Mucocutaneous candidiasis and autoimmunity against cytokines in APECED and thymoma patients: clinical and pathogenetic implications

Longitudinal Immune Profiling in Autoimmune Polyendocrine Syndrome Type 1

Autoimmune polyendocrine syndrome Type-1 (APS-1) is a rare, but severe organ-specific autoimmune disease caused by mutations in the autoimmune regulator (AIRE) gene. Lack of AIRE causes autoreactive T cells to escape negative selection and alters the T regulatory cell subset. However, little is known about how the immune cell subsets vary across the lifespan in APS-1. Here we analysed the peripheral distribution of 13 immune cell subsets along the lifespan using epigenetic quantification. We found the largest discrepancy in immune cells to appear early in APS-1 patients' lives, coinciding with the time point they obtained most of their clinical symptoms. We further revealed longitudinal changes in cell compositions both within the adaptive and the innate arms of the immune system. We found that cell frequencies of B cells, T-cell subgroups, nonclassical monocytes, and Natural Killer cells to be reduced in young APS-1 patients. We also found B-cell frequencies to decrease with ageing in both patients and healthy controls. Our results suggest that Tregs, follicular helper T, and natural killer cells have opposing trends of cell frequencies during life, indicating the importance of considering the age profiles of cohorts which could otherwise lead to conflicting conclusions.

Lessons From Prospective Longitudinal Follow-up of a French APECED Cohort

BACKGROUND

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy syndrome is a rare disease caused by biallelic mutations of the AIRE gene, usually presenting with the triad hypoparathyroidism-adrenal failure-chronic mucocutaneous candidiasis (CMC) and nonendocrine manifestations. The aim of this study was to determine the molecular profile of the AIRE gene, the prevalence of rare manifestations, and to characterize immunological disturbances in a French cohort.

PATIENTS AND METHODS

A national, multicenter prospective observational study to collect genetic, clinical, biological, and immunological data (NCT03751683).

RESULTS

Twenty-five patients (23 families) were enrolled. Eleven distinct AIRE variants were identified, 2 of which were not previously reported: an intronic variant, c.653-70G > A, and a c.1066del (p.Arg356GlyfsX22) variant (exon 9). The most common was the Finnish variant c.769C > T (16 alleles), followed by the variant c.967_979del13 (15 alleles), which seemed associated with a less severe phenotype. Seventeen out of 25 patients were homozygote. The median number of clinical manifestations was 7; 19/25 patients presented with the hypoparathyroidism-adrenal failure-CMC triad, 8/13 showed pulmonary involvement, 20/25 had ectodermal dystrophy, 8/25 had malabsorption, and 6/23 had asplenia. Fifteen out of 19 patients had natural killer cell lymphopenia with an increase in CD4+ and CD8+ T lymphocytes and an age-dependent alteration of B lymphocyte homeostasis compared with matched controls (P < .001), related to the severity of the disease. All tested sera (n = 18) were positive for anti-interferon-α, 15/18 for anti-IL-22 antibodies, and 13/18 for anti-IL-17F antibodies, without clear phenotypic correlation other than with CMC.

CONCLUSION

This first prospective cohort showed a high AIRE genotype variability, with 2 new gene variants. The prevalence of potentially life-threatening nonendocrine manifestations was higher with systematic screening. These manifestations could, along with age-dependent B-cell lymphopenia, contribute to disease severity. Systematic screening for all the manifestations of the syndrome would allow earlier diagnosis, supporting vaccination and targeted therapeutic approaches.

The ouroboros of autoimmunity

Human autoimmunity against elements conferring protective immunity can be symbolized by the 'ouroboros', a snake eating its own tail. Underlying infection is autoimmunity against three immunological targets: neutrophils, complement and cytokines. Autoantibodies against neutrophils can cause peripheral neutropenia underlying mild pyogenic bacterial infections. The pathogenic contribution of autoantibodies against molecules of the complement system is often unclear, but autoantibodies specific for C3 convertase can enhance its activity, lowering complement levels and underlying severe bacterial infections. Autoantibodies neutralizing granulocyte-macrophage colony-stimulating factor impair alveolar macrophages, thereby underlying pulmonary proteinosis and airborne infections, type I interferon viral diseases, type II interferon intra-macrophagic infections, interleukin-6 pyogenic bacterial diseases and interleukin-17A/F mucocutaneous candidiasis. Each of these five cytokine autoantibodies underlies a specific range of infectious diseases, phenocopying infections that occur in patients with the corresponding inborn errors. In this Review, we analyze this ouroboros of immunity against immunity and posit that it should be considered as a factor in patients with unexplained infection.

Type B thymomas in patients with myasthenia gravis display a distinctive pattern of αβ TCR and IL-7 receptor α expression on CD4+CD8+ thymocytes

Thymoma is closely associated with myasthenia gravis (MG). However, due to the heterogeneity of thymoma and the intricate pathogenesis of MG, it remains unclear why some patients with thymoma develop MG and others do not. In this study, we conducted a comparative phenotype analysis of thymocytes in type B thymomas in patients with MG (MG (+) thymomas) and without MG (MG (-) thymomas) via fluorescence-activated cell sorting (FACS). Our results show that the developmental stages defined by the expression of CD3, CD4, and CD8 were largely maintained in both MG (+) and MG (-) thymomas, with CD4+CD8+ cells constituting the majority of thymocytes in type B thymoma, and no significant difference between this cell population was observed in MG (+) and MG (-) thymomas.We discovered that CD4+CD8+ thymocytes in MG (+) thymomas expressed low levels of αβ TCR and high levels of IL-7 receptor α (IL-7Rα), whereas in MG (-) thymomas, CD4+CD8+ thymocytes exhibited the opposite pattern of αβ TCR and IL-7Rα expression. These results suggest that the positive and negative selection processes of CD4+CD8+ thymocytes might differ between MG (+) thymomas and MG (-) thymomas. The expression of the Helios transcription factor is induced during negative selection and marks a group of T cells that have undergone negative selection and are likely to be deleted due to strong TCR binding with self-peptides/MHC ligands. We observed that the percentage of Helios-positive CD4SP T cells was greater in MG (-) than in MG (+) thymomas. Thus, the differentially regulated selection process of CD4+CD8+ thymocytes, which involves TCR and IL-7/IL-7Rα signaling, is associated with the presence of MG in type B thymomas.

Novel Insights into the Autoimmunity from the Genetic Approach of the Human Disease

Autoimmune-polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is a monogenic inborn error of autoimmunity that is caused by damaging germline variants in the AIRE gene and clinically manifests with multiple autoimmune diseases in patients. Studies on the function of the AIRE gene, discovered in 1997, have contributed to fundamental aspects of human immunology as they have been important in understanding the basic mechanism of immune balance between self and non-self. This chapter looks back to the discovery of the AIRE gene, reviews its main properties, and discusses the key findings of its function in the thymus. However, more recent autoantibody profilings in APECED patients have highlighted a gap in our knowledge of the disease pathology and point to the need to revisit the current paradigm of AIRE function. The chapter reviews these new findings in APECED patients, which potentially trigger new thoughts on the mechanism of immune tolerance.

Vaccination prevents severe COVID-19 outcome in patients with neutralizing type 1 interferon autoantibodies

A hallmark of patients with autoimmune polyendocrine syndrome type 1 (APS-1) is serological neutralizing autoantibodies against type 1 interferons (IFN-I). The presence of these antibodies has been associated with severe course of COVID-19. The aims of this study were to investigate SARS-CoV-2 vaccine tolerability and immune responses in a large cohort of patients with APS-1 (N = 33) and how these vaccinated patients coped with subsequent infections. We report that adult patients with APS-1 were able to mount adequate SARS-CoV-2 spike-specific antibody responses after vaccination and observed no signs of decreased tolerability. Compared with age- and gender-matched healthy controls, patients with APS-1 had considerably lower peak antibody responses resembling elderly persons, but antibody decline was more rapid in the elderly. We demonstrate that vaccination protected patients with APS-1 from severe illness when infected with SARS-CoV-2 virus, overriding the systemic danger of IFN-I autoantibodies observed in previous studies.

Immunodeficiency in patients with thymoma-associated myasthenia gravis

Thymoma with immunodeficiency is sometimes accompanied by myasthenia gravis (MG), but the clinical characteristics have not been elucidated. This study aimed to characterize its clinical and immunological features. Of the 132 thymoma-associated MG patients, 9 patients presented with immunodeficiency. All suffered from severe pneumonia, and most had invasive thymoma and autoimmune disorders. DRB1*08:03 and DQB1*06:01 alleles were frequently detected. Compared to group without immunodeficiency, they showed no significant differences in the severity of MG, significantly lower IgG concentrations and higher mortality rate. Thymoma-associated MG with immunodeficiency is a distinct subset requiring special attention to prevent infection during the follow-up period.

[Anti-cytokine autoantibodies: Review of the literature]

Anti-cytokine antibodies (ACA) are an emerging cause of acquired immunodeficiency, especially in previously healthy adults. The most frequently reported are anti-IFN-γ responsible for disseminated non-tuberculous mycobacteria infections, and anti-GM-CSF mainly in mycobacteria, cryptococcosis and nocardiosis infections. The presence of anti-IFN-α in severe COVID-19 infections has recently been described. The search for and detection of these ACAs in an unusual infection situation makes it possible to set up specific therapies in addition to the anti-infective treatment. ACAs are also frequent in various autoimmune pathologies where, in addition to being indicators of the breakdown of immune tolerance, they can modulate the activity of the disease according to their cytokine target. In this review of the literature, we will focus on the epidemiology and the clinical impact of these ACAs in healthy subjects and in infectious or dysimmune diseases.

Late-onset autoimmune polyendocrine syndrome type 1: a case report and literature review

Autoimmune polyendocrine syndrome type 1 (APS-1), also referred to as autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED), a rare monogenic disorder, is classically characterized by a triad of chronic mucocutaneous candidiasis, hypoparathyroidism, and primary adrenal insufficiency. The identified causative gene is autoimmune regulator (AIRE), which encodes a critical transcription factor and is essential for self-tolerance. Here, we describe a late-onset Chinese case who presented with symptoms of persistent tetany due to hypocalcemia. Extensive clinical evaluations revealed that the patient manifested beyond the classic triad of the disease, and next-generation sequencing identified a known homozygous AIRE mutation (p.R139X). APS-1 is a rare inherited immunodeficiency disease with high clinical and genetic heterogeneity. By retrospectively analyzing the disease, we comprehensively reviewed the phenotypic features, summarized the genotype spectrum, and discussed the possible immunological mechanisms of the disease to enhance earlier recognition and implement targeted preventive and therapeutic strategies.

Functional analysis of two STAT1 gain-of-function mutations in two Iranian families with autosomal dominant chronic mucocutaneous candidiasis

Candidiasis is characterized by susceptibility to recurrent or persistent infections caused by Candida spp., typically Candida albicans, of cutaneous and mucosal surfaces. In this report, function and frequency of Th17 cells as well as genetics of patients susceptible to mucocutaneous candidiasis were studied. For patients, T-cell proliferation tests in response to Candida antigen, Th17 cell proportions, and STAT1 phosphorylation were evaluated through flow cytometry. Expression of IL17A, IL17F and IL22 genes were measured by real-time quantitative PCR. At the same time, whole exome sequencing was performed for all patients. We identified two heterozygous substitutions, one: c.821G > A (p. R274Q) was found in a multiplex family with three individuals affected, the second one: c.812A > C (p. Q271P) was found in a sporadic case. Both mutations are located in the coiled-coil domain (CCD) of STAT1. The frequency of Th17 cells, IL17A, IL17F, and IL22 gene expression in patients' peripheral blood mononuclear cells (PBMCs), and T-cell proliferation to Candida antigens were significantly reduced in the patients as compared to healthy controls. An increased STAT1 phosphorylation was observed in patients' PBMCs upon interferon (IFN)-γ stimulation as compared to healthy controls. We report two different but neighboring heterozygous mutations, located in exon 10 of the STAT1 gene, in four Iranian patients with CMC, one of whom also had hypothyroidism. These mutations were associated with impaired T cell proliferation to Candida antigen, low Th17 cell proportions, and increased STAT1 phosphorylation upon IFN-γ. We suggest that interfering with STAT1 phosphorylation might be a promising way for potential therapeutic measurements for such patients.

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’.

The Skin as a Window into Primary Immune Deficiency Diseases: Atopic Dermatitis and Chronic Mucocutaneous Candidiasis

Primary immune deficiency diseases characteristically present with recurrent, severe, or unusual infections. These infections may often involve the skin, with mucocutaneous candidal infections seen in a variety of different primary immune deficiencies. Primary immune deficiencies may also present with noninfectious cutaneous complications, of which eczema is the most common. In a patient with suspected primary immune deficiency, the presence of eczema or candidal skin infections offers critical information about the underlying immune defect, either the presence of atopy or defect in the T_H17 pathway, respectively. These skin manifestations also are often early or heralding findings of the underlying immunologic disease. Therefore, awareness of associations between these skin findings and specific immune deficiencies may aide in the early detection and treatment of serious or life-threatening immunologic defects. This review specifically will focus on the primary immune deficiencies commonly associated with eczema or mucocutaneous candidiasis.

IL-22 Paucity in APECED Is Associated With Mucosal and Microbial Alterations in Oral Cavity

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is caused by recessive mutations in the AIRE gene. The hallmark of the disease is the production of highly neutralizing autoantibodies against type I interferons and IL-22. Considering the importance of IL-22 in maintaining mucosal barrier integrity and shaping its microbial community, we sought to study potential changes in the oral cavity in this model of human IL-22 paucity. We found that besides known Th22 cell deficiency, APECED patients have significantly fewer circulating MAIT cells with potential IL-22 secreting capacity. Saliva samples from APECED patients revealed local inflammation, the presence of autoantibodies against IFN-α and IL-22, and alterations in the oral microbiota. Moreover, gene expression data of buccal biopsy samples suggested impaired antimicrobial response and cell proliferation, both of which are processes regulated by IL-22. Our data complement the knowledge gained from mouse models and support the concept of IL-22 being a critical homeostatic cytokine in human mucosal sites.

Human inborn errors of immunity underlying superficial or invasive candidiasis

Candida species, including C. albicans in particular, can cause superficial or invasive disease, often in patients with known acquired immunodeficiencies or iatrogenic conditions. The molecular and cellular basis of these infections in patients with such risk factors remained largely elusive, until the study of inborn errors of immunity clarified the basis of the corresponding inherited and "idiopathic" infections. Superficial candidiasis, also known as chronic mucocutaneous candidiasis (CMC), can be caused by inborn errors of IL-17 immunity. Invasive candidiasis can be caused by inborn errors of CARD9 immunity. In this chapter, we review both groups of inborn errors of immunity, and discuss the contribution of these studies to the deciphering of the critical mechanisms of anti-Candida immunity in patients with other conditions.

The role of IL-17A in axial spondyloarthritis and psoriatic arthritis: recent advances and controversies

Although the pathogenic mechanisms underlying axial spondyloarthritis (axSpA) and psoriatic arthritis (PsA) are not fully elucidated, several lines of evidence suggest that immune responses mediated by interleukin 17A (IL-17A) play a pivotal role in both diseases. This is best highlighted by the significant clinical efficacy shown with inhibitors of IL-17A in treating axSpA and PsA. Nevertheless, a number of knowledge gaps exist regarding the role of IL-17A in the pathophysiology of spondyloarthritis in man, including its cellular origin, its precise role in discrete disease processes such enthesitis, bone erosion, and bone formation, and the reasons for the discrepant responses to IL-17A inhibition observed in certain other spondyloarthritis manifestations. In this review, we focus on the latest data from studies investigating the role of IL-17A in ankylosing spondylitis (AS) and PsA that build on existing and emerging scientific knowledge in the field. Key remaining research questions are also highlighted to guide future research.

Deciphering the biology of thymic epithelial tumors

Thymic cancers arise from epithelial cells of the thymus and have a predilection for intrathoracic spread. Clinical behavior varies from relatively indolent to highly aggressive with a capacity to metastasize widely and adversely affect survival. Paraneoplastic autoimmune disorders are frequently observed in association with thymoma and have a significant impact on quality of life. Underlying immune deficits associated with thymic epithelial tumors (TETs) increase the risk for development of opportunistic infections and emergence of extrathymic malignancies. Advances in the molecular characterization of thymic tumors have revealed the lowest tumor mutation burden among all adult cancers and the occurrence of distinct molecular subtypes of these diseases. Mutations in general transcription factor IIi (GTF2I) are unique to TETs and are rarely observed in other malignancies. The infrequency of actionable mutations has created obstacles for the development of biologic therapies and has spurred research to uncover druggable genomic targets. Persistence of autoreactive T cells due to altered thymic function increases the risk for development of severe immune-related toxicity and limits opportunities for use of immune-based therapies, especially in patients with thymoma. In this paper we review emerging data on the molecular characterization and immunobiology of thymic tumors and highlight clinical implications of these discoveries.

Signs heralding appearance of thymomas after extended thymectomy for myasthenia gravis

Purpose of review

Thymomas appear very rarely after extended thymectomy for early-onset myasthenia gravis (EOMG). We describe 2 such cases that highlight potential early warning signs.

Recent findings

In their 20s, one woman and one man developed EOMG (AChR antibody-positive), requiring extended transsternal removal of hyperplastic thymi at ages 35 and 27, respectively. Their myasthenia gravis was readily controlled for the next 10 and 7 years before deteriorating in both, with appearance of late clinical features and anticytokine autoantibodies suggesting underlying thymomas, namely respiratory infections, genital herpes, chronic candidiasis, and alopecia in the woman and erythroderma and lichen planus in the man, followed by Pseudomonas, Klebsiella, and cytomegalovirus infections plus chronic hepatitis during intensifying immunosuppressive therapy. Type B thymomas were then detected. Despite surgery or radiotherapy, and intensive drug therapy, the patients died 7 and 1 years later.

Summary

Certain infections/dermatologic manifestations that associate with long-standing thymomas may herald their late appearance, despite previous thymectomy.

Chronic Mucocutaneous Candidiasis in Autoimmune Polyendocrine Syndrome Type 1

Autoimmune polyendocrinopathy candidiasis ectodermal dystrophy (APECED) is an autosomal recessive disease caused by mutations in the autoimmune regulator (AIRE) gene, characterized by the clinical triad of chronic mucocutaneous candidiasis (CMC), hypoparathyroidism, and adrenal insufficiency. CMC can be complicated by systemic candidiasis or oral squamous cell carcinoma (SCC), and may lead to death. The role of chronic Candida infection in the etiopathogenesis of oral SCC is unclear. Long-term use of fluconazole has led to the emergence of Candida albicans strains with decreased susceptibility to azoles. CMC is associated with an impaired Th17 cell response; however, it remains unclear whether decreased serum IL-17 and IL-22 levels are related to a defect in cytokine production or to neutralizing autoantibodies resulting from mutations in the AIRE gene.

Autoantibodies to Chemokines and Cytokines Participate in the Regulation of Cancer and Autoimmunity

We have previously shown that predominant expression of key inflammatory cytokines and chemokines at autoimmune sites or tumor sites induces loss of B cells tolerance, resulting in autoantibody production against the dominant cytokine/chemokine that is largely expressed at these sites. These autoantibodies are high-affinity neutralizing antibodies. Based on animal models studies, we suggested that they participate in the regulation of cancer and autoimmunity, albeit at the level of their production cannot entirely prevent the development and progression of these diseases. We have, therefore, named this selective breakdown of tolerance as “Beneficial Autoimmunity.” Despite its beneficial outcome, this process is likely to be stochastic and not directed by a deterministic mechanism, and is likely to be associated with the dominant expression of these inflammatory mediators at sites that are partially immune privileged. A recent study conducted on autoimmune regulator-deficient patients reported that in human this type of breakdown of B cell tolerance is T cell dependent. This explains, in part, why the response is highly restricted, and includes high-affinity antibodies. The current mini-review explores this subject from different complementary perspectives. It also discusses three optional translational aspects: amplification of autoantibody production as a therapeutic approach, development of autoantibody based diagnostic tools, and the use of B cells from donors that produce these autoantibodies for the development of high-affinity human monoclonal antibodies.

Neutralizing Anti-Cytokine Autoantibodies Against Interferon-α in Immunodysregulation Polyendocrinopathy Enteropathy X-Linked

Anti-cytokine autoantibodies (ACAAs) have been described in a growing number of primary immunodeficiencies with autoimmune features, including autoimmune polyendocrine syndrome type I (APS-1), a prototypical disease of defective T cell-mediated central tolerance. Whether defects in peripheral tolerance lead to similar ACAAs is unknown. Immunodysregulation polyendocrinopathy enteropathy X-linked (IPEX) is caused by mutations in FOXP3, a master regulator of T regulatory cells (T_reg), and consequently results in defective T cell-mediated peripheral tolerance. Unique autoantibodies have previously been described in IPEX. To test the hypothesis that ACAAs are present in IPEX, we designed and fabricated antigen microarrays. We discovered elevated levels of IgG ACAAs against interferon-α (IFN-α) in a cohort of IPEX patients. Serum from IPEX patients blocked IFN-α signaling in vitro and blocking activity was tightly correlated with ACAA titer. To show that blocking activity was mediated by IgG and not other serum factors, we purified IgG and showed that blocking activity was contained entirely in the immunoglobulin fraction. We also screened for ACAAs against IFN-α in a second geographically distinct cohort. In these samples, ACAAs against IFN-α were elevated in a post hoc analysis. In summary, we report the discovery of ACAAs against IFN-α in IPEX, an experiment of nature demonstrating the important role of peripheral T cell tolerance.

Integrity of IKK/NF-κB Shields Thymic Stroma That Suppresses Susceptibility to Autoimmunity, Fungal Infection, and Carcinogenesis

A pathogenic connection between autoreactive T cells, fungal infection, and carcinogenesis has been demonstrated in studies of human autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) as well as in a mouse model in which kinase-dead Ikkα knock-in mice develop impaired central tolerance, autoreactive T cell-mediated autoimmunity, chronic fungal infection, and esophageal squamous cell carcinoma, which recapitulates APECED. IκB kinase α (IKKα) is one subunit of the IKK complex required for NF-κB activation. IKK/NF-κB is essential for central tolerance establishment by regulating the development of medullary thymic epithelial cells (mTECs) that facilitate the deletion of autoreactive T cells in the thymus. In this review, we extensively discuss the pathogenic roles of inborn errors in the IKK/NF-κB loci in the phenotypically related diseases APECED, immune deficiency syndrome, and severe combined immunodeficiency; differentiate how IKK/NF-κB components, through mTEC (stroma), T cells/leukocytes, or epithelial cells, contribute to the pathogenesis of infectious diseases, autoimmunity, and cancer; and highlight the medical significance of IKK/NF-κB in these diseases.

Autoantibody Repertoire in APECED Patients Targets Two Distinct Subgroups of Proteins

High titer autoantibodies produced by B lymphocytes are clinically important features of many common autoimmune diseases. APECED patients with deficient autoimmune regulator (AIRE) gene collectively display a broad repertoire of high titer autoantibodies, including some which are pathognomonic for major autoimmune diseases. AIRE deficiency severely reduces thymic expression of gene-products ordinarily restricted to discrete peripheral tissues, and developing T cells reactive to those gene-products are not inactivated during their development. However, the extent of the autoantibody repertoire in APECED and its relation to thymic expression of self-antigens are unclear. We here undertook a broad protein array approach to assess autoantibody repertoire in APECED patients. Our results show that in addition to shared autoantigen reactivities, APECED patients display high inter-individual variation in their autoantigen profiles, which collectively are enriched in evolutionarily conserved, cytosolic and nuclear phosphoproteins. The APECED autoantigens have two major origins; proteins expressed in thymic medullary epithelial cells and proteins expressed in lymphoid cells. These findings support the hypothesis that specific protein properties strongly contribute to the etiology of B cell autoimmunity.

Immunotherapeutic approaches to treatment of fungal diseases

Fungal infections cause morbidity worldwide and are associated with an unacceptably high mortality despite the availability of antifungal drugs. The incidence of mycoses is rising because of the HIV pandemic and because immunomodulatory drugs are increasingly used to treat autoimmune diseases and cancer. New classes of antifungal drugs have only been partly successful in improving the prognosis for patients with fungal infection. Adjunctive host-directed therapy is therefore believed to be the only option to further improve patient outcomes. Recent advances in the understanding of complex interactions between fungi and host have led to the design and exploration of novel therapeutic strategies in cytokine therapy, vaccines, and cellular immunotherapy, each of which might become viable adjuncts to existing antifungal regimens. In this report, we discuss immunotherapeutic approaches-the rationale behind their design, the challenges in their use, and the progress that is so urgently needed to overcome the devastating effect of fungal diseases.

The Goldilocks model of immune symbiosis with Mycobacteria and Candida colonizers

Mycobacteria and Candida species include significant human pathogens that can cause localized or disseminated infections. Although these organisms may appear to have little in common, several shared pathways of immune recognition and response are important for both control and infection-related pathology. In this article, we compare and contrast the innate and adaptive components of the immune system that pertain to these infections in humans and animal models. We also explore a relatively new concept in the mycobacterial field: biological commensalism. Similar to the well-established model of Candida infection, Mycobacteria species colonize their human hosts in equilibrium with the immune response. Perturbations in the immune response permit the progression to pathologic disease at the expense of the host. Understanding the immune factors required to maintain commensalism may aid with the development of diagnostic and treatment strategies for both categories of pathogens.

Chronic mucocutaneous candidiasis disease associated with inborn errors of IL-17 immunity

Chronic mucocutaneous candidiasis (CMC) is characterized by recurrent or persistent infections affecting the nails, skin and oral and genital mucosae caused by Candida spp., mainly Candida albicans. CMC is an infectious phenotype in patients with inherited or acquired T-cell deficiency. Patients with autosomal-dominant (AD) hyper IgE syndrome (HIES), AD signal transducer and activator of transcription 1 (STAT1) gain-of-function, autosomal-recessive (AR) deficiencies in interleukin (IL)-12 receptor β1 (IL-12Rβ1), IL-12p40, caspase recruitment domain-containing protein 9 (CARD9) or retinoic acid-related orphan receptor γT (RORγT) or AR autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) develop CMC as a major infectious phenotype that is categorized as Syndromic CMC. In contrast, CMC disease (CMCD) is typically defined as CMC in patients in the absence of any other prominent clinical signs. This definition is not strict; thus, CMCD is currently used to refer to patients presenting with CMC as the main clinical phenotype. The etiology of CMCD is not related to genes that cause severe combined immunodeficiency or combined immunodeficiency, nor to genes responsible for Syndromic CMC. Four genetic etiologies, AR IL-17 receptor A, IL-17 receptor C and ACT1 deficiencies, and AD IL-17F deficiency, are reported to underlie CMCD. Each of these gene defects directly has an impact on IL-17 signaling, suggesting their nonredundant role in host mucosal immunity to Candida. Here, we review current knowledge focusing on IL-17 signaling and the genetic etiologies responsible for, and associated with, CMC.

Genetic Predictors of Susceptibility to Dermatophytoses

Countless observational studies conducted over the last century reveal that dermatophytes infect humans of every age, race, gender, and socioeconomic status with strikingly high rates. The curious disparity in dermatophyte infection patterns observed within and between populations has led countless investigators to explore whether genetics underlie a susceptibility to, or confer protection against, dermatophyte infections. This paper examines the data that offer a link between genetics and dermatophytoses and discusses the underlying mechanisms that support these observations.

Clinical features, pathogenesis, and treatment of myasthenia gravis: a supplement to the Guidelines of the German Neurological Society

Myasthenia gravis (MG) is an autoimmune antibody-mediated disorder of neuromuscular synaptic transmission. The clinical hallmark of MG consists of fluctuating fatigability and weakness affecting ocular, bulbar and (proximal) limb skeletal muscle groups. MG may either occur as an autoimmune disease with distinct immunogenetic characteristics or as a paraneoplastic syndrome associated with tumors of the thymus. Impairment of central thymic and peripheral self-tolerance mechanisms in both cases is thought to favor an autoimmune CD4(+) T cell-mediated B cell activation and synthesis of pathogenic high-affinity autoantibodies of either the IgG1 and 3 or IgG4 subclass. These autoantibodies bind to the nicotinic acetylcholine receptor (AchR) itself, or muscle-specific tyrosine-kinase (MuSK), lipoprotein receptor-related protein 4 (LRP4) and agrin involved in clustering of AchRs within the postsynaptic membrane and structural maintenance of the neuromuscular synapse. This results in disturbance of neuromuscular transmission and thus clinical manifestation of the disease. Emphasizing evidence from clinical trials, we provide an updated overview on immunopathogenesis, and derived current and future treatment strategies for MG divided into: (a) symptomatic treatments facilitating neuromuscular transmission, (b) antibody-depleting treatments, and

AIRE-Deficient Patients Harbor Unique High-Affinity Disease-Ameliorating Autoantibodies

APS1/APECED patients are defined by defects in the autoimmune regulator (AIRE) that mediates central T cell tolerance to many self-antigens. AIRE deficiency also affects B cell tolerance, but this is incompletely understood. Here we show that most APS1/APECED patients displayed B cell autoreactivity toward unique sets of approximately 100 self-proteins. Thereby, autoantibodies from 81 patients collectively detected many thousands of human proteins. The loss of B cell tolerance seemingly occurred during antibody affinity maturation, an obligatorily T cell-dependent step. Consistent with this, many APS1/APECED patients harbored extremely high-affinity, neutralizing autoantibodies, particularly against specific cytokines. Such antibodies were biologically active in vitro and in vivo, and those neutralizing type I interferons (IFNs) showed a striking inverse correlation with type I diabetes, not shown by other anti-cytokine antibodies. Thus, naturally occurring human autoantibodies may actively limit disease and be of therapeutic utility.

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.

AIRE expands: new roles in immune tolerance and beyond

More than 15 years ago, mutations in the autoimmune regulator (AIRE) gene were identified as the cause of autoimmune polyglandular syndrome type 1 (APS1). It is now clear that this transcription factor has a crucial role in promoting self-tolerance in the thymus by regulating the expression of a wide array of self-antigens that have the commonality of being tissue-restricted in their expression pattern in the periphery. In this Review, we highlight many of the recent advances in our understanding of the complex biology that is related to AIRE, with a particular focus on advances in genetics, molecular interactions and the effect of AIRE on thymic selection of regulatory T cells. Furthermore, we highlight new areas of biology that are potentially affected by this key regulator of immune tolerance.

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.

Primary immunodeficiency update: Part II. Syndromes associated with mucocutaneous candidiasis and noninfectious cutaneous manifestations

Several primary immunodeficiencies (PIDs) have recently been described that confer an elevated risk of fungal infections and noninfectious cutaneous manifestations. In addition, immunologic advances have provided new insights into our understanding of the pathophysiology of fungal infections in established PIDs. We reviewed PIDs that present with an eczematous dermatitis in part I. In part II of this continuing medical education article we discuss updates on PIDs associated with fungal infections, their biologic basis in PIDs, and noninfectious cutaneous manifestations.

Autoimmunity and Immune Dysregulation in Primary Immune Deficiency Disorders

Primary immune deficiencies are often associated with autoimmune disease due to the dysregulation of the immune system as a whole. In many immune deficiencies, lymphocytes may be present but dysfunctional, allowing for the development of excessive autoreactivity and resultant autoimmune disease. Autoimmune polyendocrinopathy candidiasis and ectodermal dystrophy, autoimmune lymphoproliferative syndrome, immunodyregulation polyendocrinopathy enteropathy X-linked, IL-10/IL-10 receptor deficiencies, and PLCG2-associated antibody deficiency and immune dysregulation are disorders in which autoimmunity is a hallmark of the clinical disease presentation. In contrast, adaptive and innate immune deficiencies, which are typically defined by their infectious susceptibilities, can be associated with variable rates of autoimmune manifestations, predominantly autoimmune cytopenias. This review describes the immune dysregulation and autoimmune manifestations that may be encountered in various immune deficiencies.

cFLIP overexpression in T cells in thymoma-associated myasthenia gravis

Objective

The capacity of thymomas to generate mature CD4+ effector T cells from immature precursors inside the tumor and export them to the blood is associated with thymoma-associated myasthenia gravis (TAMG). Why TAMG(+) thymomas generate and export more mature CD4+ T cells than MG(−) thymomas is unknown.

Methods

Unfixed thymoma tissue, thymocytes derived thereof, peripheral blood mononuclear cells (PBMCs), T-cell subsets and B cells were analysed using qRT-PCR and western blotting. Survival of PBMCs was measured by MTT assay. FAS-mediated apoptosis in PBMCs was quantified by flow cytometry. NF-κB in PBMCs was inhibited by the NF-κB-Inhibitor, EF24 prior to FAS-Ligand (FASLG) treatment for apoptosis induction.

Results

Expression levels of the apoptosis inhibitor cellular FLICE-like inhibitory protein (c-FLIP) in blood T cells and intratumorous thymocytes were higher in TAMG(+) than in MG(−) thymomas and non-neoplastic thymic remnants. Thymocytes and PBMCs of TAMG patients showed nuclear NF-κB accumulation and apoptosis resistance to FASLG stimulation that was sensitive to NF-κB blockade. Thymoma removal reduced cFLIP expression in PBMCs.

Interpretation

We conclude that thymomas induce cFLIP overexpression in thymocytes and their progeny, blood T cells. We suggest that the stronger cFLIP overexpression in TAMG(+) compared to MG(−) thymomas allows for the more efficient generation of mature CD4+ T cells in TAMG(+) thymomas. cFLIP overexpression in thymocytes and exported CD4+ T cells of patients with TAMG might contribute to the pathogenesis of TAMG by impairing central and peripheral T-cell tolerance.

Autoimmune polyendocrinopathy candidiasis ectodermal dystrophy

Autoimmune polyendocrinopathy candidiasis ectodermal dystrophy (APECED) is an autosomal recessive disease caused by mutations in the autoimmune regulator (AIRE) gene. This review focuses on the clinical and immunological features of APECED, summarizes the current knowledge on the function of AIRE and discusses the importance of autoantibodies in disease diagnosis and prognosis. Additionally, we review the outcome of recent immunomodulatory treatments in APECED patients.

The intersection of immune deficiency and autoimmunity

PURPOSE OF REVIEW

Immune deficiency and autoimmunity have been recognized as cotravelers for decades. This clinically oriented review brings together our evolving mechanistic understanding to highlight associations of particular relevance to rheumatologists.

RECENT FINDINGS

Conceptually, all autoimmunity derives from a loss of tolerance. This distinguishes it from autoinflammation in which the innate immune system is dysregulated without necessarily affecting tolerance. Studies have demonstrated the profound effects of signaling defects, apoptotic pathways and the ramifications of homeostatic proliferation on tolerance. This foundation has translated into an improved understanding of the specific associations of autoimmune diseases with immune deficiencies. This important foundation paves the way for personalized treatment strategies.

SUMMARY

This review identifies critical mechanisms important to conceptualize the association of primary immune deficiencies and autoimmunity. It highlights a growing appreciation of the hidden single gene defects affecting T-cells within the group of patients with early-onset pleomorphic autoimmunity.

Inherited IL-17RC deficiency in patients with chronic mucocutaneous candidiasis

Autosomal-recessive IL-17RA, IL-17RC, and ACT1 deficiencies and autosomal-dominant IL-17F deficiency in humans underlie susceptibility to chronic mucocutaneous candidiasis.

Chronic mucocutaneous candidiasis (CMC) is characterized by recurrent or persistent infections of the skin, nail, oral, and genital mucosae with Candida species, mainly C. albicans. Autosomal-recessive (AR) IL-17RA and ACT1 deficiencies and autosomal-dominant IL-17F deficiency, each reported in a single kindred, underlie CMC in otherwise healthy patients. We report three patients from unrelated kindreds, aged 8, 12, and 37 yr with isolated CMC, who display AR IL-17RC deficiency. The patients are homozygous for different nonsense alleles that prevent the expression of IL-17RC on the cell surface. The defect is complete, abolishing cellular responses to IL-17A and IL-17F homo- and heterodimers. However, in contrast to what is observed for the IL-17RA– and ACT1-deficient patients tested, the response to IL-17E (IL-25) is maintained in these IL-17RC–deficient patients. These experiments of nature indicate that human IL-17RC is essential for mucocutaneous immunity to C. albicans but is otherwise largely redundant.

Autoimmune channelopathies in paraneoplastic neurological syndromes

Paraneoplastic neurological syndromes and autoimmune encephalitides are immune neurological disorders occurring or not in association with a cancer. They are thought to be due to an autoimmune reaction against neuronal antigens ectopically expressed by the underlying tumour or by cross-reaction with an unknown infectious agent. In some instances, paraneoplastic neurological syndromes and autoimmune encephalitides are related to an antibody-induced dysfunction of ion channels, a situation that can be labelled as autoimmune channelopathies. Such functional alterations of ion channels are caused by the specific fixation of an autoantibody upon its target, implying that autoimmune channelopathies are usually highly responsive to immuno-modulatory treatments. Over the recent years, numerous autoantibodies corresponding to various neurological syndromes have been discovered and their mechanisms of action partially deciphered. Autoantibodies in neurological autoimmune channelopathies may target either directly ion channels or proteins associated to ion channels and induce channel dysfunction by various mechanisms generally leading to the reduction of synaptic expression of the considered channel. The discovery of those mechanisms of action has provided insights on the regulation of the synaptic expression of the altered channels as well as the putative roles of some of their functional subdomains. Interestingly, patients' autoantibodies themselves can be used as specific tools in order to study the functions of ion channels. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

IL-23/IL-17A Dysfunction Phenotypes Inform Possible Clinical Effects from Anti-IL-17A Therapies

Biologics that neutralize specific cytokines have improved outcomes for several immune-mediated disorders but may also increase risks for particular side effects. This article postulates potential immunologic consequences of inhibiting components of the IL-23/T-helper cell 17 pathway–the target of next-generation biologics for treating psoriasis–based on clinical phenotypes of inherent or acquired deficiencies in this pathway. Generally, downstream deficiencies (e.g., IL-17A, IL-17F) are associated with fewer disorders compared with upstream deficiencies, suggesting that selectively blocking downstream targets may result in a narrower range of side effects. However, safety of these specific inhibitions must be established in long-term studies.

Gastrointestinal immunity against tryptophan hydroxylase-1, aromatic L-amino-acid decarboxylase, AIE-75, villin and Paneth cells in APECED

Gastrointestinal dysfunction is a disabling manifestation of APECED possibly related to an autoimmune intestinal aggression. We evaluated its features in a cohort of 31 Finnish patients. The most frequent manifestations were constipation (48%), diarrhea, dysphagia and retrosternal pain (45%). AADC and TPH-1 autoantibodies were detected in 51% and 45% of the patients, respectively. Forty-three percent displayed a T-cell response to AADC. One third of the patients also had AIE-75 (33%) and villin (29%)-specific autoantibodies while antibodies against brush borders and Paneth cells were detected in 29% and 20%, respectively. Intestinal IL-17 expression was absent/decreased in 77% of the cases. Duodenal CgA and serotonin expression was absent/decreased in 50% and 66% of the patients, respectively. Constipation correlated with lacking serotonin expression and AADC antibodies (p < 0.05).

Thymoma related myasthenia gravis in humans and potential animal models

Thymoma-associated Myasthenia gravis (TAMG) is one of the anti-acetylcholine receptor MG (AChR-MG) subtypes. The clinico-pathological features of TAMG and its pathogenesis are described here in comparison with pathogenetic models suggested for the more common non-thymoma AChR-MG subtypes, early onset MG and late onset MG. Emphasis is put on the role of abnormal intratumorous T cell selection and activation, lack of intratumorous myoid cells and regulatory T cells as well as deficient expression of the autoimmune regulator (AIRE) by neoplastic thymic epithelial cells. We review spontaneous and genetically engineered thymoma models in a spectrum of animals and the extensive clinical and immunological overlap between canine, feline and human TAMG. Finally, limitations and perspectives of the transplantation of human and murine thymoma tissue into nude mice, as potential models for TAMG, are addressed.

Clinical and serologic parallels to APS-I in patients with thymomas and autoantigen transcripts in their tumors

Patients with the autoimmune polyendocrine syndrome type I (APS-I), caused by mutations in the autoimmune regulator (AIRE) gene, and myasthenia gravis (MG) with thymoma, show intriguing but unexplained parallels. They include uncommon manifestations like autoimmune adrenal insufficiency (AI), hypoparathyroidism, and chronic mucocutaneous candidiasis plus autoantibodies neutralizing IL-17, IL-22, and type I IFNs. Thymopoiesis in the absence of AIRE is implicated in both syndromes. To test whether these parallels extend further, we screened 247 patients with MG, thymoma, or both for clinical features and organ-specific autoantibodies characteristic of APS-I patients, and we assayed 26 thymoma samples for transcripts for AIRE and 16 peripheral tissue-specific autoantigens (TSAgs) by quantitative PCR. We found APS-I-typical autoantibodies and clinical manifestations, including chronic mucocutaneous candidiasis, AI, and asplenia, respectively, in 49 of 121 (40%) and 10 of 121 (8%) thymoma patients, but clinical features seldom occurred together with the corresponding autoantibodies. Both were rare in other MG subgroups (n = 126). In 38 patients with APS-I, by contrast, we observed neither autoantibodies against muscle Ags nor any neuromuscular disorders. Whereas relative transcript levels for AIRE and 7 of 16 TSAgs showed the expected underexpression in thymomas, levels were increased for four of the five TSAgs most frequently targeted by these patients' autoantibodies. Therefore, the clinical and serologic parallels to APS-I in patients with thymomas are not explained purely by deficient TSAg transcription in these aberrant AIRE-deficient tumors. We therefore propose additional explanations for the unusual autoimmune biases they provoke. Thymoma patients should be monitored for potentially life-threatening APS-I manifestations such as AI and hypoparathyroidism.

Detection of anti-cytokine antibodies and their clinical relevance

Cytokines regulate many aspects of cell growth and differentiation and play pivotal roles in the orchestration of immune defence against invading pathogens. Though 'self' proteins, they are potentially immunogenic and can give rise to anti-cytokine autoantibodies (aCA). The main foci of the article are a critical summary of the various methodologies applied for detecting and measuring aCA and a broad review of studies of the occurrence, characterization and clinical relevance of aCA in normal healthy individuals, patients with autoimmune diseases or microbial infections and aCA in patients whose disease is treated with recombinant cytokine products. The need for technical and methodological improvement of assays, including validation and standardization, together with approaches to harmonize calculation and reporting of results is also discussed.

Modern management of primary T-cell immunodeficiencies

The study of human T-cell PIDs with Mendelian inheritance has enabled the molecular characterization of important key functions and pathways in T-cell biology. In most cases, T-cell PIDs become apparent as combined T- and B-cell deficiencies. Severe combined immunodeficiencies (SCIDs) are characterized by a complete lack of T-cell development and, in some cases, a developmental block in other lymphoid lineages and manifest within the first year of life. Combined immunodeficiency syndromes (CIDs) result from hypomorphic mutations in typical SCID associated genes or from partial defects of T-cell development and manifest later in childhood by increased susceptibility to infection often combined with disturbances in immune homeostasis, e.g., autoimmunity and increased incidence in lymphoproliferation. The discovery of mutations and characterization of the cellular changes that underlie lymphocyte defects and immune dysregulation have led to novel, specific, successful therapies for severe diseases which are often fatal if left untreated. Over the last few years, impressive progress has been made in understanding the disease mechanisms of T-cell immunodeficiencies and in improving the long-term outcomes of potentially curative treatments, including gene therapy.