Impaired thymic AIRE expression underlies autoantibodies against type I IFNs in humans with inborn errors of the alternative NF-κB pathway

Patients with autoimmune polyendocrinopathy syndrome type 1 (APS-1) caused by autosomal recessive AIRE deficiency display autoantibodies (auto-Abs) neutralizing type I IFNs, conferring a predisposition to life-threatening COVID-19 pneumonia. We report that patients with autosomal recessive NIK or RelB deficiency, or a specific type of autosomal dominant (AD) NF-κB2 deficiency also display neutralizing auto-Abs against type I IFNs. They are prone to severe viral disease, including life-threatening COVID-19 pneumonia, influenza pneumonia, and severe form of varicella. Among patients with AD NF-κB2 deficiency, these auto-Abs are found only in heterozygotes with variants that are both transcriptionally loss-of-function (p52 activity), due to impaired p100 processing into p52, and regulatory gain-of-function (IκBδ activity), due to accumulation of unprocessed p100, thus increasing the inhibitory IκBδ activity (p52LOF/IκBδGOF). Conversely, neutralizing auto-Abs against type I IFNs are not found in individuals heterozygous for NFKB2 variants causing either p100 and p52 haploinsufficiency (p52LOF/IκBδLOF), or p52 gain-of-function (p52GOF/IκBδLOF). Unlike patients with APS-1, patients with disorders of NIK, RelB, or NF-κB2 harbor very few other auto-Abs. Their thymuses are however abnormally structured, and their medullary thymic epithelial cells (mTECs) have defective AIRE expression. Human inborn errors of the alternative NF-κB pathway impair thymic AIRE expression in mTECs, thereby underlying the production of auto-Ab against type I IFNs and predisposition to viral diseases.

Infections in the monogenic autoimmune syndrome APECED

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is caused by mutations in the Autoimmune Regulator (AIRE) gene, which impair the thymic negative selection of self-reactive T-cells and underlie the development of autoimmunity that targets multiple endocrine and non-endocrine tissues. Beyond autoimmunity, APECED features heightened susceptibility to certain specific infections, which is mediated by anti-cytokine autoantibodies and/or T-cell driven autoimmune tissue injury. These include the 'signature' APECED infection chronic mucocutaneous candidiasis (CMC), but also life-threatening coronavirus disease 2019 (COVID-19) pneumonia, bronchiectasis-associated bacterial pneumonia, and sepsis by encapsulated bacteria. Here we discuss the expanding understanding of the immunological mechanisms that contribute to infection susceptibility in this prototypic syndrome of impaired central tolerance, which provide the foundation for devising improved diagnostic and therapeutic strategies for affected patients.

Pulling RANK on Cancer: Blocking Aire-Mediated Central Tolerance to Enhance Immunotherapy

A major breakthrough in cancer treatment occurred with the development of strategies that overcome T-cell tolerance toward tumor cells. These approaches enhance antitumor immunity by overcoming mechanisms that are normally in place to prevent autoimmunity but simultaneously prevent rejection of tumor cells. Although tolerance mechanisms that restrict antitumor immunity take place both in the thymus and periphery, only immunotherapies that target peripheral tolerance mechanisms occurring outside of the thymus are currently available. We review here recent gains in our understanding of how thymic tolerance mediated by the autoimmune regulator (Aire) impedes antitumor immunity. It is now clear that transient depletion of Aire-expressing cells in the thymus can be achieved with RANKL blockade. Finally, we discuss key findings that support the repurposing of anti-RANKL as a cancer immunotherapy with a unique mechanism of action.

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.

Insights into type 1 diabetes from the autoimmune polyendocrine syndromes

PURPOSE OF REVIEW

Advances in human genetics and investigations in animal models of autoimmune disease have allowed insight into the basic mechanisms of immunologic tolerance. These advances allow us to understand the pathogenesis of type 1 diabetes and other autoimmune diseases as never before. Here, we discuss the tolerance mechanisms of the autoimmune polyendocrine syndromes and their relevance to type 1 diabetes.

RECENT FINDINGS

Defects in central tolerance with alteration of self-antigen expression levels in the thymus are a potent cause of autoimmunity. Peripheral tolerance defects that alter T-cell activation and signaling also play an important role in the pathogenesis of diabetes and other associated autoimmune disorders, with multiple modest defects working in concert to produce disease. Regulation of the immune response through the action of regulatory T cells is a potent mode of tolerance induction in autoimmunity that is important in type 1 diabetes.

SUMMARY

Rare syndromes of autoimmunity provide a valuable window into the breakdown of tolerance and identify multiple checkpoints that are critical for generation of autoimmunity. Understanding the application of these in type 1 diabetes will allow the development of future immunomodulatory therapies in the treatment and prevention of disease.

Aire deficiency promotes TRP-1-specific immune rejection of melanoma

The thymic transcription factor autoimmune regulator (Aire) prevents autoimmunity in part by promoting expression of tissue-specific self-antigens, which include many cancer antigens. For example, AIRE-deficient patients are predisposed to vitiligo, an autoimmune disease of melanocytes that is often triggered by efficacious immunotherapies against melanoma. Therefore, we hypothesized that Aire deficiency in mice may elevate immune responses to cancer and provide insights into how such responses might be triggered. In this study, we show that Aire deficiency decreases thymic expression of TRP-1 (TYRP1), which is a self-antigen in melanocytes and a cancer antigen in melanomas. Aire deficiency resulted in defective negative selection of TRP-1-specific T cells without affecting thymic numbers of regulatory T cells. Aire-deficient mice displayed elevated T-cell immune responses that were associated with suppression of melanoma outgrowth. Furthermore, transplantation of Aire-deficient thymic stroma was sufficient to confer more effective immune rejection of melanoma in an otherwise Aire wild-type host. Together, our work showed how Aire deficiency can enhance immune responses against melanoma and how manipulating TRP-1-specific T-cell negative selection may offer a logical strategy to enhance immune rejection of melanoma.

Anti-cytokine autoantibodies suggest pathogenetic links with autoimmune regulator deficiency in humans and mice

Autoimmune polyendocrinopathy candidiasis ectodermal dystrophy (APECED) is a recessive disorder resulting from mutations in the autoimmune regulator (AIRE). The patients' autoantibodies recognize not only multiple organ-specific targets, but also many type I interferons (IFNs) and most T helper type 17 (Th17) cell-associated cytokines, whose biological actions they neutralize in vitro. These anti-cytokine autoantibodies are highly disease-specific: otherwise, they have been found only in patients with thymomas, tumours of thymic epithelial cells that fail to express AIRE. Moreover, autoantibodies against Th17 cell-associated cytokines correlate with chronic mucocutaneous candidiasis in both syndromes. Here, we demonstrate that the immunoglobulin (Ig)Gs but not the IgAs in APECED sera are responsible for neutralizing IFN-ω, IFN-α2a, interleukin (IL)-17A and IL-22. Their dominant subclasses proved to be IgG1 and, surprisingly, IgG4 without IgE, possibly implicating regulatory T cell responses and/or epithelia in their initiation in these AIRE-deficiency states. The epitopes on IL-22 and IFN-α2a appeared mainly conformational. We also found mainly IgG1 neutralizing autoantibodies to IL-17A in aged AIRE-deficient BALB/c mice - the first report of any target shared by these human and murine AIRE-deficiency states. We conclude that autoimmunization against cytokines in AIRE deficiency is not simply a mere side effect of chronic mucosal Candida infection, but appears to be related more closely to disease initiation.

DNA methylation profile of Aire-deficient mouse medullary thymic epithelial cells

BACKGROUND

Medullary thymic epithelial cells (mTECs) are characterized by ectopic expression of self-antigens during the establishment of central tolerance. The autoimmune regulator (Aire), which is specifically expressed in mTECs, is responsible for the expression of a large repertoire of tissue-restricted antigens (TRAs) and plays a role in the development of mTECs. However, Aire-deficient mTECs still express TRAs. Moreover, a subset of mTECs, which are considered to be at a stage of terminal differentiation, exists in the Aire-deficient thymus. The phenotype of a specific cell type in a multicellular organism is governed by the epigenetic regulation system. DNA methylation modification is an important component of this system. Every cell or tissue type displays a DNA methylation profile, consisting of tissue-dependent and differentially methylated regions (T-DMRs), and this profile is involved in cell-type-specific genome usage. The aim of this study was to examine the DNA methylation profile of mTECs by using Aire-deficient mTECs as a model.

RESULTS

We identified the T-DMRs of mTECs (mTEC-T-DMRs) via genome-wide DNA methylation analysis of Aire(-/-) mTECs by comparison with the liver, brain, thymus, and embryonic stem cells. The hypomethylated mTEC-T-DMRs in Aire(-/-) mTECs were associated with mTEC-specific genes, including Aire, CD80, and Trp63, as well as other genes involved in the RANK signaling pathway. While these mTEC-T-DMRs were also hypomethylated in Aire(+/+) mTECs, they were hypermethylated in control thymic stromal cells. We compared the pattern of DNA methylation levels at a total of 55 mTEC-T-DMRs and adjacent regions and found that the DNA methylation status was similar for Aire(+/+) and Aire(-/-) mTECs but distinct from that of athymic cells and tissues.

CONCLUSIONS

These results indicate a unique DNA methylation profile that is independent of Aire in mTECs. This profile is distinct from other cell types in the thymic microenvironment and is indicated to be involved in the differentiation of the mTEC lineage.

Sequence variation in promoter of Ica1 gene, which encodes protein implicated in type 1 diabetes, causes transcription factor autoimmune regulator (AIRE) to increase its binding and down-regulate expression

ICA69 (islet cell autoantigen 69 kDa) is a protein implicated in type 1 diabetes mellitus in both the non-obese diabetic (NOD) mouse model and humans. ICA69 is encoded by the Ica1 gene on mouse chromosome 6 A1-A2. We previously reported reduced ICA69 expression in the thymus of NOD mice compared with thymus of several non-diabetic mouse strains. We propose that reduced thymic ICA69 expression could result from variations in transcriptional regulation of the gene and that polymorphisms within the Ica1 core promoter may partially determine this transcriptional variability. We characterized the functional promoter of Ica1 in NOD mice and compared it with the corresponding portions of Ica1 in non-diabetic C57BL/6 mice. Luciferase reporter constructs demonstrated that the NOD Ica1 promoter region exhibited markedly reduced luciferase expression in transiently transfected medullary thymus epithelial (mTEC(+)) and B-cell (M12)-derived cell lines. However, in a non-diabetic strain, C57BL/6, the Ica1 promoter region was transcriptionally active when transiently transfected into the same cell lines. We concomitantly identified five single nucleotide polymorphisms within the NOD Ica1 promoter. One of these single nucleotide polymorphisms increases the binding affinity for the transcription factor AIRE (autoimmune regulator), which is highly expressed in thymic epithelial cells, where it is known to play a key role regulating self-antigen expression. We conclude that polymorphisms within the NOD Ica1 core promoter may determine AIRE-mediated down-regulation of ICA69 expression in medullary thymic epithelial cells, thus providing a novel mechanistic explanation for the loss of immunologic tolerance to this self-antigen in autoimmunity.

The autoimmune regulator prevents premature reproductive senescence in female mice

Loss-of-function mutations in the autoimmune regulator (AIRE) gene are responsible for autoimmune polyglandular syndrome type 1 (APS-1), which commonly manifests as infertility in women. AIRE is a transcriptional regulator that promotes expression of tissue-restricted antigens in the thymus, including antigens specific to the ovary. Thymic expression of ovarian genes under AIRE's control may be critical for preventing ovarian autoimmune disease. Because mice lacking Aire are an important APS-1 model, we examined the reproductive properties of female Aire-deficient (Aire(-/-)) mice. Female Aire(-/-) mice on the BALB/c background were examined for reproductive parameters, including fertility, litter sizes, and ovarian follicular reserves. Although delayed puberty was observed in Aire(-/-) mice, all mice entered puberty and exhibited mating behavior. Only 50% of Aire(-/-) females gave an initial litter, and only 16% were able to produce two litters. Ovarian histopathologic examination revealed that 83% of previously bred females lost all ovarian follicular reserves. Among virgin females, follicular depletion was observed in 25% by 8 wk, and by 20 wk, 50%-60% of mice lost all follicles. This was associated with elevated serum follicle-stimulating hormone level and ovarian infiltration of proliferating CD3+ T lymphocytes. Ovulation rates of 6-wk-old Aire(-/-) mice were reduced by 22%, but this difference was not statistically significant. Finally, transplantation experiments revealed that follicular loss depended on factors extrinsic to the ovary. These results suggest that immune-mediated ovarian follicular depletion is a mechanism of infertility in Aire(-/-) mice. The results have important implications in the pathogenesis of ovarian autoimmune disease in women.

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.

Aire regulates the expression of differentiation-associated genes and self-renewal of embryonic stem cells

Embryonic stem cells (ESCs) are pluripotent stem cells from early embryos. It has been well recognized that ESC genomes are maintained in a globally transcriptional hyperactive state, which genetically poised ESCs to the high differentiation potential. However, the transcription factors regulating the global transcription activities in ESCs are not well defined. We show here that mouse and human ESCs express two transcription factors, Aire and Deaf1. Previously known to function in the thymus stromal cells and peripheral lymphoid organs respectively, Aire and Deaf1 help regulate the ectopic expression of diverse tissue-specific antigens to establish self-immune tolerance. Differentiation of ESCs greatly reduced Aire and Deaf1 expression, in a pattern similar to the pluripotent factors, Oct4 and Nanog. Knockdown of Aire in mouse ESCs resulted in significantly decreased clone-forming efficiency as well as attenuated cell cycle, suggesting Aire plays a role in ESC self-renewal. In addition, some differentiation-associated genes that are sporadically expressed in ESCs were reduced in expression upon Aire knockdown. These results suggest that transcription factors such as Aire and Deaf1, which exert global transcriptional regulatory functions, may play important roles in self-renewal of ESCs and maintaining ESC in a transcriptionally hyperactive state.

PHD finger of autoimmune regulator: an epigenetic link between the histone modifications and tissue-specific antigen expression in thymus

Methylation of lysine residues on histone H3 tails regulates transcription. A recent addition to the list of known methylated histone binding modules is the plant homeodomain (PHD) finger, which is usually found in nuclear proteins with chromatin-related functions. Autoimmune regulator (AIRE) protein contains two PHD fingers and mutations in AIRE gene cause the monogenic disease autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED). AIRE is expressed in thymic medullary epithelial cells where it promotes the expression of tissue-specific antigens. However the mechanism by which AIRE controls gene expression is currently unknown and the function of its domains, in particular of its PHD fingers is still elusive and controversial. In this review we discuss recent works on AIRE PHD finger(s) providing a new link between the status of histone modifications and the regulation of tissue-specific antigen expression in thymus.

Alterations of the medullary epithelial compartment in the Aire-deficient thymus: implications for programs of thymic epithelial differentiation

A widely held model of thymic epithelial differentiation is based on patterns of keratin expression, where a K8(+)K5(+) progenitor gives rise to K8(+)K5/K14(-) cortical thymic epithelium (CTEC), and medullary thymic epithelium (MTEC) are K8(-)K5(+)K14(+). The thymic phenotype of p63-deficient mice indicates that p63 is an important regulator of proximal stages of thymic epithelial differentiation. In this study, we have examined several features of the thymic medullary compartment in wild-type and Aire-deficient thymi in an effort to integrate the proapoptotic activity of Aire with these different perspectives of TE differentiation. Patterns of keratin and p63 expression by MTEC described here are difficult to reconcile with postmitotic MTEC that express a K8(-)K14(+) phenotype and suggest that the patterns of p63 and keratin expression reflecting differentiation programs of other epithelial tissues provide a useful framework for revising models of TE differentiation. Alterations of the Aire(-/-) MTEC compartment included reduced expression of p63, increased frequency of MTEC expressing truncated Aire protein, and shifts in the pattern of keratin expression and epithelial morphology. These data suggest a scenario where cellular targets of Aire-mediated apoptosis are postmitotic MTEC that have not yet completed their terminal differentiation program. According to this view, the minor population of globular K8(+)K14(-/low) MTEC observed in the Aire(+/+) thymus and significantly expanded in the Aire(-/-) thymic medulla represent end-stage, terminally differentiated MTEC. These Aire-dependent alterations of the MTEC compartment suggest that the activity of Aire is not neutral with respect to the program of MTEC differentiation.

Ectopic expression of peripheral-tissue antigens in the thymic epithelium: probabilistic, monoallelic, misinitiated

Thymic medullary epithelial cells (MECs) express a broad repertoire of peripheral-tissue antigens (PTAs), many of which depend on the transcriptional regulatory factor Aire. Although Aire is known to be critically important for shaping a self-tolerant T cell repertoire, its role in MEC maturation and function remains poorly understood. Using a highly sensitive and reproducible single-cell PCR assay, we demonstrate that individual Aire-expressing MECs transcribe a subset of PTA genes in a probabilistic fashion, with no signs of preferential coexpression of genes characteristic of particular extrathymic epithelial cell lineages. In addition, Aire-dependent PTA genes in MECs are transcribed monoallelically or biallelically in a stochastic pattern, in contrast to the usually biallelic transcription of these same genes in the relevant peripheral cells or of Aire-independent genes in MECs. Expression of PTA genes in MECs depends on transcriptional regulators and uses transcriptional start sites different from those used in peripheral cells. These findings support the "terminal differentiation" model of Aire function: as MECs mature, they transcribe more and more PTA genes, culminating in a cell population that is both capable of presenting antigens (MHCII(hi), CD80(hi)) and can draw on a large repertoire of antigens to present.

The autoimmune regulator PHD finger binds to non-methylated histone H3K4 to activate gene expression

Mutations in the gene autoimmune regulator (AIRE) cause autoimmune polyendocrinopathy candidiasis ectodermal dystrophy. AIRE is expressed in thymic medullary epithelial cells, where it promotes the expression of tissue-restricted antigens. By the combined use of biochemical and biophysical methods, we show that AIRE selectively interacts with histone H3 through its first plant homeodomain (PHD) finger (AIRE-PHD1) and preferentially binds to non-methylated H3K4 (H3K4me0). Accordingly, in vivo AIRE binds to and activates promoters containing low levels of H3K4me3 in human embryonic kidney 293 cells. We conclude that AIRE-PHD1 is an important member of a newly identified class of PHD fingers that specifically recognize H3K4me0, thus providing a new link between the status of histone modifications and the regulation of tissue-restricted antigen expression in thymus.

A robust immunoassay for anti-interferon autoantibodies that is highly specific for patients with autoimmune polyglandular syndrome type 1

High titer antibodies to type 1 interferons have been recently reported as being highly specific for patients with autoimmune polyglandular syndrome type 1 (APS1) in Finnish and Norwegian patients with mutations in the AIRE gene. Those studies employed a complex neutralization assay to define the type 1 interferon autoantibodies. Here we have established a competitive europium time resolved fluorescence assay for IFN-alpha autoantibodies and measured sera from subjects with APS1, first degree relatives of APS1 patients, patients with Addison's disease or Type 1 diabetes. The europium-based immunoassay utilizes plate bound human IFN-alpha incubated with sera with or without competition with fluid phase IFN-alpha, followed by anti-IgG biotinylated antibody and detection with streptavidin-europium. The index of IFN-alpha Ab was calculated as (CPS (Counts per second) without competition-CPS with competition)/(CPS positive standard sera without competition-CPS positive standard sera with competition). RESULTS are reported for raw CPS and indices and are compared across the different subjects.

RESULTS

For normal controls (n=100) CPS without competition were 31,237+/-17,328 CPS while after subtracting the competition value, the results were -6563+/-10,303 CPS. The initial APS1 patient (used to create the index as 1.0) gave 394,063 CPS without competition and a delta of 363,662+/-31,587 CPS with competition. Scatchard plot analysis of this patient sample revealed a high avidity for IFN-alpha (K(d) of 0.5 nM). The CPS, delta, and index for 6/7 APS1 patients were strongly positive and 3 standard deviations or more above that of the normal controls. Using a cut-off of 2 standard deviations above normal controls, relatives of APS1 patients were negative for type I interferon autoantibodies as were 71 patients with Addison's disease (non-APS1) and 141 Type 1 diabetes patients. This simple high throughput competitive europium time resolved fluorescence assay had a sensitivity of > or =86% or greater and a specificity of >99.5%.

Expression of autoimmune regulator gene (AIRE) and T regulatory cells in human thymomas

Expression of the autoimmune regulator gene (AIRE) and the presence of CD25(+)/forkhead box p3 (FoxP3)(+) T regulatory (T(reg)) cells were investigated in histologically normal adult thymi and in thymomas using immunohistochemistry and quantitative real-time polymerase chain reaction (PCR). In the normal thymus staining for AIRE was detected in the nucleus of some epithelial-like cells located in the medulla; in thymomas AIRE-positive cells were extremely rare and could be detected only in the areas of medullary differentiation of two B1 type, organoid thymomas. RNA was extracted from 36 cases of thymoma and 21 non-neoplastic thymi obtained from 11 myasthenic (MG(+)) and 10 non-myasthenic (MG(-)) patients. It was found that AIRE is 8.5-fold more expressed in non-neoplastic thymi than in thymomas (P = 0.01), and that the amount of AIRE transcripts present in the thymoma tissue are not influenced by the association with MG, nor by the histological type. A possible involvement of AIRE in the development of MG was suggested by the observation that medullary thymic epithelial cells isolated from AIRE-deficient mice contain low levels of RNA transcripts for CHRNA 1, a gene coding for acetylcholine receptor. Expression of human CHRNA 1 RNA was investigated in 34 human thymomas obtained from 20 MG(-) patients and 14 MG(+) patients. No significant difference was found in the two groups (thymoma MG(+), CHRNA1 = 0.013 +/- 0.03; thymoma MG-, CHRNA1 = 0.01 +/- 0.03). In normal and hyperplastic thymi CD25(+)/Foxp3(+) cells were located mainly in the medulla, and their number was not influenced by the presence of MG. Foxp3(+) and CD25(+) cells were significantly less numerous in thymomas. A quantitative estimate of T(reg) cells revealed that the levels of Foxp3 RNA detected in non-neoplastic thymi were significantly higher (P = 0.02) than those observed in 31 cases of thymomas. Our findings indicate that the tissue microenvironment of thymomas is defective in the expression of relevant functions that exert a crucial role in the negative selection of autoreactive lymphocytes.

How defects in central tolerance impinge on a deficiency in regulatory T cells

Both central (thymic) and peripheral (nonthymic) mechanisms are important for the induction and maintenance of T cell tolerance. Mice with a defect in Foxp3, required for the generation and activity of CD4(+)CD25(+) regulatory T cells, exhibit massive lymphoproliferation and severe inflammatory infiltration of multiple organs, in particular the lungs, liver, and skin. We have explored how this phenotype is influenced by an additional defect in central tolerance induction, generated by either crossing in a null mutation of the Aire gene or substituting the nonobese diabetic (NOD) genetic background. The double-deficient mice had fulminant autoimmunity in very early life and a gravely shortened lifespan vis-à-vis single-deficient littermates. They showed massive lymphoproliferation and exacerbated inflammatory damage, particularly in the lungs and liver. Yet, the range of affected sites was not noticeably extended, and, surprisingly, many organs, or regions of organs, remained untouched, suggesting additional important mechanisms to enforce immunological self-tolerance.