Aire in Autoimmunity

Active Wnt/beta-catenin signaling is required for embryonic thymic epithelial development and functionality ex vivo

The establishment of central immune tolerance in the thymus is occurs via thymocyte negative selection to deplete self-reactive T clones and thymic CD4+ regulatory T cell (tTreg) generation. Due to limited published data, it is largely unclear whether these two mechanisms are both defective in the involuted thymus, as a result of aging or other insults. We used mouse models with thymic epithelial cell (TEC) conditional defect (FoxN1 conditional knockout) and naturally aged defect to study mechanistic changes in central tolerance establishment. We identified a defect in thymocyte negative selection but not in tTreg generation. In comparison to tTreg with thymic conventional CD4+ T cells (tTcon) in the same thymus, the ratios were increased with severity of thymic involution, suggesting that activity of tTreg generation is increased in the involuted condition. We found that these changes were due to alterations in signaling strength received by T cell receptors, characterized by a decline of Nur77 and CD5 in CD4+ single positive thymocytes and an enhancement of Zap-70 in newly-generated tTregs. This is due to weakened signaling provided by MHC/self-peptide complex ligand from defective TECs, but not due to changes in tTreg development-required factors (TGFb, IL-2, IL-15, and NF-kB). Our results suggest that the involuted thymus attempts to balance the defective negative selection by enhancing tTreg generation to maintain central immune tolerance. If this balance is broken, age-related inflammatory diseases could take place.

Negative selection induces central tolerance in which self-reactive T cells are deleted by medullary thymic epithelial cells (mTECs) to prevent autoimmunity. The transcriptional factor, autoimmune regulator (Aire), controls the expression of tissue-specific antigens (TSAs) by mTECs for negative selection. The mechanisms by which Aire targets loci which encode TSAs are unknown in detail; recently, however, the ATF7ip-MBD1 complex was identified as an Aire-interacting transcriptional protein complex required for its targeting the loci. Lineage tracing of Aire(+) mTECs identified that mTECs have a post-Aire stage during the development, where they lost maturation markers but maintained intermediate TSA expression, and Aire is required for the terminal differentiation of mTEC's. Extrathymic Aire-expressing cells (eTACs) are identified in murine and human secondary lymphoid organs. eTACs express major histocompatibility complex class II(hi), CD80(lo), CD86(lo), epithelial cell adhesion molecule(hi), CD45(lo) bone marrow-derived peripheral antigen-presenting cell population, which is distinct from mTECs and dendritic cells. They can induce activation-induced cell death of self-reactive CD8(+) T cells and unresponsiveness of self-reactive CD4(+) T cells through a mechanism that does not require regulatory T cells, suggesting that peripheral Aire plays a complementary role for central tolerance.

Immune tolerance includes central immune tolerance and peripheral immune tolerance.The major mechanism of central tolerance is mainly due to clonal deletion of self-antigen-reactive T cells in the thymus.Peripheral tolerance mechanisms involve the deletion of peripheral mature T cells.The autoimmune regulator (Aire) plays an important role in the establishment and maintenance of central and peripheral immunological tolerance.Monoallelic mutations in Aire could cause autoimmune diseases.A large number of studies have shown that Aire may become a new target for the induction of tolerance in organ transplantation and the treatment for autoimmune diseases. Key words: Autoimmune regulator; Immunological tolerance; Negative selection; Transplant rejection reaction

Background Thymoma is thymic epithelial cell tumor. Studies have shown that thymoma associated with autoimmune disorders and possible mechanisms of autoimmune diseases is the central immune tolerance and peripheral tolerance obstacles have resulted in the breaking of the autoimmune response activation and immune tolerance. Tc17 cells and Th17 cells have been shown play an important role in tumor and autoimmune diseases’ development process. This study test the distribution of Tc17cells in thymoma and the expression of RORγt in thymus of thymoma patients with myasthenia gravis (MG) or other autoimmune diseases, the frequency of Th17/Tc17 in PBMCs, to explore the expression of Th17/Tc17 cells in thymoma accompany with autoimmune diseases or autoimmune disorders.

There is a pregnant maternal immunological tolerance that protects the fetus and promotes its growth, and nuclear factor kappa B (NF-κB) family participates in the regulation of innate immune and adaptive immune responses. The thymus is related to establishing central tolerance, and early pregnancy has effects on expression of a good number of genes and proteins in the maternal thymus in sheep. However, it is unclear whether early pregnancy changes expression of NF-κB subunits in the ovine thymus. In this study, the thymic samples were collected from day 16 of non-pregnant ewes, and days 13, 16 and 25 of pregnant ewes, and the expression of NF-κB members (NF-κB1, NF-κB2, RelA, RelB and c-Rel) was analyzed through real-time quantitative PCR, Western blot and immunohistochemical analysis. The results showed that c-Rel mRNA and protein upregulated at day 25 of pregnancy, and NF-κB1 mRNA and proteins increased at days 16 and 25 of pregnancy, and RelB mRNA and proteins enhanced during early pregnancy. However, expression levels of NF-κB2 and RelA were decreased during early pregnancy, but upregulated from day 13 to 25 of pregnancy. In addition, the RelA protein was located in the epithelial reticular cells, capillaries and thymic corpuscles. This paper reported for the first time that early pregnancy induced expression of NF-κB1, RelB and c-Rel, but inhibited expression of NF-κB2 and RelA in the maternal thymus during early pregnancy, which is involved in the central immune tolerance, and helpful for successful pregnancy in sheep.

Thymic epithelial cells (TEC) make up a majority of the thymic stroma and can be classified into cortical (c) and medullary (m) compartment. TEC are responsible for generating a self-tolerant T cell repertoire and thus potentially self-reactive thymocytes are induced to undergo apoptosis in the process termed negative selection. For this purpose, TEC express over 19,000 protein-encoding genes to represent almost the entire repertoire of protein-encoded antigens of the host. Many of these genes are typically expressed only in specific organs and are referred to as tissue-restricted antigens (TRA). The autoimmune regulator (Aire) facilitates the expression of a subset of TRA and these Aire-regulated TRA occupy chromatin regions enriched with the trimethylation of 27th lysine on histone 3 (H3K27me3), an epigenetic mark is catalysed by the methyltransferase activity of Polycomb Repressive Complex 2 (PRC2). However, the physiological significance of H3K27me3 in TEC biology remains to be elucidated. To address this issue, mice with TEC-targeted PRC2 deficiency were generated. These mice displayed severely hypocellular thymi but yet maintained intact tissue architecture and total TEC cellularity. Within the TEC population, mTEC cellularity was drastically reduced and the maturation of mTEC was also hindered. Furthermore, the decrease in number of early T lineage progenitors recruited correlated with the reduced expression of chemokines by the cTEC. The deficiency of PRC2 in TEC also interfered with efficiency of negative selection and Treg production. Single cell transcriptome and flow cytometric data demonstrated that the deficiency of PRC2 activity also provokes mTEC development along a novel lineage differentiation path. Taken together, these data provide experimental proof that PRC2 plays crucial roles in the regulation of TEC differentiation and the capacity to carry out negative selection.

Somatic mutations binding to the patient's MHC and recognized by autologous T cells (neoepitopes) are ideal cancer vaccine targets. They combine a favorable safety profile due to a lack of expression in healthy tissues with a high likelihood of immunogenicity, as T cells recognizing neoepitopes are not shaped by central immune tolerance. Proteins mutated in cancer (neoantigens) shared by patients have been explored as vaccine targets for many years. Shared ("public") mutations, however, are rare, as the vast majority of cancer mutations in a given tumor are unique for the individual patient. Recently, the novel concept of truly individualized cancer vaccination emerged, which exploits the vast source of patient-specific "private" mutations. Concurrence of scientific advances and technological breakthroughs enables the rapid, cost-efficient, and comprehensive mapping of the "mutanome," which is the entirety of somatic mutations in an individual tumor, and the rational selection of neoepitopes. How to transform tumor mutanome data to actionable knowledge for tailoring individualized vaccines "on demand" has become a novel research field with paradigm-shifting potential. This review gives an overview with particular focus on the clinical development of such vaccines.

Identification of epitopes that are recognized by diabetogenic T cells and cause selective beta cell destruction in type 1 diabetes (T1D) has focused on peptides originating from native beta cell proteins. Translational errors represent a major potential source of antigenic peptides to which central immune tolerance is lacking. Here, we describe an alternative open reading frame within human insulin mRNA encoding a highly immunogenic polypeptide that is targeted by T cells in T1D patients. We show that cytotoxic T cells directed against the N-terminal peptide of this nonconventional product are present in the circulation of individuals diagnosed with T1D, and we provide direct evidence that such CD8+ T cells are capable of killing human beta cells and thereby may be diabetogenic. This study reveals a new source of nonconventional polypeptides that act as self-epitopes in clinical autoimmune disease.

Myocarditis, or inflammation of the heart, is a potentially devastating disease that can result from both viral infection and autoimmune attack of self antigens in the heart. In the current issue of the JCI, Lv and colleagues use a genetically susceptible mouse model to show that myocarditis is a T cell-mediated autoimmune disease that occurs due to insufficient thymic negative selection of α-myosin-reactive T cells.

Cardiovascular Characteristics and Progressions of Hypertrophic Cardiomyopathy and Pulmonary Stenosis in RASopathy Syndrome in the Genomic Era

Autoimmune diseases (ADs) comprise a heterogeneous group of conditions characterized by the presence of autoantibodies and/or T- or B-lymphocyte reactivity against autoantigens. In many conditions the precise relationship between autoimmune responses and clinical features remains to be defined, but the prevailing notion is that failure of central or peripheral immune tolerance leading to autoimmunity precedes clinically overt autoimmune disease which in the case of rheumatic autoimmune conditions is characterized by systemic inflammation, vasculopathy and signs and symptoms of musculoskeletal involvement. Except for rheumatoid arthritis (RA), rheumatic autoimmune diseases are rare, affecting less than 1% of the population. Nevertheless, they account for a high share of public health expenditure, due to their chronic debilitating nature [Gabriel and Michaud, 2009]. It is not therefore surprising that new therapeutic avenues are constantly being explored. While biologicals have resulted in major breakthroughs in the treatment of RA and juvenile idiopathic arthritis (JIA), connective tissue diseases such as systemic lupus erythematosus (SLE) and systemic sclerosis (SSc) still pose major challenges to clinicians seeking effective treatment options. Biologicals which interfere with the immune response such as rituximab (anti-CD20 mAb) and abatacept (CTLA4-Ig) have not been proven more effective than placebo in controlled clinical trials, which contrasts with the positive collective rituximab experience from large case series. Belimumab (anti-BAFF mAb) is the first new drug to be licensed for use in SLE for several decades, but its efficacy is modest, and its place in the treatment paradigm of lupus remains to be established. Imatinib was hailed as a promising drug for the treatment of systemic sclerosis based on its mechanism of action and on studies in animal models of scleroderma, but it is unlikely that its clinical development in systemic sclerosis will be pursued following disappointing results from pilot studies. Conventional immunosuppressive drugs including glucocorticoids, cyclophosphamide, azathioprine, methotrexate and mycophenolate mofetil therefore still remain the cornerstone in the treatment of connective tissue diseases. However, long-term drug-free remissions are rare and adverse drug reactions and clinical sequelae of long-term use contribute to compliance problems.

e18516 Background: Acute myeloid leukemia (AML) is one of the most common leukemia affecting adult. Regulatory T cells (Tregs) are a subset of CD4 (+) T cells that plays a central role immune tolerance. Objective: We aimed to explore the role of interleukin- 27 (IL27) & interleukin- 35 (IL35) produced by T regs and its associations with clinical characteristics and prognostic markers of AML patients. Methods: The study included 70 patients with acute myeloid leukemia (AML) and 30 healthy controls. We used flowcytometry immunophenotyping to confirm the diagnosis of AML. Serum level of interleukin- 27 (IL 27) & interleukin- 35 (IL 35) were measured at diagnosis by enzyme-linked immunosorbentassay (ELISA). Results: Higher levels of IL27 and IL35 were detected in AML patients than the control group (p ≤ 0.001). We used Receiver operating characteristic (ROC) analysis for detection of optimum IL27 & IL35 cut off level needed for predicting AML. ROC curve analysis demonstrated IL27 optimum cutoff is > 43, AUC 0.926 with a sensitivity 74% and Specificity 96.6% (P-value <0.00). IL35 optimum cutoff was > 27.8 AUC 0.972 with 88% and 98% sensitivity and specificity respectively (P-value <0.001). Serum IL27 & IL35 could well identify AML patients from healthy individuals. More importantly IL27 & IL35 correlated with clinical variable, and could be served as an independent prognostic factor. Conclusions: IL27 & IL 35 might have an application as a diagnostic and prognostic indicator for AML patients and could be served as an independent prognostic factor.

The ubiquitin-proteasome pathway is responsible for the turnover of different cellular proteins, such as transport proteins, presentation of antigens to the immune system, control of the cell cycle, and activities that promote cancer. The enzymes which remove ubiquitin, deubiquitylating enzymes (DUBs), play a critical role in central and peripheral immune tolerance to prevent the development of autoimmune diseases and thus present a potential therapeutic target for the treatment of autoimmune diseases. DUBs function by removing ubiquitin(s) from target protein and block ubiquitin chain elongation. The addition and removal of ubiquitin molecules have a significant impact on immune responses. DUBs and E3 ligases both specifically cleave target protein and modulate protein activity and expression. The balance between ubiquitylation and deubiquitylation modulates protein levels and also protein interactions. Dysregulation of the ubiquitin-proteasome pathway results in the development of various autoimmune diseases such as inflammatory bowel diseases (IBD), psoriasis, multiple sclerosis (MS), systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). This review summarizes the current understanding of ubiquitination in autoimmune diseases and focuses on various DUBs responsible for the progression of autoimmune diseases.

Stealing Tregs’ Identity (by Deleting NF-κB)