in these mice, despite the resulting marked reduction in B-lineage cells. Although superimposing a BAFF transgene (resulting in constitutive BAFF overexpression) onto CD152-deficient mice did lead to increases in B-lineage cells and serum levels of certain SLE-associated IgG autoantibodies, renal immunopathology remained largely unaffected. Taken together, these results demonstrate that global T cell dysregulation, even in an otherwise non-autoimmune-prone host, can promote systemic humoral autoimmunity and immunopathology in a BAFF-independent manner. Moreover, supraphysiologic expression of BAFF in the setting of ongoing autoimmunity does not necessarily lead to greater immunopathology. These findings may help explain the limited clinical efficacy appreciated to date of BAFF antagonists in human SLE.

IFNG +874T/A, IL10 -1082G/A and TNF -308G/A polymorphisms in association with tuberculosis susceptibility: a meta-analysis study

Susceptibility to infectious diseases is influenced by genetic background and efficient cellular immune activation is responsible for protection. In tuberculosis (TB), interferon-gamma (IFNgamma) is crucial to control intracellular growth of Mycobacterium tuberculosis while interleukin-10 (IL-10) has an antagonistic role. Tumor necrosis factor (TNF) is a central mediator of granuloma formation and control of bacilli spread synergizing with IFNgamma to hamper M. tuberculosis infection. Single nucleotide polymorphisms (SNPs) located at these genes could influence cytokine levels and regulate resistance and susceptibility to TB. The aim of this study was to determine the association of the interferon-gamma gene (IFNG) +874T/A, interleukin-10 gene (IL10) -1082G/A and tumor necrosis factor gene (TNF) -308G/A SNPs with TB in several populations using meta-analysis. We searched for association studies correlating these polymorphisms and TB using pre-established keywords in Medline. Meta-analysis was conducted with random effects models to account for heterogeneity between studies. Eleven studies were included in the IFNG +874T/A meta-analysis, while eight were used for the IL10 -1082G/A, and 10 were employed for TNF -308G/A. Data were analyzed in respect to associations between alleles, genotypes and minor allele carriers. Statistically significant results were found only for IFNG. The +874T allele of IFNG showed a protective significant association (OR = 0.75; 95% CI, 0.634-0.887; P = 0.0008). Though not significant, IL10 presented a trend towards protection when only studies with pulmonary TB patients were considered. This data reinforces the critical importance of IFNG +874T/A as a genetic marker for TB resistance and this information can be used for better design of a TB vaccine.

General aspects of the genetics of SLE

The application of genetic techniques to the study of systemic lupus erythematosus (SLE) has identified candidate genes with diverse immunological function. There is a growing understanding that susceptibility to SLE is due to a complex interaction of multiple genes and environmental factors, and that many of these may be shared with other autoimmune diseases. In this first of a series of review articles we outline our current understanding of SLE genetics, in particular summarising the results of recent association studies.

Interferon regulatory factor-5 is genetically associated with systemic lupus erythematosus in African Americans

Increased expression of interferon (IFN)-inducible genes is implicated in the pathogenesis of systemic lupus erythematosus (SLE). One transcription factor responsible for regulating IFN, interferon regulatory factor-5 (IRF5), has been associated with SLE in genetic studies of Asian, Caucasian and Hispanic populations. We genotyped up to seven polymorphic loci in or near IRF5 in a total of 4870 African-American and Caucasian subjects (1829 SLE sporadic cases and 3041 controls) from two independent studies. Population-based case-control comparisons were performed using the Pearson's chi(2)-test statistics and haplotypes were inferred using HaploView. We observed significant novel associations with the IRF5 variants rs2004640 and rs3807306 in African Americans and replicated previously reported associations in Caucasians. While we identified risk haplotypes, the majority of haplotypic effects were accounted for by one SNP (rs3807306) in conditional analyses. We conclude that genetic variants of IRF5 associate with SLE in multiple populations, providing evidence that IRF5 is likely to be a crucial component in SLE pathogenesis among multiple ethnic groups.

Interacting alleles of the coinhibitory immunoreceptor genes cytotoxic T-lymphocyte antigen 4 and programmed cell-death 1 influence risk and features of primary biliary cirrhosis

Autoimmune diseases such as primary biliary cirrhosis (PBC) result from failure in the immune mechanisms that establish and maintain self-tolerance. Evidence suggests that these processes are shared among the spectrum of autoimmune syndromes and are likely genetically determined. Cytotoxic T-lymphocyte antigen 4 (CTLA4) and programmed cell-death 1 (PDCD1) are two genes encoding coinhibitory immunoreceptors that harbor polymorphisms with demonstrated associations to multiple autoimmune disorders. We aimed to assess functional single nucleotide polymorphisms (SNPs) in these two genes for association with PBC. SNPs in CTLA4 and PDCD1 were genotyped in 351 PBC patients and 205 controls. Allele and genotype frequencies were evaluated for association with PBC and/or antimitochondrial antibody (AMA) positivity with logistic regression. Haplotypes were inferred with an expectation-maximization algorithm, and allelic interaction was analyzed by logistic regression modeling. Individual SNPs demonstrated no association to PBC. However, the GG genotype of CTLA4 49AG was significantly associated with AMA positivity among the PBC patients. Also, individual SNPs and a haplotype of CTLA4 as well as a rare genotype of the PDCD1 SNP PD1.3 were associated with orthotopic liver transplantation. As well, we identified the influence of an interaction between the putatively autoimmune-protective CTLA4 49AG:CT60 AA haplotype and autoimmune-risk PDCD1 PD1.3 A allele on development of PBC.

CONCLUSION

Our findings illustrate the complex nature of the genetically induced risk of PBC and emphasize the importance of considering definable subphenotypes of disease, such as AMA positivity, or definitive measures of disease severity/progression, like orthotopic liver transplantation, when genetic analyses are being performed. Comprehensive screening of genes involved with immune function will lead to a greater understanding of the genetic component of autoimmunity in PBC while furthering our understanding of the pathogenic properties of this enigmatic disease.

The genetic basis of thyroid autoimmunity

Autoimmune thyroid diseases (AITDs), including Graves' disease (GD) and Hashimoto's thyroiditis (HT), are prevalent autoimmune diseases, affecting up to 5% of the general population. AITDs arise due to interplay between environmental and genetic factors. In the past decade, significant progress has been made in our understanding of the genetic contribution to the etiology of AITDs. Excitingly, several AITD susceptibility genes have been identified and characterized. Some of these susceptibility genes are specific to either GD or HT, while others confer susceptibility to both conditions. The first AITD susceptibility gene locus identified was the Human-Leukocyte-Antigen DR (HLA-DR) gene locus. Subsequently, a quintet of non-HLA genes, including the cytotoxic T lymphocyte antigen (CTLA-4), CD40, protein tyrosine phosphatase-22 (PTPN22), thyroglobulin, and thyroid-stimulating hormone receptor (TSHR) gene, has been shown to contribute to the susceptibility to AITDs. Recently, the mechanisms by which these new AITD genes predispose to AITDs have been dissected. In this review, we overview and highlight the recent data on the genes predisposing to AITDs and the putative mechanisms by which they confer susceptibility to disease.

T-cell regulatory gene CTLA-4 polymorphism/haplotype association with autoimmune pancreatitis

BACKGROUND

Autoimmune pancreatitis (AIP) is a distinct disease entity of chronic pancreatitis. Cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) is a key negative regulator of the T-cell immune response, and its gene is highly polymorphic. Many positive associations between cytotoxic T-lymphocyte-associated protein 4 (CTLA4) single-nucleotide polymorphisms and various autoimmune diseases have been identified. We investigated possible genetic associations of CTLA4 in a Chinese population with AIP.

METHODS

We performed genotyping for CTLA4 (49 A/G, -318 C/T, and CT60 A/G) and tumor necrosis factor (TNF)-alpha promoter (-857 C/T, -863 C/A, and -1031 C/T) by use of PCR sequence-specific primers and direct sequencing, respectively, in 46 patients with AIP, 78 patients with chronic calcifying pancreatitis (CCP), and 200 healthy individuals.

RESULTS

We found a significant increase in CTLA4 49A carriers in patients with AIP compared with healthy individuals (78.3% vs 48%; P <0.0001). The frequency of CTLA4 49A was also significantly higher in patients with AIP compared with CCP (78.3% vs 37.1%; P <0.0001). CTLA4 49A conferred a higher risk of AIP [with CCP, odds ratio (OR) 7.20; P <0.0001]. The -318C/+49A/CT60G haplotype was associated with a higher susceptibility to AIP (OR 8.53; P = 0.001). The TNF-alpha promoter -863A was associated with extrapancreatic involvement in patients with AIP.

CONCLUSION

CTLA-4 49A polymorphism and -318C/+49A/CT60G haplotype are associated with AIP in a Chinese population.

No evidence for association of CTLA-4 gene polymorphisms with the risk of developing multiple sclerosis: a meta-analysis

We conducted a meta-analysis concerning the association of cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) gene polymorphisms with the risk of developing multiple sclerosis (MS). We identified 18 eligible studies summarizing information about 3375 MS cases and 2930 healthy controls. Two polymorphisms were of interest: the exon 1 +49 A/G polymorphism (in 18 studies) and the promoter-318 C/T polymorphism (in 10 studies). Using random-effects methods we found no evidence for association of the various contrasts of genotypes (or allele frequencies) with the disease. There was significant between-studies heterogeneity that could not be explained by the ethnicity of the populations studied or by other summary measures (gender, disease course, latitude). The major finding of the meta-analysis, apart from the lack of an overall association, consists of detecting a significant time trend of the OR for the contrast of GA versus GG+AA genotypes of the exon 1 +49 A/G polymorphism. In particular, using cumulative meta-analysis we found that the large number of conflicting results on the subject was triggered by the early appearance of a highly significant published result (a study that indicated a significant association of the genotype with the disease).

The CD40, CTLA-4, thyroglobulin, TSH receptor, and PTPN22 gene quintet and its contribution to thyroid autoimmunity: back to the future

Autoimmune thyroid diseases (AITD) are common autoimmune diseases, affecting up to 5% of the general population. Thyroid-directed autoimmunity is manifested in two classical autoimmune conditions, Hashimoto's thyroiditis, resulting in hypothyroidism and Graves' disease resulting in hyperthyroidism. Autoimmune thyroid diseases arise due to an interplay between environmental and genetic factors. In the past decade significant progress has been made in our understanding of the genetic contribution to the etiology of AITD. Indeed, several AITD susceptibility genes have been identified. Some of these susceptibility genes are specific to either Graves' disease or Hashimoto's thyroiditis, while others confer susceptibility to both conditions. Both immunoregulatory genes and thyroid specific genes contribute to the pathogenesis of AITD. The time is now ripe to examine the mechanistic basis for the contribution of genetic factors to the etiology of AITD. In this review, we will focus on the contribution of non-MHC II genes.

Current status of lupus genetics

Over the past 40 years more than 100 genetic risk factors have been defined in systemic lupus erythematosus through a combination of case studies, linkage analyses of multiplex families, and case-control analyses of single genes. Multiple investigators have examined patient cohorts gathered from around the world, and although we doubt that all of the reported associations will be replicated, we have probably already discovered many of the genes that are important in lupus pathogenesis, including those encoding human leukocyte antigen-DR, Fcgamma receptor 3A, protein tyrosine phosphatase nonreceptor 22, cytotoxic T lymphocyte associated antigen 4, and mannose-binding lectin. In this review we will present what is known, what is disputed, and what remains to be discovered in the world of lupus genetics.

CTLA-4 gene exon-1 +49 A/G polymorphism: lack of association with autoimmune disease in patients with common variable immune deficiency

The presence of the G allele of exon-1 +49 A/G polymorphisms of the cytotoxic T lymphocyte antigen 4 (CTLA-4) gene has been described as a risk factor associated with the development of autoimmune diseases. Since Common Variable Immune Deficiency (CVID) is associated with autoimmune manifestations in approximately 25% of patients, we sought to examine the association of the CTLA-4 single nucleotide polymorphism with autoimmunity and other inflammatory complications. Sixteen of 47 CVID (34%) patients had a history of autoimmunity, and 15 (32%) had known granulomatous disease with or without lymphoid hyperplasia. CTLA-4 genotype frequencies were AA 40% (19), AG 45% (21), and GG 15% (7). Allele frequencies were A 63% and G 37%, similar to control populations. There were no significant associations between CTLA-4 exon-1 +49 A/G polymorphism and autoimmune or lymphoid hyperplasia and granulomatous disease in this mostly Caucasian CVID patient population.

Systemic lupus erythematosus: multiple immunological phenotypes in a complex genetic disease

Systemic lupus erythematosus (SLE) is a complex polygenic autoimmune disease characterized by the presence of anti-nuclear autoantibodies (ANAs) that are often detectable years prior to the onset of clinical disease. The disease is associated with a chronic activation of the immune system, with the most severe forms progressing to inflammatory damage that can impact multiple organ systems in afflicted individuals. Current therapeutic strategies poorly control disease manifestations and are generally immunosuppressive. Recent studies in human patient populations and animal models have associated elements of the innate immune system and abnormalities in the immature B lymphocyte receptor repertoires with disease initiation. A variety of cytokines, most notably type I interferons, play important roles in disease pathogenesis and effector mechanisms. The genetic basis for disease susceptibility is complex, and analyses in humans and mice have identified multiple susceptibility loci, several of which are located in genomic regions that are syntenic between humans and mice. The complexities of the genetic interactions that mediate lupus have been investigated in murine model systems by characterizing the progressive development of disease in strains expressing various combinations of susceptibility alleles. These analyses indicate that genetic epistasis dramatically impact disease development and support the feasibility of identifying molecular pathways that can suppress disease progression without completely impairing normal immune function.

Chimerism in systemic lupus erythematosus—three hypotheses

Systemic lupus erythematosus (SLE) is an immune-mediated disease characterized by the presence of autoantibodies and a wide array of clinical symptoms. Despite intensive research, the aetiology of SLE is still unknown and is probably multifactorial. Both genetic and environmental factors have been associated with SLE, but these factors alone are insufficient to explain the onset of SLE. Recently, it has been suggested that chimerism plays a role in the pathogenesis of autoimmune diseases, including SLE. Chimerism indicates the presence of cells from one individual in another individual. In an experimental mouse model, the injection of chimeric cells induces a lupus-like disease. In addition, chimerism is found more often in kidneys of women with SLE than in healthy controls. There are several mechanisms by which chimeric cells could be involved in the pathogenesis of SLE. In this review, three hypotheses on the role of chimerism in SLE are discussed. The first two hypotheses describe the possibilities that chimeric cells induce either a graft-vs-host reaction in the host (comparable with reactions seen after bone marrow transplantation) or a host-vs-graft reaction (comparable with reactions seen after solid organ transplantation). The third hypothesis discusses the possible beneficial role chimeric cells may play in repair mechanisms due to their stem cell-like properties. This review provides insights into the mechanisms by which chimerism may be involved in SLE and proposes several lines of inquiry to further investigate chimerism in SLE.

Evidence for unique association signals in SLE at the CD28-CTLA4-ICOS locus in a family-based study

CD28, CTLA4 (cytotoxic T lymphocyte-associated protein 4) and ICOS (inducible T cell co-stimulator) are good candidate genes for systemic lupus erythematosus (SLE) because of their role in regulating T cell activation. CTLA4 inhibits CD28-mediated T cell activation. CTLA4 is expressed on CD4+ and CD8+ activated T cells, and also B cells, but CD28 and ICOS are largely restricted to T cells. An interval encompassing the CD28-CTLA4-ICOS locus on chromosome 2q33 was linked to lupus in two genome-wide linkage scans. This large family-based association study in 532 UK SLE families represents the first high-density genetic screen of 80 SNPs at this locus. There are seven haplotype blocks across the locus. In CTLA4, the strongest signal comes from two variants, located 2.1 kb downstream from the 3'-UTR. These polymorphisms, rs231726 (SNP 43) and rs231726 (SNP 44), are in complete linkage disequilibrium (LD) (r(2)=1) and are associated with SLE P=0.0008 (GH) and P=0.01 (family-based association test). There is also a signal in the distal 3' flanking region of CTLA4/ICOS promoter (P=0.003). There was no confirmation of published associations for SLE in the promoter or coding region of CTLA4. These SLE risk alleles are more distal than those identified in Graves' disease and are in LD with Graves' disease protective alleles identified in both of these regions of CTLA4 (Ueda et al. 2003). These factors suggest an SLE-specific pattern of association. The functional consequences of the associated polymorphisms are likely to influence CTLA4 expression, although it is possible that genetically modulated ICOS expression is involved in SLE susceptibility.

Association of uteroglobin G38A polymorphism with IgA nephropathy: a meta-analysis

Both uteroglobin knockout and antisense transgenic mice develop pathological and clinical features similar to immunoglobulin A (IgA) nephropathy. However, several association studies of uteroglobin G38A polymorphism and IgA nephropathy showed controversial findings. We used meta-analysis to assess the impact of the uteroglobin G38A polymorphism on susceptibility to and progression of IgA nephropathy. Six studies involving uteroglobin G38A genotyping of 930 patients with IgA nephropathy and 768 healthy controls were included. No significant publication bias was found (Egger's linear regression, P = 0.763; 95% confidence interval [CI], -0.610 to 0.476). All control samples were in Hardy-Weinberg proportion. No association between the AA genotype and risk for IgA nephropathy relative to both other genotypes (odds ratio [OR], 1.05; 95% CI, 0.71 to 1.54) or A allele and risk for IgA nephropathy (OR, 0.96; 95% CI, 0.84 to 1.11) were shown in the total meta-analysis. In both Asian and European subgroups, the overall effect of the AA genotype and A allele also showed no significant difference. There also was no significant association between uteroglobin AA genotype or A allele and IgA nephropathy progression (OR, 3.62; 95% CI, 0.59 to 22.34; OR, 2.19, 95% CI, 0.37 to 13.14, respectively). We suggest that uteroglobin G38A polymorphism is not related to the development and progression of IgA nephropathy.

New insights into the pathogenesis of systemic lupus erythematosus

Although the etiology of systemic lupus erythematosus is unknown, recent studies have shed light on the pathogenetic pathways that lead to tissue damage. The immune system in systemic lupus erythematosus is characterized by a complex interplay between overactive B cells, abnormally activated T cells, and antigen-presenting cells. This leads to the production of an array of inflammatory cytokines, diverse autoantibodies, and immune complexes that in turn activate effector cells and the complement system leading to the clinical manifestations of the disease.

HLA class II disease associations in southern Africa

Southern Africa harbors several population groups representing a diversity of gene pool origins. This provides a unique opportunity to study genetic disease predisposition in these populations against a common environmental background. Human leukocyte antigen (HLA) association studies of these populations could improve knowledge on inter-population variation and HLA-related disease susceptibility. The aim of this paper is to review HLA class II disease associations reported for southern African population groups, compare them with findings in other populations and identify those unique to southern Africa. A number of HLA class II disease associations appear to be unique to southern African populations. These include DRB1*14011 association with insulin-dependent diabetes mellitus susceptibility in the Xhosa and DRB1*10 and DQB1*0302 with rheumatoid arthritis susceptibility in the South African (SA) Indian and SA Coloreds, respectively. A noteworthy similarity in class II disease association was observed among southern African Caucasoid and their European parental populations. Unique HLA class II disease associations observed in southern Africa are consistent with the notion that unique environmental and natural selective factors have resulted in certain ethnic-specific HLA class II disease associations, while common HLA class II disease associations found across different populations support the notion that common diseases are caused by common, ancient alleles present in indigenous African populations.

Genetic analysis and functional evaluation of the C/T(-318) and A/G(-1661) polymorphisms of the CTLA-4 gene in patients affected with Graves' disease

In this study, we evaluated the A/G(-1661), C/T(-318), A/G49 and A/G6230 single nucleotide polymorphisms (SNPs) of the cytotoxic T lymphocyte antigen 4 (CTLA-4) gene for association with Graves' disease (GD) in 126 Russian simplex families. The conditional TDT analysis revealed significant overtransmission of the A(-1661)G(-318) haplotype (P = 0.033) and undertransmission of the GT haplotype (P = 0.0043) from parents homozygous for both +49 and +6230 polymorphisms. Parents homozygous for both (-1661) and (-318) markers significantly overtransmitted the G49G6230 haplotype (P = 0.0013) and undertransmitted the AG haplotype (P = 0.035) to affected offspring. This suggests in favor of the independent genetic effects of the 3' and 5'ends of CTLA-4 in conferring the susceptibility to GD. Both SNPs located at the 5' untranslated region of CTLA-4 were functionally analyzed using the luciferase reporter assay. We observed differential activation of the C/T(-318) promoter variant when Jurkat T cells and HeLa cells were cotransfected with a plasmid expressing lymphoid enhancing factor 1 (LEF1) and various CTLA-4 promoter constructs. The (-318) SNP modifies a putative binding site for LEF1 so that it alters the stimulating effect of LEF1 on the expression ability of the CTLA-4 promoter. The (-1661) dimorphism modifies a potential binding site for myocyte enhancer factor 2 (MEF2). No significant correlation between the (-1661) SNP and MEF2 activity in cotransfection experiments was found. Observed data help for further understanding a functional role of CTLA-4 promoter polymorphisms in the pathogenic mechanism of GD.

Meta-analysis of the association of CTLA-4 exon-1 +49A/G polymorphism with rheumatoid arthritis

Rheumatoid arthritis (RA) is a common autoimmune disease. Cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) is a highly suspected candidate gene for RA susceptibility. However, association studies on the polymorphism of CTLA-4 exon-1 +49A/G in RA have shown conflicting results. Therefore, we performed a meta-analysis to better assess the purported association. In order to look for ethnic effect, we performed subgroup meta-analysis in populations of European descent and Asian descent. Meta-regression analysis was also performed to explore the possible heterogeneity between the two subgroups. Ten studies (11 comparisons) with the CTLA-4 exon-1 +49A/G genotyping on 2,315 patients with RA and 2,536 controls were selected for our meta-analysis. Overall, the fixed-effects odds ratio (OR) for the G versus A allele was 1.11 (P=0.02, 95% confidence interval (CI) 1.02-1.21), with no between-study heterogeneity. Subgroup and meta-regression analysis according to the ethnicity (European or Asian) demonstrated different scenarios concerning the CTLA-4 exon-1 +49A/G polymorphism's role in RA susceptibility for the two different subgroups. No effect of G on susceptibility was seen in European descent (five comparisons; OR=1.04, P=0.30, 95% CI 0.95-1.19; no significant between-study heterogeneity). However, there is a significant association in Asian descent under both fixed [OR=1.21, 95% CI (1.06-1.39), P=0.005] and random-effect models [OR=1.19, 95% CI (1.01-1.42), P=0.04]. Meta-regression analysis also supports the heterogeneity between the two subgroups (P=0.082). We also explored the role of this polymorphism on RA risk under other various interested genetic contrasts. These results further support that this polymorphism could not be a risk factor for Europeans. Interestingly, we find that in Asians the G allele has a greater tendency to cause RA in a recessive genetic model. However, sensitivity analysis showed that the combined result of Asian populations was unstable. In conclusion, our meta-analysis results suggest that CTLA-4 exon-1 +49G allele would not be a risk factor for RA in Europeans but might play a role in RA susceptibility for Asians.