The role of islet autoantigen-specific T cells in the onset and treatment of type 1 diabetes mellitus.

Type 1 diabetes mellitus (T1DM), a complex chronic disease with an intricate etiology and pathogenesis, involves the recognition of self-antigens by pancreatic islet autoantigen-specific T cells and plays crucial roles in both early- and late-stage destruction of beta cells, thus impacting disease progression. Antigen-specific T cells regulate and execute immune responses by recognizing particular antigens, playing broad roles in the treatment of various diseases. Immunotherapy targeting antigen-specific T cells holds promising potential as a targeted treatment approach. This review outlines the pathogenesis of diabetes, emphasizing the pivotal role of pancreatic islet autoantigen-specific T cells in the progression and treatment of T1DM. Exploring this avenue in research holds promise for identifying novel therapeutic targets for effectively managing diabetes.

An autoreactive T cell's perception of a land of plenty.

Understanding the nature of human autoantigen-specific CD4+ T cells is limited by the difficulty of characterizing these cells ex vivo. In this issue of Immunity, Saggau et al. use ARTE technology to profile CD4+ T cells specific to disease-relevant autoantigens and find that such cells develop an exhausted phenotype that includes FOXP3 expression and persist for extended periods of time.

Performance Assessment of the New EUROLINE Neurologic Syndrome 15 Ag (IgG) for the Determination of Autoantibodies Associated with Neurological Disorders.

OBJECTIVE: Here, we assess the performance of the new EUROLINE Neurologic Syndrome 15 Ag (IgG) which expands the EUROLINE Paraneoplastic Neurologic Syndrome 12 Ag by adding CDR2L (together with CDR2 targeted by anti-Yo), AK5, and Neurochondrin (NCDN). BACKGROUND: Many paraneoplastic as well as non-paraneoplastic autoantibodies (AAbs) have been described in neurological disorders in the last decade. By integrating the associated antigens into existing assays, the diagnostic work-up of patients is being improved and diagnostic gaps reduced. DESIGN/METHODS: Sensitivity of each AAb was analyzed using a total of 194 clinically and diagnostically pre-characterized samples (Table 1). Specificity of each AAb was investigated using a minimum of 100 sera from healthy blood donors. RESULTS: Using the EUROLINE Neurologic Syndrome 15 Ag, autoantibody positivity was confirmed in 89-100% of samples. In particular, all samples for which clinical and tissue-based indirect immunofluorescence assay pre-characterization indicated anti-Yo positivity were anti-CDR2 and -CDR2L double positive. Anti-AK5 was determined in serum and cerebrospinal fluid (CSF) with a sensitivity of 90 and 100%, respectively, and anti-NCDN with a sensitivity of 100%. The individual specificities were ≥99%. CONCLUSIONS: This kit is a tool for the qualitative in vitro determination of AAbs against a large panel of 15 different neuronal autoantigens to support the diagnosis of neurologic syndromes. The parallel detection of anti-CDR2 and anti-CDR2L (both anti-Yo) increases the diagnostic significance, as double positivity is strongly related to paraneoplastic cerebellar degeneration.[Table: see text].

Expression of thyroid antigens in the female reproductive system.

Thyroid autoimmunity (TAI) has been linked to fertility disorders and pregnancy complications, even in euthyroid women. However, the exact pathophysiological mechanism underlying this association is not fully understood. This study seeks to investigate the expression of thyroid antigens within the human female reproductive system, potentially identifying targets for thyroid antibodies. Human biopsies of endometrium and follicular granulosa cells were collected and thyroperoxidase (TPO) and thyroglobulin (TG) expression was evaluated in these tissues by immunohistochemistry. Results showed, for the first time, the expression of TG protein and confirmed the presence of thyroid TPO in human endometrium and granulosa cells. Results suggest that TPO antibodies (TPOAbs) and TG antibodies (TGAbs) could interact with TPO and TG expressed in the reproductive system in patients with positive thyroid antibodies, thereby disrupting the function of TPO and TG and generating an inflammatory response, leading to fertility disorders and pregnancy complications.

L'auto-immunité thyroïdienne (AIT) est associée à des troubles de la fertilité et à des complications de grossesse, même chez les femmes euthyroïdiennes. Cependant, le mécanisme physiopathologique sous-jacent à cette association n'est pas entièrement élucidé. Cette étude vise à examiner l'expression des antigènes thyroïdiens dans le système reproducteur féminin humain, afin d'identifier des cibles potentielles pour les anticorps antithyroïdiens. Des biopsies d'endomètre et de cellules de granulosa ont été analysées pour l'expression de la thyroperoxydase (TPO) et de la thyroglobuline (TG) par immunohistochimie. Les résultats montrent, pour la première fois, l'expression de la TG et confirment la présence de la TPO dans l'endomètre et les cellules de granulosa humaines. Ces résultats suggèrent que les anticorps anti-TPO et anti-TG pourraient interagir avec la TPO et TG exprimés au niveau du système reproducteur des patientes présentant des anticorps thyroïdiens positifs, perturbant ainsi leur fonction et entraînant une réponse inflammatoire pouvant conduire à des troubles de la fertilité et des complications de grossesse.

The emerging role of neutrophil extracellular traps in the progression of rheumatoid arthritis.

Rheumatoid arthritis (RA) is a chronic autoimmune disease with a complex etiology. Neutrophil extracellular traps (NETs are NETwork protein structures activated by neutrophils to induce the cleavage and release of DNA-protein complexes). Current studies have shown the critical involvement of NETs in the progression of autoimmune diseases, Neutrophils mostly gather in the inflammatory sites of patients and participate in the pathogenesis of autoimmune diseases in various ways. NETs, as the activated state of neutrophils, have attracted much attention in immune diseases. Many molecules released in NETs are targeted autoantigens in autoimmune diseases, such as histones, citrulline peptides, and myeloperoxidase. All of these suggest that NETs have a direct causal relationship between the production of autoantigens and autoimmune diseases. For RA in particular, as a disorder of the innate and adaptive immune response, the pathogenesis of RA is inseparable from the generation of RA. In this article, we investigate the emerging role of NETs in the pathogenesis of RA and suggest that NETs may be an important target for the treatment of inflammatory autoimmune diseases.

The possible and intriguing relationship between bullous pemphigoid and melanoma: speculations on significance and clinical relevance.

Bullous pemphigoid (BP) is the most common autoimmune bullous disease: it most commonly affects individuals over 70 years old and impacts severely on their quality of life. BP represents a paradigm for an organ-specific autoimmune disease and is characterized by circulating IgG autoantibodies to hemidesmosomal components: BP180 and BP230. While the crucial role of these autoantibodies in triggering BP inflammatory cascade is fully acknowledged, many ancillary etiological mechanisms need to be elucidated yet. Cutaneous melanoma is due to a malignant transformation of skin melanocytes, that produce and distribute pigments to surrounding keratinocytes. Melanoma is the most fatal skin cancer because of its increasing incidence and its propensity to metastasize. Several data such as: i) reported cases of concomitant melanoma and BP; ii) results from association studies; iii) BP onset following immune check-point inhibitors therapy; iv) expression of BP antigens in transformed melanocytes; and vi) circulating autoantibodies to BP antigens in melanoma patients suggest an intriguing, although unproven, possible association between melanoma and BP. However, a possible causative link is still debated and the putative pathogenetic mechanism underlying this association is unclear. This review aims to describe and discuss the possible relationship between BP and melanoma and give an overview of the speculations for or against this association. Of note, if demonstrated, this association could unwrap considerations of clinical relevance that represent new research frontiers.

Autoantigens of Small Nerve Fibers and Human Coronavirus Antigens: Is There a Possibility for Molecular Mimicry?

In post-COVID-19 syndrome, clinical presentation of the nerve fiber dysfunction plays an important role. The possibility of autoantigen cross-mimicry of human coronaviruses and the peripheral nervous system needs to be investigated. The bioinformatic analysis was applied to search for possible common protein sequences located in the immunoreactive epitopes. Among the autoantigens of the human nervous system, fibroblast growth factor receptor protein 3, myelin protein P0, myelin protein P2, sodium channel protein type 9, alpha protein subunit, plexin-D1 protein and ubiquitin-carboxyl-terminal hydrolase protein of the L1 isoenzyme were selected. The original "Alignmentaj" analytical program was created. The UniProt database, Protein Data Bank, and AlphaFold databases were used. The analysis of protein sequence similarities of spike glycoproteins in human coronaviruses revealed common pentapeptides of the MERS-CoV-2 virus with the fibroblast growth factor receptor 3 and myelin protein P2. Among seasonal coronaviruses, common peptide sequences were identified in HCoV-HKU-1 virus with sodium channel protein type 9 subunit alpha and Plexin-D1, HCoV-OC43 with Plexin-D1, as well as HCoV-NL63 with Plexin-D1 and Ubiquitin carboxyl-terminal hydrolase isozyme L1. Some shared peptides belong to immunoreactive epitopes. The most important targets for the molecular similarities are the sodium channel subunits and fibroblast growth factor receptor 3, both for seasonal and highly pathogenic coronaviruses. The data obtained make it possible to identify new potential targets for the development of autoimmune reactions that may occur against the background of the infections with highly pathogenic as well as seasonal coronaviruses.

Type V collagen-induced nasal tolerance prevents lung damage in an experimental model: new evidence of autoimmunity to collagen V in COPD.

Background: Chronic obstructive pulmonary disease (COPD) has been linked to immune responses to lung-associated self-antigens. Exposure to cigarette smoke (CS), the main cause of COPD, causes chronic lung inflammation, resulting in pulmonary matrix (ECM) damage. This tissue breakdown exposes collagen V (Col V), an antigen typically hidden from the immune system, which could trigger an autoimmune response. Col V autoimmunity has been linked to several lung diseases, and the induction of immune tolerance can mitigate some of these diseases. Evidence suggests that autoimmunity to Col V might also occur in COPD; thus, immunotolerance to Col V could be a novel therapeutic approach. Objective: The role of autoimmunity against collagen V in COPD development was investigated by analyzing the effects of Col V-induced tolerance on the inflammatory response and lung remodeling in a murine model of CS-induced COPD. Methods: Male C57BL/6 mice were divided into three groups: one exposed to CS for four weeks, one previously tolerated for Col V and exposed to CS for four weeks, and one kept in clean air for the same period. Then, we proceeded with lung functional and structural evaluation, assessing inflammatory cells in bronchoalveolar lavage fluid (BALF) and inflammatory markers in the lung parenchyma, inflammatory cytokines in lung and spleen homogenates, and T-cell phenotyping in the spleen. Results: CS exposure altered the structure of elastic and collagen fibers and increased the pro-inflammatory immune response, indicating the presence of COPD. Col V tolerance inhibited the onset of emphysema and prevented structural changes in lung ECM fibers by promoting an immunosuppressive microenvironment in the lung and inducing Treg cell differentiation. Conclusion: Induction of nasal tolerance to Col V can prevent inflammatory responses and lung remodeling in experimental COPD, suggesting that autoimmunity to Col V plays a role in COPD development.

Microbial mimics supersize the pathogenic self-response.

Microbial mimicry, the process in which a microbial antigen elicits an immune response and breaks tolerance to a structurally related self-antigen, has long been proposed as a mechanism in autoimmunity. In this issue of the JCI, Dolton et al. extend this paradigm by demonstrating that a naturally processed peptide from Klebsiella oxytoca acts as a superagonist for autoreactive T cells in type 1 diabetes (T1D). Reframing microbial mimics as superagonists that are thousands of times better at binding disease-associated autoreactive T cell receptors than self-peptides serves to narrow the search space for relevant sequences in the vast microbial proteome. Moreover, the identified superagonists have implications for the intervention and personalized monitoring of T1D that may carry over to other autoimmune diseases with microbial mimicry.

Design of TOLERANT: phase I/II safety assessment of intranodal administration of HSP70/mB29a self-peptide antigen-loaded autologous tolerogenic dendritic cells in patients with rheumatoid arthritis.

INTRODUCTION: In rheumatoid arthritis (RA), immunosuppressive therapies may achieve symptomatic relief, but do not induce long-term, drug-free remission. Meanwhile, the lifelong use of immunosuppressive drugs confers increased risk for malignancy and infections. As such, there is an unmet need for novel treatments that selectively target the pathogenic immune response in RA by inducing tolerance to autoantigens. Autologous cell therapy using antigen-loaded tolerogenic dendritic cells (tolDCs) aims to reinstate autoantigen-specific immunological tolerance in RA and could potentially meet this need. METHODS AND ANALYSIS: We report here the design of the phase I/II, investigator-initiated, open-label, dose-escalation trial TOLERANT. In this study, we will evaluate the intranodal administration of tolDCs in patients with RA that are in remission under immunosuppressive therapy. The tolDCs in this trial are loaded with the heat shock protein 70-derived peptide mB29a, which is an effective surrogate autoantigen in animal models of arthritis. Within this study, three dose-escalation cohorts (two intranodal injections of 5×106, 10×106 and 15×106 tolDCs), each consisting of three patients, are evaluated to identify the highest safe dose (recommended dose), and an extension cohort of nine patients will be treated with the recommended dose. The (co-)primary endpoints of this study are safety and feasibility, which we assess by the number of AEs and the successful production of tolDCs. The secondary endpoints include the immunological effects of the treatment, which we assess with a variety of high-dimensional and antigen-specific immunological assays. Clinical effects are exploratory outcomes. ETHICS AND DISSEMINATION: Ethical approval for this study has been obtained from the Netherlands Central Committee on Research Involving Human Subjects. The outcomes of the trial will be disseminated through publications in open-access, peer-reviewed scientific journals, scientific conferences and to patient associations. TRIAL REGISTRATION NUMBERS: NCT05251870; 2019-003620-20 (EudraCT); NL71296.000.20 (CCMO register).

Cellular and Immunological Analysis of 2D2/Th Hybrid Mice Prone to Experimental Autoimmune Encephalomyelitis in Comparison with 2D2 and Th Lines.

Previously, we described the mechanisms of development of autoimmune encephalomyelitis (EAE) in 3-month-old C57BL/6, Th, and 2D2 mice. The faster and more profound spontaneous development of EAE with the achievement of deeper pathology occurs in hybrid 2D2/Th mice. Here, the cellular and immunological analysis of EAE development in 2D2/Th mice was carried out. In Th, 2D2, and 2D2/Th mice, the development of EAE is associated with a change in the differentiation profile of hemopoietic bone marrow stem cells, which, in 2D2/Th, differs significantly from 2D2 and Th mice. Hybrid 2D2/Th mice demonstrate a significant difference in these changes in all strains of mice, leading to the production of antibodies with catalytic activities, known as abzymes, against self-antigens: myelin oligodendrocyte glycoprotein (MOG), DNA, myelin basic protein (MBP), and five histones (H1-H4) hydrolyze these antigens. There is also the proliferation of B and T lymphocytes in different organs (blood, bone marrow, thymus, spleen, lymph nodes). The patterns of changes in the concentration of antibodies and the relative activity of abzymes during the spontaneous development of EAE in the hydrolysis of these immunogens are significantly or radically different for the three lines of mice: Th, 2D2, and 2D2/Th. Several factors may play an essential role in the acceleration of EAE in 2D2/Th mice. The treatment of mice with MOG accelerates the development of EAE pathology. In the initial period of EAE development, the concentration of anti-MOG antibodies in 2D2/Th is significantly higher than in Th (29.1-fold) and 2D2 (11.7-fold). As shown earlier, antibodies with DNase activity penetrate cellular and nuclear membranes and activate cell apoptosis, stimulating autoimmune processes. In the initial period of EAE development, the concentration of anti-DNA antibodies in 2D2/Th hybrids is higher than in Th (4.6-fold) and 2D2 (25.7-fold); only 2D2/Th mice exhibited a very strong 10.6-fold increase in the DNase activity of IgGs during the development of EAE. Free histones in the blood are cytotoxic and stimulate the development of autoimmune diseases. Only in 2D2/Th mice, during different periods of EAE development, was a sharp increase in the anti-antibody activity in the hydrolysis of some histones observed.

Autoantigen-specific CD4+ T cells acquire an exhausted phenotype and persist in human antigen-specific autoimmune diseases.

Pro-inflammatory autoantigen-specific CD4+ T helper (auto-Th) cells are central orchestrators of autoimmune diseases (AIDs). We aimed to characterize these cells in human AIDs with defined autoantigens by combining human leukocyte antigen (HLA)-tetramer-based and activation-based multidimensional ex vivo analyses. In aquaporin4-antibody-positive neuromyelitis optica spectrum disorder (AQP4-NMOSD) patients, auto-Th cells expressed CD154, but proliferative capacity and pro-inflammatory cytokines were strongly reduced. Instead, exhaustion-associated co-inhibitory receptors were expressed together with FOXP3, the canonical regulatory T cell (Treg) transcription factor. Auto-Th cells responded in vitro to checkpoint inhibition and provided potent B cell help. Cells with the same exhaustion-like (ThEx) phenotype were identified in soluble liver antigen (SLA)-antibody-autoimmune hepatitis and BP180-antibody-positive bullous pemphigoid, AIDs of the liver and skin, respectively. While originally described in cancer and chronic infection, our data point to T cell exhaustion as a common mechanism of adaptation to chronic (self-)stimulation across AID types and link exhausted CD4+ T cells to humoral autoimmune responses, with implications for therapeutic targeting.

Autoantibody profiling of patients with immune checkpoint inhibitor-associated myocarditis: a pilot study.

Background: Immune checkpoint inhibitor (ICI)-associated myocarditis is a rare, but potentially fatal, immune-related adverse event. Hence, identifying biomarkers is critical for selecting and managing patients receiving ICI treatment. Serum autoantibodies (AAbs) in patients with ICI myocarditis may serve as potential biomarkers for predicting, diagnosing, and prognosing ICI myocarditis. We conducted a pilot study using a human proteome microarray with approximately 17,000 unique full-length human proteins to investigate AAbs associated with ICI myocarditis. Methods and results: AAb profiling was performed using sera collected from three patients with ICI myocarditis before the start of ICI treatment and immediately after myocarditis onset. All patients received anti-programmed death-1 antibody monotherapy. At baseline, 116, 296, and 154 autoantigens reacted positively to immunoglobulin G (IgG) in the serum samples from Cases 1, 2, and 3, respectively. Among these proteins, the recombination signal-binding protein for the immunoglobulin kappa J region (RBPJ) was recognized by all three samples, and 32 autoantigens were recognized by any two of the three samples. At the onset of ICI myocarditis, compared to baseline, 48, 114, and 5 autoantigens reacted more strongly with IgG in the serum samples from Cases 1, 2, and 3, respectively. Among these, antibodies against eukaryotic translation initiation factor 4E binding protein 3 (EIF4EBP3) were the most upregulated, with a 38-fold increase. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses highlighted that B-cell receptor signaling, leukocyte transendothelial migration, and thymus development were among the most affected pathways. Enrichment analyses using DisGeNET revealed that proteins reacting to AAbs detected in patients with ICI myocarditis are associated with several diseases, including dilated cardiomyopathy and muscle weakness. Conclusions: This pilot study provides the first integrated analysis of serum AAb profiling in patients with ICI myocarditis and identifies novel candidate markers associated with an increased risk of developing ICI myocarditis and its pathogenesis. However, our results require further independent validation in clinical trials involving a larger number of patients.

Crinophagic granules in pancreatic ß cells contribute to mouse autoimmune diabetes by diversifying pathogenic epitope repertoire.

Autoimmune attack toward pancreatic ß cells causes permanent loss of glucose homeostasis in type 1 diabetes (T1D). Insulin secretory granules store and secrete insulin but are also thought to be tissue messengers for T1D. Here, we show that the crinophagic granules (crinosome), a minor set of vesicles formed by fusing lysosomes with the conventional insulin dense-core granules (DCG), are pathogenic in T1D development in mouse models. Pharmacological inhibition of crinosome formation in ß cells delays T1D progression without affecting the dominant DCGs. Mechanistically, crinophagy inhibition diminishes the epitope repertoire in pancreatic islets, including cryptic, modified and disease-relevant epitopes derived from insulin. These unconventional insulin epitopes are largely undetectable in the MHC-II epitope repertoire of the thymus, where only canonical insulin epitopes are presented. CD4+ T cells targeting unconventional insulin epitopes display autoreactive phenotypes, unlike tolerized T cells recognizing epitopes presented in the thymus. Thus, the crinophagic pathway emerges as a tissue-intrinsic mechanism that transforms insulin from a signature thymic self-protein to a critical autoantigen by creating a peripheral-thymic mismatch in the epitope repertoire.

The fate of immune complexes in membranous nephropathy.

The most characteristic feature of membranous nephropathy (MN) is the presence of subepithelial electron dense deposits and the consequential thickening of the glomerular basement membrane. There have been great advances in the understanding of the destiny of immune complexes in MN by the benefit of experimental models represented by Heymann nephritis. Subepithelial immune complexes are formed in situ by autoantibodies targeting native autoantigens or exogenous planted antigens such as the phospholipase A2 receptor (PLA2R) and cationic BSA respectively. The nascent immune complexes would not be pathogenic until they develop into immune deposits. Podocytes are the major source of autoantigens in idiopathic membranous nephropathy. They also participate in the modulation and removal of the immune complexes to a large extent. The balance between deposition and clearance is regulated by a wide range of factors such as the composition and physicochemical properties of the immune complexes and the complement system. Complement components such as C3 and C1q have been reported to be precipitated with the deposits whereas a complement regulatory protein CR1 expressed by podocytes is involved in the phagocytosis of immune complexes by podocytes. Podocytes regulate the dynamic change of immune complexes which is disturbed in membranous nephropathy. To elucidate the precise fate of the immune complexes is essential for developing more rational and novel therapies for membranous nephropathy.

A citrullinated antigenic vaccine in treatment of autoimmune arthritis.

Rheumatoid arthritis (RA) is an inflammatory autoimmune disease triggered by antigenic peptides with environmental and genetic risk factors. It has been shown that antigen-specific targeting could be a promising therapeutical strategy for RA by restoring immune tolerance to self-antigens without compromising normal immunity. Citrullination of antigens enhances antigenic properties and induces autoimmune responses. Here, we showed that citrullinated antigenic (citAg) vaccine ameliorated collagen-induced arthritis with decreased T-helper 1 (Th1) and Th17 cells, downregulated proinflammatory cytokines including interlukin-6 and tumor necrosis factor-α, and inhibited antigen recall responses. B cell receptor sequencing further revealed that citAg vaccine could dampen the dysregulated V(D)J recombination, restoring the immune repertoire. Taken together, the results demonstrated that citAg vaccine might have a therapeutic effect on RA.

Epitope landscape in autoimmune neurological disease and beyond.

Autoantibody binding has a central role in autoimmune diseases and has also been linked to cancer, infections, and behavioral disorders. Autoimmune neurological diseases remain misclassified also due to an incomplete understanding of the underlying disease-specific epitopes. Such epitopes are crucial for both pathology and diagnosis, but have historically been overlooked. Recent technological advancements have enabled the exploration of these epitopes, potentially opening novel clinical avenues. The precise identification of novel B and T cell epitopes and their autoreactivity has led to the discovery of autoantigen-specific biomarkers for patients at high risk of autoimmune neurological diseases. In this review, we propose utilizing newly available synthetic and cellular-surface display technologies and guide epitope-focused studies to unlock the potential of disease-specific epitopes for improving diagnosis and treatments. Additionally, we offer recommendations to guide emerging epitope-focused studies to broaden the current landscape.

Antigen-specific T cells and autoimmunity.

Autoimmune diseases (ADs) showcase the intricate balance between the immune system's protective functions and its potential for self-inflicted damage. These disorders arise from the immune system's erroneous targeting of the body's tissues, resulting in damage and disease. The ability of T cells to distinguish between self and non-self-antigens is pivotal to averting autoimmune reactions. Perturbations in this process contribute to AD development. Autoreactive T cells that elude thymic elimination are activated by mimics of self-antigens or are erroneously activated by self-antigens can trigger autoimmune responses. Various mechanisms, including molecular mimicry and bystander activation, contribute to AD initiation, with specific triggers and processes varying across the different ADs. In addition, the formation of neo-epitopes could also be implicated in the emergence of autoreactivity. The specificity of T cell responses centers on the antigen recognition sequences expressed by T cell receptors (TCRs), which recognize peptide fragments displayed by major histocompatibility complex (MHC) molecules. The assortment of TCR gene combinations yields a diverse array of T cell populations, each with distinct affinities for self and non-self antigens. However, new evidence challenges the traditional notion that clonal expansion solely steers the selection of higher-affinity T cells. Lower-affinity T cells also play a substantial role, prompting the "two-hit" hypothesis. High-affinity T cells incite initial responses, while their lower-affinity counterparts perpetuate autoimmunity. Precision treatments that target antigen-specific T cells hold promise for avoiding widespread immunosuppression. Nevertheless, detection of such antigen-specific T cells remains a challenge, and multiple technologies have been developed with different sensitivities while still harboring several drawbacks. In addition, elements such as human leukocyte antigen (HLA) haplotypes and validation through animal models are pivotal for advancing these strategies. In brief, this review delves into the intricate mechanisms contributing to ADs, accentuating the pivotal role(s) of antigen-specific T cells in steering immune responses and disease progression, as well as the novel strategies for the identification of antigen-specific cells and their possible future use in humans. Grasping the mechanisms behind ADs paves the way for targeted therapeutic interventions, potentially enhancing treatment choices while minimizing the risk of systemic immunosuppression.

Lipidomic scanning of self-lipids identifies headless antigens for natural killer T cells.

To broadly measure the spectrum of cellular self-antigens for natural killer T cells (NKT), we developed a sensitive lipidomics system to analyze lipids trapped between CD1d and NKT T cell receptors (TCRs). We captured diverse antigen complexes formed in cells from natural endogenous lipids, with or without inducing endoplasmic reticulum (ER) stress. After separating protein complexes with no, low, or high CD1d-TCR interaction, we eluted lipids to establish the spectrum of self-lipids that facilitate this interaction. Although this unbiased approach identified fifteen molecules, they clustered into only two related groups: previously known phospholipid antigens and unexpected neutral lipid antigens. Mass spectrometry studies identified the neutral lipids as ceramides, deoxyceramides, and diacylglycerols, which can be considered headless lipids because they lack polar headgroups that usually form the TCR epitope. The crystal structure of the TCR-ceramide-CD1d complex showed how the missing headgroup allowed the TCR to predominantly contact CD1d, supporting a model of CD1d autoreactivity. Ceramide and related headless antigens mediated physiological TCR binding affinity, weak NKT cell responses, and tetramer binding to polyclonal human and mouse NKT cells. Ceramide and sphingomyelin are oppositely regulated components of the "sphingomyelin cycle" that are altered during apoptosis, transformation, and ER stress. Thus, the unique molecular link of ceramide to NKT cell response, along with the recent identification of sphingomyelin blockers of NKT cell activation, provide two mutually reinforcing links for NKT cell response to sterile cellular stress conditions.