Association analysis of the AIRE and insulin genes in Finnish type 1 diabetic patients

Type 1 diabetes and inborn errors of immunity: Complete strangers or 2 sides of the same coin?

Type 1 diabetes (T1D) is a polygenic disease and does not follow a mendelian pattern. Inborn errors of immunity (IEIs), on the other hand, are caused by damaging germline variants, suggesting that T1D and IEIs have nothing in common. Some IEIs, resulting from mutations in genes regulating regulatory T-cell homeostasis, are associated with elevated incidence of T1D. The genetic spectrum of IEIs is gradually being unraveled; consequently, molecular pathways underlying human monogenic autoimmunity are being identified. There is an appreciable overlap between some of these pathways and the genetic variants that determine T1D susceptibility, suggesting that after all, IEI and T1D are 2 sides of the same coin. The study of monogenic IEIs with a variable incidence of T1D has the potential to provide crucial insights into the mechanisms leading to T1D. These insights contribute to the definition of T1D endotypes and explain disease heterogeneity. In this review, we discuss the interconnected pathogenic pathways of autoimmunity, β-cell function, and primary immunodeficiency. We also examine the role of environmental factors in disease penetrance as well as the circumstantial evidence of IEI drugs in preventing and curing T1D in individuals with IEIs, suggesting the repositioning of these drugs also for T1D therapy.

Effects of Aire on perforin expression in BMDCs via TLR7/8 and its therapeutic effect on type 1 diabetes

AIMS

Type 1 diabetes, as a kind of autoimmune diseases, usually results from the broken-down of self-tolerance. Autoimmune regulator (Aire), as a transcription factor, induces peripheral tolerance by regulating Toll-like receptor (TLR) expression in dendritic cells (DCs). Several studies have recently identified a small population of perforin-expressing DCs, which is an important population of tolerogenic DCs (tolDCs) that restricts autoreactive T cells in vivo through a perforin-mediated mechanism. Thus, the present study explored the specific relationship among Aire, perforin-expressing DCs and immune tolerance, as well as their roles in type 1 diabetes.

METHODS

We conducted studies based on the Aire-overexpressing bone marrow-derived dendritic cell (BMDC) model. And through in vitro and in vivo experiments to observe that Aire-overexpressing BMDCs which express perforin induce immune tolerance and treat type 1 diabetes via TLR7/8.

RESULTS

Aire enhances the expression of perforin in BMDCs after treatment with the TLR7/8 ligand as well as promotes the expression of TLR7/8 and myeloid differentiation primary response gene 88 (MyD88)-dependent pathway molecules. Aire-overexpressing BMDCs mediate apoptosis of allogeneic CD8⁺ T cells via perforin in vitro. Moreover, Aire-overexpressing BMDCs enhance the therapeutic effect of type 1 diabetes in non-obese diabetic (NOD) mice via perforin and induce apoptosis of autoreactive CD8⁺ T cells in vivo.

CONCLUSIONS

These results provide an experimental basis for comprehensively elucidating the role and significance of Aire expression in peripheral DCs, thereby providing new ideas for the treatment of autoimmune diseases by using Aire as a target to induce the production of perforin-expressing DCs.

In Search for the Missing Link in APECED-like Conditions: Analysis of the AIRE Gene in a Series of 48 Patients

Autoimmune diseases are a heterogeneous group of disorders of the immune system. They can cluster in the same individual, revealing various preferential associations for polyendocrine autoimmune syndromes. Clinical observation, together with advances in genetics and the understanding of pathophysiological processes, has further highlighted that autoimmunity can be associated with immunodeficiency; autoimmunity may even be the first primary immunodeficiency manifestation. Analysis of susceptibility genes for the development of these complex phenotypes is a fundamental issue. In this manuscript, we revised the clinical and immunologic features and the presence of AIRE gene variations in a cohort of 48 patients affected by high polyautoimmunity complexity, i.e., APECED-like conditions, also including patients affected by primary immunodeficiency. Our results evidenced a significant association of the S278R polymorphism of the AIRE gene with APECED-like conditions, including both patients affected by autoimmunity and immunodeficiency and patients with polyautoimmunity compared to healthy controls. A trend of association was also observed with the IVS9+6 G>A polymorphism. The results of this genetic analysis emphasize the need to look for additional genetic determinants playing in concert with AIRE polymorphisms. This will help to improve the diagnostic workup and ensure a precision medicine approach to targeted therapies in APECED-like patients.

Association of AIRE (rs2075876), but not CTLA4 (rs231775) polymorphisms with systemic lupus erythematosus

BACKGROUND

The AIRE (rs2075876) and CTLA4 (rs231775) variants have a crucial function in controlling the negative selection and suppression of T lymphocytes. Numerous reports studied the association of AIRE and CTLA4 variants with different autoimmune disorders, but with inconclusive conclusions. The main purpose of this work is to evaluate the association of these two variants with SLE susceptibility among Egyptian patients.

SUBJECTS AND METHODS

A total of 247 participants (100 SLE patients and 147 healthy controls) were enrolled in this case-controlled study. The genomic DNA of these dual variants was genotyped using the TaqMan genotyping method.

RESULTS

The AIRE (rs2075876) variant conferred protection against developing SLE disease under allelic [A allele vs. G allele; OR = 0.16, 95%CI = 0.09-0.28], and dominant [GA + AA vs. GG; OR = 0.14, 95%CI = 0.05-0.34] models. Moreover, patients with AIRE rs2075876 (A/A) genotype revealed a statistically significant with lower levels of complement 3 (p-value = 0.007). Nonetheless, the CTLA4 (rs231775) variant was not associated with increased risk of SLE under all genetic association models (p-value > 0.05). However, CTLA4 rs231775 (G/G) genotype observed significant difference with recurrent infection and hematuria.

CONCLUSIONS

Our findings indicated that the AIRE (rs2075876) variant conferred protection against developing SLE disease, but not the CTLA4 (rs231775) variant.

Thymus and autoimmunity

The thymus prevents autoimmune diseases through mechanisms that operate in the cortex and medulla, comprising positive and negative selection and the generation of regulatory T-cells (Tregs). Egress from the thymus through the perivascular space (PVS) to the blood is another possible checkpoint, as shown by some autoimmune/immunodeficiency syndromes. In polygenic autoimmune diseases, subtle thymic dysfunctions may compound genetic, hormonal and environmental cues. Here, we cover (a) tolerance-inducing cell types, whether thymic epithelial or tuft cells, or dendritic, B- or thymic myoid cells; (b) tolerance-inducing mechanisms and their failure in relation to thymic anatomic compartments, and with special emphasis on human monogenic and polygenic autoimmune diseases and the related thymic pathologies, if known; (c) polymorphisms and mutations of tolerance-related genes with an impact on positive selection (e.g. the gene encoding the thymoproteasome-specific subunit, PSMB11), promiscuous gene expression (e.g. AIRE, PRKDC, FEZF2, CHD4), Treg development (e.g. SATB1, FOXP3), T-cell migration (e.g. TAGAP) and egress from the thymus (e.g. MTS1, CORO1A); (d) myasthenia gravis as the prototypic outcome of an inflamed or disordered neoplastic ‘sick thymus’.

Targeting Glycoproteins as a therapeutic strategy for diabetes mellitus and its complications

OBJECTIVES

Glycoproteins are organic compounds formed from proteins and carbohydrates, which are found in many parts of the living systems including the cell membranes. Furthermore, impaired metabolism of glycoprotein components plays the main role in the pathogenesis of diabetes mellitus. The aim of this study is to investigate the influence of glycoprotein levels in the treatment of diabetes mellitus.

METHODS

All relevant papers in the English language were compiled by searching electronic databases, including Scopus, PubMed and Cochrane library. The keywords of glycoprotein, diabetes mellitus, glycan, glycosylation, and inhibitor were searched until January 2019.

RESULTS

Glycoproteins are pivotal elements in the regulation of cell proliferation, growth, maturation and signaling pathways. Moreover, they are involved in drug binding, drug transportation, efflux of chemicals and stability of therapeutic proteins. These functions, structure, composition, linkages, biosynthesis, significance and biological effects are discussed as related to their use as a therapeutic strategy for the treatment of diabetes mellitus and its complications.

CONCLUSIONS

The findings revealed several chemical and natural compounds have significant beneficial effects on glycoprotein metabolism. The comprehension of glycoprotein structure and functions are very essential and inevitable to enhance the knowledge of glycoengineering for glycoprotein-based therapeutics as may be required for the treatment of diabetes mellitus and its associated complications. Graphical abstract.

The study on the risk of other endocrine glands autoimmune diseases in patients with type 1 diabetes mellitus

To study the changes of pancreas, thyroid, adrenal, parathyroid and gonadal organ-specific antibodies in patients with type 1 diabetic patients and to explore the risk of development to other endocrine gland autoimmune diseases.Fifty one patients with type 1 diabetes mellitus were selected. ELISA was used to detect islet, adrenal gland, Parathyroid, gonadal organ-specific antibody levels, the level of thyroid-related antibodies by lectrochemiluminescence.Compared with the healthy control group, the levels of the 17-α-OHAb, 21-OHAb, NALP5Ab, P450sccAb, and CaSRAb in the T1DM group were significantly higher. GADAb-positive patients were more likely to have TPOAb-positive patients than GADAb-negative patients, and the positive rate of 2 thyroid antibodies in GADAb-positive patients was significantly higher than that in GADAb-negative patients. The presence of these antibodies is related to the age of onset of type 1 diabetes or Patient age. In combination with 1 or 2 islet antibody-positive patients, the combined non-islet antibody positive rate was higher than that of islet antibody-negative patients.Patients with type 1 diabetes with other autoimmune diseases at risk significantly increased compared with normal, of which the most common thyroid autoimmune disease, thyroid antibodies and hormone levels should be routinely detected at the first visit and long-term follow-up.

Genetic profile considerations for induction of allogeneic chimerism as a therapeutic approach for type 1 diabetes mellitus

The major therapeutic modality for type 1 diabetes mellitus (T1DM) remains sustaining euglycemia by exogenous administration of insulin. Based on a new understanding of bone marrow structural and functional dynamics, a conditioning-free bone marrow transplantation (BMT), with reduced adverse effects, opens the possibility for evaluating β cell regeneration and restoration of euglycemia by induction of allogeneic chimerism in patients T1DM, as shown in a mouse model. With this therapeutic modality, donor bone marrow (BM) selection based on T1DM-predisposing and preventive phenotypes will improve treatment outcomes by limiting the risk of exacerbating the autoimmune processes in the BM recipient.

The rs878081 polymorphism of AIRE gene increases the risk of rheumatoid arthritis in a Chinese Han population: a case-control study

The autoimmune regulator (AIRE), a transcriptional regulator expressed in medullary thymic epithelial cells, plays an important role in thymocyte education and negative selection. Several citations studying the association between the rs878081 exon polymorphism of the AIRE gene and the risk of rheumatoid arthritis (RA) in different populations have yielded conflicting findings. Thus, this case-control study involving 300 RA cases and 300 controls was aimed to identify whether such association existed in a Chinese Han population from East China. The rs878081 polymorphism of the AIRE gene was genotyped. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using the chi-squared test, genetic model analysis, and stratification analysis. Genetic model analysis showed significant correlations between the TT genotype and the risk of RA (OR: 1.89, 95%CI: 1.03-3.47 in TT vs CC; OR: 1.84, 95%CI: 1.02-3.31 in TT vs CC+TC). Stratification analyses of sex, age, smoking, and alcoholism suggested that the rs878081 polymorphism of the AIRE gene increased RA risk among non-smokers. In conclusion, rs878081 polymorphism of AIRE gene increases the risk of RA in a Chinese Han population.

Association of AIRE Polymorphism and the Susceptibility to Multiple Sclerosis in Iranian Population

Background:

Multiple Sclerosis (MS) is the most common cause of neurologic disability in young adults. Recently, the AIRE gene was identified as a genetic risk factor for several autoimmune diseases in genome wide association studies. The aim of this study was to further investigate the possible role of the AIRE gene in susceptibility to MS in Iranian population.

Methods:

A total of 112 MS patients and 94 ethnically matched controls were included in the study. The Single-Nucleotide Polymorphism (SNP) (rs1800520, C>G) with a global MAF=0.2282/1143 was selected and genotyped using HRM real-time PCR method.

Results:

Results showed that AIRE SNP rs1800520 was significantly less common in the MS patients than in healthy controls (17.8 vs. 28.7%, pc=0.032, OR=0.54,95% CI 0.279, 1.042). Also, the frequency of allele G was significantly higher among the control group than in the case group (37.77 vs. 25%, pc=0.014). Interestingly, mRNA transcribed on the rs1800520 SNP showed decreased free energy than the wild type suggesting that its increased stability may be responsible for the different activities of the polymorphic AIRE molecule.

Conclusions:

This is the first study investigating the relationship between AIRE gene and the susceptibility to MS. These results indicated that the rs1800520 SNP is not a susceptibility gene variant for the development of MS in Iranian population.

Rs3761389 polymorphism in autoimmune regulator (AIRE) gene is associated with susceptibility of myasthenia gravis in Chinese patients

Polymorphism in autoimmune regulator (AIRE) gene is associated with various autoimmune disorders. Abnormal AIRE expression is associated with the development of myasthenia gravis (MG). We investigated the association of polymorphism in AIRE gene and the clinical features and severity of MG. The frequencies of alleles and genotypes were compared between 480MG patients and 487 healthy controls, as well as among subgroups of MG patients. The frequencies of rs3761389G allele in MG group (OR=1.213, CI 95% 1.014-1.451, p=0.035) and in mild (Oosterhuis score 0-2) subgroup (OR=1.393, CI 95% 1.110-1.751, p=0.004) were significantly higher than those in the control group. There were significant differences in the frequencies of rs3761389 genotypes (OR=1.20, CI 95% 1.00-1.43, p=0.046, log-additive model) and mild subgroup (OR=1.32, CI 95% 1.03-1.69, p=0.0058, log-additive model) compared with the control group. A Logistic regression analysis did not identify rs3761389 genotype as an independent risk factor to predict the severity of MG. This study provides the necessary preliminary data on the association with rs3761389 in AIRE gene with the susceptibility of MG, but not with the severity of MG.

A single nucleotide polymorphism of AIRE gene located in the 21q22.3 increases the risk of rheumatoid arthritis

Several studies addressed the association of autoimmune regulator (AIRE) gene polymorphism with the risk of rheumatoid arthritis (RA); however, their conclusions were inconsistent. For better investigating the effects of this polymorphism on the risk of RA, we conducted this study to evaluate the role of AIRE rs2075786 polymorphism in the risk of RA. Four eligible studies involving 6,755 cases and 7,970 controls were identified by searching the databases of PubMed, CNKI and EMBASE up to February 2017. Our study revealed that AIRE rs2075786 polymorphism was associated with an increased risk of RA under all genetic models. In the subgroup analysis, AIRE rs2075786 polymorphism contributed to RA susceptibility among Asians, but not among Caucasians. To summarize,, this meta-analysis confirms that AIRE rs2075786 polymorphism may play a significant role in increasing the risk of RA. Stratification analysis by ethnicity reveals that AIRE rs2075786 polymorphism is associated with an increased risk of RA among Asians, but not among Caucasians. These findings need further validation in the large multicenter case-control studies.

AIRE genetic variants and predisposition to polygenic autoimmune disease: The case of Graves' disease and a systematic literature review

Autoimmune Regulator (AIRE) is a transcriptional regulator that is crucial for establishing central tolerance as illustrated by the Mendelian Autoimmune Polyendocrinopathy-Candidiasis-Ectodermal Dystrophy (APECED) syndrome associated with AIRE-inactivating recessive or dominant mutations. Polymorphisms in AIRE have been proposed to be implicated in genetic susceptibility to non-Mendelian organ specific autoimmune diseases. Because there is evidence that in predisposition to Graves' disease (GD) central tolerance is crucial, we investigated whether AIRE polymorphisms could modulate risk of GD. A case-control association study using 29 variants and conducted in 150 GD patients and 200 controls did not detect any significant association. This result is not exceptional: a systematic review of the literature, including GWAS, on the association of AIRE variants with organ specific autoimmune diseases did not show clear associations; similarly heterozygous recessive mutations are not associated to non-Mendelian autoimmunity. Dominant negative mutations of AIRE are associated to autoimmunity but as mild forms of APECED rather than to non-Mendelian organ specific autoimmunity. The lack of association of common AIRE polymorphisms with polygenic autoimmune diseases is counterintuitive as many other genes less relevant for immunological tolerance have been found to be associated. These findings give rise to the intriguing possibility that evolution has excluded functionally modifying polymorphisms in AIRE.

Type 1 Diabetes in Autoimmune Polyendocrinopathy-Candidiasis-Ectodermal Dystrophy Syndrome (APECED): A "Rare" Manifestation in a "Rare" Disease

Type 1 autoimmune polyglandular syndrome (APS1) is a rare autosomal recessive disease, caused by mutations in the autoimmune regulator gene (AIRE); the encoded Aire protein plays an important role in the establishment of the immunological tolerance acting as a transcriptional regulator of the expression of organ-specific antigens within the thymus in perinatal age. While a high prevalence for this rare syndrome is reported in Finland and Scandinavia (Norway), autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy syndrome (APECED) cohorts of patients are also detected in continental Italy and Sardinia, among Iranian Jews, as well as in other countries. The syndrome is diagnosed when patients present at least two out of the three fundamental disorders including chronic mucocutaneous candidiasis, hypoparathyroidism, and Addison's disease. Among the associated conditions insulin-dependent diabetes mellitus (Type 1 diabetes) has been rarely reported in different series of patients and occurring more frequently in Finnish APECED patients. In this review, we analyze the incidence of Type 1 diabetes as a clinical manifestation of APECED in different populations highlighting the peculiar genetic and immunological features of the disease when occurring in the context of this syndrome.

Insulin gene VNTR polymorphisms -2221MspI and -23HphI are associated with type 1 diabetes and latent autoimmune diabetes in adults: a meta-analysis

AIMS

A variable number of tandem repeat (VNTRs) region in the insulin gene (INS) possibly influences the progression of type 1 diabetes (T1D) and latent autoimmune diabetes in adults (LADA). However, effects of INS VNTR polymorphisms in these contexts remain inconclusive.

METHODS

We performed a systematic review of work on the INS VNTR -2221MspI and -23HphI polymorphisms to estimate the overall effects thereof on disease susceptibility; we included 17,498 T1D patients and 24,437 controls, and 1960 LADA patients and 5583 controls.

RESULTS

For T1D, the C allele at -2221MspI and the A allele at -23HphI were associated with estimated relative risks of 2.13 (95 % CI 1.94, 2.35) and 0.46 (95 % CI 0.44, 0.48), which contributed to absolute increases of 46.76 and 46.98 % in the risk of all T1D, respectively. The estimated lambda values were 0.44 and 0.42, respectively, suggesting that a co-dominant model most likely explained the effects of -2221MspI and -23HphI on T1D. For -23HphI, the A allele carried an estimated relative risk of 0.55 (95 % CI 0.50, 0.61) for LADA and increased the risk of all LADA by 36.94 %. The λ value was 0.43, suggesting that a co-dominant model most likely explained the effect of -23HphI on LADA.

CONCLUSIONS

Our results support the existence of associations of INS with T1D and LADA.

Dominant Mutations in the Autoimmune Regulator AIRE Are Associated with Common Organ-Specific Autoimmune Diseases

The autoimmune regulator (AIRE) gene is crucial for establishing central immunological tolerance and preventing autoimmunity. Mutations in AIRE cause a rare autosomal-recessive disease, autoimmune polyendocrine syndrome type 1 (APS-1), distinguished by multi-organ autoimmunity. We have identified multiple cases and families with mono-allelic mutations in the first plant homeodomain (PHD1) zinc finger of AIRE that followed dominant inheritance, typically characterized by later onset, milder phenotypes, and reduced penetrance compared to classical APS-1. These missense PHD1 mutations suppressed gene expression driven by wild-type AIRE in a dominant-negative manner, unlike CARD or truncated AIRE mutants that lacked such dominant capacity. Exome array analysis revealed that the PHD1 dominant mutants were found with relatively high frequency (>0.0008) in mixed populations. Our results provide insight into the molecular action of AIRE and demonstrate that disease-causing mutations in the AIRE locus are more common than previously appreciated and cause more variable autoimmune phenotypes.

Experiments by nature: lessons on type 1 diabetes

The etiology and pathogenesis of type 1 diabetes (T1D) - one of the most frequent chronic, life-debilitating diseases in humans - have long fascinated endocrinologists, pathologists and biologists alike. Currently conventional wisdom portrays T1D as a chronic T cell-mediated autoimmune disease that leads to the specific destruction of pancreatic insulin-producing β cells. The process of β cell destruction is accompanied (or preceded) by the production of autoantibodies (autoAb) to β cell antigens (i.e. insulin, GAD65, IA-2 and ZnT8). These autoAb have proved to be instrumental in identifying subjects at risk of developing the disease prior to overt hyperglycemia, and they help to distinguish T1D from T2D patients (who have no autoAb), but are not deemed to be pathogenic. This review will examine to which extent this well-established disease-dogmas are sustained by experiments by nature, which should not suffer from the common biases and errors of experiments by humans.

Is autoimmunity or insulin resistance the primary driver of type 1 diabetes?

Diabetes is usually classified as autoimmune or metabolic but, as difficulties have arisen with the taxonomy of diabetes, it may help to forego the conventional classification for a more inclusive model. Thus, all diabetes can be ascribed to beta cell insufficiency-hyperglycemia occurs only when the insulin supply fails to meet demand. Humans enter the world with a reserve of beta cells, which is eroded variably by apoptosis over the course of a lifetime. For most, the loss is slow and inconsequential but, for others fast enough to be critical within a lifetime. The challenge now is to define the factors that vary the tempo of beta cell loss, because tempo, not type, seems likely to determine whether diabetes occurs at all, in adulthood or in childhood. Insulin resistance is generally believed to underpin T2D, but has been a feature of insulin-dependent diabetes as well for nearly 80 years, though largely ignored until immunotherapy trials to test the autoimmunity hypothesis persistently failed to bring patient benefit. It seems possible that insulin resistance accelerates beta cell loss generally, its impact modulated by an immune response (autoimmunity) to the beta-cell stress whose intensity varies with immunogenotype. If so, the target for prevention of T1D might more logically lie with insulin sensitivity than with immunoregulation.

Analysis of the autoimmune regulator gene in patients with autoimmune non-APECED polyendocrinopathies

The pathogenesis of autoimmunity was derived from a complex interaction of genetic and environmental factors. Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy is a rare autosomal recessive disease caused by mutations in the autoimmune regulator (AIRE) gene. AIRE gene variants and, in particular, heterozygous loss-of-function mutations were also discovered in organ-specific autoimmune disorders, possibly contributing to their etiopathogenesis. It was suggested that even predisposition to develop certain autoimmune conditions may be derived from AIRE gene polymorphisms including S278R and intronic IVS9+6 G>A. In this study we unravel the hypothesis on whether AIRE gene variants may predispose individuals to associated autoimmune conditions in 41 Italian patients affected by non-APECED autoimmune polyendocrinopathies. We could not detect any heterozygous mutations of the AIRE gene. Although a trend of association was observed, heterozygous polymorphisms S278R and IVS9+6 G>A were detected in patients without statistically significant prevalence than in controls. Their putative contribution to autoimmune polyendocrinopathies and their predictive value in clinical strategies of disease development could be unravelled by analysing a larger sample of diseased patients and healthy individuals.

Monogenic autoimmunity

Monogenic autoimmune syndromes provide a rare yet powerful glimpse into the fundamental mechanisms of immunologic tolerance. Such syndromes reveal not only the contribution of an individual breakpoint in tolerance but also patterns in the pathogenesis of autoimmunity. Disturbances in innate immunity, a system built for ubiquitous sensing of danger signals, tend to generate systemic autoimmunity. For example, defects in the clearance of self-antigens and chronic stimulation of type 1 interferons lead to the systemic autoimmunity seen in C1q deficiency, SPENCDI, and AGS. In contrast, disturbances of adaptive immunity, which is built for antigen specificity, tend to produce organ-specific autoimmunity. Thus, the loss of lymphocyte homeostasis, whether through defects in apoptosis, suppression, or negative selection, leads to organ-specific autoimmunity in ALPS, IPEX, and APS1. We discuss the unique mechanisms of disease in these prominent syndromes as well as how they contribute to the spectrum of organ-specific or systemic autoimmunity. The continued study of rare variants in autoimmune disease will inform future investigations and treatments directed at rare and common autoimmune diseases alike.

Recent insights into the role and molecular mechanisms of the autoimmune regulator (AIRE) gene in autoimmunity

Since many years immunologists have being tried to answer the tantalizing enigma of immunological tolerance. Complex mechanisms in both thymus (central tolerance) and peripheral lymphoid organs (peripheral tolerance) underly lymphocyte tolerance and its maintenance. The genesis of autoimmunity involves environmental and genetic mechanisms, both contributing to the disruption and deregulation of central and peripheral tolerance, allowing autoreactive pathogenetic T and B-cell clones arising. Among genetic factors the autoimmune regulator (AIRE) gene is one of the best candidates to understand the complex scenario of autoimmunity. Autoimmune polyendocrinopathy syndrome type 1 is a rare autosomal recessive disease caused by mutations in the AIRE gene. Therefore, the disorder has certainly been a powerful model to address the question concerning how a tolerant state is achieved or maintained and to explore how it has gone lost in the context of autoimmunity. AIRE has been proposed to function as a 'non classical' transcription factor, strongly implicated in the regulation of organ-specific antigen expression in thymic epithelial cells and in the imposition of T cell tolerance, thus regulating the negative selection of autoreactive T cell clones. A plethora of proposal have been suggested for AIRE's potential mechanism of action, thus regulating the negative selection of autoreactive T cells. In this review recent discoveries are presented into the role and molecular mechanisms of the AIRE protein in APECED and other autoimmune diseases.

AIRE gene mutations and autoantibodies to interferon omega in patients with chronic hypoparathyroidism without APECED

OBJECTIVE

To assess autoimmune regulator (AIRE) gene mutations, class II HLA haplotypes, and organ- or non-organ-specific autoantibodies in patients with chronic hypoparathyroidism (CH) without associated Addison's disease (AD) or chronic candidiasis (CC).

DESIGN, PATIENTS AND MEASUREMENTS

Twenty-four patients who had CH without AD or CC were included in the study. AIRE gene mutations in all 14 exons were studied using PCR in 24 patients, 105 healthy controls and 15 first-degree relatives of CH patients with AIRE mutations. Human leucocyte antigens (HLA) were determined for all 24 patients and 105 healthy controls. Autoantibodies to a range of antigens including NACHT leucine-rich-repeat protein-5 (NALP5) and interferon omega (IFNω) were tested in all 24 patients.

RESULTS

AIRE gene mutations were found in 6 of 24 (25%) patients, all females, and this was significantly higher (P < 0·001) compared with AIRE mutations found in healthy controls (2/105). Three patients (12·5%) had homozygous AIRE mutations characteristic of Autoimmune-Poly-Endocrinopathy-Candidiasis-Ectodermal-Dystrophy and all three were also positive for IFNω-autoantibodies. Three patients (12·5%) had heterozygous AIRE mutations; two of these were novel mutations. One of the patients with heterozygous AIRE mutations was positive for both NACHT leucine-rich-repeat protein 5 and IFNω autoantibodies. Heterozygous AIRE mutations were found in 10 of 15 first-degree relatives of CH patients with AIRE mutations, although none was affected by CH. Class II HLA haplotypes were not statistically different in patients with CH compared to healthy controls.

CONCLUSIONS

Analysis of AIRE gene mutations together with serum autoantibody profile should be helpful in the assessment of patients with CH, in particular young women with associated autoimmune diseases.

The role of AIRE polymorphisms in melanoma

Polymorphisms of AIRE, a transcription factor that up-regulates intrathymic expression of tissue-specific antigens including melanoma-associated antigens (MAAs), may variably affect the selection of MAAs-specific thymocytes, generating T-cell repertoires protecting or predisposing individuals to melanoma. We found that AIRE single nucleotide polymorphisms (SNPs) rs1055311, rs1800520 and rs1800522 were significantly more frequent in healthy subjects than in melanoma patients, independently from sex, age and stages of melanoma. The presence of these SNPs was associated with increased frequency of two T-cell clonotypes specific for MAGE-1 linking their protective effect to selection/expansion of MAA-specific T cells. Interestingly, mRNA transcribed on the rs1800520 SNP showed increased free energy than the wild type suggesting that its reduced stability may be responsible for the different activity of the polymorphic AIRE molecule. This finding may contribute at identifying subjects with increased risk of developing melanoma or patients with melanoma that may take benefit from immunotherapy.

Prediction and pathogenesis in type 1 diabetes

A combination of genetic and immunological features is useful for prediction of autoimmune diabetes. Patterns of immune response correspond to the progression from a preclinical phase of disease to end-stage islet damage, with biomarkers indicating transition from susceptibility to active autoimmunity, and to a final loss of immune regulation. Here, we review the markers that provide evidence for immunological checkpoint failure and that also provide tools for assessment of individualized disease risk. When viewed in the context of genetic variation that influences immune response thresholds, progression from susceptibility to overt disease displays predictable modalities of clinical presentation resulting from a sequential series of failed homeostatic checkpoints for selection and activation of immunity.

Monogenic autoimmune diseases: insights into self-tolerance

Autoimmune diseases affect a significant segment of the population and are typically thought to be multifactorial in etiology. Autoimmune diseases due to single gene defects are rare, but offer an invaluable window into understanding how defects in the immune system can lead to autoimmunity. In this review, we will focus on autoimmune polyendocrinopathy syndrome type 1 and recent advances in our understanding of this disease. We will also discuss two other monogenic autoimmune diseases: immunodysregulation, polyendocrinopathy, and enteropathy, X-linked and Autoimmune lymphoproliferative syndrome. Importantly, the knowledge and principles gained from studying these diseases have been applicable to more common autoimmune diseases and have opened the door to better diagnostic and therapeutic modalities.

Aire

Mutations in the transcriptional regulator, Aire, cause APECED, a polyglandular autoimmune disease with monogenic transmission. Animal models of APECED have revealed that Aire plays an important role in T cell tolerance induction in the thymus, mainly by promoting ectopic expression of a large repertoire of transcripts encoding proteins normally restricted to differentiated organs residing in the periphery. The absence of Aire results in impaired clonal deletion of self-reactive thymocytes, which escape into the periphery and attack a variety of organs. In addition, Aire is a proapoptotic factor, expressed at the final maturation stage of thymic medullary epithelial cells, a function that may promote cross-presentation of the antigens encoded by Aire-induced transcripts in these cells. Transcriptional regulation by Aire is unusual in being very broad, context-dependent, probabilistic, and noisy. Structure/function analyses and identification of its interaction partners suggest that Aire may impact transcription at several levels, including nucleosome displacement during elongation and transcript splicing or other aspects of maturation.

Aire deficiency causes increased susceptibility to streptozotocin-induced murine type 1 diabetes

Aire-deficient mice are a model of the human monogenic disorder autoimmune polyendocrine syndrome type I (APS I) characterized by a progressive autoimmune destruction of multiple endocrine glands such as the adrenal cortex, the parathyroids and the beta-cells of the pancreas. The disease is caused by mutations in the autoimmune regulator (AIRE) gene, a putative transcription factor expressed in thymic medullary epithelial cells and in antigen-presenting cells of the myeloid lineage in peripheral lymphoid organs. As Aire(-/-) mice do not spontaneously develop endocrinopathies, we wanted to evaluate the autoimmune multiple low-dose streptozotocin (MLDSTZ) diabetes model in Aire(-/-) mice. Surprisingly, Aire heterozygote mice were most susceptible to MLDSTZ-induced diabetes, whereas Aire(-/-) mice displayed an intermediate sensitivity to diabetes. Furthermore, Aire(-/-) macrophages produced higher levels of TNF-alpha and lower levels of IL-10 following streptozotocin stimulation, and Aire(-/-) mice developed a higher frequency of islet cells autoantibodies as a sign of increased activation. However, the number of islet infiltrating F4/80(+) Aire(-/-) macrophages was significantly decreased which was attributed to an increased susceptibility to streptozotocin cytotoxicity of Aire(-/-) macrophages. In conclusion, Aire(-/-) macrophages display an increased activation after STZ stimuli, but suffer from increased susceptibility to STZ cytotoxicity. These results support an important function of Aire in the control of peripheral tolerance through myeloid antigen-presenting cells.

Advances in type I diabetes associated tolerance mechanisms

Type 1 diabetes (T1D) is an autoimmune disease resulting from the destruction of insulin-producing pancreatic beta cells by autoreactive T cells. The polygenic trait for T1D risk implicates many genes that have an impact on fundamental immunological processes such as central and peripheral tolerance. Several pieces of evidence have suggested that many of the genetic loci that are directly linked to type 1 diabetes susceptibility modulate the generation and/or the activation of autoreactive T-lymphocytes. We and others have proposed a critical role for medullary thymic epithelial cells (mTEC) forming the Hassall's corpuscles in T-cell tolerance. Indeed, mTEC have been found to express promiscuous self-antigens, used directly or through thymic dendritic cells to drive either negative selection of insulin-reacting precursors or their differentiation into naturally occurring regulatory Foxp3+ CD4+ CD25+ T cells. In the periphery, naturally occurring Foxp3+ CD4+ CD25+regulatory T (Treg) cells represent the master cells in dominant peripheral T-cell tolerance. The development and function of Treg cells are ultimately linked to IL-2 and Foxp3 expression. This review addresses recent literature and emerging concepts of central and peripheral T-cell tolerance with regards to T1D.

AIRE variations in Addison's disease and autoimmune polyendocrine syndromes (APS): partial gene deletions contribute to APS I

Autoimmune Addison's disease (AAD) is often associated with other components in autoimmune polyendocrine syndromes (APS). Whereas APS I is caused by mutations in the AIRE gene, the susceptibility genes for AAD and APS II are unclear. In the present study, we investigated whether polymorphisms or copy number variations in the AIRE gene were associated with AAD and APS II. First, nine SNPs in the AIRE gene were analyzed in 311 patients with AAD and APS II and 521 healthy controls, identifying no associated risk. Second, in a subgroup of 25 of these patients, AIRE sequencing revealed three novel polymorphisms. Finally, the AIRE copy number was determined by duplex quantitative PCR in 14 patients with APS I, 161 patients with AAD and APS II and in 39 healthy subjects. In two Scandinavian APS I patients previously reported to be homozygous for common AIRE mutations, we identified large deletions of the AIRE gene covering at least exon 2 to exon 8. We conclude that polymorphisms in the AIRE gene are not associated with AAD and APS II. We further suggest that DNA analysis of the parents of patients found to be homozygous for mutations in AIRE, always should be performed.

Highly variable expression of tissue-restricted self-antigens in human thymus: Implications for self-tolerance and autoimmunity

Induction of T cell tolerance in the thymus (central tolerance) is essential for preventing organ-specific autoimmunity. This apparent paradox is in part explained by promiscuous expression of numerous tissue-restricted self-antigens (TRA) in medullary thymic epithelial cells (mTEC), which is highly conserved between mice and man. In animal models, the threshold of central tolerance towards such TRA is surprisingly sensitive towards minor shifts in antigen expression levels and this might also be the case in humans. To precisely assess the inter-individual variability of TRA expression in man, we determined the level of transcription of several auto-antigens in purified human mTEC and subsets thereof by quantitative RT-PCR. We detected two expression patterns: first, high variability (>20-fold) correlated with autoimmune regulator (Aire) expression and mTEC differentiation, and secondly, non-correlated low variability. Importantly, our approach revealed a significantly higher Aire-correlated insulin transcription in mTEC of carriers of the protective insulin-dependent diabetes mellitus locus 2 haplotype compared to the non-protective haplotype. The considerable, yet selective variability in thymic expression levels of target auto-antigen expression might constitute a hitherto underestimated risk factor for the susceptibility of autoimmune diseases in man.

Aire-ing self antigen variability and tolerance

Positional cloning of the underlying genes for the rare syndrome autoimmune polyendocrinopathy candidadiasis extrodermal dystrophy (APECED) opened a new venue of research on the role of central tolerance in autoimmunity. The associated autoimmune regulator gene (AIRE), was found to be expressed in medullary thymus epithelial cells (mTEC) in both man and mice, and to control promiscuous expression of sets of self antigens. The lack of AIRE in both mice and man led to the development of a quite specific, but also an inter-individual variable, set of autoimmune and infectious diseases. An article in this issue of the European Journal of Immunology demonstrates that several autoantigens controlled by AIRE are variably expressed in different human individuals. Most importantly it is shown that carriers of the type 1 diabetes (T1D) associated locus IDDM2 show lower expression of insulin in mTEC, as controlled by AIRE. The genetic variability of autoantigen expression in the thymus thus seems to determine the variable predisposition to autoimmunity.