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• The immune cell repertoire is controlled through T cell receptor and costimulatory molecule dependant selection of CD4+ and Foxp3+ T cells in the thymus. • The immune response to antigen is fine-tuned through activation induced cell death. • Chronic exposure to antigen leads to desensitization of immune responses through anergy and the generation of regulatory type 1 responses. • Differentiation of anergic Tr1 cells arises from radically reduced cell signalling and epigenetic priming of tolerance associated genes. • Autoimmune responses are successfully controlled by chronic exposure to antigen processing independent T cell epitopes. Lymphocyte receptors confer antigen specificity on the adaptive immune response. Increasing evidence points to the role of adaptive tuning particularly amongst CD4+ T cell responses. This review summarises how T cell tuning impacts on critically important aspects of immune regulation including thymic selection, the immune response to chronic antigen exposure and antigen-specific immunotherapy of autoimmune conditions. Recent work has revealed a novel mechanism for T cell anergy and regulatory type 1 T cell differentiation through a limitation of T cell receptor mediated signalling combined with epigenetic priming of tolerance associated genes. [ABSTRACT FROM AUTHOR]

• Specific immunotherapy is the 'holy grail' for treatment of autoimmunity. • Antigens are delivered by either direct or indirect presentation mechanisms. • Liver APC and steady state DC mediate distinct forms of immune regulation. • Tr1 cell induction involves epigenetic modification of tolerance associated genes. • Trials reveal that antigen-specific immunotherapy can control autoimmune diseases. Current treatments for autoimmune diseases do not address the immune pathology underlying their initiation and progression and too often rely on non-specific immunosuppressive drugs for control of symptoms. Antigen-specific immunotherapy aims to induce tolerance selectively among the cells causing the disease while leaving the rest of the adaptive immune system capable of protecting against infectious diseases and cancers. Here we describe how novel approaches for antigen-specific immunotherapy are designed to manipulate antigen presentation and promote tolerance to specific self-antigens. This analysis points to liver antigen presenting cells, targeted by carrier particles, and steady-state dendritic cells, to which antigen-processing independent T-cell epitopes (apitopes) bind directly, as the principal targets for antigen-specific immunotherapy. Delivery of antigens to these cells holds great promise for effective control of this rapidly expanding group of diseases. [ABSTRACT FROM AUTHOR]

Allergen‐specific immunotherapy (AIT) is the only means of altering the natural immunological course of allergic diseases and achieving long‐term remission. Pharmacological measures are able to suppress the immune response and/or ameliorate the symptoms but there is a risk of relapse soon after these measures are withdrawn. Current AIT approaches depend on the administration of intact allergens, often comprising crude extracts of the allergen. We propose that the challenges arising from current approaches, including the risk of serious side‐effects, burdensome duration of treatment, poor compliance and high cost, are overcome by application of peptides based on CD4+ T cell epitopes rather than whole allergens. Here we describe evolving approaches, summarize clinical trials involving peptide AIT in allergic rhinitis and asthma, discuss the putative mechanisms involved in their action, address gaps in evidence and propose future directions for research and clinical development. [ABSTRACT FROM AUTHOR]

Background: Some patients infected with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) go on to experience post-COVID-19 condition or long COVID. Preliminary findings have given rise to the theory that long COVID may be due in part to a deranged immune response. In this study, we assess whether there is an association between SARS-CoV-2 infection and the incidence of immune-mediated inflammatory diseases (IMIDs). Methods: Matched cohort study using primary care electronic health record data from the Clinical Practice Research Datalink Aurum database. The exposed cohort included 458,147 adults aged 18 years and older with a confirmed SARS-CoV-2 infection and no prior diagnosis of IMIDs. They were matched on age, sex, and general practice to 1,818,929 adults with no diagnosis of confirmed or suspected SARS-CoV-2 infection. The primary outcome was a composite of any of the following IMIDs: autoimmune thyroiditis, coeliac disease, inflammatory bowel disease (IBD), myasthenia gravis, pernicious anaemia, psoriasis, rheumatoid arthritis (RA), Sjogren's syndrome, systemic lupus erythematosus (SLE), type 1 diabetes mellitus (T1DM), and vitiligo. The secondary outcomes were each of these conditions separately. Cox proportional hazard models were used to estimate adjusted hazard ratios (aHR) and 95% confidence intervals (CI) for the primary and secondary outcomes, adjusting for age, sex, ethnic group, smoking status, body mass index, relevant infections, and medications. Results: Six hundred and nighty six (0.15%) and 2230 (0.12%) patients in the exposed and unexposed cohort developed an IMID during the follow-up period over 0.29 person-years, giving a crude incidence rate of 4.59 and 3.65 per 1000 person-years, respectively. Patients in the exposed cohort had a 22% increased risk of developing an IMID, compared to the unexposed cohort (aHR 1.22, 95% CI 1.12 to 1.33). The incidence of three IMIDs was significantly associated with SARS-CoV-2 infection. These were T1DM (aHR 1.56, 1.09 to 2.23), IBD (aHR 1.36, 1.18 to 1.56), and psoriasis (1.23, 1.05 to 1.42). Conclusions: SARS-CoV-2 was associated with an increased incidence of IMIDs including T1DM, IBD and psoriasis. However, these findings could be potentially due to ascertainment bias. Further research is needed to replicate these findings in other populations and to measure autoantibody profiles in cohorts of individuals with COVID-19. [ABSTRACT FROM AUTHOR]

Adoptive transfer of antigen-specific, in vitro-induced Foxp3 + Treg (iTreg) cells protects against autoimmune disease. To generate antigen-specific iTreg cells at high purity, however, remains a challenge. Whereas polyclonal T cell stimulation with anti-CD3 and anti-CD28 antibody yields Foxp3 + iTreg cells at a purity of 90–95%, antigen-induced iTreg cells typically do not exceed a purity of 65–75%, even in a TCR-transgenic model. In a similar vein to thymic Treg cell selection, iTreg cell differentiation is influenced not only by antigen recognition and the availability of TGF-β but also by co-factors including costimulation and adhesion molecules. In this study, we demonstrate that blockade of the T cell integrin Leukocyte Function-associated Antigen-1 (LFA-1) during antigen-mediated iTreg cell differentiation augments Foxp3 induction, leading to approximately 90% purity of Foxp3 + iTreg cells. This increased efficacy not only boosts the yield of Foxp3 + iTreg cells, it also reduces contamination with activated effector T cells, thus improving the safety of adoptive transfer immunotherapy. [ABSTRACT FROM AUTHOR]

Tissues of the CNS, such as the brain, optic nerves, and spinal cord, may be affected by a range of insults including genetic, autoimmune, infectious, or neurodegenerative diseases and cancer. The immune system is involved in the pathogenesis of many of these, either by causing tissue damage or alternatively by responding to disease and contributing to repair. It is clearly vital that cells of the immune system patrol the CNS and protect against infection. However, in contrast to other tissues, damage caused by immune pathology in the CNS can be irreparable. The nervous and immune systems have, therefore, coevolved to permit effective immune surveillance while limiting immune pathology. Here we will consider aspects of adaptive immunity in the CNS and the retina, both in the context of protection from infection as well as cancer and autoimmunity, while focusing on immune responses that compromise health and lead to significant morbidity. [ABSTRACT FROM AUTHOR]

The neuropeptide galanin is widely expressed by many differing subsets of neurons in the nervous system. There is a marked upregulation in the levels of the peptide in a variety of nerve injury models and in the basal forebrain of humans with Alzheimer's disease. Here we demonstrate that galanin expression is specif ically and markedly upregulated in microglia both in multiple sclerosis (MS) lesions and shadow plaques. Galanin expression is also upregulated in the experimental autoimmune encephalomyelitis (EAE) model of MS. although solely in oligodendrocytes. To study whether the observed increase in expression of galanin in inflammatory demyelination might modulate disease activity, we applied the EAE model to a panel of galanin transgenic lines. Over-expression of galanin in transgenic mice (Gal-OE) abolishes disease in the EAE model, whilst loss-of-function mutations in galanin or galanin receptor-2 (GalR2) increase disease severity. The pronounced effects of altered endogenous galanin or GaIR2 expression on EAE disease activity may reflect a direct neuroprotective effect of the neuropeptide via activation of GalR2, similar to that previously described in a number of neuronal injury paradigms. Irrespective of the mechanism(s) by which galanin alters EAE disease activity, our findings imply that galanin/GalR2 agofists may have future therapeutic implications for MS. [ABSTRACT FROM AUTHOR]

Allergic and autoimmune diseases are forms of immune hypersensitivity that increasingly cause chronic ill health. Most current therapies treat symptoms rather than addressing underlying immunological mechanisms. The ability to modify antigen-specific pathogenic responses by therapeutic vaccination offers the prospect of targeted therapy resulting in long-term clinical improvement without nonspecific immune suppression. Examples of specific immune modulation can be found in nature and in established forms of immune desensitization. Understanding and exploiting common mechanisms such as the ability to induce antigen-specific regulatory cells should allow the development of effective therapeutic strategies for both forms of immunopathology. Targeting pathogenic T cells using vaccines consisting of synthetic peptides representing T cell epitopes is one such strategy that is currently being evaluated with encouraging results. Future challenges in the development of therapeutic vaccines include selection of appropriate antigens and peptides, optimization of peptide dose and route of administration and identifying strategies to induce bystander suppression. [ABSTRACT FROM AUTHOR]

The immune system is a delicately balanced network of interacting cells. In recent years, the concept of immune regulation/suppression has been firmly established, and both natural and induced regulatory cells play vital roles in protection from autoimmune disease. Recent work has revealed the diverse nature of regulatory CD4+ T (Treg) cells and the molecules involved in their function. Innate and adaptive responses to infection are able to override the suppressive properties of such regulatory cells, whereas several reports point to deficiencies in regulatory cell function in autoimmune disease. Protocols have been developed that allow the expansion of Treg cells in vitro and their antigen-specific induction in vivo. A full understanding of Treg differentiation and function will facilitate the development of improved strategies for prevention and treatment of autoimmune diseases. [Copyright &y& Elsevier]

T-cells provide antigen specific focus to the adaptive immune response. However, the receptors that initiate functional responses are not in themselves specific, as they can recognise many different ligands. In this paper, we propose that the immune system deals with TCR degeneracy by an adaptive process that effects both T-cell activation and T-cell function, and exploits TCR degeneracy to limit pathogenic autoimmune disease. [Copyright &y& Elsevier]

As many as one in 20 people in Europe and North America have some form of autoimmune disease. These diseases arise in genetically predisposed individuals but require an environmental trigger. Of the many potential environmental factors, infections are the most likely cause. Microbial antigens can induce cross-reactive immune responses against self-antigens, whereas infections can non-specifically enhance their presentation to the immune system. The immune system uses fail-safe mechanisms to suppress infection-associated tissue damage and thus limits autoimmune responses. The association between infection and autoimmune disease has, however, stimulated a debate as to whether such diseases might also be triggered by vaccines. Indeed there are numerous claims and counter claims relating to such a risk. Here we review the mechanisms involved in the induction of autoimmunity and assess the implications for vaccination in human beings. [ABSTRACT FROM AUTHOR]

The immune system must avoid aggressive T-cell responses against self-antigens. But, paradoxically, exposure to self-peptides seems to have an important role in positive selection in the thymus and the maintenance of a broad T-cell repertoire in the periphery. Recent experiments have highlighted situations that allow high-avidity self-reactive T cells to avoid negative selection in the thymus. Accumulating evidence indicates that other, non-deleting mechanisms control the avidity with which T cells recognize self-antigens ? a phenomenon that is known as 'tuning'. This might maximize the peripheral T-cell repertoire by allowing the survival of T cells that can respond to self, but only at concentrations that are not normally reached in vivo. [ABSTRACT FROM AUTHOR]

Abstract: Recent advances in immunology have led to exciting new possibilities in medicine. We now understand how to design vaccine capable of resetting the balance between immune effector and regulatory cells in people suffering from autoimmune and allergic diseases. These approaches are effective while avoiding the side effects associated with non-specific immune suppression. [Copyright &y& Elsevier]

Much has been learned since Jan Klein first defined immunology as the “science of self non-self discrimination.” A paper in this issue of Immunity provides important insight into how such discrimination is achieved (). [Copyright &y& Elsevier]

Background: Graves' disease is one of the most common autoimmune conditions, but treatment remains imperfect. This study explores the first-in-human use of antigen-specific immunotherapy with a combination of two thyrotropin receptor (TSHR) peptides (termed ATX-GD-59) in Graves' hyperthyroidism. Methods: Twelve participants (11 female) with previously untreated mild to moderate Graves' hyperthyroidism were enrolled in a Phase I open label trial to receive 10 doses of ATX-GD-59 administered intradermally over an 18-week period. Adverse events, tolerability, changes in serum free thyroid hormones, and TSHR autoantibodies were measured. Results: Ten subjects received all 10 doses of ATX-GD-59, five (50%) of whom had free triiodothyronine within the reference interval by the 18-week visit. Two further subjects had improved free thyroid hormones by the end of the study (7/10 responders), whereas three subjects showed worsening thyrotoxicosis during the study. Serum TSHR autoantibody concentrations reduced during the study and correlated with changes in free thyroid hormones (r = 0.85, p = 0.002 for TSHR autoantibody vs. free triiodothyronine). Mild injection-site swelling and pain were the most common adverse events. Conclusions: These preliminary data suggest that ATX-GD-59 is a safe and well-tolerated treatment. The improvement in free thyroid hormones in 70% of subjects receiving the medication suggests potential efficacy as a novel treatment for Graves' hyperthyroidism. [ABSTRACT FROM AUTHOR]

The article discusses the possible relations between infection in the central nervous system (CNS) and rabies vaccine. It mentions the higher rate of meningitis among children aged 5-17 months whose mothers were given vaccination in age-matched controls. It discusses the characteristics of meningitis as a disease caused by rabies vaccination.

Post-acute cardiac sequelae, following SARS-CoV-2 infection, are well recognized as complications of COVID-19. We have previously shown the persistence of autoantibodies against antigens in skin, muscle, and heart in individuals following severe COVID-19; the most common staining on skin tissue displayed an inter-cellular cement pattern consistent with antibodies against desmosomal proteins. Desmosomes play a critical role in maintaining the structural integrity of tissues. For this reason, we analyzed desmosomal protein levels and the presence of anti-desmoglein (DSG) 1, 2, and 3 antibodies in acute and convalescent sera from patients with COVID-19 of differing clinical severity. We find increased levels of DSG2 protein in sera from acute COVID-19 patients. Furthermore, we find that DSG2 autoantibody levels are increased significantly in convalescent sera following severe COVID-19 but not in hospitalized patients recovering from influenza infection or healthy controls. Levels of autoantibody in sera from patients with severe COVID-19 were comparable to levels in patients with non-COVID-19-associated cardiac disease, potentially identifying DSG2 autoantibodies as a novel biomarker for cardiac damage. To determine if there was any association between severe COVID-19 and DSG2, we stained post-mortem cardiac tissue from patients who died from COVID-19 infection. This confirmed DSG2 protein within the intercalated discs and disruption of the intercalated disc between cardiomyocytes in patients who died from COVID-19. Our results reveal the potential for DSG2 protein and autoimmunity to DSG2 to contribute to unexpected pathologies associated with COVID-19 infection. We find raised levels of anti-DSG2 autoantibodies in sera from individuals following severe COVID-19. Staining of post-mortem cardiac tissue from individuals that died from COVID-19 with an anti-DSG2 antibody revealed disruption of the intercalated disc between cardiomyocytes that was consistent with separation of the DSG2 protein homodimer. Our results reveal the potential for DSG2 protein and autoimmunity to DSG2 to contribute to unexpected pathologies associated with COVID-19 infection. [ABSTRACT FROM AUTHOR]

Myocarditis, the principal cause of dilated cardiomyopathy and heart failure in young adults, is associated with autoimmunity to human cardiac α-myosin (hCAM) and the DR4 allele of human major histocompatibility II (MHCII). We developed an hCAM-induced myocarditis model in human HLA-DR4 transgenic mice that lack all mouse MHCII genes, demonstrating that immunization for 3 weeks significantly increased splenic T-cell proliferative responses and titres of IgG1 and IgG2c antibodies, abolished weight gain, provoked cardiac inflammation and significantly impaired cardiac output and fractional shortening, by echocardiography, compared to adjuvant-injected mice. Neither cardiac dilatation nor fibrosis occurred at this time point but prolonging the experiment was associated with mortality. Treatment with mixtures of hCAM derived peptides predicted to have high affinity for DR4 significantly preserved ejection fraction and fractional shortening. Our new humanized mouse model of autoimmune cardiomyopathy should be useful to refine hCAM-derived peptide treatment. [ABSTRACT FROM AUTHOR]

In multiple sclerosis ( MS) T cells aberrantly recognize self-peptides of the myelin sheath and attack the central nervous system ( CNS). Antigen-specific peptide immunotherapy, which aims to restore tolerance while avoiding the use of non-specific immunosuppressive drugs, is a promising approach to combat autoimmune disease, but the cellular mechanisms behind successful therapy remain poorly understood. Myeloid-derived suppressor cells ( MDSCs) have been studied intensively in the field of cancer and to a lesser extent in autoimmunity. Because of their suppressive effect on the immune system in cancer, we hypothesized that the development of MDSCs and their interaction with CD4+ T cells could be beneficial for antigen-specific immunotherapy. Hence, changes in the quantity, phenotype and function of MDSCs during tolerance induction in our model of MS were evaluated. We reveal, for the first time, an involvement of a subset of MDSCs, known as polymorphonuclear ( PMN)- MDSCs, in the process of tolerance induction. PMN- MDSCs were shown to adopt a more suppressive phenotype during peptide immunotherapy and inhibit CD4+ T-cell proliferation in a cell-contact-dependent manner, mediated by arginase-1. Moreover, increased numbers of tolerogenic PMN- MDSCs, such as observed over the course of peptide immunotherapy, were demonstrated to provide protection from disease in a model of experimental autoimmune encephalomyelitis. [ABSTRACT FROM AUTHOR]

This article focuses on the role of T-cells in autoimmune disease. The presentation to T cells of complexes between MHC molecules and peptide fragments of foreign antigens lies at the heart of the immune response. Classically, those peptides displaying the highest affinity for their MHC ligand are considered immunodominant, outcompeting subdominant or cryptic determinants for interaction with the peptide-binding groove. Autoimmunity, however, represents the failure of tolerance to establish a state of non-responsiveness to self, and is characterized by the persistence of autoreactive T cells.

Antigen-specific immunotherapy aims to selectively restore tolerance to innocuous antigens in cases of autoimmune or allergic disease, without the need for general immune suppression. Although the principle of antigen-specific immunotherapy was discovered more than a century ago, its clinical application to date is limited, particularly in the control of autoimmunity. This has resulted mainly from a lack of in-depth understanding of the underlying mechanism. More recently, the differentiation of extra-thymically induced T regulatory ( Treg) cell subsets has been shown to be instrumental in peripheral tolerance induction. Two main types of inducible Treg cells, interleukin-10-secreting or Foxp3+, have now been described, each with distinct characteristics and methods of therapeutic induction. It is crucial, therefore, to identify the suitability of either subset in the control of specific immune disorders. This review explores their natural function, the known mechanisms of therapeutic differentiation of either subset as well as their in vivo functionality and discusses new developments that may aid their use in antigen-specific immunotherapy, with a focus on autoimmune disease. [ABSTRACT FROM AUTHOR]

Nearly a century has passed since the first report describing antigen-specific immunotherapy (antigen-SIT) was published. Research into the use of antigen-SIT in the treatment of both allergic and autoimmune disease has increased dramatically since, although its mechanism of action is only slowly being unravelled. It is clear though, from recent studies, that success of antigen-SIT depends on the induction of regulatory T (T reg) cell subsets that recognise potentially disease-inducing epitopes. The major challenge remaining for the widespread use of antigen-SIT is to safely administer high doses of immunodominant and potentially pathogenic epitopes in a manner that induces T cell tolerance rather than activation. This review illustrates that intelligent design of treatment agents and strategies can lead to the development of safe and effective antigen-SIT. [ABSTRACT FROM AUTHOR]

Abstract: We have shown previously that intranasal administration of encephalitogenic peptides in soluble form to H-2u and H-2s mice affords protection from experimental autoimmune encephalomyelitis (EAE). Here we demonstrate that this method of disease protection can be induced in C57BL/6 mice by administration of the soluble peptide 35–55 from myelin oligodendrocyte glycoprotein. This protective effect was demonstrated by the evaluation of both clinical EAE scores and central nervous system histopathology; the latter showing minimal inflammatory infiltrates in treated mice. The employment of an IL-10−/− congenic strain allowed an appraisal of the involvement of IL-10 in this process. The lack of disease protection in these mice clearly demonstrates the non-redundant role of IL-10 in this process. [Copyright &y& Elsevier]

Altered peptide ligands (APL) with increased MHC-binding properties are highly effective at inducing T cell tolerance after systemic administration in soluble form, preventing experimental autoimmune encephalomyelitis (EAE) induced with the myelin basic protein (MBP) Ac1-9 peptide. We have previously described a diverse Ac1-9-reactive T cell repertoire with differing TCR affinities. A remaining question is what proportion of this repertoire is silenced by peptide therapy? Here, we show that the sensitivity of a T cell to peptide-induced tolerance is related to its avidity for native Ac1-9. These data provide new evidence that self-reactive T cells bearing low-affinity TCRs are able to escape therapeutic induction of tolerance. [Copyright &y& Elsevier]

The peripheral T-cell population is educated to recognize a maximum of pathogen-derived epitopes while ignoring self-antigens. As the total number of T-cell clones is limited, each T-cell receptor (TCR) needs to be cross-reactive in order to achieve a wide repertoire. This opens the possibility for T cells to diverge from their defending role and induce auto-aggression by mistake. The factors involved in the initiation of such autoimmune responses remain to be fully understood. In an attempt to assess the role of antigen presenting cells (APC) in the triggering of autoimmunity, we studied the cross-reactivity of TCR transgenic Tg4 T cells, reactive to the Ac1-9 peptide of myelin basic protein (MBP). Using different APC populations and a range of peptide analogues of Ac1-9, we found that the activation of APC enhanced the cross-reactivity of Tg4 cells, and that this effect could be mimicked by resting APC supplemented with exogenous co-stimulation. Further, we observed that the inhibitory effect of an antagonist peptide of the Tg4 TCR was greatly reduced when activated APC were used. However, when co-stimulation was blocked, TCR antagonism was restored to its normal level. Our results show for the first time that the activation of naturally occuring APC, namely dendritic cells, B cells and macrophages, can modulate the reactivity of T cells, both in terms of cross-reactivity and TCR antagonism, and that this effect is most likely due to enhanced levels of co-stimulation. [Copyright &y& Elsevier]

Detecting antibody responses during and after SARS‐CoV‐2 infection is essential in determining the seroepidemiology of the virus and the potential role of antibody in disease. Scalable, sensitive and specific serological assays are essential to this process. The detection of antibody in hospitalized patients with severe disease has proven relatively straightforward; detecting responses in subjects with mild disease and asymptomatic infections has proven less reliable. We hypothesized that the suboptimal sensitivity of antibody assays and the compartmentalization of the antibody response may contribute to this effect. We systematically developed an ELISA, optimizing different antigens and amplification steps, in serum and saliva from non‐hospitalized SARS‐CoV‐2‐infected subjects. Using trimeric spike glycoprotein, rather than nucleocapsid, enabled detection of responses in individuals with low antibody responses. IgG1 and IgG3 predominate to both antigens, but more anti‐spike IgG1 than IgG3 was detectable. All antigens were effective for detecting responses in hospitalized patients. Anti‐spike IgG, IgA and IgM antibody responses were readily detectable in saliva from a minority of RT‐PCR confirmed, non‐hospitalized symptomatic individuals, and these were mostly subjects who had the highest levels of anti‐spike serum antibodies. Therefore, detecting antibody responses in both saliva and serum can contribute to determining virus exposure and understanding immune responses after SARS‐CoV‐2 infection. [ABSTRACT FROM AUTHOR]

Summary: Coronavirus 19 (COVID‐19) has been associated with both transient and persistent systemic symptoms that do not appear to be a direct consequence of viral infection. The generation of autoantibodies has been proposed as a mechanism to explain these symptoms. To understand the prevalence of autoantibodies associated with severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection, we investigated the frequency and specificity of clinically relevant autoantibodies in 84 individuals previously infected with SARS‐CoV‐2, suffering from COVID‐19 of varying severity in both the acute and convalescent setting. These were compared with results from 32 individuals who were on the intensive therapy unit (ITU) for non‐COVID reasons. We demonstrate a higher frequency of autoantibodies in the COVID‐19 ITU group compared with non‐COVID‐19 ITU disease control patients and that autoantibodies were also found in the serum 3–5 months post‐COVID‐19 infection. Non‐COVID patients displayed a diverse pattern of autoantibodies; in contrast, the COVID‐19 groups had a more restricted panel of autoantibodies including skin, skeletal muscle and cardiac antibodies. Our results demonstrate that respiratory viral infection with SARS‐CoV‐2 is associated with the detection of a limited profile of tissue‐specific autoantibodies, detectable using routine clinical immunology assays. Further studies are required to determine whether these autoantibodies are specific to SARS‐CoV‐2 or a phenomenon arising from severe viral infections and to determine the clinical significance of these autoantibodies. [ABSTRACT FROM AUTHOR]

Although anti-S IgA and IgG were more similar in children and adult COVID-19 patients, anti-N IgA and IgG antibodies were higher in ITU patients (Figure 1C,D). Since antibody isotypes can reflect recent infection (IgM), or more historic infections (IgG and IgA), we examined individual antibody isotypes and presented these results as area under the curve (AUC). Therefore, children with Kawasaki-like inflammatory syndrome, negative by PCR, can have IgG1, IgG3, and IgA antibody levels to SARS-CoV-2 in the absence of maintained IgM responses. Screening of sera, diluted 1:40, to detect IgG, IgA, and IgM demonstrated that all children had antibodies against the SARS-CoV-2 S glycoprotein (Figure 1A). [Extracted from the article]

Secretion of interleukin-10 (IL-10) by CD4+ T cells is an essential immunoregulatory mechanism. The work presented here assesses the role of the signaling molecule protein kinase C theta (PKCθ) in the induction of IL-10 expression in CD4+ T cells. Using wildtype and PKCθ-deficient Tg4 T cell receptor transgenic mice, we implemented a well-described protocol of repeated doses of myelin basic protein (MBP)Ac1-9[4Y] antigen to induce Tr1-like IL-10+ T cells. We find that PKCθ is required for the efficient induction of IL-10 following antigen administration. Both serum concentrations of IL-10 and the proportion of IL-10+ T cells were reduced in PKCθ-deficient mice relative to wildtype mice following [4Y] treatment. We further characterized the T cells of [4Y] treated PKCθ-deficient Tg4 mice and found reduced expression of the transcription factors cMaf, Nfil3 and FoxP3 and the surface receptors PD-1 and Tim3, all of which have been associated with the differentiation or function of IL-10+ T cells. Finally, we demonstrated that, unlike [4Y] treated wildtype Tg4 T cells, cells from PKCθ-deficient mice were unable to suppress the priming of naïve T cells in vitro and in vivo. In summary, we present data demonstrating a role for PKCθ in the induction of suppressive, IL-10-secreting T cells induced in TCR-transgenic mice following chronic antigen administration. This should be considered when contemplating PKCθ as a suitable drug target for inducing immune suppression and graft tolerance. [ABSTRACT FROM AUTHOR]

Although the association of a chronic low-grade inflammation with obesity has long been appreciated, its molecular basis is yet to be defined. The proven involvement of adaptive immunity, coupled with a phenotypic switch from autoimmune suppressive tolerogenic Treg to pro-inflammatory CD4+ Th1 and CD8+ T cells, during progression of obesity necessitates the presence of a triggering antigen as an activator of T and B cells. Not surprisingly in this context, it is found that visceral adipose tissue-specific T cells show severely biased T cell receptor Vα repertoires in diet induced obese mice (Winer et al. 2009), implying an antigen-specific clonal expansion of T cells during obesity. HSP60 is an evolutionary conserved mitochondrial chaperonin that assists the correct folding of other mitochondrial proteins. However, its occurrence is not restricted to mitochondria and it can be located in the cytosol or exposed on the cell membrane also. An increase in cell membrane HSP60, which may be accompanied by HSP60 release into circulation, is especially considered a signal of autoimmunity. HSP60 has been associated with a broad range of diseases so far, particularly those with an autoimmune component. More recently, HSP60 is also linked to obesity as a mediator of adipose tissue inflammation and insulin resistance. Moreover, circulating HSP60 levels are found to be higher in obese individuals than lean controls (Märker et al. 2012). We observed an adaptive immune response against HSP60 at both T cell and B cell (antibody) levels during continuous high fat feeding of C57bl6 mice. Hence HSP60 appears to be one of the mystery auto-antigens triggering the early T and B cell responses during obesity. Furthermore, we attempted a peptide therapy in a dose escalation protocol aiming to down-regulate the inflammatory related adverse effects of obesity by achieving tolerance in T cell populations and suppressing the pathogenic antibody response. Treatment with a mixture of three proven immunomodulatory HSP60 peptides did not reduce weight but completely reversed the increase in VLDL/LDL levels and partially reversed the glucose intolerance in obese mice, which encourages further research to improve peptide therapy. [ABSTRACT FROM AUTHOR]

Myocarditis is the principal cause of heart failure in young adults. Frequently triggered acutely by an episode of viral infection, its progression to dilated cardiomyopathy is associated with the development of auto-immunity, especially to human cardiac α-myosin (hCAM). Consistent with this, HLA genotype influences prevalence of the disease. Previous studies showed that humanised DQ8 transgenic non-obese diabetic mice spontaneously developed autoimmune cardiomyopathy, whereas the DR4 allele is over represented in patients and there is no association with diabetes. We therefore attempted to induce experimental autoimmune myocarditis in DR4 transgenic mice (DR4 mice) as a more relevant model of the human disease. DR4 mice were injected with purified hCAM or vehicle subcutaneously in complete Freund's adjuvant (CFA). After 3 weeks, anesthetized mice were subjected to cardiac ultrasonography, following which blood was obtained from the abdominal aorta under terminal anaesthesia. The hearts were then perfused fixed for histology and spleens were harvested for proliferation assay. Potential immunomodulatory peptides were predicted in silico. Peptides were then proven water soluble and effective in T-cell proliferation assays. For immunotherapy, mice were pre-dosed with escalating doses of mixtures of 3 each of 6 soluble hCAM-derived peptides (pools 1 and 2) according to an established protocol. DR4 mice did not develop spontaneous myocarditis. However, all mice immunized with hCAM developed high titres of both IgG1 and IgG2c antibodies. Consistent with this, splenic T-cell proliferation responses to hCAM significantly increased compared to un-immunized mice. DR4 mice immunized with hCAM failed to gain weight and by echocardiography showed a significant decline in cardiac output and fractional shortening and increase in diastolic dimension compared to those injected with PBS in CFA alone. 5/5 immunized vs 0/5 control mice showed cardiac inflammation based on histology. 3/5 immunized mice died if the experiment was prolonged for 6 weeks. Pre-treatment with hCAM derived peptide pools 1 or 2 blunted the T-cell proliferation response and pool 2 also decreased both IgG1 and IgG2c levels. Pools 1 and 2 significantly improved the left ventricular cardiac function by increasing the percentage of ejection fraction and fractional shortening. Pool 2 also significantly reduced cardiac inflammation. We have developed a novel, more relevant humanized mouse model of autoimmune cardiomyopathy and demonstrated its ability to validate the immunomodulatory activity of hCAM derived peptides. Further use of our approach should prove valuable in developing optimized, clinically applicable peptide cocktails to prevent the progression of myocarditis to dilated cardiomyopathy. [ABSTRACT FROM AUTHOR]

Background & Aims It is well-known that the liver can induce immune tolerance, yet this knowledge could, thus far, not be translated into effective treatments for autoimmune diseases. We have previously shown that liver sinusoidal endothelial cells (LSECs) could substantially contribute to hepatic tolerance through their ability to induce CD4+ Foxp3+ regulatory T cells (Tregs). Here, we explored whether the Treg-inducing potential of LSECs could be harnessed for the treatment of autoimmune disease. Methods We engineered a polymeric nanoparticle (NP) carrier for the selective delivery of autoantigen peptides to LSECs in vivo . In the well-characterized autoimmune disease model of experimental autoimmune encephalomyelitis (EAE), we investigated whether administration of LSEC-targeting autoantigen peptide-loaded NPs could protect mice from autoimmune disease. Results We demonstrate that NP-based autoantigen delivery to LSECs could completely and permanently prevent the onset of clinical EAE. More importantly, in a therapeutic approach, mice with already established EAE improved rapidly and substantially following administration of a single dose of autoantigen peptide-loaded NPs, whereas the control group deteriorated. Treatment efficacy seemed to depend on Tregs. The Treg frequencies in the spleens of mice treated with autoantigen peptide-loaded NPs were significantly higher than those in vehicle-treated mice. Moreover, NP-mediated disease control was abrogated after Treg depletion by repeated administration of Treg-depleting antibody. Conclusion Our findings provide proof of principle that the selective delivery of autoantigen peptides to LSECs by NPs can induce antigen-specific Tregs and enable effective treatment of autoimmune disease. These findings highlight the importance of Treg induction by LSECs for immune tolerance. [ABSTRACT FROM AUTHOR]

CD4+ CD25+ Foxp3+ regulatory T cells (Tregs) have a profound ability to control immune responses. We have previously shown that the liver is a major source of peripherally induced Tregs. Here, we investigate the liver cell types and molecular mechanisms responsible for hepatic Treg induction. Methods To assess the Treg-inducing potential of liver resident antigen-presenting cell types, we studied the conversion of Foxp3− non-Tregs into Foxp3+ Tregs induced by liver dendritic cells (DCs), liver sinusoidal endothelial cells (LSECs), or Kupffer cells (KCs). The dependency of Treg induction on TGF-β was tested in Treg conversion assays using T cells with reduced TGF-β sensitivity. The suppressive potential of liver cell-induced Tregs was assessed by an in vitro suppression assay and in vivo, in the model of experimental autoimmune encephalomyelitis (EAE). Results All tested liver cell types were capable of inducing Foxp3+ Tregs; however, LSECs were most efficient in inducing Tregs. Treg-induction was antigen-specific and depended on TGF-β. LSECs featured membrane-bound LAP/TGF-β and the anchor molecule GARP, which is required for tethering LAP/TGF-β to the cell membrane. LSEC-induced Tregs suppressed proliferation and cytokine secretion of effector T cells in vitro. LSEC-induced Tregs were also functional suppressors in vivo, as neuroantigen-specific Tregs induced by LSECs were able to suppress EAE. Conclusions We demonstrate that LSECs are the major liver cell type responsible for TGF-β dependent hepatic Treg induction. The extraordinary capacity of LSECs to induce Tregs was associated with their unique ability to tether TGF-β to their membrane. [ABSTRACT FROM AUTHOR]

In vitro induced Foxp3+ T regulatory (iTreg) cells form a novel and promising target for therapeutic tolerance induction. However, the potential of these cells as a target for the treatment of various immune diseases, as well as the factors involved in their development and function, remain debated. Here, we demonstrate in a myelin basic protein (MBP)-specific murine model of CNS autoimmune disease that adoptive transfer of antigen-specific iTreg cells ameliorates disease progression. Moreover, we show that the co-stimulatory molecule CTLA-4 mediates in vitro differentiation of iTreg cells. Finally, we demonstrate that the secreted, immunosuppressive cytokine IL-10 controls the ability of antigen-specific iTreg cells to suppress autoimmune disease. Overall, we conclude that antigen-specific iTreg cells, which depend on various immune regulatory molecules for their differentiation and function, represent a major target for effective immunotherapy of autoimmune disease. [ABSTRACT FROM AUTHOR]

T regulatory (Treg) cells expressing the transcription factor FoxP3 play a key role in protection against autoimmune disease. GFP-FoxP3 reporter mice have been used widely to study the induction, function and stability of both thymically- and peripherally-induced Treg cells. The N-terminal modification of FoxP3, however, affects its interaction with transcriptional co-factors; this can alter Treg cell development and function in certain self-antigen specific animal models. Interestingly, Treg cell function can be negatively or positively affected, depending on the nature of the model. In this study, we focused on the effect of the GFP-FoxP3 reporter on Treg cell development and function in the Tg4 mouse model. In this model, T cells express a transgenic T cell receptor (TCR) specific for the Myelin Basic Protein (MBP) peptide Ac1-9, making the animals susceptible to experimental autoimmune encephalomyelitis (EAE), a disease akin to multiple sclerosis in humans. Unlike diabetes-susceptible mice, Tg4 FoxP3gfp mice did not develop spontaneous autoimmune disease and did not demonstrate augmented susceptibility to induced disease. Concurrently, thymic generation of natural Treg cells was not negatively affected. The induction of FoxP3 expression in naive peripheral T cells was, however, significantly impaired as a result of the transgene. This study shows that the requirements for the interaction of FoxP3 with co-factors, which governs its regulatory ability, differ not only between natural and inducible Treg cells but also between animal models of diseases such as diabetes and EAE. [ABSTRACT FROM AUTHOR]

Today it is generally accepted that B cells require cognate interactions with CD4+ T cells to develop high-affinity antibodies against proteins. CD4+ T ceils recognize peptides (epitopes) presented by MHC class II molecules that are expressed on antigen-presenting cells. Structural features of both the MHC class II molecule and the peptide determine the specificity of CD4+ T cells that can bind to the MHC class ll-peptide complex. We used a new humanized hemophilic mouse model to identify FVIII peptides presented by HLA-DRB1*1501. This model carries a knockout of all murine MHC class II molecules and expresses a chimeric murine-human MHC class II complex that contains the peptide-binding sites of the human HLA-DRB1*1501. When mice were treated with human FVIII, the proportion of mice that developed antibodies depended on the application route of FVIII and the activation state of the innate immune system. We identified 8 FVIII peptide regions that contained CD4+ T-ceil epitopes presented by HLA-DRB1*1501 to CD4+ T cells during immune responses against FVIII. CD4+ T-cell responses after intravenous and subcutaneous application of FVIII involved the same immunodominant FVIII epitopes. Interestingly, most of the 8 peptide regions contained promiscuous epitopes that bound to several different HLA-DR proteins in in vitro binding assays. [ABSTRACT FROM AUTHOR]

Abstract: Recent studies have expanded our understanding of the role of the anti-inflammatory cytokine interleukin (IL)–10, produced by multiple lineages of both human and murine T cells, in regulating the immune response. Here, we demonstrate that the small percentage of circulating CD4+ T cells that secrete IL-10 can be isolated from human peripheral blood and, importantly, we have optimized a protocol to expand these cells in both antigen-specific and polyclonal manners. Expanded CD4+IL-10+ T cells abrogate proliferation and T helper (Th) 1–like cytokine production in an antigen-specific manner, and to a lesser extent exhibit bystander suppressive capacity. CD4+IL-10+ T cells are suppressive in a cell contact–dependent way, though they do not require secretion of IL-10 for their suppressive role in vitro. CD4+IL-10+ T cells have an activated phenotype, with high expression of CD25, CD69, and cytotoxic T-lymphocyte antigen-4, and are largely FoxP3 negative. This novel method for the isolation and expansion of suppressive IL-10–secreting T cells has important implications both for further research and clinical therapeutic development. [Copyright &y& Elsevier]

it is generally acknowledged that cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4/CD152) plays a pivotal role in the regulation of T-cell activation and the establishment of self-tolerance in the periphery. CTLA-4-deficient (CTLA-4KO) mice develop a lymphoproliferative disorder and die within 4 weeks of birth, suggesting a role for CTLA-4 in T-cell homeostasis or the development and activity of T-regulatory (Treg) cells. To study the role of CTLA-4 in the control of experimental autoimmune encephalomyelitis (EAE), we have generated a CTLA-4KO mouse in which >90% of all CD4+ cells bear a Vβ8.2 transgenic T-cell receptor that is specific for myelin basic protein peptide Ac1-9 (ASQKRPSQR). These mice do not develop spontaneous lymphoproliferative disease or EAE and are resistant to disease induction. This correlates with a higher frequency of functional FoxP3+ Treg cells in the spleen and thymus of CTLA-4KO mice. The absence of CTLA-4-mediated suppression of CD28 signaling resulted in the early expression of FoxP3 on double-positive cells in the thymic cortex. We conclude that CTLA-4 is not essential for the peripheral function of FoxP3+ Treg cells but plays a pivotal role in their thymic selection. [ABSTRACT FROM AUTHOR]

How T cell receptor (TCR) signal strength modulates T cell function and to what extent this is modified by immune checkpoint blockade (ICB) are key questions in immunology. Using Nr4a3 -Tocky mice, we characterized early quantitative and qualitative changes that occur in CD4+ T cells in relation to TCR signaling strength. We captured how dose- and time-dependent programming of distinct co-inhibitory receptors rapidly recalibrates T cell activation thresholds and visualized the immediate effects of ICB on T cell re-activation. Our findings reveal that anti-PD1 immunotherapy leads to an increased TCR signal strength. We defined a strong TCR signal metric of five genes upregulated by anti-PD1 in T cells (TCR.strong), which was superior to a canonical T cell activation gene signature in stratifying melanoma patient outcomes to anti-PD1 therapy. Our study therefore reveals how analysis of TCR signal strength—and its manipulation—can provide powerful metrics for monitoring outcomes to immunotherapy. [Display omitted] • TCR signal strength drives dynamic and time-dependent changes in CD4+ T cells • Inhibitory receptor expression recalibrates T cell activation thresholds • PD1 blockade leads to a strong TCR signal signature in T cells (TCR.strong) • TCR.strong can stratify melanoma patient responses to anti-PD1 therapy How antigen and immune checkpoint engagement regulate T cell function is not completely understood. Elliot et al. reveal how antigen abundance regulates immune checkpoint expression and recalibrates T cell activation thresholds. PD1 blockade lowers the T cell activation threshold, resulting in a transcriptional signature that stratifies responses to immunotherapy. [ABSTRACT FROM AUTHOR]

Tregs are important mediators of immune tolerance to self antigens, and it has been suggested that Treg inactivation may cause autoimmune disease. Therefore, immunotherapy approaches that aim to restore or expand autoantigen-specific Treg activity might be beneficial for the treatment of autoimmune disease. Here we report that Treg-mediated suppression of autoimmune disease can be achieved in vivo by taking advantage of the ability of the liver to promote immune tolerance. Expression of the neural autoantigen myelin basic protein (MBP) in the liver was accomplished stably in liver-specific MBP transgenic mice and transiently using gene transfer to liver cells in vivo. Such ectopic MBP expression induced protection from autoimmune neuroinflammation in a mouse model of multiple sclerosis. Protection from autoimmunity was mediated by MBP-specific CD4+CD25+Foxp3+ Tregs, as demonstrated by the ability of these cells to prevent disease when adoptively transferred into nontransgenic mice and to suppress conventional CD4+CD25- T cell proliferation after antigen-specific stimulation with MBP in vitro. The generation of MBP-specific CD4+CD25+Foxp3+ Tregs in vivo depended on expression of MBP in the liver, but not in skin, and occurred by TGF-beta-dependent peripheral conversion from conventional non-Tregs. Our findings indicate that autoantigen expression in the liver may generate autoantigen-specific Tregs. Thus, targeting of autoantigens to hepatocytes may be a novel approach to prevention or treatment of autoimmune diseases. [ABSTRACT FROM AUTHOR]

Experimental autoimmune encephalomyelitis (EAE) is a T cell-mediated autoimmune disease commonly employed as a model for multiple sclerosis. Extensive studies have demonstrated that EAE may be prevented or ameliorated by the intranasal administration of soluble peptides representing encephalitogenic epitopes. There is increasing evidence that this peptide administration may function via the generation of regulatory cells. The mechanism of action of these cells remains controversial and it seems likely that it may vary between experimental models. At present the majority of work on regulatory cells has centred on characterising naturally occurring regulators, or those generated artificially ex vivo, and less is known about induced regulatory cells produced following peptide administration. This report aims to briefly outline the evidence for the existence of natural regulatory T cells and to introduce the sub-types of induced regulatory T cells now recognised.In several of these regulatory cell systems investigated to date, interleukin-10 (IL-10) has been shown to be important in cell function. This has not been directly investigated in a model employing peptide therapy to induce peripheral tolerance, hence the purpose of this study was to investigate the role of IL-10 in the generation of these regulatory cells. This work has employed both a TCR transgenic mouse system, for predominantly in vitro studies of cell function, and an IL-10 knock-out mouse strain to investigate in vivo disease protection. The results summarised in this report demonstrate that IL-10 is fundamentally important in the generation of disease protection following intranasal peptide therapy. [Copyright &y& Elsevier]

NZB mice spontaneously develop autoimmune haemolytic anaemia (AIHA) due to a T helper-dependent autoantibody response against the erythrocyte anion channel protein, Band 3. Here, we characterize the recognition of the Band 3 sequence 861–874, which carries the dominant, I-Ed-restricted T cell epitope. The ability of N and C-terminal truncated versions of peptide 861–874 to elicit NZB splenic T-cell proliferation indicated that the core epitope spans residues 862–870. Next, a set of alanine substitution analogues was tested to determine which residues functioned either as MHC anchor or TCR contact residues. A combination of proliferation and MHC:peptide binding assays identified residues 862(L), 864(V), 865(L), and 869(K) as I-Ed anchor residues, and 868(V) as the only TCR contact residue. The ability of the wild-type sequence 861–874 to compete with a high affinity reference peptide for binding to I-Ed indicates that the escape of pathogenic NZB T cells from purging of the autoreactive repertoire cannot be attributed to ineffective presentation of peptide 861–874 by its restricting element. It will now be possible to design altered peptide ligands of Band 3 861–874, in order to further dissect the mechanisms responsible for the maintenance and loss of T cell tolerance to RBC autoantigens, and to modulate the immune response in AIHA. [Copyright &y& Elsevier]

The rules governing which T cells are inactivated during peptide-induced tolerance are unclear. Here we show that MBP(89?101) contains three overlapping but distinct T cell epitopes that are restricted by a single major histocompatibility complex (MHC) class II molecule. The dominant epitope is not processed from MBP and is not relevant to the induction of autoimmunity. Pathogenic T cells recognize two minor epitopes that are processed from MBP but are presented only poorly after exposure to MBP(89?101). Induction of immunological tolerance by MBP(89?101) therefore inactivates T cells that recognize the dominant epitope and disease-relevant T cells escape tolerance. The topology of the three epitopes implicates asparagine endopeptidase as the enzyme that controls recognition of this region of MBP. Our results highlight the need to use peptides that mimic the binding of processed antigen fragments to MHC molecules for successful modulation of disease-relevant T cells. [ABSTRACT FROM AUTHOR]

Little is known about the processing of putative human autoantigens and why tolerance is established to some T cell epitopes but not others. Here we show that a principal human HLA-DR2?restricted epitope?amino acids 85?99 of myelin basic protein, MBP(85?99)?contains a processing site for the cysteine protease asparagine endopeptidase (AEP). Presentation of this epitope by human antigen-presenting cells is inversely proportional to the amount of cellular AEP activity: inhibition of AEP in living cells greatly enhances presentation of the MBP(85?99) epitope, whereas overexpression of AEP diminishes presentation. These results indicate that central tolerance to this encephalitogenic MBP epitope may not be established because destructive processing limits its display in the thymus. Consistent with this hypothesis, AEP is expressed abundantly in thymic antigen-presenting cells. [ABSTRACT FROM AUTHOR]

Peripheral immune regulation is critical for the maintenance of self-tolerance. Here we have investigated signaling processes that distinguish T cells with regulatory capability from effector T cells. The murine Tg4 T cell receptor recognizes a peptide derived from the self-antigen myelin basic protein. T cells from Tg4 T cell receptor transgenic mice can be used to generate effector T cells and three types of T cells with regulatory capability, inducible regulatory T cells, T cells tolerized by repeated in vivo antigenic peptide exposure or T cells treated with the tolerogenic drug UCB9608 (a phosphatidylinositol 4 kinase IIIβ inhibitor). We comparatively studied signaling in all of these T cells by activating them with the same antigen presenting cells presenting the same myelin basic protein peptide. Supramolecular signaling structures, as efficiently detected by large-scale live cell imaging, are critical mediators of T cell activation. The formation of a supramolecular signaling complex anchored by the adaptor protein linker for activation of T cells (LAT) was consistently terminated more rapidly in Tg4 T cells with regulatory capability. Such termination could be partially reversed by blocking the inhibitory receptors CTLA-4 and PD-1. Our work suggests that attenuation of proximal signaling may favor regulatory over effector function in T cells. [ABSTRACT FROM AUTHOR]