Localization of a type 1 diabetes locus in the IL2RA/CD25 region by use of tag single-nucleotide polymorphisms

Can we vaccinate against Type 1 diabetes?

Vaccination is the administration of antigenic material to stimulate the immune system to develop adaptive immunity to a disease. As the most successful prophylactic in medical history, there is now an emerging interest as to whether vaccination can be applied in autoimmune and inflammatory conditions. These are diseases of failed immune regulation; vaccination in this context aims to exploit the power of antigenic material to stimulate immune homeostasis in the form of active, adaptive, regulatory immune responses. Type 1 diabetes is an autoimmune disease that could benefit from the therapeutic potential of vaccination. The major conditions necessary to make prophylaxis feasible are in place; the self antigens are known, the failure of existing immune regulation has been demonstrated, early studies of vaccine approaches have proved safe, and the preclinical prodrome of the disease can be easily detected by simple blood tests. Challenges for future implementation include finding the best mode of delivery and the best blend of adjunctive therapies that create the favorable conditions required for a vaccine to be effective.

Immunogenetic mechanisms leading to thyroid autoimmunity: recent advances in identifying susceptibility genes and regions

The autoimmune thyroid diseases (AITD) include Graves’ disease (GD) and Hashimoto’s thyroiditis (HT), which are characterised by a breakdown in immune tolerance to thyroid antigens. Unravelling the genetic architecture of AITD is vital to better understanding of AITD pathogenesis, required to advance therapeutic options in both disease management and prevention. The early whole-genome linkage and candidate gene association studies provided the first evidence that the HLA region and CTLA-4 represented AITD risk loci. Recent improvements in; high throughput genotyping technologies, collection of larger disease cohorts and cataloguing of genome-scale variation have facilitated genome-wide association studies and more thorough screening of candidate gene regions. This has allowed identification of many novel AITD risk genes and more detailed association mapping. The growing number of confirmed AITD susceptibility loci, implicates a number of putative disease mechanisms most of which are tightly linked with aspects of immune system function. The unprecedented advances in genetic study will allow future studies to identify further novel disease risk genes and to identify aetiological variants within specific gene regions, which will undoubtedly lead to a better understanding of AITD patho-physiology.

A genome-wide association study of inflammatory biomarker changes in response to fenofibrate treatment in the Genetics of Lipid Lowering Drug and Diet Network

OBJECTIVE

Despite the evidence in support of the anti-inflammatory and triglyceride-lowering effects of fenofibrate, little is known about genetic determinants of the observed heterogeneity in treatment response. This study provides the first genome-wide examination of fenofibrate effects on systemic inflammation.

METHODS

Biomarkers of inflammation were measured in participants of the Genetics of Lipid Lowering Drugs and Diet Network (n=1092) before and after a 3-week daily treatment with 160 mg of fenofibrate. Two inflammatory patterns [high-sensitivity C-reactive protein-interleukin-6 and monocyte chemoattractant protein-1-tumor necrosis factor (MCP1-TNF-α)] were derived using principal component analysis. Associations between single nucleotide polymorphisms on the Affymetrix 6.0 chip and phenotypes were assessed using mixed linear models, adjusted for age, sex, study center, and ancestry as fixed effects and pedigree as a random effect.

RESULTS

Before fenofibrate treatment, the strongest evidence for association was observed for polymorphisms near or within the IL2RA gene with the high-sensitivity C-reactive protein-interleukin-6 (IL6) pattern (rs7911500, P=5×10 and rs12722605, P=5×10). Associations of the MCP1-TNF-α pattern with loci in several biologically plausible genes [CYP4F8 (rs3764563), APBB1IP (rs1775246), COL13A1 (rs2683572), and COMMD10 (rs1396485)] approached genome-wide significance (P=3×10, 5×10, 6×10, and 7×10, respectively) before fenofibrate treatment. After fenofibrate treatment, the rs12722605 locus in IL2RA was also associated with the MCP1-TNF-α pattern (P=3×10). The analyses of individual biomarker response to fenofibrate did not yield genome-wide significant results, but the rs6517147 locus near the immunologically relevant IFNAR2 gene was suggestively associated with IL6 (P=7×10).

CONCLUSION

We have identified several novel biologically relevant loci associated with systemic inflammation before and after fenofibrate treatment.

Interleukin-2 and type 1 diabetes: new therapeutic perspectives

A new sort of CD4+T cells, so-called regulatory T cells (Tregs), has been described in 1996. Tregs are suggested to have an important function consisting in controlling autoimmune reactions. In humans, absence of Tregs induces the IPEX syndrome characterized by the presence of several autoimmune diseases. These cells depend on interleukin-2 (IL-2) for proliferating and controlling the T effector cells (Teff) reaction, but they do not have the capacity to produce IL-2. In type 1 diabetes (T1DM), a hypothesis is that a lack of IL-2 in pancreas could prevent Tregs action and lead to beta cells destruction. In NOD mice, low dose IL-2 treatment at the initial time of diabetes can rescue insulin secretion by restoring proteins expression that are necessary for Tregs regulatory function in the pancreas. Using low doses instead of high doses IL-2 prevents Teff activation which also depends on IL-2. These results led to conduct a dose-effect trial in human T1DM. This trial aimed at determining the therapeutic condition, which induces Tregs activation without major side effects, in a therapeutic perspective to recover insulin secretion at the apparition of diabetes.

Improving power of genome-wide association studies with weighted false discovery rate control and prioritized subset analysis

The issue of large-scale testing has caught much attention with the advent of high-throughput technologies. In genomic studies, researchers are often confronted with a large number of tests. To make simultaneous inference for the many tests, the false discovery rate (FDR) control provides a practical balance between the number of true positives and the number of false positives. However, when few hypotheses are truly non-null, controlling the FDR may not provide additional advantages over controlling the family-wise error rate (e.g., the Bonferroni correction). To facilitate discoveries from a study, weighting tests according to prior information is a promising strategy. A 'weighted FDR control' (WEI) and a 'prioritized subset analysis' (PSA) have caught much attention. In this work, we compare the two weighting schemes with systematic simulation studies and demonstrate their use with a genome-wide association study (GWAS) on type 1 diabetes provided by the Wellcome Trust Case Control Consortium. The PSA and the WEI both can increase power when the prior is informative. With accurate and precise prioritization, the PSA can especially create substantial power improvements over the commonly-used whole-genome single-step FDR adjustment (i.e., the traditional un-weighted FDR control). When the prior is uninformative (true disease susceptibility regions are not prioritized), the power loss of the PSA and the WEI is almost negligible. However, a caution is that the overall FDR of the PSA can be slightly inflated if the prioritization is not accurate and precise. Our study highlights the merits of using information from mounting genetic studies, and provides insights to choose an appropriate weighting scheme to FDR control on GWAS.

Type 1 diabetes-associated IL2RA variation lowers IL-2 signaling and contributes to diminished CD4+CD25+ regulatory T cell function

Numerous reports have demonstrated that CD4(+)CD25(+) regulatory T cells (Tregs) from individuals with a range of human autoimmune diseases, including type 1 diabetes, are deficient in their ability to control autologous proinflammatory responses when compared with nondiseased, control individuals. Treg dysfunction could be a primary, causal event or may result from perturbations in the immune system during disease development. Polymorphisms in genes associated with Treg function, such as IL2RA, confer a higher risk of autoimmune disease. Although this suggests a primary role for defective Tregs in autoimmunity, a link between IL2RA gene polymorphisms and Treg function has not been examined. We addressed this by examining the impact of an IL2RA haplotype associated with type 1 diabetes on Treg fitness and suppressive function. Studies were conducted using healthy human subjects to avoid any confounding effects of disease. We demonstrated that the presence of an autoimmune disease-associated IL2RA haplotype correlates with diminished IL-2 responsiveness in Ag-experienced CD4(+) T cells, as measured by phosphorylation of STAT5a, and is associated with lower levels of FOXP3 expression by Tregs and a reduction in their ability to suppress proliferation of autologous effector T cells. These data offer a rationale that contributes to the molecular and cellular mechanisms through which polymorphisms in the IL-2RA gene affect immune regulation, and consequently upon susceptibility to autoimmune and inflammatory diseases.

Genetic factors of autoimmune thyroid diseases in Japanese

Autoimmune thyroid diseases (AITDs), including Graves' disease (GD) and Hashimoto's thyroiditis (HT), are caused by immune response to self-thyroid antigens and affect approximately 2–5% of the general population. Genetic susceptibility in combination with external factors, such as smoking, viral/bacterial infection, and chemicals, is believed to initiate the autoimmune response against thyroid antigens. Abundant epidemiological data, including family and twin studies, point to a strong genetic influence on the development of AITDs. Various techniques have been employed to identify genes contributing to the etiology of AITDs, including candidate gene analysis and whole genome screening. These studies have enabled the identification of several loci (genetic regions) that are linked to AITDs, and, in some of these loci, putative AITD susceptibility genes have been identified. Some of these genes/loci are unique to GD and HT and some are common to both diseases, indicating that there is a shared genetic susceptibility to GD and HT. Known AITD-susceptibility genes are classified into three groups: HLA genes, non-HLA immune-regulatory genes (e.g., CTLA-4, PTPN22, and CD40), and thyroid-specific genes (e.g., TSHR and Tg). In this paper, we will summarize the latest findings on AITD susceptibility genes in Japanese.

The Correlation between the CLEC16A Gene and Genetic Susceptibility to Type 1 Diabetes in Chinese Children

Objective. The CLEC16A gene is related to the genetic susceptibility to T1DM with racial variability. This study investigated the association between CLEC16A gene polymorphisms and T1DM in Chinese children. Methods. 131 Chinese children with T1DM were selected for study, and 121 healthy adult blood donors were selected as normal controls. PCR and mass spectrometry was used to study the distributions of 17 CLEC16A alleles in patients and controls. The relationship between CLEC16A gene polymorphisms and T1DM was studied. Results. The distributions of two polymorphisms (rs12921922, rs12931878) of CLEC16A in T1DM and healthy controls were significantly different, while the distributions of other CLEC16A polymorphisms show no significant differences. The alleles of rs12921922 are C and T. The frequency of the T allele was significantly increased in patients versus healthy controls. The alleles of rs12931878 are A and C. The frequencies of the A allele are significantly increased in T1DM patients versus healthy controls. Conclusion. Two polymorphisms in the CLEC16A gene correlate with increased susceptibility to T1DM in Chinese children, revealing that it was another new gene that correlates with susceptibility to T1DM in multiple populations.

A variant of the Il2ra / Cd25 gene predisposing to graves' disease is associated with increased levels of soluble interleukin-2 receptor

Alpha-subunit of the IL-2 receptor (IL-2Rα) encoded by the IL2RA/CD25 gene binds IL-2 that plays a pivotal role in the regulation of T cell function. Levels of a soluble form of IL-2Rα (sIL-2Rα) lacking the transmembrane and cytoplasmic domains were shown to be increased in several autoimmune diseases including Graves' disease (GD). Recent studies showed association between the IL2RA/CD25 gene variants and several autoimmune diseases including GD. In this study, we analyzed whether polymorphic markers rs2104286, rs41295061, and rs11594656 located at the IL2RA/CD25 locus confer susceptibility to GD and are related to increased concentrations of sIL-2Rα. A total of 1474 Russian GD patients and 1609 control subjects were genotyped for rs2104286, rs41295061, and rs11594656 using a Taqman assay. Concentrations of sIL-2Rα in sera of affected and non-affected individuals were measured using an ELISA test. A minor allele A of rs41295061 showed significant association with increased risk of GD [odds ratio (OR) = 1.43, P(c)  = 0.00102]. The allele A of rs41295061 and allele A of rs11594656 constitute a higher risk haplotype AA (OR = 1.47, P(c)  = 0.0477). Compared to carriers of the protective haplogenotype GT/GT, the carriage of two copies of the haplogenotype AA/AA was associated with elevated levels of sIL-2Rα in both GD patients (AA/AA versus GT/GT: 1.35 ± 0.47 ng/ml versus 1.12 ± 0.45 ng/ml, P = 0.0065) and healthy controls (AA/AA versus GT/GT: 0.67 ± 0.28 ng/ml versus 0.51 ± 0.33 ng/ml, P = 0.0098). This is the first report presenting correlation between the carriage of disease-associated variants of IL2RA/CD25 with increased levels of sIL-2Rα in GD.

Determination of the real effect of genes identified in GWAS: the example of IL2RA in multiple sclerosis

Genome-wide association studies (GWAS), although efficient to detect genes involved in complex diseases, are not designed to measure the real effect of the genes. This is illustrated here by the example of IL2RA in multiple sclerosis (MS). Association between IL2RA and MS is clearly established, although the functional variation is still unknown: the effect of IL2RA might be better described by several SNPs than by a single one. This study investigates whether a pair of SNPs better explains the observed linkage and association data than a single SNP. In total, 522 trio families and 244 affected sib-pairs were typed for 26 IL2RA SNPs. For each SNP and pairs of SNPs, the phased genotypes of patients and controls were compared to determine the SNP set offering the best risk discrimination. Consistency between the genotype risks provided by the retained set and the identical by descent allele sharing in affected sib-pairs was assessed. After controlling for multiple testing, the set of SNPs rs2256774 and rs3118470, provides the best discrimination between the case and control genotype distributions (P-corrected=0.009). The relative risk between the least and most at-risk genotypes is 3.54 with a 95% confidence interval of [2.14-5.94]. Furthermore, the linkage information provided by the allele sharing between affected sibs is consistent with the retained set (P=0.80) but rejects the SNP reported in the literature (P=0.006). Establishing a valid modeling of a disease gene is essential to test its potential interaction with other genes and to reconstruct the pathophysiological pathways.

Understanding type 1 diabetes through genetics: advances and prospects

Starting with early crucial discoveries of the role of the major histocompatibility complex, genetic studies have long had a role in understanding the biology of type 1 diabetes (T1D), which is one of the most heritable common diseases. Recent genome-wide association studies (GWASs) have given us a clearer picture of the allelic architecture of genetic susceptibility to T1D. Fine mapping and functional studies are gradually revealing the complex mechanisms whereby immune self-tolerance is lost, involving multiple aspects of adaptive immunity. The triggering of these events by dysregulation of the innate immune system has also been implicated by genetic evidence. Finally, genetic prediction of T1D risk is showing promise of use for preventive strategies.

Genome-wide association studies (GWAS): impact on elucidating the aetiology of diabetes

It has proven to be challenging to isolate the genes underlying the genetic components conferring susceptibility to type 1 and type 2 diabetes. Unlike previous approaches, 'genome-wide association studies' have extensively delivered on the promise of uncovering genetic determinants of complex diseases, with a number of novel disease-associated variants being largely replicated by independent groups. This review provides an overview of these recent breakthroughs in the context of type 1 and type 2 diabetes, and outlines strategies on how these findings will be applied to impact clinical care for these two highly prevalent disorders.

The past, present, and future of genetic associations in type 1 diabetes

Type 1 diabetes mellitus (T1DM) is an autoimmune disease affecting approximately one in 300 individuals in the United States. The majority of genetic research to date has focused on the heritability that predisposes to islet autoimmunity and T1DM. The evidence so far points to T1DM being a polygenic, common, complex disease with major susceptibility lying in the major histocompatibility complex (MHC) on chromosome 6 with other smaller effects seen in loci outside of the MHC. With recent advances in technology, novel means of exploring the human genome have given way to new information in the development of T1DM. The newest technologies, namely high-throughput polymorphism typing and sequencing, have led to a paradigm shift in studying common diseases such as T1DM. In this review we highlight the advances in genetic associations in T1DM in the last several decades and how they have led to a better understanding of T1DM pathogenesis.

A genome-wide meta-analysis of six type 1 diabetes cohorts identifies multiple associated loci

Diabetes impacts approximately 200 million people worldwide, of whom approximately 10% are affected by type 1 diabetes (T1D). The application of genome-wide association studies (GWAS) has robustly revealed dozens of genetic contributors to the pathogenesis of T1D, with the most recent meta-analysis identifying in excess of 40 loci. To identify additional genetic loci for T1D susceptibility, we examined associations in the largest meta-analysis to date between the disease and ∼2.54 million SNPs in a combined cohort of 9,934 cases and 16,956 controls. Targeted follow-up of 53 SNPs in 1,120 affected trios uncovered three new loci associated with T1D that reached genome-wide significance. The most significantly associated SNP (rs539514, P = 5.66×10⁻¹¹) resides in an intronic region of the LMO7 (LIM domain only 7) gene on 13q22. The second most significantly associated SNP (rs478222, P = 3.50×10⁻⁹) resides in an intronic region of the EFR3B (protein EFR3 homolog B) gene on 2p23; however, the region of linkage disequilibrium is approximately 800 kb and harbors additional multiple genes, including NCOA1, C2orf79, CENPO, ADCY3, DNAJC27, POMC, and DNMT3A. The third most significantly associated SNP (rs924043, P = 8.06×10⁻⁹) lies in an intergenic region on 6q27, where the region of association is approximately 900 kb and harbors multiple genes including WDR27, C6orf120, PHF10, TCTE3, C6orf208, LOC154449, DLL1, FAM120B, PSMB1, TBP, and PCD2. These latest associated regions add to the growing repertoire of gene networks predisposing to T1D.

Despite the fact that there is clearly a large genetic component to type 1 diabetes (T1D), uncovering the genes contributing to this disease has proven challenging. However, in the past three years there has been relatively major progress in this regard, with advances in genetic screening technologies allowing investigators to scan the genome for variants conferring risk for disease without prior hypotheses. Such genome-wide association studies have revealed multiple regions of the genome to be robustly and consistently associated with T1D. More recent findings have been a consequence of combining of multiple datasets from independent investigators in meta-analyses, which have more power to pick up additional variants contributing to the trait. In the current study, we describe the largest meta-analysis of T1D genome-wide genotyped datasets to date, which combines six large studies. As a consequence, we have uncovered three new signals residing at the chromosomal locations 13q22, 2p23, and 6q27, which went on to be replicated in independent sample sets. These latest associated regions add to the growing repertoire of gene networks predisposing to T1D.

Replication and further characterization of a Type 1 diabetes-associated locus at the telomeric end of the major histocompatibility complex

BACKGROUND

We recently reported an association between Type 1 diabetes and the telomeric major histocompatibility complex (MHC) single nucleotide polymorphism (SNP) rs1233478. As further families have been analyzed in the Type 1 Diabetes Genetics Consortium (T1DGC), we tested replication of the association and, with more data, analyzed haplotypic associations.

METHODS

An additional 2717 case and 1315 control chromosomes have been analyzed from the T1DGC, with human leukocyte antigen (HLA) typing and data for 2837 SNPs across the MHC region.

RESULTS

We confirmed the association of rs1233478 (new data only: P=2.2E-5, OR=1.4). We also found two additional SNPs nearby that were significantly associated with Type 1 diabetes (new data only rs3131020: P=8.3E-9, OR=0.65; rs1592410: P=2.2E-8, OR=1.5). For studies of Type 1 diabetes in the MHC region, it is critical to account for linkage disequilibrium with the HLA genes. Logistic regression analysis of these new data indicated that the effects of rs3131020 and rs1592410 on Type 1 diabetes risk are independent of HLA alleles (rs3131020: P=2.3E-3, OR=0.73; rs1592410: P=2.1E-3, OR=1.4). Haplotypes of 12 SNPs (including the three highly significant SNPs) stratify diabetes risk (high risk, protective, and neutral), with high-risk haplotypes limited to approximately 20,000 bp in length. The 20,000-bp region is telomeric of the UBD gene and contains LOC729653, a hypothetical gene.

CONCLUSIONS

We believe that polymorphisms of the telomeric MHC locus LOC729653 may confer risk for Type 1 diabetes.

Nonsegmental vitiligo and autoimmune mechanism

Nonsegmental vitiligo is a depigmented skin disorder showing acquired, progressive, and depigmented lesions of the skin, mucosa, and hair. It is believed to be caused mainly by the autoimmune loss of melanocytes from the involved areas. It is frequently associated with other autoimmune diseases, particularly autoimmune thyroid diseases including Hashimoto's thyroiditis and Graves' disease, rheumatoid arthritis, type 1 diabetes, psoriasis, pernicious anemia, systemic lupus erythematosus, Addison's disease, and alopecia areata. This indicates the presence of genetically determined susceptibility to not only vitiligo but also to other autoimmune disorders. Here, we summarize current understanding of autoimmune pathogenesis in non-segmental vitiligo.

The HLA Region and Autoimmune Disease: Associations and Mechanisms of Action

The HLA region encodes several molecules that play key roles in the immune system. Strong association between the HLA region and autoimmune disease (AID) has been established for over fifty years. Association of components of the HLA class II encoded HLA-DRB1-DQA1-DQB1 haplotype has been detected with several AIDs, including rheumatoid arthritis, type 1 diabetes and Graves' disease. Molecules encoded by this region play a key role in exogenous antigen presentation to CD4+ Th cells, indicating the importance of this pathway in AID initiation and progression. Although other components of the HLA class I and III regions have also been investigated for association with AID, apart from the association of HLA-B*27 with ankylosing spondylitis, it has been difficult to determine additional susceptibility loci independent of the strong linkage disequilibrium (LD) with the HLA class II genes. Recent advances in the statistical analysis of LD and the recruitment of large AID datasets have allowed investigation of the HLA class I and III regions to be re-visited. Association of the HLA class I region, independent of known HLA class II effects, has now been detected for several AIDs, including strong association of HLA-B with type 1 diabetes and HLA-C with multiple sclerosis and Graves' disease. These results provide further evidence of a possible role for bacterial or viral infection and CD8+ T cells in AID onset. The advances being made in determining the primary associations within the HLA region and AIDs will not only increase our understanding of the mechanisms behind disease pathogenesis but may also aid in the development of novel therapeutic targets in the future.

Type I diabetes-associated tolerogenic properties of interleukin-2

Type 1 Diabetes (T1D) results from insulin-producing beta cells destruction by diabetogenic T lymphocytes in humans and nonobese diabetic (NOD) mice. The breakdown of tolerance has been associated with a defect in the number and the function of naturally occurring regulatory T cells (nTreg) that are the master player in peripheral tolerance. Gene knockout experiments in mouse models have shown a nonredundant activity of IL-2 related to its critical role in inducing nTreg and controlling peripheral T cell tolerance. Whereas strong evidence has suggested that IL-2 is critically required for nTreg-mediated T1D control, several fundamental questions remain to be addressed. In this paper, we highlight the recent findings and controversies regarding the tolerogenic properties of IL-2 mediated through nTreg. We further discuss a potential link between the immunomodulatory role of interleukin-2 and the pathogenesis of type 1 diabetes.

An update on the use of NOD mice to study autoimmune (Type 1) diabetes

The widely used nonobese diabetic (NOD) mouse model of autoimmune (Type 1) diabetes mellitus shares multiple characteristics with the human disease, and studies employing this model continue to yield clinically relevant and important information. Here, we review some of the recent key findings obtained from NOD mouse investigations that have both advanced our understanding of disease pathogenesis and suggested new therapeutic targets and approaches. Areas discussed include antigen discovery, identification of genes and pathways contributing to disease susceptibility, development of strategies to image islet inflammation and the testing of therapeutics. We also review recent technical advances that, combined with an improved understanding of the NOD mouse model's limitations, should work to ensure its popularity, utility and relevance in the years ahead.

Inherited variation in vitamin D genes is associated with predisposition to autoimmune disease type 1 diabetes

OBJECTIVE

Vitamin D deficiency (25-hydroxyvitamin D [25(OH)D] <50 nmol/L) is commonly reported in both children and adults worldwide, and growing evidence indicates that vitamin D deficiency is associated with many extraskeletal chronic disorders, including the autoimmune diseases type 1 diabetes and multiple sclerosis.

RESEARCH DESIGN AND METHODS

We measured 25(OH)D concentrations in 720 case and 2,610 control plasma samples and genotyped single nucleotide polymorphisms from seven vitamin D metabolism genes in 8,517 case, 10,438 control, and 1,933 family samples. We tested genetic variants influencing 25(OH)D metabolism for an association with both circulating 25(OH)D concentrations and disease status.

RESULTS

Type 1 diabetic patients have lower circulating levels of 25(OH)D than similarly aged subjects from the British population. Only 4.3 and 18.6% of type 1 diabetic patients reached optimal levels (≥75 nmol/L) of 25(OH)D for bone health in the winter and summer, respectively. We replicated the associations of four vitamin D metabolism genes (GC, DHCR7, CYP2R1, and CYP24A1) with 25(OH)D in control subjects. In addition to the previously reported association between type 1 diabetes and CYP27B1 (P = 1.4 × 10(-4)), we obtained consistent evidence of type 1 diabetes being associated with DHCR7 (P = 1.2 × 10(-3)) and CYP2R1 (P = 3.0 × 10(-3)).

CONCLUSIONS

Circulating levels of 25(OH)D in children and adolescents with type 1 diabetes vary seasonally and are under the same genetic control as in the general population but are much lower. Three key 25(OH)D metabolism genes show consistent evidence of association with type 1 diabetes risk, indicating a genetic etiological role for vitamin D deficiency in type 1 diabetes.

Intrinsic and extrinsic control of peripheral T-cell tolerance by costimulatory molecules of the CD28/ B7 family

Positive and negative costimulation by members of the CD28 family is critical for the development of productive immune responses against foreign pathogens and their proper termination to prevent inflammation-induced tissue damage. In addition, costimulatory signals are critical for the establishment and maintenance of peripheral tolerance. This paradigm has been established in many animal models and has led to the development of immunotherapies targeting costimulation pathways for the treatment of cancer, autoimmune disease, and allograft rejection. During the last decade, the complexity of the biology of costimulatory pathways has greatly increased due to the realization that costimulation does not affect only effector T cells but also influences regulatory T cells and antigen-presenting cells. Thus, costimulation controls T-cell tolerance through both intrinsic and extrinsic pathways. In this review, we discuss the influence of costimulation on intrinsic and extrinsic pathways of peripheral tolerance, with emphasis on members of the CD28 family, CD28, cytotoxic T-lymphocyte antigen-4 (CTLA-4), and programmed death-1 (PD-1), as well as the downstream cytokine interleukin-1 (IL-2).

Diseases associated with thyroid autoimmunity: explanations for the expanding spectrum

Anyone who has been in an endocrine clinic will appreciate that associations exist between autoimmune thyroid disease (AITD) and other autoimmune disorders. However, the full extent of these associations is still not fully appreciated, and new associations are being uncovered which may shed new light on the pathogenic basis for these connections, and the underlying reasons for them are only now becoming understood. This review is based on the British Thyroid Association Pitt-Rivers Lecture 2010. The first section provides an update on studies which have detailed the strength of various autoimmune disease associations, the second section discusses the environmental and genetic factors which underlie these associations and the final section describes some recently identified, unexpected AITD associations. Unravelling these associations further will illuminate the pathogenesis of autoimmune diseases and offers the prospect of new therapeutic approaches.

Single-cell quantification of IL-2 response by effector and regulatory T cells reveals critical plasticity in immune response

The sensitivity of T cells to interleukin-2 (IL-2) can vary by three orders of magnitude and is determined by the surface densities of the IL-2 receptor α subunits.

Regulatory T cells inflict a double hit on effector T cells by lowering the bulk IL-2 concentration as well as the sensitivity of effector T cells to this crucial cytokine.

This double hit deprives weakly activated effector T cells of pSTAT5 survival signals while having only minimal effects on strongly activated effector cells that express increased levels of the IL-2 receptor.

Short-term signaling differences lead to a differential functional in terms of proliferation and cell division: regulatory T cell specifically suppress weakly activated effector T cells even at large numbers; small numbers of strongly activated effector T cells overcome the suppression.

Self-/non-self-discrimination in the adaptive immune system relies, to a large extent, on distinctions between self-antigens and foreign antigens as made by individual T cells. As such, single-cell decisions are prone to errors a reliable immune response can be expected to incorporate further proofreading schemes. One such scheme involves long time scale, population-level interactions between effector (T_eff) and regulatory (T_reg) T cells. T_reg cells are often described as immune suppressors; their role as immune regulators can be understood by mapping out the scenarios in which T_reg suppression is either significant or insignificant.

In this study, we have focused on one mechanism that allows T_reg cells to suppress T_eff survival, namely, interleukin-2 (IL-2) deprivation. Following antigen activation, T_eff cells secrete IL-2 and express the α subunit of the IL-2 receptor (IL-2r). The binding of extracellular IL-2 to the IL-2r is crucial for T_eff survival and proliferation and consequently for a full-blown immune response. T_reg cells deplete this IL-2 from the environment and deprive the T_eff cells of this important survival signal. In this tug-of-war for IL-2, we sought to quantitatively describe those scenarios in which IL-2 uptake by T_reg cells suffices to suppress T_eff cell activation and those where it does not.

The core of this competition for IL-2 lies in the fact that IL-2rα is expressed on both T_eff and T_reg cells. To understand how IL-2 binds to its receptor, we measured IL-2r subunit levels on single cells, together with STAT5 phosphorylation as evoked by varied IL-2. Contrary to previous descriptions that set the EC₅₀ of IL-2/IL-2r interaction at 10 pM, we found that the sensitivity of T cells to IL-2 varies over three orders of magnitude concentrations (Figure 1E, experiment). T_eff cells with higher levels of IL-2rα receptor subunit are more sensitive to IL-2, T_reg cells with higher levels of IL-2rα are more efficient in the scavenging of IL-2. IL-2rβ levels, on the other hand, determine response amplitudes. We describe a short time scale, two-step model to quantitatively describe IL-2 binding onto individual cells (Figure 1E, theory).

IL-2r expression levels are therefore a crucial parameter for determining the outcome of the competition for IL-2. We measured the regulation of IL-2r subunits on longer time scales in cultures of either T_eff or T_reg cells. For both cell types, IL-2r levels depend on the exposure to IL-2. For T_eff cells, there is a further dependence on the concentration of antigen by which they were activated.

We then measured IL-2r expression in cocultures of T_reg and T_eff cells. We show how IL-2 secreted by activated T_eff cells suffices in inducing IL-2rα upregulation in the T_reg population. We further show that the presence of T_reg cells decreased IL-2r upregulation in cocultured weakly activated T_eff cells. T_reg cells thus inflict a double hit on T_eff cells by reducing not only extracellular IL-2 concentrations but also the T_eff cells' ability to sense IL-2. T_eff cells activated by high-antigen concentrations exhibit sustained IL-2rα expression that is less prone to this effect. We compared IL-2r levels on T_reg cells and T_eff activated by varied antigen concentrations and found a critical crossover: at low-antigen concentrations T_reg cells have higher IL-2rα than T_eff cells, but this is reversed at high-antigen concentrations.

We constructed a long time scale computational model to quantify the significance of this crossover. The model describes IL-2/IL-2r binding and the regulation of IL-2 and IL-2r expression in populations of T_reg and T_eff cells. For a pure T_eff population, our model predicted a ‘quorum-sensing' threshold implying that sustained pSTAT5 signaling requires a minimal concentration of cells that increases with decreasing activation strength. The model further predicts that the addition of T_reg cells will greatly increase the quorum concentration for weakly activated T_eff cells but have no effect on strongly activated T_eff cells.

We validated the model's predictions in vitro. We show a quorum-sensing threshold for activated T_eff cells. We also show that the presence of a T_reg population suppressed pSTAT5 signaling in a large number of weakly but has little effect on even a few strongly activated T_eff cells (Figure 6C and D). On longer time scales, this translates to the suppression of cell division (Figure 6G and H) and proliferation (Figure 6I) in a manner that discriminates between strongly and weakly activated cells.

We then went to demonstrate that IL-2 deprivation by T_reg cells takes place in vivo. We used IL-2 injections to upregulate IL-2rα levels in T_reg cells. As predicted by our in vitro results, such treatment leads to a suppressive environment in which T_eff cells activated by subsequent antigen/LPS immunization proliferate to a lesser extent. We were able to reverse this suppressive effect by continuing IL-2 treatment post-immunization. This highlights IL-2 as a limiting factor for T_eff proliferation and renders its scavenging by T_reg cells an important mechanism of suppression in vivo.

In conclusion, we formulated a quantitative description of IL-2/IL-2r regulation in mixed population of T_reg and T_eff cells. Population feedback loops that depend on cell numbers, molecular cell surface densities, free molecular densities and timing critically affect the outcome of the competition for IL-2. Such a description allows us to precisely identify the scenarios in which IL-2 deprivation by T_reg cells has a major suppressive role in vitro and better understand the role of this mechanism in vivo.

Understanding how the immune system decides between tolerance and activation by antigens requires addressing cytokine regulation as a highly dynamic process. We quantified the dynamics of interleukin-2 (IL-2) signaling in a population of T cells during an immune response by combining in silico modeling and single-cell measurements in vitro. We demonstrate that IL-2 receptor expression levels vary widely among T cells creating a large variability in the ability of the individual cells to consume, produce and participate in IL-2 signaling within the population. Our model reveals that at the population level, these heterogeneous cells are engaged in a tug-of-war for IL-2 between regulatory (T_reg) and effector (T_eff) T cells, whereby access to IL-2 can either increase the survival of T_eff cells or the suppressive capacity of T_reg cells. This tug-of-war is the mechanism enforcing, at the systems level, a core function of T_reg cells, namely the specific suppression of survival signals for weakly activated T_eff cells but not for strongly activated cells. Our integrated model yields quantitative, experimentally validated predictions for the manipulation of T_reg suppression.

Genetics of type 1 diabetes

BACKGROUND

Type 1 diabetes, a multifactorial disease with a strong genetic component, is caused by the autoimmune destruction of pancreatic β cells. The major susceptibility locus maps to the HLA class II genes at 6p21, although more than 40 non-HLA susceptibility gene markers have been confirmed.

CONTENT

Although HLA class II alleles account for up to 30%-50% of genetic type 1 diabetes risk, multiple non-MHC loci contribute to disease risk with smaller effects. These include the insulin, PTPN22, CTLA4, IL2RA, IFIH1, and other recently discovered loci. Genomewide association studies performed with high-density single-nucleotide-polymorphism genotyping platforms have provided evidence for a number of novel loci, although fine mapping and characterization of these new regions remain to be performed. Children born with the high-risk genotype HLADR3/4-DQ8 comprise almost 50% of children who develop antiislet autoimmunity by the age of 5 years. Genetic risk for type 1 diabetes can be further stratified by selection of children with susceptible genotypes at other diabetes genes, by selection of children with a multiple family history of diabetes, and/or by selection of relatives that are HLA identical to the proband.

SUMMARY

Children with the HLA-risk genotypes DR3/4-DQ8 or DR4/DR4 who have a family history of type 1 diabetes have more than a 1 in 5 risk for developing islet autoantibodies during childhood, and children with the same HLA-risk genotype but no family history have approximately a 1 in 20 risk. Determining extreme genetic risk is a prerequisite for the implementation of primary prevention trials, which are now underway for relatives of individuals with type 1 diabetes.

Type 1 Diabetes: Etiology, Immunology, and Therapeutic Strategies

Type 1 diabetes (T1D) is a chronic autoimmune disease in which destruction or damaging of the beta-cells in the islets of Langerhans results in insulin deficiency and hyperglycemia. We only know for sure that autoimmunity is the predominant effector mechanism of T1D, but may not be its primary cause. T1D precipitates in genetically susceptible individuals, very likely as a result of an environmental trigger. Current genetic data point towards the following genes as susceptibility genes: HLA, insulin, PTPN22, IL2Ra, and CTLA4. Epidemiological and other studies suggest a triggering role for enteroviruses, while other microorganisms might provide protection. Efficacious prevention of T1D will require detection of the earliest events in the process. So far, autoantibodies are most widely used as serum biomarker, but T-cell readouts and metabolome studies might strengthen and bring forward diagnosis. Current preventive clinical trials mostly focus on environmental triggers. Therapeutic trials test the efficacy of antigen-specific and antigen-nonspecific immune interventions, but also include restoration of the affected beta-cell mass by islet transplantation, neogenesis and regeneration, and combinations thereof. In this comprehensive review, we explain the genetic, environmental, and immunological data underlying the prevention and intervention strategies to constrain T1D.

Endocrine autoimmune disease: genetics become complex

The endocrine system is a frequent target in pathogenic autoimmune responses. Type 1 diabetes and autoimmune thyroid disease are the prevailing examples. When several diseases cluster together in one individual, the phenomenon is called autoimmune polyglandular syndrome. Progress has been made in understanding the genetic factors involved in endocrine autoimmune diseases. Studies on monogenic autoimmune diseases such as autoimmune polyglandular syndrome type 1, immunodysregulation, polyendocrinopathy, enteropathy, X-linked and primary immune deficiencies helped uncover the role of key regulators in the preservation of immune tolerance. Alleles of the major histocompatibility complex have been known to contribute to the susceptibility to most forms of autoimmunity for more than 3 decades. Furthermore, sequencing studies revealed three non-major histocompatibility complex loci and some disease specific loci, which control T lymphocyte activation or signalling. Recent genome-wide association studies (GWAS) have enabled acceleration in the identification of novel (non-HLA) loci and hence other relevant immune response pathways. Interestingly, several loci are shared between autoimmune diseases, and surprisingly some work in opposite direction. This means that the same allele which predisposes to a certain autoimmune disease can be protective in another. Well powered GWAS in type 1 diabetes has led to the uncovering of a significant number of risk variants with modest effect. These studies showed that the innate immune system may also play a role in addition to the adaptive immune system. It is anticipated that next generation sequencing techniques will uncover other (rare) variants. For other autoimmune disease (such as autoimmune thyroid disease) GWAS are clearly needed.

IL-2 as a therapeutic target for the restoration of Foxp3+ regulatory T cell function in organ-specific autoimmunity: implications in pathophysiology and translation to human disease

Peripheral immune tolerance requires a finely controlled balance between tolerance to self-antigens and protective immunity against enteric and invading pathogens. Self-reactive T cells sometimes escape thymic clonal deletion, and can subsequently provoke autoimmune diseases such as type 1 diabetes (T1D) unless they are controlled by a network of tolerance mechanisms in the periphery, including CD4+ regulatory T cells (Treg) cells. CD4+ Treg cells are characterized by the constitutive expression of the IL-2Rα chain (CD25) and preferentially express the forkhead winged helix transcriptional regulator Foxp3. These cells have been shown to possess immunosuppressive properties towards various immune cell subsets and their defects are thought to contribute to many autoimmune disorders. Strong evidence shows that IL-2 is one of the important stimulatory signals for the development, function and fitness of Treg cells. The non-obese diabetic (NOD) mouse model, a prototypic model of spontaneous autoimmunity, mimics many features of human T1 D. Using this model, the contribution of the IL-2-IL-2R pathway to the development of T1 D and other autoimmune disorders has been extensively studied. In the past years, strong genetic and molecular evidence has indicated an essential role for the IL-2/IL-2R pathway in autoimmune disorders. Thus, the major role of IL-2 is to maintain immune tolerance by promoting Treg cell development, functional fitness and stability. Here we first summarize the genetic and experimental evidence demonstrating a role for IL-2 in autoimmunity, mainly through the study of the NOD mouse model, and analyze the cellular and molecular mechanisms of its action on Treg cells. We then move on to describe how this data can be translated to applications for human autoimmune diseases by using IL-2 as a therapeutic agent to restore Treg cell fitness, numbers and functions.

IL-2 reverses established type 1 diabetes in NOD mice by a local effect on pancreatic regulatory T cells

Regulatory T cells (T reg cells) play a major role in controlling the pathogenic autoimmune process in type 1 diabetes (T1D). Interleukin 2 (IL-2), a cytokine which promotes T reg cell survival and function, may thus have therapeutic efficacy in T1D. We show that 5 d of low-dose IL-2 administration starting at the time of T1D onset can reverse established disease in NOD (nonobese diabetic) mice, with long-lasting effects. Low-dose IL-2 increases the number of T reg cells in the pancreas and induces expression of T reg cell–associated proteins including Foxp3, CD25, CTLA-4, ICOS (inducible T cell costimulator), and GITR (glucocorticoid-induced TNF receptor) in these cells. Treatment also suppresses interferon γ production by pancreas-infiltrating T cells. Transcriptome analyses show that low-dose IL-2 exerts much greater influence on gene expression of T reg cells than effector T cells (T eff cells), suggesting that nonspecific activation of pathogenic T eff cells is less likely. We provide the first preclinical data showing that low-dose IL-2 can reverse established T1D, suggesting that this treatment merits evaluation in patients with T1D.

Association of the protein tyrosine phosphatase nonreceptor 22 haplotypes with autoimmune thyroid disease in the Japanese population

BACKGROUND

A missence single-nucleotide polymorphism (SNP) in the protein tyrosine phosphatase nonreceptor 22 (PTPN22) gene known as R620W (rs2476601) was recently reported to be associated with several autoimmune diseases including Graves' disease (GD). The association was repeatedly confirmed in the populations of North European ancestry. However, this amino acid was reported to be nonpolymorphic in the Asian populations. Since the gene confers an impact on autoimmune diseases, we attempt to explore an association between the PTPN22 gene and autoimmune thyroid disease (AITD) in a Japanese population without restricting to rs2476601. Previous investigations have also demonstrated that two intronic SNPs (rs706778 and rs3118470) in the interleukin-2 receptor-alpha (IL2RA) gene were associated with type 1 diabetes in the Japanese population.

PATIENTS AND METHODS

We genotyped the five SNPs (rs12760457, rs2797415, rs1310182, rs2476599, and rs3789604) of the PTPN22 and the two SNPs (rs706778 and rs3118470 in the IL2RA gene) in 456 Japanese patients with AITD (286 with GD, 170 with Hashimoto's thyroiditis) and 221 matched Japanese control subjects. Seven SNPs were analyzed by either the SNAPshot method or the high-resolution melting and unlabeled probe methods. Case-control association studies were performed using the chi(2) and Fisher's exact tests with Yates correction. Haplotype was conducted using the expectation-maximization algorithm.

RESULTS

No association was found between any of the individual SNPs of the PTPN22 gene and AITD. Permutation analysis revealed that the distribution of one haplotype is significantly different between patients with AITD and controls (p = 0.0036). A novel protective effect of a haplotype containing five SNPs was observed (p < 0.0001 for AITD, p < 0.0001 for GD, and p < 0.0001 for Hashimoto's thyroiditis, respectively). The GG allele of rs3118470 in the IL2RA gene was significantly associated with GD (p = 0.03), although the association was weak.

CONCLUSIONS

Significant difference in the distribution of the haplotype suggests that the PTPN22 gene rather than rs2476601 is involved in the development of AITD in the Japanese population.

Genetic susceptibility to autoimmune thyroid disease: past, present, and future

BACKGROUND

Autoimmune thyroid diseases (AITD), including Graves' disease and Hashimoto's thyroiditis, arise due to complex interactions between environmental and genetic factors. There are sound data coming from epidemiological, family, and twin studies demonstrating a strong genetic influence on the development of AITD. In this review we summarize the new findings on the genetic susceptibility to AITD focusing on emerging mechanisms of susceptibility.

SUMMARY

Candidate gene analysis, whole-genome linkage screening, genome-wide association studies, and whole-genome sequencing are the major technologies that have advanced this field, leading to the identification of at least seven genes whose variants have been associated with AITD. One of the major ones is the HLA-DR gene locus. Recently, it was shown that substitution of the neutral amino acids Ala or Gln with arginine at position beta 74 in the HLA-DR peptide-binding pocket is key to the etiology of both Graves' disease and Hashimoto's thyroiditis. Several other genes have also been shown to confer susceptibility to AITD. These can be classified into two groups: (i) immune regulatory genes (cytotoxic T lymphocyte-associated protein 4, CD40, protein tyrosine phosphatase-22, and CD25) and (ii) thyroid-specific genes (thyroglobulin and thyrotropin receptor genes). The influence of individual genes on the development of AITD when assessed in a population appears to be weaker than would be expected from the data showing strong genetic susceptibility to AITD. Two possible mechanisms explaining this discrepancy are gene-gene interactions and subset effects.

CONCLUSIONS

Significant progress has been made in our understanding of the immunogenetic mechanisms leading to thyroid autoimmunity. For the first time we are beginning to unravel these mechanisms at the molecular level. It is hoped that these new data will be translated into novel therapies and prevention strategies in AITD, such as costimulatory blockade.

Genetics of type 2 diabetes

PURPOSE OF REVIEW

To provide an overview of the genetics of type 2 diabetes in the context of recent progress in the understanding of the genetic architecture of the disease and its applicability to the pathogenesis of the disease as well as efforts to individualize therapy in type 2 diabetes. Efforts are underway to understand how these loci alter measurable physiologic processes in nondiabetic humans. However, it is important to understand the potential pitfalls in such studies and the limitations underlying measurement of insulin secretion and action using qualitative methodologies.

RECENT FINDINGS

The availability of large population-based cohorts and the ease with which large numbers of common genetic variants can be genotyped has enabled the discovery of multiple loci and pathways associated with type 2 diabetes. Recent efforts examining quantitative traits such as fasting glucose concentrations have led to the discovery of other genes likely to be important in the development of diabetes.

SUMMARY

The past 4 years have witnessed a significant increase in our understanding of genetic predisposition to type 2 diabetes. Hopefully more progress will be made in applying this knowledge to the pathophysiology of type 2 diabetes in the coming years.

Identification of therapeutic targets for quiescent, chemotherapy-resistant human leukemia stem cells

Human acute myeloid leukemia (AML) originates from rare leukemia stem cells (LSCs). Because these chemotherapy-resistant LSCs are thought to underlie disease relapse, effective therapeutic strategies specifically targeting these cells may be beneficial. Here, we report identification of a primary human LSC gene signature and functional characterization of human LSC-specific molecules in vivo in a mouse xenotransplantation model. In 32 of 61 (53%) patients with AML, either CD32 or CD25 or both were highly expressed in LSCs. CD32- or CD25-positive LSCs could initiate AML and were cell cycle-quiescent and chemotherapy-resistant in vivo. Normal human hematopoietic stem cells depleted of CD32- and CD25-positive cells maintained long-term multilineage hematopoietic reconstitution capacity in vivo, indicating the potential safety of treatments targeting these molecules. In addition to CD32 and CD25, quiescent LSCs within the bone marrow niche also expressed the transcription factor WT1 and the kinase HCK. These molecules are also promising targets for LSC-specific therapy.

Recent insights into CD4+ T-cell specificity and function in type 1 diabetes

Type 1 diabetes (T1D) is caused by T-cell-mediated destruction of the insulin-producing beta-cells in the pancreas. Genetic and immunological evidence from humans and mouse models indicates that CD4(+) T cells play a crucial role in the development and prevention of T1D. The dichotomy between CD4(+) T regulatory and effector T cells has encouraged research into the role of these cell subsets in T1D. New antigens and epitopes recognized by CD4(+) T cells in affected individuals have been identified. Growing knowledge of T-cell specificity and function is helping to develop new assays for analyzing islet antigen-specific CD4(+) T cells from human blood. Here we discuss, with particular reference to human studies, advances in our understanding of CD4(+) T-cell responses in T1D.

Variant of TYR and autoimmunity susceptibility loci in generalized vitiligo

BACKGROUND

Generalized vitiligo is an autoimmune disease characterized by melanocyte loss, which results in patchy depigmentation of skin and hair, and is associated with an elevated risk of other autoimmune diseases.

METHODS

To identify generalized vitiligo susceptibility loci, we conducted a genomewide association study. We genotyped 579,146 single-nucleotide polymorphisms (SNPs) in 1514 patients with generalized vitiligo who were of European-derived white (CEU) ancestry and compared the genotypes with publicly available control genotypes from 2813 CEU persons. We then tested 50 SNPs in two replication sets, one comprising 677 independent CEU patients and 1106 CEU controls and the other comprising 183 CEU simplex trios with generalized vitiligo and 332 CEU multiplex families.

RESULTS

We detected significant associations between generalized vitiligo and SNPs at several loci previously associated with other autoimmune diseases. These included genes encoding major-histocompatibility-complex class I molecules (P=9.05x10(-23)) and class II molecules (P=4.50x10(-34)), PTPN22 (P=1.31x10(-7)), LPP (P=1.01x10(-11)), IL2RA (P=2.78x10(-9)), UBASH3A (P=1.26x10(-9)), and C1QTNF6 (P=2.21x10(-16)). We also detected associations between generalized vitiligo and SNPs in two additional immune-related loci, RERE (P=7.07x10(-15)) and GZMB (P=3.44x10(-8)), and in a locus containing TYR (P=1.60x10(-18)), encoding tyrosinase.

CONCLUSIONS

We observed associations between generalized vitiligo and markers implicating multiple genes, some associated with other autoimmune diseases and one (TYR) that may mediate target-cell specificity and indicate a mutually exclusive relationship between susceptibility to vitiligo and susceptibility to melanoma.

The long and winding road to understanding and conquering type 1 diabetes

Autoimmune diseases with high population prevalence such as type 1 diabetes (T1D) develop as a result of ill-defined interactions between putative environmental triggers and a constellation of genetic elements scattered throughout the genome. In T1D, these interactions somehow trigger a loss of tolerance to pancreatic beta cells, manifested in the form of a chronic autoimmune response that mobilizes virtually every cell type of the immune system and progressively erodes the host's beta cell mass. The five accompanying review articles focus on key areas of T1D research, ranging from genetics and pathogenesis to prediction and therapy. Here, I attempt to integrate and bring into focus the most salient points of these reviews in the context of other findings, with an emphasis on identifying knowledge gaps and research opportunities.

Autoimmune polyendocrine syndromes: clues to type 1 diabetes pathogenesis

Autoimmune diseases such as type 1 diabetes are complex in their pathogenesis. One approach to improving our understanding of type 1 diabetes is the study of diseases that represent more extreme examples of autoimmunity. Autoimmune polyendocrine syndromes (APS) are relatively rare diseases that often include type 1 diabetes as part of the disease phenotype. Recently, there has been tremendous progress in unraveling some of the underlying mechanisms of APS. Here, we highlight the APS disorders with the perspective of the clues they can offer to the pathogenesis and treatment of type 1 diabetes.

Polymorphisms in the IL2, IL2RA and IL2RB genes in multiple sclerosis risk

Interleukin (IL)-2/IL-2R signalling promotes proliferation and survival of activated T cells and has an essential non-redundant role in the production of regulatory T cells. Associations with different autoimmune diseases of polymorphisms in a linkage disequilibrium block in which the IL2/IL21 genes map (4q27), and also in genes encoding the IL2RA and IL2RB subunits (located in 10p15 and 22q13, respectively), were identified through genome-wide studies. Polymorphisms in these three genes were studied in 430 multiple sclerosis (MS) patients and in 550 ethnically matched controls from Madrid (Spain). Replication and meta-analysis with results from an independent cohort of 771 MS patients and 759 controls from Andalucía (Spain) confirmed the association of polymorphisms in the IL2RA gene (P(Mantel-Haenszel,) odds ratio (OR)(M-H) (95% confidence interval, CI) for rs2104286: 0.0001, 0.75 (0.65-0.87); for rs11594656/rs35285258: 0.004, 1.19 (1.06-1.34); for rs41295061: 0.03, 0.77 (0.60-0.98)); showed a trend for association of the IL2/IL21 rs6822844 (P(M-H)=0.07, OR(M-H) (95% CI)=0.86 (0.73-1.01)), but did not corroborate the association for IL2RB. Regression analyses of the combined Spanish cohort revealed the independence of two IL2RA association signals: rs2104286 and rs11594656/rs35285258. The relevant role of the IL2RA gene on MS susceptibility adds support to its common effect on autoimmune risk and the suggestive association of IL2/IL21 warrants further investigation.

The Type I Diabetes Genetics Consortium 'Rapid Response' family-based candidate gene study: strategy, genes selection, and main outcome

Candidate gene studies have long been the principal method for identification of susceptibility genes for type I diabetes (T1D), resulting in the discovery of HLA, INS, PTPN22, CTLA4, and IL2RA. However, many of the initial studies that relied on this strategy were largely underpowered, because of the limitations in genomic information and genotyping technology, as well as the limited size of available cohorts. The Type I Diabetes Genetic Consortium (T1DGC) has established resources to re-evaluate earlier reported genes associated with T1D, using its collection of 2298 Caucasian affected sib-pair families (with 11 159 individuals). A total of 382 single-nucleotide polymorphisms (SNPs) located in 21 T1D candidate genes were selected for this study and genotyped in duplicate on two platforms, Illumina and Sequenom. The genes were chosen based on published literature as having been either 'confirmed' (replicated) or not (candidates). This study showed several important features of genetic association studies. First, it showed the major impact of small rates of genotyping errors on association statistics. Second, it confirmed associations at INS, PTPN22, IL2RA, IFIH1 (earlier confirmed genes), and CTLA4 (earlier confirmed, with distinct SNPs) loci. Third, it did not find evidence for an association with T1D at SUMO4, despite confirmed association in Asian populations, suggesting the potential for population-specific gene effects. Fourth, at PTPN22, there was evidence for a novel contribution to T1D risk, independent of the replicated effect of the R620W variant. Fifth, among the candidate genes selected for replication, the association of TCF7-P19T with T1D was newly replicated in this study. In summary, this study was able to replicate some genetic effects, reject others, and provide suggestions of association with several of the other candidate genes in stratified analyses (age at onset, HLA status, population of origin). These results have generated additional interesting functional hypotheses that will require further replication in independent cohorts.

The type I diabetes association of the IL2RA locus

To confirm and fine map previous reports of association, the Type I Diabetes (T1D) Genetics Consortium (T1DGC) assembled a large collection of DNA samples from affected sib-pair (ASP) families with T1D (5003 affected individuals) and genotyped polymorphic markers. One of these loci, involving the IL2RA gene, had been reported to be due to three independent effects. The T1DGC genotyped 69 single-nucleotide polymorphisms (SNPs) that span approximately 88 kb from the 5' flanking to 3' flanking region of the IL2RA locus. The most highly associated SNP reported earlier (ss52580101) was not included in the genotyping list; however, a 5-SNP (rs3134883, rs3118470, rs7072793, rs4749955 and rs12251307) haplotype (H5) was identified that strongly tagged its minor allele with r(2)=0.869 (95% CI, 0.850-0.885). This haplotype was significantly protective (P=3.2 x 10(-5)) in the T1D ASP families, with an odds ratio virtually identical to that reported for ss52580101. The SNP marking the second independent locus, (rs11594656) showed no association in the T1DGC set and the third (rs2104286) could not be distinguished, by conditional regression, from H5. Instead, the most significant independent effect was detected from the 5' flanking IL2RA SNP rs4749955, which remained significant after regression for H5. Thus, we confirm independent effects at the IL2RA locus.