Critical immunological pathways are downregulated in APECED patient dendritic cells

Novel homozygous mutations in AIRE leading to APS-1 and potential mechanisms based on bioinformatics analysis

BACKGROUND

Autoimmune Poly-endocrine Syndrome Type 1 (APS-1), also known as autoimmune poly-endocrinopathy-candidiasis-ectodermal dystrophy (APECED), is a single-gene hereditary disorder usually characterized by chronic mucocutaneous candidiasis, hypoparathyroidism, and autoimmune adrenocortical insufficiency. This syndrome is very rare in China.

METHODS

For our reported patient, we employed clinical and laboratory examinations along with genetic identification. For previously reported cases, we summarized findings based on meta-analysis principles. To investigate the AIRE gene's role in disease, we utilized bioinformatics analysis with existing databases and R language processing.

RESULTS

Nucleotide sequence analysis revealed two novel homozygous missense mutations (c.74C > G; c.1612C > T) in the patient's AIRE gene, confirming APS-1 diagnosis. The 3D structure of these mutation sites was described for the first time, showing that altered side chains could affect AIRE protein function. We analyzed 16 genetically diagnosed APS-1 Chinese patients, summarized the AIRE genetic spectrum, and found that exons 1, 2, 3, and 5 were most commonly affected. Hypoparathyroidism and adrenal insufficiency were the most common clinical manifestations (56%-93%), followed by hypothyroidism (31.25%), hypogonadism (12.5%), type 2 diabetes (6.25%), and type 1 diabetes (6.25%). Bioinformatics analysis indicated that AIRE mutations cause antigen presentation abnormalities in immune cells, leading to excessive endogenous and reduced exogenous antigen presentation.

CONCLUSIONS

Our study summarized the clinical features of APS-1 caused by AIRE gene mutations and explored underlying mechanisms. For some patients, the prophylactic use of antimicrobial agents may be beneficial. These findings guide early genetic screening and inform potential research directions for treatment strategies.

AIRE is expressed in breast cancer TANs and TAMs to regulate the extrinsic apoptotic pathway and inflammation

The autoimmune regulator (AIRE) is a transcriptional regulator expressed in the thymus and is necessary for maintaining immunological self-tolerance. Extrathymic AIRE expression is rare, and a role for AIRE in tumor-associated innate immune cells has not yet been established. In this study, we show that AIRE is expressed in human pro-tumor neutrophils. In breast cancer, AIRE was primarily located to tumor-associated neutrophils (TANs), and to a lesser extent to tumor-associated macrophages (TAMs) and tumor cells. Expression of AIRE in TAN/TAMs, but not in cancer cells, was associated with an adverse prognosis. We show that the functional role for AIRE in neutrophils and macrophages is to regulate expression of immune mediators and the extrinsic apoptotic pathway involving the Fas/TNFR death receptors and cathepsin G. Here, we propose that the role for AIRE in TAN/TAMs in breast tumors is to regulate cell death and inflammation, thus promoting tumor progression.

Extrathymic AIRE-Expressing Cells: A Historical Perspective

Since its discovery, Aire has been the topic of numerous studies in its role as a transcriptional regulator in the thymus where it promotes the "promiscuous" expression of a large repertoire of tissue-restricted antigens (TRAs) that are normally expressed only in the immune periphery. This process occurs in specialized medullary thymic epithelial cells (mTECs) and mediates the elimination of self-reactive T cells or promotes their conversion to the Foxp3+ regulatory T cell lineage, both of which are required for the prevention of autoimmunity. In recent years, there has been increasing interest in the role of extrathymic Aire expression in peripheral organs. The focus has primarily been on the identification of the cellular source(s) and mechanism(s) by which extrathymic AIRE affects tolerance-related or other physiological processes. A cadre of OMICs tools including single cell RNA sequencing and novel transgenic models to trace Aire expression to perform lineage tracing experiments have shed light on a phenomenon that is more complex than previously thought. In this chapter, we provide a deeper analysis of how extrathymic Aire research has developed and progressed, how cellular sources were identified, and how the function of AIRE was determined. Current data suggests that extrathymic AIRE fulfills a function that differs from what has been observed in the thymus and strongly argues that its main purpose is to regulate transcriptional programs in a cell content-dependent manner. Surprisingly, there is data that also suggests a non-transcriptional role of extrathymic AIRE in the cytoplasm. We have arrived at a potential turning point that will take the field from the classical understanding of AIRE as a transcription factor in control of TRA expression to its role in immunological and non-immunological processes in the periphery.

APECED and the place of AIRE in the puzzle of the immune network associated with autoimmunity

In the last 20 years, discoveries about the autoimmune regulator (AIRE) protein and its critical role in immune tolerance have provided fundamental insights into understanding the molecular basis of autoimmunity. This review provides a comprehensive overview of the effect of AIRE on immunological tolerance and the characteristics of autoimmune diseases in Autoimmune Polyendocrinopathy-Candidiasis-Ectodermal Dystrophy (APECED), which is caused by biallelic AIRE mutations. A better understanding of the immunological mechanisms of AIRE deficiency may enlighten immune tolerance mechanisms and new diagnostic and treatment strategies for autoimmune diseases. Considering that not all clinical features of APECED are present in a given follow-up period, the diagnosis is not easy in a patient at the first visit. Longer follow-up and a multidisciplinary approach are essential for diagnosis. It is challenging to prevent endocrine and other organ damage compared with other diseases associated with multiple autoimmunities, such as FOXP3, LRBA, and CTLA4 deficiencies. Unfortunately, no curative therapy like haematopoietic stem cell transplantation or specific immunomodulation is present that is successful in the treatment.

Genes and Microbiota Interaction in Monogenic Autoimmune Disorders

Monogenic autoimmune disorders represent an important tool to understand the mechanisms behind central and peripheral immune tolerance. Multiple factors, both genetic and environmental, are known to be involved in the alteration of the immune activation/immune tolerance homeostasis typical of these disorders, making it difficult to control the disease. The latest advances in genetic analysis have contributed to a better and more rapid diagnosis, although the management remains confined to the treatment of clinical manifestations, as there are limited studies on rare diseases. Recently, the correlation between microbiota composition and the onset of autoimmune disorders has been investigated, thus opening up new perspectives on the cure of monogenic autoimmune diseases. In this review, we will summarize the main genetic features of both organ-specific and systemic monogenic autoimmune diseases, reporting on the available literature data on microbiota alterations in these patients.

Extrathymic AIRE-expressing cells: Friends or foes in autoimmunity and cancer?

Auto-immune regulator (AIRE) is a transcription factor that is mainly known for its crucial role in the thymus. Here, AIRE ensures central tolerance by promoting the expression of peripheral tissue antigens in thymic epithelial cells, which is essential for the negative selection of autoreactive T cells. Intriguingly, AIRE expressing cells have recently been identified in other tissues outside the thymus as well. However, the exact function of these extrathymic AIRE expressing cells (eTACs) remains largely enigmatic. Human eTACs are mainly found in secondary lymphoid tissues under homeostatic conditions, but are also found in pathologies such as the inflamed tissues of patients with autoimmune diseases and in various cancer tissues. eTACs have been demonstrated to express dendritic cell (DC)-like markers, such as MHCII, CD40 and CD127, but also CCR7, IDO and PD-L1. Interestingly, eTACs lack high expression of co-stimulatory molecules, such as CD80 or CD86. In mice, different types of peripheral AIRE expressing cells have been described, including cells with an innate lymphoid cell-like phenotype and antigen presenting cell (APC) function. These findings suggest that eTACs are APCs with the possibility to modulate or inhibit immune responses, which is confirmed by functional murine studies demonstrating the ability of eTACs to induce tolerance in autoreactive T cells. The potential immunomodulatory function of eTACs makes them promising targets to restore tolerance in autoimmunity or improve immunotherapy in cancer settings. Yet, this requires a better understanding of these cells and the molecular mechanisms involved. In this review we aim to summarize the current knowledge and understanding of eTACs, including their putative roles in health and disease.

Association of Autoimmune Regulator Gene Rs2075876 Variant, but Not Gene Expression with Alopecia Areata in Males: A Case-control Study

Alopecia areata (AA) is a non-scarring hair loss of autoimmune etiology. The autoimmune regulator (AIRE) gene is believed to be an important driver in AA pathogenesis. Genetic variants can alter mRNA expression levels which may provoke an autoimmune response. A total of 337 males (97 AA patients and 240 controls) were enrolled in the current case-control study. On screening of the most frequent variants in the gene, rs2075876 (A/G) polymorphism in intron 5 was selected and genotyped using Real-Time PCR (polymerase chain reaction) technology. Additionally, circulatory AIRE expression levels were quantified by quantitative reverse-transcription PCR (qRT-PCR). Allelic discrimination analysis revealed GG genotype to be more frequent in patients (90.7% in AA compared to 32.5% in controls, p < .001). G variant conferred increased risk to alopecia under homozygote comparison (GG versus AA: OR = 16.1, 95%CI = 5.57-46.3), dominant model (GG+AG versus AA: OR = 7.24, 95%CI = 2.5-20.5), recessive model (GG versus AG+AA: OR = 20.3, 95%CI = 9.7-42.4), and allelic model (G versus A: OR = 11.6, 95%CI = 6.47-21.1). The expression levels of AIRE gene did not differ significantly between patients and controls and were not related to rs2075876 variant. In conclusion, the intronic variant (rs2075876) is suggested to be a potent susceptibility variant for AA development in the studied population.Abbreviations: AA: Alopecia areata; AIRE: Autoimmune Regulator; APECED: Autoimmune, Polyendocrinopathy Candidiasis Ectodermal Dystrophy; DLQI: Dermatology life quality index questionnaire; MIQE: Minimum information for publication of quantitative real-time PCR experiments; mTEC: Medullary thymic epithelial cells; PHD: Plant homeodomain; qRT-PCR: Quantitative reversetranscription-polymerase chain reaction; RA: Rheumatoid arthritis.

Maturing Human CD127+ CCR7+ PDL1+ Dendritic Cells Express AIRE in the Absence of Tissue Restricted Antigens

Expression of the Autoimmune regulator (AIRE) outside of the thymus has long been suggested in both humans and mice, but the cellular source in humans has remained undefined. Here we identify AIRE expression in human tonsils and extensively analyzed these "extra-thymic AIRE expressing cells" (eTACs) using combinations of flow cytometry, CyTOF and single cell RNA-sequencing. We identified AIRE+ cells as dendritic cells (DCs) with a mature and migratory phenotype including high levels of antigen presenting molecules and costimulatory molecules, and specific expression of CD127, CCR7, and PDL1. These cells also possessed the ability to stimulate and re-stimulate T cells and displayed reduced responses to toll-like receptor (TLR) agonists compared to conventional DCs. While expression of AIRE was enriched within CCR7+CD127+ DCs, single-cell RNA sequencing revealed expression of AIRE to be transient, rather than stable, and associated with the differentiation to a mature phenotype. The role of AIRE in central tolerance induction within the thymus is well-established, however our study shows that AIRE expression within the periphery is not associated with an enriched expression of tissue-restricted antigens (TRAs). This unexpected finding, suggestive of wider functions of AIRE, may provide an explanation for the non-autoimmune symptoms of APECED patients who lack functional AIRE.

The heterogeneity of autoimmune polyendocrine syndrome type 1: Clinical features, new mutations and cytokine autoantibodies in a Brazilian cohort from tertiary care centers

Autoimmune polyendocrine syndrome type 1 (APS1) is characterized by multiorgan autoimmunity. We aim at characterizing a multi-center Brazilian cohort of APS1 patients by clinical evaluation, searching mutation in the AIRE gene, measuring serum autoantibodies, and investigating correlations between findings. We recruited patients based on the clinical criteria and tested them for AIRE mutations, antibodies against interferon type I and interleukins 17A, 17F and 22. We identified 12 unrelated families (13 patients) with typical signs of APS1 in the proband, and the screening of relatives recognized an asymptomatic child. Candidiasis was present in all cases, and 19 other manifestations were observed. All patients carried one of 10 different mutations in AIRE, being 3 new ones, and were positive for anti-interferon type I serum antibody. Anti-interleukin-17A levels inversely correlated with the number of manifestations in each patient. This negative correlation may suggest a protective effect of anti-interleukin-17A with a potential therapeutic application.

The Role of Autoimmune Regulator (AIRE) in Peripheral Tolerance

Autoimmune regulator (AIRE), whose gene mutation is considered to be a causative factor of autoimmune polyglandular syndrome type 1 (APS1), is an important transcriptional regulator. Studies on the role of AIRE in the central immune system have demonstrated that AIRE can eliminate autoreactive T cells by regulating the expression of a series of tissue specific antigens promiscuously in medullary thymic epithelial cells (mTECs) and induce regulatory T cell (Treg) production to maintain central immune tolerance. However, the related research of AIRE in peripheral tolerance is few. In order to understand the current research progress on AIRE in peripheral tolerance, this review mainly focuses on the expression and distribution of AIRE in peripheral tissues and organs, and the role of AIRE in peripheral immune tolerance such as regulating Toll-like receptor (TLR) expression and the maturation status of antigen presenting cells (APCs), inducing T cell tolerance and differentiation. This review will show us that AIRE also plays an indispensable role in the periphery.

Mode of Tolerance Induction and Requirement for Aire Are Governed by the Cell Types That Express Self-Antigen and Those That Present Antigen

Aire controls the fate of autoreactive thymocytes (i.e., clonal deletion or development into regulatory T cells [Tregs]) through transcriptional control of the expression of tissue-restricted self-antigens (TRAs) from medullary thymic epithelial cells (mTECs) and bone marrow (BM)-derived cells. Although TRAs expressed by mTECs and BM-derived cells are suggested to complement each other to generate a full spectrum of TRAs, little is known about the relative contribution of TRAs from each component for establishment of self-tolerance. Furthermore, the precise role of Aire in specific types of Aire-expressing APCs remains elusive. We have approached these issues by generating two different types of transgenic mouse (Tg) model, which express a prefixed model self-antigen driven by the insulin promoter or the Aire promoter. In the insulin-promoter Tg model, mTECs alone were insufficient for clonal deletion, and BM-derived APCs were required for this action by utilizing Ag transferred from mTECs. In contrast, mTECs alone were able to induce Tregs, although at a much lower efficiency in the absence of BM-derived APCs. Importantly, lack of Aire in mTECs, but not in BM-derived APCs, impaired both clonal deletion and production of Tregs. In the Aire-promoter Tg model, both mTECs and BM-derived APCs could independently induce clonal deletion without Aire, and production of Tregs was impaired by the lack of Aire in mTECs, but not in BM-derived APCs. These results suggest that the fate of autoreactive thymocytes together with the requirement for Aire depend on the cell types that express self-antigens and the types of APCs involved in tolerance induction.

AIRE is not essential for the induction of human tolerogenic dendritic cells

Loss-of-function mutations of the Autoimmune Regulator (AIRE) gene results in organ-specific autoimmunity and disease Autoimmune Polyendocrinopathy type 1 (APS1)/Autoimmune Polyendocrinopathy Candidiasis Ectodermal Dystrophy (APECED). The AIRE protein is crucial in the induction of central tolerance, promoting ectopic expression of tissue-specific antigens in medullary thymic epithelial cells and enabling removal of self-reactive T-cells. AIRE expression has recently been detected in myeloid dendritic cells (DC), suggesting AIRE may have a significant role in peripheral tolerance. DC stimulation of T-cells is critical in determining the initiation or lack of an immune response, depending on the pattern of costimulation and cytokine production by DCs, defining immunogenic/inflammatory (inflDC) and tolerogenic (tolDC) DC. In AIRE-deficient patients and healthy controls, we validated the role of AIRE in the generation and function of monocyte-derived inflDC and tolDCs by determining mRNA and protein expression of AIRE and comparing activation markers (HLA-DR/DP/DQ,CD83,CD86,CD274(PDL-1),TLR-2), cytokine production (IL-12p70,IL-10,IL-6,TNF-α,IFN-γ) and T-cell stimulatory capacity (mixed lymphocyte reaction) of AIRE+ and AIRE- DCs. We show for the first time that: (1) tolDCs from healthy individuals express AIRE; (2) AIRE expression is not significantly higher in tolDC compared to inflDC; (3) tolDC can be generated from APECED patient monocytes and (4) tolDCs lacking AIRE retain the same phenotype and reduced T-cell stimulatory function. Our findings suggest that AIRE does not have a role in the induction and function of monocyte-derived tolerogenic DC in humans, but these findings do not exclude a role for AIRE in peripheral tolerance mediated by other cell types.

Anticommensal Responses Are Associated with Regulatory T Cell Defect in Autoimmune Polyendocrinopathy-Candidiasis-Ectodermal Dystrophy Patients

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is a monogenic autoimmune disease caused by mutations in the AIRE gene. Although mainly an endocrine disease, a substantial fraction of patients have gastrointestinal manifestations. In this study, we have examined the role of anticommensal responses and their regulation. APECED patients had increased levels of Abs against Saccharomyces cerevisiae (p < 0.0001) and against several species of commensal gut bacteria, but not against species predominantly associated with other locations. The anticommensal Ab levels did not correlate with gastrointestinal autoantibodies, neutralizing anti-IL-17 or -IL-22 Abs, or gastrointestinal symptoms, although scarcity of the available clinical data suggests that further study is required. However, the anti-S. cerevisiae Ab levels showed a significant inverse correlation with FOXP3 expression levels in regulatory T cells (Treg), previously shown to be dysfunctional in APECED. The correlation was strongest in the activated CD45RO(+) population (ρ = -0.706; p < 0.01). APECED patients also had decreased numbers of FOXP3(+) cells in gut biopsies. These results show that APECED patients develop early and sustained responses to gut microbial Ags in a pattern reminiscent of Crohn's disease. This abnormal immune recognition of gut commensals is linked to a systemic Treg defect, which is also reflected as a local decrease of gut-associated Treg. To our knowledge, these data are the first to show dysregulated responses to non-self commensal Ags in APECED and indicate that AIRE contributes to the regulation of gut homeostasis, at least indirectly. The data also raise the possibility of persistent microbial stimulation as a contributing factor in the pathogenesis of APECED.

Autoimmune regulator‑overexpressing dendritic cells induce T helper 1 and T helper 17 cells by upregulating cytokine expression

The autoimmune regulator (Aire) protein is a transcriptional activator that is essential in central immune tolerance, as it regulates the ectopic expression of many tissue‑restricted antigens in medullary thymic epithelial cells. Aire expression has also been described in hematopoietic cells, such as monocytes/macrophages and dendritic cells (DCs), in the peripheral immune system. However, the role of Aire expression in peripheral immune system cells, including DCs, remains to be elucidated. In the present study, the effects of secreted cytokines from Aire‑overexpressing DCs on cluster of differentiation (CD)4+ T cell subsets were investigated. The dendritic cell line, DC2.4, which overexpresses Aire, was co‑cultured with CD4+ T cells from splenocytes using Transwell inserts. The results indicate that Aire‑overexpressing cells induce T helper (Th)1 subsets by increasing interleukin (IL)‑12 expression, and induce Th17 subsets by upregulating IL‑6 and transforming growth factor (TGF)‑β production. In addition, it was observed that increased levels of phosphorylated extracellular signal‑regulated kinases and p38 upregulated the expression of cytokines in Aire‑overexpressing cells. These data suggest that Aire may have a role in inducing Th1 and Th17 differentiation by upregulating cytokine expression in DCs.

Lymphopenia-induced proliferation in the absence of functional Autoimmune regulator (Aire) induces colitis in mice

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is caused by mutations in Autoimmune regulator (Aire), a transcriptional regulator of negative selection in thymus. However, Aire is also expressed in periphery, but the full range of Aire's peripheral function is unknown. Here, we transferred lymphocytes from wildtype donors into lymphopenic recipients with or without functional Aire. Following cell proliferation thus took place in Aire-sufficient or deficient environment. The wildtype lymphocytes hyperproliferated and induced disease in lymphopenic Aire(-/-) but not in Aire(+/+) recipients. The disease was characterized by diarrhea, inflammation, and colitis, and in some recipients pancreatitis, gastritis, and hepatitis was also found. Our results identify Aire as an important regulator of peripheral T cell homeostasis in gastrointestinal tissues. Given a suitable trigger the absence of peripheral Aire leads to dysregulated T cell proliferation and disease.

The contribution of NF-κB signalling to immune regulation and tolerance

BACKGROUND

Immune regulation is necessary to control inflammatory responses and to prevent autoimmune diseases. Therefore, mechanisms of central and peripheral tolerance have evolved to ensure that T cells recognize antigens as self- or non-self-antigens. The thymus is crucially important for central tolerance induction to self-antigens via negative selection of T cells. However, if T cells escape negative selection in the thymus and enter the periphery, peripheral mechanisms are active to warrant immune tolerance. Secondary lymphoid organs, as well as tolerogenic dendritic cells and regulatory T cells, play an important role in peripheral tolerance. In chronic inflammatory diseases, tertiary lymphoid organs are sometimes formed that may also be involved in the induction of peripheral tolerance. This review discusses the main processes that are involved in immune regulation and tolerance, and focuses on the contribution of NF-κB signalling to these processes.

MATERIAL AND METHODS

This narrative review is based on peer-reviewed publications listed on PubMed up to December 2014. The focus of our literature search was on studies investigating the role of (non)canonical NF-κB signalling in central and peripheral mechanisms of tolerance. Only studies published in English language were considered.

RESULTS

This review discusses the immune phenotype of mutant mice with defective (non)canonical NF-κB signalling, corroborated with human data, and emphasizes the contribution of the noncanonical NF-κB pathway to immune regulation and tolerance induction.

CONCLUSIONS

Noncanonical NF-κB signalling has an important immunoregulatory role in the immune system and contributes to both central and peripheral mechanisms of tolerance.

Human APECED; a Sick Thymus Syndrome?

Loss-of-function mutations in the Autoimmune Regulator (AIRE) gene cause a rare inherited form of autoimmune disease, autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy, also known as autoimmune polyglandular syndrome type 1. The patients suffer from multiple endocrine deficiencies, the most common manifestations being hypoparathyroidism, Addison’s disease, hypogonadism, and secondary amenorrhea, usually accompanied by typical autoantibodies against the target tissues. Chronic mucocutaneous candidiasis is also a prominent part of the disease. The highest expression of AIRE is found in medullary thymic epithelial cells (mTECs). Murine studies suggest that it promotes ectopic transcription of self antigens in mTECs and is thus important for negative selection. However, failed negative selection alone is not enough to explain key findings in human patients, necessitating the search for alternative or additional pathogenetic mechanisms. A striking feature of the human AIRE-deficient phenotype is that all patients develop high titers of neutralizing autoantibodies against type I interferons, which have been shown to downregulate the expression of interferon-controlled genes. These autoantibodies often precede clinical symptoms and other autoantibodies, suggesting that they are a reflection of the pathogenetic process. Other cytokines are targeted as well, notably those produced by Th17 cells; these autoantibodies have been linked to the defect in anti-candida defenses. A defect in regulatory T cells has also been reported in several studies and seems to affect already the recent thymic emigrant population. Taken together, these findings in human patients point to a widespread disruption of T cell development and regulation, which is likely to have its origins in an abnormal thymic milieu. The absence of functional AIRE in peripheral lymphoid tissues may also contribute to the pathogenesis of the disease.

Macrophages overexpressing Aire induce CD4+Foxp3+ T cells

Aire plays an important role in central immune tolerance by regulating the transcription of thousands of genes. However, the role of Aire in the peripheral immune system is poorly understood. Regulatory T (Treg) cells are considered essential for the maintenance of peripheral tolerance, but the effect of Aire on Treg cells in the peripheral immune system is currently unknown. In this study, we investigated the effects of macrophages overexpressing Aire on CD4+Foxp3+ Treg cells by co-culturing Aire-overexpressing RAW264.7 cells or their supernatant with splenocytes. The results show that macrophages overexpressing Aire enhanced the expression of Foxp3 mRNA and induced different subsets of Treg cells in splenocytes through cell-cell contact or a co-culture supernatants. TGF-β is a key molecule in the increases of CD4+CD45RA+Foxp3hi T cell and activating Treg (aTreg) levels observed following cell‑supernatant co-culturing. Subsets of Treg cells were induced by Aire-overexpressing macrophages, and the manipulation of Treg cells by the targeting of Aire may provide a method for the treatment of inflammatory or autoimmune diseases.

Expression of the autoimmune regulator gene and its relevance to the mechanisms of central and peripheral tolerance

The autoimmune polyendocrine syndrome type 1 (APS-1) is a monogenic disease due to pathogenic variants occurring in the autoimmune regulator (AIRE) gene. Its related protein, AIRE, activates the transcription of genes encoding for tissue-specific antigens (TsAgs) in a subset of medullary thymic epithelial cells: the presentation of TsAgs to the maturating thymocytes induces the apoptosis of the autoreactive clones and constitutes the main form of central tolerance. Dysregulation of thymic AIRE expression in genetically transmitted and acquired diseases other than APS-1 may contribute to further forms of autoimmunity. As AIRE and its murine homolog are also expressed in the secondary lymphoid organs, the extent and relevance of AIRE participation in the mechanisms of peripheral tolerance need to be thoroughly defined.

Inter-tissue networks between the basal forebrain, hippocampus, and prefrontal cortex in a model for depression caused by disturbed sleep

Disturbances in sleep are encountered in the majority of patients with depressive disorder. To elucidate the molecular mechanisms behind this relationship, we examined gene expression changes in a rodent model for disturbed sleep and depression. The animals were treated with daily injections of clomipramine to affect their sleep during early infancy. This early interference with sleep is known to induce depression-like behavior in adult animals. After 2 weeks of treatment, the change in gene expression was examined using the Affymetrix Rat 230.2 chip. We studied the gene expression in the basal forebrain, hippocampus, and frontal cortex and combined the results to reveal the otherwise indissectible networks between and around the tissues. The major disrupted pathways between the three brain areas were related to synaptic transmission, regulation of translation, and ubiquitinylation. The involved pathways were within the cellular components of the axons, growth cones, melanosomes, and pigment granules. A network analysis allowing for additional interactors, in the form of chemicals or gene products, revealed a disturbed communicational network between the different brain areas. This disturbed network is centered around serotonin, Mn(II), and Rhoa. The findings elucidate inter-tissue pathways and networks in the brain that are involved in sleep and mood regulation. The findings are of uttermost interest, some are quite predictable and obvious, but some are novel or have only been proposed by rare theoretical speculations (such as the melanosome and Mn(II) involvement). Equally important as the findings are the methods described in this article. In this study, we present two novel simple ways to perform system biological analysis based on gene expression array data. We used two already existing tools in a new way, and by careful planning of the input data, managed to extrapolate intricate hidden inter-tissue networks to build a molecular picture of disease.

Autoimmune regulator (AIRE) contributes to Dectin-1-induced TNF-α production and complexes with caspase recruitment domain-containing protein 9 (CARD9), spleen tyrosine kinase (Syk), and Dectin-1

BACKGROUND

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) syndrome is a complex immunologic disease caused by mutation of the autoimmune regulator (AIRE) gene. Autoimmunity in patients with APECED syndrome has been shown to result from deficiency of AIRE function in transcriptional regulation of thymic peripheral tissue antigens, which leads to defective T-cell negative selection. Candidal susceptibility in patients with APECED syndrome is thought to result from aberrant adaptive immunity.

OBJECTIVE

To determine whether AIRE could function in anticandidal innate immune signaling, we investigated an extrathymic role for AIRE in the immune recognition of β-glucan through the Dectin-1 pathway, which is required for defense against Candida species.

METHODS

Innate immune signaling through the Dectin-1 pathway was assessed in both PBMCs from patients with APECED syndrome and a monocytic cell line. Subcellular localization of AIRE was assessed by using confocal microscopy.

RESULTS

PBMCs from patients with APECED syndrome had reduced TNF-α responses after Dectin-1 ligation but in part used a Raf-1-mediated pathway to preserve function. In the THP-1 human monocytic cell line, reducing AIRE expression resulted in significantly decreased TNF-α release after Dectin-1 ligation. AIRE formed a transient complex with the known Dectin-1 pathway components phosphorylated spleen tyrosine kinase and caspase recruitment domain-containing protein 9 after receptor ligation and localized with Dectin-1 at the cell membrane.

CONCLUSION

AIRE can participate in the Dectin-1 signaling pathway, indicating a novel extrathymic role for AIRE and a defect that likely contributes to fungal susceptibility in patients with APECED syndrome.

Autoimmune polyendocrine syndrome type 1: case report and review of literature

Autoimmune polyendocrine syndrome type 1 (APECED) is a rare autosomal recessive disorder characterized by autoimmune multiorgan attack. The disease is caused by mutations in the autoimmune regulator gene (AIRE), resulting in defective AIRE protein, which is essential for selftolerance. Clinical manifestations are widely variable. Although the classic triad is composed by mucocutaneous candidiasis, hypoparathyroidism and adrenal failure, many other components may develop. Treatment is based on supplementation of the various deficiencies, and patients require regular follow-up throughout their lifespan. This article describes the case of a patient with the disease, and reviews literature data on the epidemiology, clinical course, immunogenetic aspects, diagnosis and treatment of the syndrome.

Autoimmune polyendocrinopathy candidiasis ectodermal dystrophy: insights into genotype-phenotype correlation

Autoimmune polyendocrinopathy candidiasis ectodermal dystrophy (APECED) is a rare autosomal recessive disease, caused by mutations of a single gene named autoimmune regulator gene (AIRE) which results in a failure of T cell tolerance within the thymus. Chronic mucocutaneous candidiasis, chronic hypoparathyroidism, and Addison's disease are the hallmarks of the syndrome. APECED is also characterized by several autoimmune endocrine and nonendocrine manifestations, and the phenotype is often complex. Moreover, even though APECED is a monogenic disease, its clinical picture is generally dominated by a wide heterogeneity both in the severity and in the number of components even among siblings with the same AIRE genotype. The variability of its clinical expression implies that diagnosis can be challenging, and a considerable delay often occurs between the appearance of symptoms and the diagnosis. Since a prompt diagnosis is essential to prevent severe complications, clinicians should be aware of all symptoms and signs of suspicion. The aim of this paper is to give an overview on the clinical presentation and diagnostic criteria of APECED and to focus on current knowledge on genotype-phenotype correlation.

Overexpressing autoimmune regulator regulates the expression of toll-like receptors by interacting with their promoters in RAW264.7 cells

Autoimmune regulator (Aire) is a transcriptional activator that regulates the ectopic expression of many tissue-restricted antigens in medullary thymic epithelial cells, and that has an important role in the negative selection of autoreactive T cells. However, the roles of Aire expression in peripheral lymphoid tissues and hematopoietic cells, especially monocytes/macrophages, remain poorly understood. In this study, we found that the mRNA and protein expression levels of toll-like receptor (TLR)1, TLR3, and TLR8 were notably up-regulated in a mouse macrophage-like cell line (RAW264.7) stably expressing Aire, while the expression of TLR2, TLR4, TLR5, TLR6, TLR7, and TLR9 were not significantly changed. In addition, the mRNA expression of TLR3 and TLR8 were significantly increased in primary peritoneal macrophages transiently transfected with Aire. Using chromatin immunoprecipitation and a luciferase activity assay, we also found that Aire interacted with the TLR1, TLR3, and TLR8 promoters and increased the luciferase transcriptional activity of these promoters in RAW264.7 cells. Moreover, after stimulation by Pam(3)CSK(4), a TLR1 ligand, and poly(I:C), a TLR3 ligand, we found that the mRNA expression levels of IL-1α, TNFα, iNOS, and IFNα were increased in RAW264.7 cells stably expressing Aire. Together, these data suggest that Aire has a crucial role in the recognition of pathogenic microorganisms and peripheral immune tolerance in antigen-presenting cells (APCs) by regulating the expression of TLRs.

Expression and function of the autoimmune regulator (Aire) gene in non-thymic tissue

Educational immune tolerance to self-antigens is induced primarily in the thymus where tissue-restricted antigens (TRAs) are presented to T lymphocytes by cells of the thymic stroma - a process known as central tolerance. The expression of these TRAs is controlled in part by a transcription factor encoded by the autoimmune regulatory (Aire) gene. Patients with a mutation of this gene develop a condition known as autoimmune-polyendocrinopathy-candidiasis-ectodermal-dystrophy (APECED), characterized by autoimmune destruction of endocrine organs, fungal infection and dental abnormalities. There is now evidence for TRA expression and for mechanisms of functional tolerance outside the thymus. This has led to a number of studies examining Aire expression and function at these extra-thymic sites. These investigations have been conducted across different animal models using different techniques and have often shown discrepant results. Here we review the studies of extra thymic Aire and discuss the evidence for its expression and function in both human and murine systems.

Chronic mucocutaneous candidiasis in APECED or thymoma patients correlates with autoimmunity to Th17-associated cytokines

Chronic mucocutaneous candidiasis (CMC) is frequently associated with T cell immunodeficiencies. Specifically, the proinflammatory IL-17A-producing Th17 subset is implicated in protection against fungi at epithelial surfaces. In autoimmune polyendocrinopathy candidiasis ectodermal dystrophy (APECED, or autoimmune polyendocrine syndrome 1), CMC is often the first sign, but the underlying immunodeficiency is a long-standing puzzle. In contrast, the subsequent endocrine features are clearly autoimmune, resulting from defects in thymic self-tolerance induction caused by mutations in the autoimmune regulator (AIRE). We report severely reduced IL-17F and IL-22 responses to both Candida albicans antigens and polyclonal stimulation in APECED patients with CMC. Surprisingly, these reductions are strongly associated with neutralizing autoantibodies to IL-17F and IL-22, whereas responses were normal and autoantibodies infrequent in APECED patients without CMC. Our multicenter survey revealed neutralizing autoantibodies against IL-17A (41%), IL-17F (75%), and/ or IL-22 (91%) in >150 APECED patients, especially those with CMC. We independently found autoantibodies against these Th17-produced cytokines in rare thymoma patients with CMC. The autoantibodies preceded the CMC in all informative cases. We conclude that IL-22 and IL-17F are key natural defenders against CMC and that the immunodeficiency underlying CMC in both patient groups has an autoimmune basis.

Pattern recognition receptor expression is not impaired in patients with chronic mucocutanous candidiasis with or without autoimmune polyendocrinopathy candidiasis ectodermal dystrophy

Patients with chronic mucocutaneous candidiasis (CMC) have an unknown primary immune defect and are unable to clear infections with the yeast Candida. CMC includes patients with AIRE gene mutations who have autoimmune polyendocrinopathy candidiasis ectodermal dystrophy (APECED), and patients without known mutations. CMC patients have dysregulated cytokine production, suggesting that defective expression of pattern recognition receptors (PRRs) may underlie disease pathogenesis. In 29 patients with CMC (13 with APECED) and controls, we assessed dendritic cell (DC) subsets and monocyte Toll-like receptor (TLR) expression in blood. We generated and stimulated monocyte-derived (mo)DCs with Candida albicans, TLR-2/6 ligand and lipopolysaccharide and assessed PRR mRNA expression by polymerase chain reaction [TLR-1-10, Dectin-1 and -2, spleen tyrosine kinase (Syk) and caspase recruitment domain (CARD) 9] in immature and mature moDCs. We demonstrate for the first time that CMC patients, with or without APECED, have normal blood levels of plasmocytoid and myeloid DCs and monocyte TLR-2/TLR-6 expression. We showed that in immature moDCs, expression levels of all PRRs involved in anti-Candida responses (TLR-1, -2, -4, -6, Dectin-1, Syk, CARD9) were comparable to controls, implying that defects in PRR expression are not responsible for the increased susceptibility to Candida infections seen in CMC patients. However, as opposed to healthy controls, both groups of CMC patients failed to down-regulate PRR mRNA expression in response to Candida, consistent with defective DC maturation, as we reported recently. Thus, impaired DC maturation and consequent altered regulation of PRR signalling pathways rather than defects in PRR expression may be responsible for inadequate Candida handling in CMC patients.

gammadelta T cells develop independently of Aire

Mutations in the transcriptional regulator Aire disrupt thymic alphabeta T cell selection, causing in humans Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED). However, it is not known whether Aire is needed for normal gammadelta T cell development. We show that Aire(-/-) mice have a normal frequency of gammadelta T cells, with TCR repertoire comparable to that of wild-type mice, and normal amount of TCR Cdelta mRNA in ileum and skin. gammadelta T cells did not express increased amounts of CD25 or display hyperproliferation, and were not involved in pathological salivary gland infiltrates. Lastly, the frequency of circulating gammadelta T cells was similar in APECED patients and healthy controls. These data indicate that gammadelta T cells develop independently of Aire and are unlikely to have a significant pathogenetic or protective role in APECED. The antigens responsible for gammadelta and alphabeta T cell selection are thus probably largely different.

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.

Transcriptional regulation by AIRE: molecular mechanisms of central tolerance

The negative selection of T cells in the thymus is necessary for the maintenance of self tolerance. Medullary thymic epithelial cells have a key function in this process as they express a large number of tissue-specific self antigens that are presented to developing T cells. Mutations in the autoimmune regulator (AIRE) protein cause a breakdown of central tolerance that is associated with decreased expression of self antigens in the thymus. In this Review, we discuss the role of AIRE in the thymus and recent advances in our understanding of how AIRE might function at the molecular level to regulate gene expression.