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Progressive memory loss and cognitive dysfunction, encompassing deficits in learning, memory, problem solving, spatial reasoning, and verbal expression, are characteristics of Alzheimer's disease and related dementia. A wealth of studies has described multiple roles of the immune system in the development or exacerbation of dementia. Individuals with autoimmune disorders can also develop cognitive dysfunction, a phenomenon termed "autoimmune dementia." Together, these findings underscore the pivotal role of the neuroimmune axis in both Alzheimer's disease and related dementia and autoimmune dementia. The dynamic interplay between adaptive and innate immunity, both in and outside the brain, significantly affects the etiology and progression of these conditions. Multidisciplinary research shows that cognitive dysfunction arises from a bidirectional relationship between the nervous and immune systems, though the specific mechanisms that drive cognitive impairments are not fully understood. Intriguingly, this reciprocal regulation occurs at multiple levels, where neuronal signals can modulate immune responses, and immune system-related processes can influence neuronal viability and function. In this review, we consider the implications of autoimmune responses in various autoimmune disorders and Alzheimer's disease and explore their effects on brain function. We also discuss the diverse cellular and molecular crosstalk between the brain and the immune system, as they may shed light on potential triggers of peripheral inflammation, their effect on the integrity of the blood-brain barrier, and brain function. Additionally, we assess challenges and possibilities associated with developing immune-based therapies for the treatment of cognitive decline., Competing Interests: Conflict of interest statement. The authors declare no conflict of interest., (© The Author(s) 2024. Published by Oxford University Press on behalf of Society for Leukocyte Biology. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Regulatory T-cells (Tregs) can facilitate immune evasion by tumor cells by dampening anti-tumor immunity. Reduced Teff/Treg ratio and enhanced Treg functional activity have been observed in patients suffering from different types of cancers, and attenuated Treg numbers/functions can serve as prognostic indicators. Normally, Tregs play an essential role in the maintenance of immune tolerance and prevention of autoimmunity. The most common immune checkpoint blockers (ICB) targeting co-inhibitory receptors such as anti-CTLA4 (ipilimumab and tremelimumab) and anti-PD1 (pembrolizumab and nivolumab)/anti-PD-L1 (atezolizumab) have achieved unprecedented success in cancer treatment by facilitating an effective anti-tumor immune response, at least in part, by blocking Treg mediated immunosuppression. While ICBs have shown remarkable success in cancer immunotherapy, immune-related adverse events (IRAEs) arising from ICB have forced consideration of ways to maintain immune homeostasis post ICB treatment. Preclinical models of IRAEs have shown a negative correlation between Treg numbers and IRAEs. Therefore, understanding the "ying-yang" role of Tregs in the regulation of autoimmunity and anti-tumor immunity is critical to provoking an effective anti-tumor response while maintaining immune homeostasis. Studies aimed at developing effective approaches to minimize IRAEs without compromising anti-tumor immunity are underway. Herein, we discuss 1) the critical role of key co-inhibitory receptors on Treg homeostasis and tumor tolerance; 2) how co-receptor blockade by cancer immunotherapy can lead to autoimmune adverse events; and 3) recently emerging management strategies to minimize autoimmune adverse events arising from ICB., (Published by Elsevier Ltd.)

Self-tolerance, the state of unresponsiveness to self-tissues/antigens, is maintained through central and peripheral tolerance mechanisms, and a breach of these mechanisms leads to autoimmune diseases. Foxp3 + T-regulatory cells (Tregs) play an essential role in suppressing autoimmune response directed against self-antigens and thereby regulate self-tolerance. Natural Tregs are differentiated in the thymus on the basis of their higher TCR-affinity to self-antigens and migrate to the periphery where they maintain peripheral tolerance. In addition, extra-thymic differentiation of induced Tregs can occur in the periphery which can control abrupt immune responses under inflammatory conditions. A defect in Treg cell numbers and/or function is found to be associated with the development of autoimmune disease in several experimental models and human autoimmune diseases. Moreover, augmentation of Tregs has been shown to be beneficial in treating autoimmunity in preclinical models, and Treg based cellular therapy has shown initial promise in clinical trials. However, emerging studies have identified an unstable subpopulation of Tregs which expresses pro-inflammatory cytokines under both homeostatic and autoimmune conditions, as well as in ex vivo cultures. In addition, clinical translation of Treg cellular therapy is impeded by limitations such as lack of easier methods for selective expansion of Tregs and higher cost associated with GMP-facilities required for cell sorting, ex vivo expansion and infusion of ex vivo expanded Tregs. Here, we discuss the recent advances in molecular mechanisms regulating Treg differentiation, Foxp3 expression and lineage stability, the role of Tregs in the prevention of various autoimmune diseases, and critically review their clinical utility for treating human autoimmune diseases., (Copyright © 2018 Elsevier Inc. All rights reserved.)

GM-CSF was originally identified as a colony stimulating factor (CSF) because of its ability to induce granulocyte and macrophage populations from precursor cells. Multiple studies have demonstrated that GM-CSF is also an immune-modulatory cytokine, capable of affecting not only the phenotype of myeloid lineage cells, but also T-cell activation through various myeloid intermediaries. This property has been implicated in the sustenance of several autoimmune diseases like arthritis and multiple sclerosis. In contrast, several studies using animal models have shown that GM-CSF is also capable of suppressing many autoimmune diseases such as Crohn's disease, Type-1 diabetes, Myasthenia gravis and experimental autoimmune thyroiditis. Knockout mouse studies have suggested that the role of GM-CSF in maintaining granulocyte and macrophage populations in the physiological steady state is largely redundant. Instead, its immune-modulatory role plays a significant role in the development or resolution of autoimmune diseases. This is mediated either through the differentiation of precursor cells into specialized non-steady state granulocytes, macrophages and dendritic cells, or through the modulation of the phenotype of mature myeloid cells. Thus, outside of myelopoiesis, GM-CSF has a profound role in regulating the immune response and maintaining immunological tolerance., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Apoptosis or programmed cell death plays a central role in regulating not only the development of lymphocytes but also in their homeostasis. A breakdown in apoptosis related signaling mechanisms could result in the development of autoimmune disorders. The past decade has witnessed an explosive increase in knowledge with respect to various apoptotic signaling pathways and their aberrant behavior in autoimmune disorders. Although Fas/FasL mediated signaling appears to be a common paradigm that has emerged from studies in various autoimmune disorders, examples suggesting a role for other cell death pathways have also surfaced. Understanding the definitive role of apoptosis in various autoimmune disorders is likely to define novel targets for future therapeutic intervention.

Understanding autoimmune thyroid diseases provides an unique perspective on the role of various components of the immune system in the pathogenesis of organ specific autoimmune diseases, whether the effector mechanism involves autoantibodies or T cells. Hashimoto's thyroiditis (HT) is largely mediated by thyroglobulin specific T cells, while Graves' disease (GD) is mediated by thyrotropin receptor specific autoantibodies. HT is characterized by thyroid destruction mediated by infiltrating or activated resident immune cells through a variety of mechanisms. In contrast GD is characterized by excessive production of thyroid hormone with little or no glandular destruction. Irrespective of the effector mechanism involved, dendritic cells (DCs) are required for the induction of an efficient primary response and thus are the first cells involved in an autoimmune response. DCs also provide the essential link between the innate and the adaptive immune system through co-stimulatory molecules and the production of cytokines and chemokines. Furthermore, inflammatory cytokines also appear to enhance the susceptibility of thyrocytes to apoptosis. In this review, we discuss the role of innate immunity in initiating an adaptive autoimmune response against the thyroid. We will explore the role of different mechanisms involved in breaking self-tolerance to thyroid antigens. Further, we will discuss recent developments in the development of experimental therapeutics against AITD. [ABSTRACT FROM AUTHOR]

Multiple sclerosis is a T cell mediated chronic demyelinating disease of the central nervous system. Although currently available therapies reduce relapses, they do not facilitate tolerization of myelin antigen-specific T lymphocytes to ensure prolonged protection against multiple sclerosis. Here, we show that treatment of NOD mice with the histone deacetylase inhibitor, Trichostatin A affords robust protection against myelin peptide induced experimental autoimmune encephalomyelitis, a mouse model of multiple sclerosis. Protection was accompanied by histone hyperacetylation, and reduced inflammation and axonal damage in the spinal cord. Drug treatment diminished the generation of CD4 + memory T cells and induced tolerance in CD4 + T cells recognizing the immunizing myelin peptide. During the early immunization period, CD4 + T cells producing GM-CSF + IFN-γ, GM-CSF + IL-17A, as well as those expressing both IL-17A + IFN-γ (double-producers) were detected in the secondary lymphoid organs followed by the appearance of cells producing IFN-γ and GM-CSF. On the other hand, IFN-γ producing Th1 cells appear first in the spinal cord followed by cells producing IL-17A and GM-CSF. Treatment with Trichostatin A substantially reduced the frequencies of all T cells secreting various lymphokines both in the periphery and in the spinal cord. These data indicate that epigenetic modifications induced by histone hyperacetylation facilitates T cell tolerance induction in the periphery leading to reduced migration of T cells to the spinal cord and mitigation of neuronal damage and improved clinical outcome. These results suggest that epigenetic modulation of the genome may similarly offer benefits to multiple sclerosis patients via abrogating the function of encephalitogenic T lymphocytes without exerting severe side effects associated with currently used disease-modifying therapies. [ABSTRACT FROM AUTHOR]

Type-1 Diabetes (T1D) is the major autoimmune disease affecting the juvenile population in which insulin-producing pancreatic β-cells are destroyed by self-reactive T-cells and B-cells. Emerging studies have identified the presence of autoantibodies and altered T-cell reactivity against several autoantigens in individuals who are at risk of developing T1D even before the clinical onset of diabetes. Whilst these findings could lead to the development of predictive biomarkers for early diagnosis, growing evidence on the generation of neoepitopes, epitope spreading and diverse antigen repertoire in T1D poses a major challenge for developing approaches to induce antigen-specific tolerance. Mechanisms of neoepitope generation include post-translational modifications of existing epitopes, aberrant translational products, peptide fusion, and differences in MHC binding registers. Here, we focus our discussion on how post-translational modifications can give rise to immunogenic neoepitopes in T1D and present our perspective on how it could affect the development of therapeutic approaches to induce antigen-specific tolerance. • Post-translational modifications induced by oxidative and ER stress pathways contribute to neoepitope generation in T1D. • Post-translationally modified neoepitopes give rise to a highly diverse repertoire of diabetogenic epitopes. • The diverse nature of the neoepitopes poses a major challenge in developing antigen-specific tolerance in T1D. [ABSTRACT FROM AUTHOR]

Foxp3+T regulatory cells (Tregs) control autoimmune response by suppressing proliferation and effector functions of self-reactive Foxp3-CD4+/CD8+ T cells and thereby maintain the critical balance between self-tolerance and autoimmunity. Earlier, we had shown that OX40L-JAG1 cosignaling mediated through their cognate receptors OX40 and Notch3 preferentially expressed on murine Tregs can selectively induce their proliferation in the absence of TCR stimulation. However, the differential molecular mechanisms regulating TCR-independent versus TCR-dependent Treg proliferation and lineage stability of the expanded Tregs remained unknown. In this study, we show that OX40L-JAG1 treatment induced TCR-independent proliferation of Tregs in the thymus and periphery. The use of Src kinase inhibitor permitted us to demonstrate selective inhibition of TCR-dependent T cell proliferation with little to no effect on OX40L-JAG1--induced TCR-independent Treg expansion in vitro, which was critically dependent on noncanonical NF-κB signaling. OX40L-JAG1--expanded Tregs showed sustained lineage stability as indicated by stable demethylation marks in Treg signature genes such as Foxp3, Il2ra, Ctla4, Ikzf2, and Ikzf4. Furthermore, OX40L-JAG1 treatment significantly increased CTLA4+ and TIGIT+ Tregs and alleviated experimental autoimmune thyroiditis in mice. Relevance of our findings to humans became apparent when human OX40L and JAG1 induced TCR-independent selective expansion of human Tregs in thymocyte cultures and increased human Tregs in the liver tissue of humanized NSG mice. Our findings suggest that OX40L-JAG1--induced TCR-independent Treg proliferation is a conserved mechanism that can be used to expand lineage-stable Tregs to treat autoimmune diseases. [ABSTRACT FROM AUTHOR]

Myasthenia gravis (MG) is an autoimmune disorder caused by target-specific pathogenic antibodies directed toward postsynaptic neuromuscular junction (NMJ) proteins, most commonly the skeletal muscle nicotinic acetylcholine receptor (AChR). In MG, high-affinity anti-AChR Abs binding to the NMJ lead to loss of functional AChRs, culminating in neuromuscular transmission failure and myasthenic symptoms. Intravenous immune globulin (IVIg) has broad therapeutic application in the treatment of a range of autoimmune diseases, including MG, although its mechanism of action is not clear. Recently, the anti-inflammatory and anti-autoimmune activities of IVIg have been attributed to the IgG Fc domains. Soluble immune aggregates bearing intact Fc fragments have been shown to be effective treatment for a number of autoimmune disorders in mice, and fully recombinant multimeric Fc molecules have been shown to be effective in treating collagen-induced arthritis, murine immune thrombocytopenic purpura, and experimental inflammatory neuritis. In this study, a murine model of MG (EAMG) was used to study the effectiveness of this novel recombinant polyvalent IgG2a Fc (M045) in treating established myasthenia, with a direct comparison to treatment with IVIg. M045 treatment had profound effects on the clinical course of EAMG, accompanied by down-modulation of pathogenic antibody responses. These effects were associated with reduced B cell activation and T cell proliferative responses to AChR, an expansion in the population of FoxP3+ regulatory T cells, and enhanced production of suppressive cytokines, such as IL-10. Treatment was at least as effective as IVIg in suppressing EAMG, even at doses 25-30 fold lower. Multimeric Fc molecules offer the advantages of being recombinant, homogenous, available in unlimited quantity, free of risk from infection and effective at significantly reduced protein loads, and may represent a viable therapeutic alternative to polyclonal IVIg. [ABSTRACT FROM AUTHOR]