IL-6-specific autoantibodies among APECED and thymoma patients

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.

Anti-Interleukin-23 Autoantibodies in Adult-Onset Immunodeficiency

BACKGROUND

Autoantibodies against interleukin-12 (anti-interleukin-12) are often identified in patients with thymoma, but opportunistic infections develop in only some of these patients. Interleukin-12 (with subunits p40 and p35) shares a common subunit with interleukin-23 (subunits p40 and p19). In a patient with disseminated Burkholderia gladioli infection, the identification of both anti-interleukin-23 and anti-interleukin-12 prompted further investigation.

METHODS

Among the patients (most of whom had thymoma) who were known to have anti-interleukin-12, we screened for autoantibodies against interleukin-23 (anti-interleukin-23). To validate the potential role of anti-interleukin-23 with respect to opportunistic infection, we tested a second cohort of patients with thymoma as well as patients without either thymoma or known anti-interleukin-12 who had unusual infections.

RESULTS

Among 30 patients with anti-interleukin-12 who had severe mycobacterial, bacterial, or fungal infections, 15 (50%) also had autoantibodies that neutralized interleukin-23. The potency of such neutralization was correlated with the severity of these infections. The neutralizing activity of anti-interleukin-12 alone was not associated with infection. In the validation cohort of 91 patients with thymoma, the presence of anti-interleukin-23 was associated with infection status in 74 patients (81%). Overall, neutralizing anti-interleukin-23 was detected in 30 of 116 patients (26%) with thymoma and in 30 of 36 patients (83%) with disseminated, cerebral, or pulmonary infections. Anti-interleukin-23 was present in 6 of 32 patients (19%) with severe intracellular infections and in 2 of 16 patients (12%) with unusual intracranial infections, including Cladophialophora bantiana and Mycobacterium avium complex.

CONCLUSIONS

Among patients with a variety of mycobacterial, bacterial, or fungal infections, the presence of neutralizing anti-interleukin-23 was associated with severe, persistent opportunistic infections. (Funded by the National Institute of Allergy and Infectious Diseases and others.).

Anti-cytokine autoantibodies: mechanistic insights and disease associations

Anti-cytokine autoantibodies (ACAAs) are increasingly recognized as modulating disease severity in infection, inflammation and autoimmunity. By reducing or augmenting cytokine signalling pathways or by altering the half-life of cytokines in the circulation, ACAAs can be either pathogenic or disease ameliorating. The origins of ACAAs remain unclear. Here, we focus on the most common ACAAs in the context of disease groups with similar characteristics. We review the emerging genetic and environmental factors that are thought to drive their production. We also describe how the profiling of ACAAs should be considered for the early diagnosis, active monitoring, treatment or sub-phenotyping of diseases. Finally, we discuss how understanding the biology of naturally occurring ACAAs can guide therapeutic strategies.

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.

Insights from a Case of Good's Syndrome (Immunodeficiency with Thymoma)

Immunodeficiency with thymoma was described by R.A. Good in 1954 and is also named after him. The syndrome is characterized by hypogammaglobulinemia associated with thymoma and recurrent infections, bacterial but also viral, fungal and parasitic. Autoimmune diseases, mainly pure red cell aplasia, other hematological disorders and erosive lichen planus are a common finding. We describe here a typical case exhibiting all these clinical features and report a detailed immunophenotypic assessment, as well as the positivity for autoantibodies against three cytokines (IFN-alpha, IL-6 and GM-CSF), which may add to known immune abnormalities. A review of the published literature, based on case series and immunological studies, offers some hints on the still unsolved issues of this rare condition.

Autoantibodies to Interferons in Infectious Diseases

Anti-cytokine autoantibodies and, in particular, anti-type I interferons are increasingly described in association with immunodeficient, autoimmune, and immune-dysregulated conditions. Their presence in otherwise healthy individuals may result in a phenotype characterized by a predisposition to infections with several agents. For instance, anti-type I interferon autoantibodies are implicated in Coronavirus Disease 19 (COVID-19) pathogenesis and found preferentially in patients with critical disease. However, autoantibodies were also described in the serum of patients with viral, bacterial, and fungal infections not associated with COVID-19. In this review, we provide an overview of anti-cytokine autoantibodies identified to date and their clinical associations; we also discuss whether they can act as enemies or friends, i.e., are capable of acting in a beneficial or harmful way, and if they may be linked to gender or immunosenescence. Understanding the mechanisms underlying the production of autoantibodies could improve the approach to treating some infections, focusing not only on pathogens, but also on the possibility of a low degree of autoimmunity in patients.

Autoantibodies of inflammatory cytokines as serum biomarkers in OSA patients

As many as 90% of patients with obstructive sleep apnea (OSA) may be undiagnosed. It is necessary to explore the potential value of autoantibodies against CRP, IL-6, IL-8 and TNF-α in the diagnosis of OSA. ELISA was performed to detect the level of autoantibodies against CRP, IL-6, IL-8 and TNF-α in sera from 264 OSA patients and 231 normal controls (NCs). The expression level of autoantibodies against CRP, IL-6 and IL-8 in OSA were significantly higher than that in NC while the level of anti-TNF-α was lower in OSA than that in NC. The per SD increment of anti-CRP, anti-IL-6 and anti-IL-8 autoantibodies were significantly associated with a 430%, 100% and 31% higher risk for OSA, respectively. The AUC of anti-CRP was 0.808 (95% CI: 0.771-0.845) when comparing OSA with NC, while the AUC increased to 0.876 (95% CI: 0.846-0.906) combining four autoantibodies. For discrimination of severe OSA versus NC and non-severe OSA versus NC, the AUC for four autoantibodies combination was 0.885 (95% CI: 0.851-0.918) and 0.876 (95% CI: 0.842-0.913). This study revealed the association between autoantibodies against inflammatory factors and OSA, and the combination of autoantibodies against CRP, IL-6, IL-8 and TNF-α may function as novel biomarker for monitoring the presence of OSA.

Advancing Luciferase-Based Antibody Immunoassays to Next-Generation Mix and Read Testing

Antibody measurements play a central role in the diagnosis of many autoimmune and infectious diseases. One antibody detection technology, Luciferase Immunoprecipitation Systems (LIPS), utilizes genetically encoded recombinant luciferase antigen fusion proteins in an immunoglobulin capture format to generate robust antibody measurement with high diagnostic sensitivity and specificity. The LIPS technology has been highly useful in detecting antibodies for research diagnostics and the discovery of new autoantigens. The methodology of the assay requires immunoglobulin binding reagents such as protein A/G beads and washing steps to process the immune complex before antibody levels are measured by light production with a luminometer. Recently, simplified mix and read immunoassays based on split components of the nanoluciferase enzyme in a complementation format have been developed for antibody measurements without requiring immunoglobulin-capturing beads or washing steps. The mix and read immunoassays utilize two or three nanoluciferase fragments which when reconstituted via antigen-specific antibody binding generate a functional enzyme. At present, these split luciferase tests have been developed mainly for detecting SARS-CoV-2 antibodies. Here, we describe the traditional LIPS technology and compare it to the new split luciferase methodologies focusing on their technical features, strengths, limitations, and future opportunities for diagnostic research, and clinical applications.

Inactive disease in patients with lupus is linked to autoantibodies to type I interferons that normalize blood IFNα and B cell subsets

Systemic lupus erythematosus (SLE) is characterized by increased expression of type I interferon (IFN)-regulated genes in 50%-75% of patients. We report that out of 501 patients with SLE analyzed, 73 (14%) present autoantibodies against IFNα (anti-IFN-Abs). The presence of neutralizing-anti-IFN-Abs in 4.2% of patients inversely correlates with low circulating IFNα protein levels, inhibition of IFN-I downstream gene signatures, and inactive global disease score. Hallmarks of SLE pathogenesis, including increased immature, double-negative plasmablast B cell populations and reduction in regulatory B cell (Breg) frequencies, were normalized in patients with neutralizing anti-IFN-Abs compared with other patient groups. Immunoglobulin G (IgG) purified from sera of patients with SLE with neutralizing anti-IFN-Abs impedes CpGC-driven IFNα-dependent differentiation of B cells into immature B cells and plasmablasts, thus recapitulating the neutralizing effect of anti-IFN-Abs on B cell differentiation in vitro. Our findings highlight a role for neutralizing anti-IFN-Abs in controlling SLE pathogenesis and support the use of IFN-targeting therapies in patients with SLE lacking neutralizing-anti-IFN-Abs.

[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.

Anticytokine autoantibodies: Autoimmunity trespassing on antimicrobial immunity

Anticytokine autoantibodies can cause immunodeficiency or dysregulate immune responses. They may phenocopy genetically defined primary immunodeficiencies. We review current anti-type 1 and anti-type 2 interferon; anti-IL-12/23, anti-IL-17, and anti-GM-CSF autoantibodies; HLA associations; disease associations; and mechanistically based treatment options. Suspecting the presence of these autoantibodies in patients and identifying them at the onset of symptoms should ameliorate disease and improve outcomes.

The Role of GM-CSF Autoantibodies in Infection and Autoimmune Pulmonary Alveolar Proteinosis: A Concise Review

Autoantibodies to multiple cytokines have been identified and some, including antibodies against granulocyte-macrophage colony-stimulating factor (GM-CSF), have been associated with increased susceptibility to infection. High levels of GM-CSF autoantibodies that neutralize signaling cause autoimmune pulmonary alveolar proteinosis (aPAP), an ultrarare autoimmune disease characterized by accumulation of excess surfactant in the alveoli, leading to pulmonary insufficiency. Defective GM-CSF signaling leads to functional deficits in multiple cell types, including macrophages and neutrophils, with impaired phagocytosis and host immune responses against pulmonary and systemic infections. In this article, we review the role of GM-CSF in aPAP pathogenesis and pulmonary homeostasis along with the increased incidence of infections (particularly opportunistic infections). Therefore, recombinant human GM-CSF products may have potential for treatment of aPAP and possibly other infectious and pulmonary diseases due to its pleotropic immunomodulatory actions.

The Role of IL-17-Producing Cells in Cutaneous Fungal Infections

The skin is the outermost layer of the body and is exposed to many environmental stimuli, which cause various inflammatory immune responses in the skin. Among them, fungi are common microorganisms that colonize the skin and cause cutaneous fungal diseases such as candidiasis and dermatophytosis. The skin exerts inflammatory responses to eliminate these fungi through the cooperation of skin-component immune cells. IL-17 producing cells are representative immune cells that play a vital role in anti-fungal action in the skin by producing antimicrobial peptides and facilitating neutrophil infiltration. However, the actual impact of IL-17-producing cells in cutaneous fungal infections remains unclear. In this review, we focused on the role of IL-17-producing cells in a series of cutaneous fungal infections, the characteristics of skin infectious fungi, and the recognition of cell components that drive cutaneous immune cells.

Update on IgG4-mediated autoimmune diseases: New insights and new family members

Antibodies of IgG4 subclass are exceptional players of the immune system, as they are considered to be immunologically inert and functionally monovalent, and as such may be part of classical tolerance mechanisms. IgG4 antibodies are found in a range of different diseases, including IgG4-related diseases, allergy, cancer, rheumatoid arthritis, helminth infection and IgG4 autoimmune diseases, where they may be pathogenic or protective. IgG4 autoimmune diseases are an emerging new group of diseases that are characterized by pathogenic, antigen-specific autoantibodies of IgG4 subclass, such as MuSK myasthenia gravis, pemphigus vulgaris and thrombotic thrombocytopenic purpura. The list of IgG4 autoantigens is rapidly growing and to date contains 29 candidate antigens. Interestingly, IgG4 autoimmune diseases are restricted to four distinct organs: 1) the central and peripheral nervous system, 2) the kidney, 3) the skin and mucous membranes and 4) the vascular system and soluble antigens in the blood circulation. The pathogenicity of IgG4 can be validated using our classification system, and is usually excerted by functional blocking of protein-protein interaction.

Autoantibodies against cytokines: phenocopies of primary immunodeficiencies?

Anti-cytokine autoantibodies may cause immunodeficiency and have been recently recognized as ‘autoimmune phenocopies of primary immunodeficiencies’ and are found in particular, but not exclusively in adult patients. By blocking the cytokine’s biological function, patients with anti-cytokine autoantibodies may present with a similar clinical phenotype as the related inborn genetic disorders. So far, autoantibodies to interferon (IFN)-γ, GM-CSF, to a group of TH-17 cytokines and to IL-6 have been found to be causative or closely associated with susceptibility to infection. This review compares infectious diseases associated with anti-cytokine autoantibodies with primary immunodeficiencies affecting similar cytokines or related pathways.

Functional Analysis of Anti-cytokine Autoantibodies Using Flow Cytometry

Autoantibodies to cytokines are increasingly being detected in association with immunodeficient, autoimmune and immune dysregulated states. Presence of these autoantibodies in an otherwise healthy individual may result in a unique phenotype characterized by predisposition to infection with specific organisms. The ability to detect these autoantibodies is of importance as it may direct treatment toward a combination of anti-microbial agents and immunomodulatory therapies that decrease autoantibody levels, thereby releasing the immune system from autoantibody-mediated inhibition. Ligand binding assays such as ELISA or bead multiplex assays have been used to detect these antibodies. However, not all anti-cytokine autoantibodies have demonstrable function in vitro and therefore their clinical significance is unclear. Assays that evaluate the functionality of anti-cytokine autoantibodies can supplement such ligand binding assays and add valuable functional information that, when viewed in the context of the clinical phenotype, may guide the use of adjunctive immunomodulatory therapy. This mini review provides an overview of anti-cytokine autoantibodies identified to date and their clinical associations. It also describes the use of flow cytometry for the functional analysis of anti-IFNγ and anti-GM-CSF autoantibodies.

Response to comment on 'AIRE-deficient patients harbor unique high-affinity disease-ameliorating autoantibodies'

In 2016, we reported four substantial observations of APECED/APS1 patients, who are deficient in AIRE, a major regulator of central T cell tolerance (Meyer et al., 2016). Two of those observations have been challenged. Specifically, ‘private’ autoantibody reactivities shared by only a few patients but collectively targeting >1000 autoantigens have been attributed to false positives (Landegren, 2019). While acknowledging this risk, our study-design included follow-up validation, permitting us to adopt statistical approaches to also limit false negatives. Importantly, many such private specificities have now been validated by multiple, independent means including the autoantibodies’ molecular cloning and expression. Second, a significant correlation of antibody-mediated IFNα neutralization with an absence of disease in patients highly disposed to Type I diabetes has been challenged because of a claimed failure to replicate our findings (Landegren, 2019). However, flaws in design and implementation invalidate this challenge. Thus, our results present robust, insightful, independently validated depictions of APECED/APS1, that have spawned productive follow-up studies.

Clinical features of Sjögren's syndrome patients with autoantibodies against interferons

Background

Sjögren’s syndrome (SS) is an autoimmune disease characterized by immune attack on the salivary and lacrimal glands. Given the known cytokine activation and type I interferon gene expression signature found in SS, we hypothesized that anticytokine autoantibodies might be detectable by Luciferase immunoprecipitation systems in some SS patients and correlate with clinical symptoms.

Results

Luciferase immunoprecipitation systems was used to screen for serum anti-cytokine autoantibodies in 57 primary SS patients and 25 healthy volunteers. Autoantibodies were detected against GMCSF, interferon-γ, -α and, -ω in one, two, two and six patients with SS, respectively. None of the healthy volunteers showed anticytokine autoantibodies and none of the SS or control subjects showed autoantibodies against interferon-λ. One 51-year old female SS subject with the highest anti-interferon-α and -ω autoantibody levels had stable autoantibody levels over the course of a year. In vitro functional testing of serum autoantibodies from this subject demonstrated partially neutralizing activity for interferon-α signaling. Clinical information on this individual revealed a low focus score and high levels of unstimulated salivary flow, suggesting the possibility that interferon-α autoantibody neutralizing activity may have contributed to the milder sicca symptoms.

Conclusion

Overall, these findings demonstrate that a subset of SS patients (16%) harbor autoantibodies against GMCSF, interferon-γ, interferon-ω, and interferon-α. These data support the observation that high levels of interferon-α autoantibodies may attenuate disease symptoms in SS.

Lessons from primary immunodeficiencies: Autoimmune regulator and autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy

The discovery of the autoimmune regulator (AIRE) protein and the delineation of its critical contributions in the establishment of central immune tolerance has significantly expanded our understanding of the immunological mechanisms that protect from the development of autoimmune disease. The parallel identification and characterization of patient cohorts with the monogenic disorder autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED), which is typically caused by biallelic AIRE mutations, has underscored the critical contribution of AIRE in fungal immune surveillance at mucosal surfaces and in prevention of multiorgan autoimmunity in humans. In this review, we synthesize the current clinical, genetic, molecular and immunological knowledge derived from basic studies in Aire-deficient animals and from APECED patient cohorts. We also outline major advances and research endeavors that show promise for informing improved diagnostic and therapeutic approaches for patients with APECED.

Altered Immune Activation and IL-23 Signaling in Response to Candida albicans in Autoimmune Polyendocrine Syndrome Type 1

OBJECTIVE

Autoimmune polyendocrine syndrome type 1 (APS-1) is a rare, childhood onset disease caused by mutations in the autoimmune regulator (AIRE) gene. Chronic mucocutaneous candidiasis (CMC) is one of the three major disease components and is, to date, mainly explained by the presence of neutralizing auto-antibodies against cytokines [interleukin (IL)-17A, IL-17F, and IL-22] from T helper 17 cells, which are critical for the protection against fungal infections. However, patients without current auto-antibodies also present CMC and we, therefore, hypothesized that other immune mechanisms contribute to CMC in APS-1.

METHODS

Whole blood was stimulated with Candida albicans (C. albicans) in a standardized assay, and immune activation was investigated by analyzing 46 secreted immune mediators. Then, peripheral blood mononuclear cells were stimulated with curdlan, a Dectin-1 agonist and IL-23 inducer, and the IL-23p19 response in monocytes was analyzed by flow cytometry.

RESULTS

We found an altered immune response in APS-1 patients compared with healthy controls. Patients fail to increase the essential ILs, such as IL-2, IL-17A, IL-22, and IL-23, when stimulating whole blood with C. albicans. A significantly altered IL-23p19 response was detected in patients' monocytes upon stimulation with curdlan.

CONCLUSION

APS-1 patients have an altered immune response to C. albicans including a dysregulation of IL-23p19 production in monocytes. This probably contributes to the selective susceptibility to CMC found in the majority of patients.

Pathogenic and Protective Autoantibodies in Autoimmune Polyendocrinopathy-Candidiasis-Ectodermal Dystrophy (APECED)

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is a rare disorder caused by mutations in the autoimmune regulator (AIRE) gene, leading to defects in T cell selection. The disease manifestations include both autoimmune tissue destruction and immunodeficiency, with specific susceptibility to chronic mucocutaneous candidiasis. Studies have demonstrated a wide repertoire of high affinity tissue- and cytokine-specific antibodies in patients with APECED. Here, we review the antigenic targets and function of these disease-causing and disease-ameliorating antibodies.