Protective and Regenerative Roles of T Cells in Central Nervous System Disorders

CD4+ T-cell subsets are associated with chronic stress effects in newly diagnosed anxiety disorders

Aim

Prior research has indicated a connection between CD4+ T cells and the development of anxiety, but the specific CD4+ T cell subsets linked to anxiety disorders remain uncertain. Our study seeks to investigate the relationship between distinct CD4+ T cell subsets and anxiety, as well as to explore whether CD4+ T cell subsets mediate the effect of chronic psychological stress on anxiety.

Methods

56 eligible matched participants were recruited in Peking Union Medical College Hospital. The diagnosis was made based on DSM-5 diagnostic criteria. The severity of anxiety and depression symptoms was assessed using the Hamilton Anxiety Rating Scale and Hamilton Depression Rating Scale, respectively. The Life Events Scale (LES) evaluated the chronic stress level. CD4+ T cell subsets were characterized using multiparametric flow cytometry. To assess the impact of CD4+ T cells on the effect of chronic psychological stress on anxiety, Partial Least Squares Structural Equation Modeling (PLS-SEM) analysis was employed.

Results

We discovered fifteen notably distinct CD4+ T-cell subsets in anxiety disorder patients compared to healthy controls. Multiple linear regression analysis unveiled an association between anxiety severity and CD27+CD45RA- Th cells, CD27+CD28+ Tregs, and the total Life Events Scale (LES) score. The PLS-SEM analysis demonstrated that CD4+ T cell subsets and LES could explain 80.2% of the variance in anxiety. Furthermore, it was observed that CD27+CD28+ Th/Treg cells acted as inverse mediators of the effects of LES on anxiety (P = 0.031).

Conclusions

Drug naïve anxiety disorder patients exhibited significant alterations in numerous CD4+ T-cell subsets. Specifically, the memory subset of CD27+CD45RA- Th cells and the naïve subset of CD27+CD28+ Treg cells were found to be independent factors associated with the severity of anxiety. Additionally, the CD27+CD28+ Th and Treg cell subsets played a significant mediating role in the influence of long-term psychological stress on anxiety.

The dynamic changes of peripheral blood cell counts predict the clinical outcomes of aneurysmal subarachnoid hemorrhage

Background

Aneurysmal subarachnoid hemorrhage (aSAH) is a serious type of hemorrhagic stroke. It is very important to predict the prognosis at early phase. In this work, we intend to characterize early changes in peripheral blood cells after aSAH and explore the association between peripheral blood cells and clinical outcomes after aSAH.

Methods

aSAH patients admitted between December 2019 and September 2022 were enrolled. A retrospective observational study was performed. Total leukocytes, monocytes, neutrophils, erythrocytes, lymphocytes and platelets counts were recorded on the day of admission (day 1), day 3, day 5 and day 7. Statistical tests included Chi-square test, analysis of variance and multivariate logistic regression (MLR) models. 197 patients were analyzed.

Results

Leukocytes and neutrophils were higher in poor outcome groups from day 1 to day 7 and in delayed cerebral ischemia (DCI) groups from day 3 to day 7. Lymphocytes were higher at day 5 and day 7 in good outcome groups and no DCI groups. Neutrophil-to-lymphocyte ratio (NLR) was lower from day 3 to day 7 in good outcome groups and no DCI groups. Erythrocytes were higher from day 3 to day 7 in good outcome groups and no DCI groups. Lymphocytes were negatively related to poor outcomes on day 1 (OR = 0.457), indicating higher lymphocytes predicted good outcomes, Neutrophils were positively related to poor outcomes on day 3 (OR = 3.003) indicating higher neutrophils predicted poor outcomes. Lymphocytes were negatively related to DCI on day 5 (OR = 0.388) indicating higher lymphocytes predicted no DCI, Erythrocytes were negatively related to DCI on day 5 (OR = 0.335) and day 7 (OR = 0.204) indicating higher erythrocytes predicted no DCI. The improved ability of neutrophils, lymphocytes and erythrocytes to predict DCI or poor functional outcomes were revealed by ROC curve analysis.

Conclusions

The dynamic changes of peripheral blood cell counts were related to poor functional outcomes and DCI after aSAH. Elevated neutrophils, leukocytes, NLR, and decreased lymphocytes, erythrocytes were accompanied by DCI and poor outcome. Neutrophils, lymphocytes and erythrocytes counts could be beneficial to predict DCI and outcomes after aSAH.

Towards early diagnosis of Alzheimer's disease: advances in immune-related blood biomarkers and computational approaches

Alzheimer's disease has an increasing prevalence in the population world-wide, yet current diagnostic methods based on recommended biomarkers are only available in specialized clinics. Due to these circumstances, Alzheimer's disease is usually diagnosed late, which contrasts with the currently available treatment options that are only effective for patients at an early stage. Blood-based biomarkers could fill in the gap of easily accessible and low-cost methods for early diagnosis of the disease. In particular, immune-based blood-biomarkers might be a promising option, given the recently discovered cross-talk of immune cells of the central nervous system with those in the peripheral immune system. Here, we give a background on recent advances in research on brain-immune system cross-talk in Alzheimer's disease and review machine learning approaches, which can combine multiple biomarkers with further information (e.g. age, sex, APOE genotype) into predictive models supporting an earlier diagnosis. In addition, mechanistic modeling approaches, such as agent-based modeling open the possibility to model and analyze cell dynamics over time. This review aims to provide an overview of the current state of immune-system related blood-based biomarkers and their potential for the early diagnosis of Alzheimer's disease.

A Potential Role of Interleukin-5 in the Pathogenesis and Progression of Amyotrophic Lateral Sclerosis: A New Molecular Perspective

Cumulative data suggest that neuroinflammation plays a prominent role in amyotrophic lateral sclerosis (ALS) pathogenesis. The purpose of this work was to assess if patients with ALS present a specific peripheral cytokine profile and if it correlates with neurological disability assessed by ALSFRS-R, the rate of disease progression, and the pattern of disease progression (horizontal spreading [HSP] versus vertical spreading [VSP]). We determined the levels of 15 cytokines in the blood of 59 patients with ALS and 40 controls. We identified a positive correlation between levels of pro-inflammatory cytokines (interleukin [IL]-17F, IL-33, IL-31) and the age of ALS patients, as well as a positive correlation between IL-12p/70 and survival from ALS onset and ALS diagnosis. Additionally, there was a positive correlation between the ALSFRS-R score in the upper limb and respiratory domain and IL-5 levels. In our ALS cohort, the spreading pattern was 42% horizontal and 58% vertical, with patients with VSP showing a faster rate of ALS progression. Furthermore, we identified a negative correlation between IL-5 levels and the rate of disease progression, as well as a positive correlation between IL-5 and HSP of ALS. To the best of our knowledge, this is the first study reporting a "protective" role of IL-5 in ALS.

Immune-cell-mediated tissue engineering strategies for peripheral nerve injury and regeneration

During the process of peripheral nerve repair, there are many complex pathological and physiological changes, including multi-cellular responses and various signaling molecules, and all these events establish a dynamic microenvironment for axon repair, regeneration, and target tissue/organ reinnervation. The immune system plays an indispensable role in the process of nerve repair and function recovery. An effective immune response not only involves innate-immune and adaptive-immune cells but also consists of chemokines and cytokines released by these immune cells. The elucidation of the orchestrated interplay of immune cells with nerve regeneration and functional restoration is meaningful for the exploration of therapeutic strategies. This review mainly enumerates the general immune cell response to peripheral nerve injury and focuses on their contributions to functional recovery. The tissue engineering-mediated strategies to regulate macrophages and T cells through physical and biochemical factors combined with scaffolds are discussed. The dynamic immune responses during peripheral nerve repair and immune-cell-mediated tissue engineering methods are presented, which provide a new insight and inspiration for immunomodulatory therapies in peripheral nerve regeneration.

CD4 T-cell aging exacerbates neuroinflammation in a late-onset mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is an adult-onset progressive neurodegenerative disorder characterized by the loss of upper and lower motor neurons in the brain and spinal cord. Accumulating evidence suggests that ALS is not solely a neuronal cell- or brain tissue-autonomous disease and that neuroinflammation plays a key role in disease progression. Furthermore, whereas both CD4 and CD8 T cells were observed in spinal cords of ALS patients and in mouse models of the disease, their role in the neuroinflammatory process, especially considering their functional changes with age, is not fully explored. In this study, we revealed the structure of the CD4 T-cell compartment during disease progression of early-onset SOD1G93A and late-onset SOD1G37R mouse models of ALS. We show age-related changes in the CD4 T-cell subset organization between these mutant SOD1 mouse models towards increased frequency of effector T cells in spleens of SOD1G37R mice and robust infiltration of CD4 T cells expressing activation markers and the checkpoint molecule PD1 into the spinal cord. The frequency of infiltrating CD4 T cells correlated with the frequency of infiltrating CD8 T cells which displayed a more exhausted phenotype. Moreover, RNA-Seq and immunohistochemistry analyses of spinal cords from SOD1G37R mice with early clinical symptoms demonstrated immunological trajectories reminiscent of a neurotoxic inflammatory response which involved proinflammatory T cells and antigen presentation related pathways. Overall, our findings suggest that age-related changes of the CD4 T cell landscape is indicative of a chronic inflammatory response, which aggravates the disease process and can be therapeutically targeted.

Immunological shifts during early-stage Parkinson's disease identified with DNA methylation data on longitudinally collected blood samples

Parkinson's disease (PD) is the second most common neurodegenerative disease in the United States. Decades before motor symptoms manifest, non-motor symptoms such as hyposmia and rapid eye movement (REM) sleep behavior disorder are highly predictive of PD. Previous immune profiling studies have identified alterations to the proportions of immune cells in the blood of clinically defined PD patients. However, it remains unclear if these phenotypes manifest before the clinical diagnosis of PD. We utilized longitudinal DNA methylation (DNAm) microarray data from the Parkinson's Progression Marker's Initiative (PPMI) to perform immune profiling in clinically defined PD and prodromal PD patients (Prod). We identified previously reported changes in neutrophil, monocyte, and T cell numbers in PD patients. Additionally, we noted previously unrecognized decreases in the naive B cell compartment in the defined PD and Prod patient group. Over time, we observed the proportion of innate immune cells in PD blood increased, but the proportion of adaptive immune cells decreased. We identified decreases in T and B cell subsets associated with REM sleep disturbances and early cognitive decline. Lastly, we identified increases in B memory cells associated with both genetic (LRRK2 genotype) and infectious (cytomegalovirus seropositivity) risk factors of PD. Our analysis shows that the peripheral immune system is dynamic as the disease progresses. The study provides a platform to understand how and when peripheral immune alterations occur in PD and whether intervention at particular stages may be therapeutically advantageous.

The association of blood biomarkers with cerebral white matter and myelin content in bipolar disorder: a systematic review

OBJECTIVES

Evidence from diffusion tensor imaging (DTI) and postmortem studies has demonstrated white-matter (WM) deficits in bipolar disorder (BD). Changes in peripheral blood biomarkers have also been observed; however, studies evaluating the potential relationship between brain alterations and the periphery are scarce. The objective of this systematic review is to investigate the relationship between blood-based biomarkers and WM in BD.

METHODS

PubMed, Embase, and PsycINFO were used to conduct literature searches. Cross-sectional or longitudinal studies reporting original data which investigated both a blood-based biomarker and WM (by neuroimaging) in BD were included.

RESULTS

Of 3,750 studies retrieved, 23 were included. Several classes of biomarkers were found to have a significant relationship with WM in BD. These included cytokines and growth factors (interleukin-8 [IL-8], tumor necrosis factor alpha [TNF-a], and insulin-like growth factor binding protein 3 [IGFBP-3]), innate immune system (natural killer cells [NK]), metabolic markers (lipid hydroperoxidase, cholesterol, triglycerides), the kynurenine (Kyn) pathway (5-hydroxyindoleacetic acid, kynurenic acid [Kyna]), and various gene polymorphisms (serotonin-transporter-linked promoter region).

CONCLUSION

This systematic review revealed that blood-based biomarkers are associated with markers of WM deficits observed in BD. Longitudinal studies investigating the potential clinical utility of these specific biomarkers are encouraged.

CD8+ T cells in brain injury and neurodegeneration

The interaction between the peripheral immune system and the brain is increasingly being recognized as an important layer of neuroimmune regulation and plays vital roles in brain homeostasis as well as neurological disorders. As an important population of T-cell lymphocytes, the roles of CD8+ T cells in infectious diseases and tumor immunity have been well established. Recently, increasing number of complex functions of CD8+ T cells in brain disorders have been revealed. However, an advanced summary and discussion of the functions and mechanisms of CD8+ T cells in brain injury and neurodegeneration are still lacking. Here, we described the differentiation and function of CD8+ T cells, reviewed the involvement of CD8+ T cells in the regulation of brain injury including stroke and traumatic brain injury and neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD), and discussed therapeutic prospects and future study goals. Understanding these processes will promote the investigation of T-cell immunity in brain disorders and provide new intervention strategies for the treatment of brain injury and neurodegeneration.

On the use of QDE-SVM for gene feature selection and cell type classification from scRNA-seq data

Cell type identification is one of the fundamental tasks in single-cell RNA sequencing (scRNA-seq) studies. It is a key step to facilitate downstream interpretations such as differential expression, trajectory inference, etc. scRNA-seq data contains technical variations that could affect the interpretation of the cell types. Therefore, gene selection, also known as feature selection in data science, plays an important role in selecting informative genes for scRNA-seq cell type identification. Generally speaking, feature selection methods are categorized into filter-, wrapper-, and embedded-based approaches. From the existing literature, methods from filter- and embedded-based approaches are widely applied in scRNA-seq gene selection tasks. The wrapper-based method that gives promising results in other fields has yet been extensively utilized for selecting gene features from scRNA-seq data; in addition, most of the existing wrapper methods used in this field are clustering instead of classification-based. With a large number of annotated data available today, this study applied a classification-based approach as an alternative to the clustering-based wrapper method. In our work, a quantum-inspired differential evolution (QDE) wrapped with a classification method was introduced to select a subset of genes from twelve well-known scRNA-seq transcriptomic datasets to identify cell types. In particular, the QDE was combined with different machine-learning (ML) classifiers namely logistic regression, decision tree, support vector machine (SVM) with linear and radial basis function kernels, as well as extreme learning machine. The linear SVM wrapped with QDE, namely QDE-SVM, was chosen by referring to the feature selection results from the experiment. QDE-SVM showed a superior cell type classification performance among QDE wrapping with other ML classifiers as well as the recent wrapper methods (i.e., FSCAM, SSD-LAHC, MA-HS, and BSF). QDE-SVM achieved an average accuracy of 0.9559, while the other wrapper methods achieved average accuracies in the range of 0.8292 to 0.8872.

Unconventional T cells in brain homeostasis, injury and neurodegeneration

The interaction between peripheral immune cells and the brain is an important component of the neuroimmune axis. Unconventional T cells, which include natural killer T (NKT) cells, mucosal-associated invariant T (MAIT) cells, γδ T cells, and other poorly defined subsets, are a special group of T lymphocytes that recognize a wide range of nonpolymorphic ligands and are the connection between adaptive and innate immunity. Recently, an increasing number of complex functions of these unconventional T cells in brain homeostasis and various brain disorders have been revealed. In this review, we describe the classification and effector function of unconventional T cells, review the evidence for the involvement of unconventional T cells in the regulation of brain homeostasis, summarize the roles and mechanisms of unconventional T cells in the regulation of brain injury and neurodegeneration, and discuss immunotherapeutic potential as well as future research goals. Insight of these processes can shed light on the regulation of T cell immunity on brain homeostasis and diseases and provide new clues for therapeutic approaches targeting brain injury and neurodegeneration.

T Lymphocytes and Their Potential Role in Dementia with Lewy Bodies

Dementia with Lewy bodies (DLB) is the second most common neurodegenerative cause of dementia. People with DLB have an inferior prognosis compared to Alzheimer's disease (AD), but the diseases overlap in their neuropathology and clinical syndrome. It is imperative that we enhance our understanding of the aetiology and pathogenesis of DLB. The impact of peripheral inflammation on the brain in dementia has been increasingly explored in recent years, with T lymphocyte recruitment into brain parenchyma identified in AD and Parkinson's disease. There is now a growing range of literature emerging on the potential role of innate and adaptive immune cells in DLB, including T lymphocytes. In this review, we examine the profile of T lymphocytes in DLB, focusing on studies of post-mortem brain tissue, cerebrospinal fluid, and the blood compartment. We present an integrated viewpoint on the results of these studies by proposing how changes to the T lymphocyte profile in the brain and periphery may relate to each other. Improving our understanding of T lymphocytes in DLB has the potential to guide the development of disease-modifying treatments.

CD8+ T cell depletion prevents neuropathology in a mouse model of globoid cell leukodystrophy

Globoid cell leukodystrophy (GLD) or Krabbe's disease is a fatal genetic demyelinating disease of the central nervous system caused by loss-of-function mutations in the galactosylceramidase (galc) gene. While the metabolic basis for disease is known, the understanding of how this results in neuropathology is not well understood. Herein, we report that the rapid and protracted elevation of CD8+ cytotoxic T lymphocytes occurs coincident with clinical disease in a mouse model of GLD. Administration of a function-blocking antibody against CD8α effectively prevented disease onset, reduced morbidity and mortality, and prevented CNS demyelination in mice. These data indicate that subsequent to the genetic cause of disease, neuropathology is driven by pathogenic CD8+ T cells, thus offering novel therapeutic potential for treatment of GLD.

The contribution of the peripheral immune system to neurodegeneration

Microglial cells are the major immune cells of the central nervous system (CNS), and directly react to neurodegeneration, but other immune cell types are also able to react to pathology and can modify the course of neurodegenerative processes. These mainly include monocytes/macrophages and lymphocytes. While these peripheral immune cells were initially considered to act only after infiltrating the CNS, recent evidence suggests that some of them can also act directly from the periphery. We will review the existing and emerging evidence for a role of peripheral immune cells in neurodegenerative diseases, both with and without CNS infiltration. Our focus will be on amyotrophic lateral sclerosis, but we will also compare to Alzheimer's disease and Parkinson's disease to highlight similarities or differences. Peripheral immune cells are easily accessible, and therefore may be an attractive therapeutic target for neurodegenerative diseases. Thus, understanding how these peripheral immune cells communicate with the CNS deserves deeper investigation.

Ovalbumin-specific CD4+ and CD8+ T cells contribute to different susceptibility for Theiler's murine encephalomyelitis virus persistence

Theiler's murine encephalomyelitis virus (TMEV) is the causative agent of TMEV-induced demyelinating disease (TMEV-IDD); a well-established animal model for the chronic progressive form of human multiple sclerosis (MS). In susceptible mice with an inadequate immune response, TMEV-IDD is triggered by virus persistence and maintained by a T cell mediated immunopathology. OT-mice are bred on a TMEV-resistant C57BL/6 background and own predominantly chicken ovalbumin (OVA)-specific populations of CD8⁺ T cells (OT-I) or CD4⁺ T cells (OT-II), respectively. It is hypothesized that the lack of antigen specific T cell populations increases susceptibility for a TMEV-infection in OT-mice on a TMEV-resistant C57BL/6 background. OT-I, OT-II, and C57BL/6 control mice were infected intracerebrally with the TMEV-BeAn strain. Mice were scored weekly for clinical disease and after necropsy, histological and immunohistochemical evaluation was performed. OT-I mice started to develop progressive motor dysfunction between 7 and 21 days post infection (dpi), leading up to hind limb paresis and critical weight loss, which resulted in euthanasia for humane reasons between 14 and 35 dpi. OT-I mice displayed a high cerebral virus load, an almost complete absence of CD8⁺ T cells from the central nervous system (CNS) and a significantly diminished CD4⁺ T cell response. Contrarily, only 60% (12 of 20) of infected OT-II mice developed clinical disease characterized by mild ataxia. 25% of clinically affected OT-II mice (3 of 12) made a full recovery. 5 of 12 OT-II mice with clinical disease developed severe motor dysfunction similar to OT-I mice and were euthanized for humane reasons between 13 and 37 dpi. OT-II mice displayed only low virus-immunoreactivity, but clinical disease correlated well with severely reduced infiltration of CD8⁺ T cells and the increased presence of CD4⁺ T cells in the brains of OT-II mice. Though further studies are needed to reveal the underlying pathomechanisms following TMEV infection in OT mice, findings indicate an immunopathological process as a main contributor to clinical disease in OT-II mice, while a direct virus-associated pathology may be the main contributor to clinical disease in TMEV-infected OT-I mice.

The adaptation model of immunity: A new insight into aetiology and treatment of multiple sclerosis

Current research and drug development for multiple sclerosis (MS) is fully influenced by the self-nonself (SNS) model of immunity, suggesting that breakage of immunological tolerance towards self-antigens expressed in the central nervous system (CNS) is responsible for pathogenesis of MS; thus, immune suppressive drugs are recommended for the management of the disease. However, this model provides incomplete understanding of the causes and pathways involved in the onset and progression of MS and limits our ability to effectively treat this neurological disease. Some pre-clinical and clinical reports have been misunderstood; some others have been underappreciated because of the lack of a theoretical model that can explain them. Also, current immunotherapies are guided according to the models that are not designed to explain the functional outcomes of an immune response. The adaptation model of immunity is proposed to offer a new understanding of the existing data and galvanize a new direction for the treatment of MS. According to this model, the immune system continuously communicates with the CNS through the adaptation receptors (AdRs) and adaptation ligands (AdLs) or co-receptors, signal IV, to support cell growth and neuroplasticity. Alterations in the expression of the neuronal AdRs results in MS by shifting the cerebral inflammatory immune responses from remyelination to demyelination. Therefore, novel therapeutics for MS should be focused on the discovery and targeting of the AdR/AdL axis in the CNS rather than carrying on with immune suppressive interventions.

N-acetylneuraminic acid links immune exhaustion and accelerated memory deficit in diet-induced obese Alzheimer's disease mouse model

Systemic immunity supports lifelong brain function. Obesity posits a chronic burden on systemic immunity. Independently, obesity was shown as a risk factor for Alzheimer's disease (AD). Here we show that high-fat obesogenic diet accelerated recognition-memory impairment in an AD mouse model (5xFAD). In obese 5xFAD mice, hippocampal cells displayed only minor diet-related transcriptional changes, whereas the splenic immune landscape exhibited aging-like CD4+ T-cell deregulation. Following plasma metabolite profiling, we identified free N-acetylneuraminic acid (NANA), the predominant sialic acid, as the metabolite linking recognition-memory impairment to increased splenic immune-suppressive cells in mice. Single-nucleus RNA-sequencing revealed mouse visceral adipose macrophages as a potential source of NANA. In vitro, NANA reduced CD4+ T-cell proliferation, tested in both mouse and human. In vivo, NANA administration to standard diet-fed mice recapitulated high-fat diet effects on CD4+ T cells and accelerated recognition-memory impairment in 5xFAD mice. We suggest that obesity accelerates disease manifestation in a mouse model of AD via systemic immune exhaustion.

The role of T cells in acute ischemic stroke

Acute ischemic stroke (AIS) is associated with high rates of disability and mortality, exerting a substantial impact on overall survival and health-related quality of life. Treatment of AIS remains challenging given that the underlying pathologic mechanisms remain unclear. However, recent research has demonstrated that the immune system plays a key role in the development of AIS. Numerous studies have reported infiltration of T cells into ischemic brain tissue. While some types of T cells can promote the development of inflammatory responses and aggravate ischemic damage in patients with AIS, other T cells appear to exert neuroprotective effects via immunosuppression and other mechanisms. In this review, we discuss the recent findings regarding the infiltration of T cells into ischemic brain tissue, and the mechanisms governing how T cells can facilitate tissue injury or neuroprotection in AIS. Factors influencing the function of T cells, such as intestinal microflora and sex differences, are also discussed. We also explore the recent research on the effect of non-coding RNA on T cells after stroke, as well as the potential for specifically targeting T cells in the treatment of stroke patients.

Modulating neuroinflammation through molecular, cellular and biomaterial-based approaches to treat spinal cord injury

The neuroinflammatory response that is elicited after spinal cord injury contributes to both tissue damage and reparative processes. The complex and dynamic cellular and molecular changes within the spinal cord microenvironment result in a functional imbalance of immune cells and their modulatory factors. To facilitate wound healing and repair, it is necessary to manipulate the immunological pathways during neuroinflammation to achieve successful therapeutic interventions. In this review, recent advancements and fresh perspectives on the consequences of neuroinflammation after SCI and modulation of the inflammatory responses through the use of molecular-, cellular-, and biomaterial-based therapies to promote tissue regeneration and functional recovery will be discussed.

The Role of T Cells in Alzheimer's Disease Pathogenesis

Alzheimer's disease (AD) is a progressive neurodegenerative disorder associated with memory decline and cognitive impairment, which is related to hallmark protein aggregates, amyloid-β (Аβ) plaques and neurofibrillary tangles; the latter are accumulated with hyperphosphorylated Tau protein. Immune cells play an important role in AD pathogenesis. Although the role of T cells in AD remains controversial, studies have shown that T cell deficiency is associated with increased AD pathology. In contrast, transplantation of T cells reduces AD pathology. T cells can help B cells generate anti-Аβ antibody to neutralize the toxin of Аβ and hyperphosphorylated Tau. T cells also activate macrophages to phagocytose misfolded proteins including Аβ and Tau. Recent data have also shown that AD animals have a damaged thymic microenvironment, especially thymic epithelial cells (TECs), resulting in decreased T cell numbers, which contribute to AD pathology. Therefore, regulation of T cell regeneration, for example by rejuvenating the thymic microenvironment, has the potential to be used in the treatment of AD.

Glia as antigen-presenting cells in the central nervous system

The contribution of the cells within the central nervous system (CNS) toward adaptive immune responses is emerging and incompletely understood. Recent findings indicate important functional interactions between T-cells and glial cells within the CNS that may contribute to disease and neuropathology through antigen presentation. Although glia are not classically considered antigen-presenting cell (APC) types, there is growing evidence indicating that glial antigen presentation plays an important role in several neurological diseases. This review discusses these findings which incriminate microglia, astrocytes, and oligodendrocyte lineage cells as CNS-resident APC types with implications for understanding disease.

TRPV4 mRNA is elevated in the caudate nucleus with NPH but not in Alzheimer's disease

Symptoms of normal pressure hydrocephalus (NPH) and Alzheimer's disease (AD) are somewhat similar, and it is common to misdiagnose these two conditions. Although there are fluid markers detectable in humans with NPH and AD, determining which biomarker is optimal in representing genetic characteristics consistent throughout species is poorly understood. Here, we hypothesize that NPH can be differentiated from AD with mRNA biomarkers of unvaried proximity to telomeres. We examined human caudate nucleus tissue samples for the expression of transient receptor potential cation channel subfamily V member 4 (TRPV4) and amyloid precursor protein (APP). Using the genome data viewer, we analyzed the mutability of TRPV4 and other genes in mice, rats, and humans through matching nucleotides of six genes of interest and one house keeping gene with two factors associated with high mutation rate: 1) proximity to telomeres or 2) high adenine and thymine (A + T) content. We found that TRPV4 and microtubule associated protein tau (MAPT) mRNA were elevated in NPH. In AD, mRNA expression of TRPV4 was unaltered unlike APP and other genes. In mice, rats, and humans, the nucleotide size of TRPV4 did not vary, while in other genes, the sizes were inconsistent. Proximity to telomeres in TRPV4 was <50 Mb across species. Our analyses reveal that TRPV4 gene size and mutability are conserved across three species, suggesting that TRPV4 can be a potential link in the pathophysiology of chronic hydrocephalus in aged humans (>65 years) and laboratory rodents at comparable ages.

Genetic variants associated with psychiatric disorders are enriched at epigenetically active sites in lymphoid cells

Multiple psychiatric disorders have been associated with abnormalities in both the innate and adaptive immune systems. The role of these abnormalities in pathogenesis, and whether they are driven by psychiatric risk variants, remains unclear. We test for enrichment of GWAS variants associated with multiple psychiatric disorders (cross-disorder or trans-diagnostic risk), or 5 specific disorders (cis-diagnostic risk), in regulatory elements in immune cells. We use three independent epigenetic datasets representing multiple organ systems and immune cell subsets. Trans-diagnostic and cis-diagnostic risk variants (for schizophrenia and depression) are enriched at epigenetically active sites in brain tissues and in lymphoid cells, especially stimulated CD4⁺ T cells. There is no evidence for enrichment of either trans-risk or cis-risk variants for schizophrenia or depression in myeloid cells. This suggests a possible model where environmental stimuli activate T cells to unmask the effects of psychiatric risk variants, contributing to the pathogenesis of mental health disorders.

Neuro faces of beneficial T cells: essential in brain, impaired in aging and neurological diseases, and activated functionally by neurotransmitters and neuropeptides

T cells are essential for a healthy life, performing continuously: immune surveillance, recognition, protection, activation, suppression, assistance, eradication, secretion, adhesion, migration, homing, communications, and additional tasks. This paper describes five aspects of normal beneficial T cells in the healthy or diseased brain. First, normal beneficial T cells are essential for normal healthy brain functions: cognition, spatial learning, memory, adult neurogenesis, and neuroprotection. T cells decrease secondary neuronal degeneration, increase neuronal survival after central nervous system (CNS) injury, and limit CNS inflammation and damage upon injury and infection. Second, while pathogenic T cells contribute to CNS disorders, recent studies, mostly in animal models, show that specific subpopulations of normal beneficial T cells have protective and regenerative effects in several neuroinflammatory and neurodegenerative diseases. These include Multiple Sclerosis (MS), Alzheimer's disease, Parkinson's disease, Amyotrophic Lateral Sclerosis (ALS), stroke, CNS trauma, chronic pain, and others. Both T cell-secreted molecules and direct cell-cell contacts deliver T cell neuroprotective, neuroregenerative and immunomodulatory effects. Third, normal beneficial T cells are abnormal, impaired, and dysfunctional in aging and multiple neurological diseases. Different T cell impairments are evident in aging, brain tumors (mainly Glioblastoma), severe viral infections (including COVID-19), chronic stress, major depression, schizophrenia, Parkinson's disease, Alzheimer's disease, ALS, MS, stroke, and other neuro-pathologies. The main detrimental mechanisms that impair T cell function are activation-induced cell death, exhaustion, senescence, and impaired T cell stemness. Fourth, several physiological neurotransmitters and neuropeptides induce by themselves multiple direct, potent, beneficial, and therapeutically-relevant effects on normal human T cells, via their receptors in T cells. This scientific field is called "Nerve-Driven Immunity". The main neurotransmitters and neuropeptides that induce directly activating and beneficial effects on naïve normal human T cells are: dopamine, glutamate, GnRH-II, neuropeptide Y, calcitonin gene-related peptide, and somatostatin. Fifth, "Personalized Adoptive Neuro-Immunotherapy". This is a novel unique cellular immunotherapy, based on the "Nerve-Driven Immunity" findings, which was recently designed and patented for safe and repeated rejuvenation, activation, and improvement of impaired and dysfunctional T cells of any person in need, by ex vivo exposure of the person's T cells to neurotransmitters and neuropeptides. Personalized adoptive neuro-immunotherapy includes an early ex vivo personalized diagnosis, and subsequent ex vivo → in vivo personalized adoptive therapy, tailored according to the diagnosis. The Personalized Adoptive Neuro-Immunotherapy has not yet been tested in humans, pending validation of safety and efficacy in clinical trials, especially in brain tumors, chronic infectious diseases, and aging, in which T cells are exhausted and/or senescent and dysfunctional.

The effects and potential of microglial polarization and crosstalk with other cells of the central nervous system in the treatment of Alzheimer's disease

Microglia are resident immune cells in the central nervous system. During the pathogenesis of Alzheimer's disease, stimulatory factors continuously act on the microglia causing abnormal activation and unbalanced phenotypic changes; these events have become a significant and promising area of research. In this review, we summarize the effects of microglial polarization and crosstalk with other cells in the central nervous system in the treatment of Alzheimer's disease. Our literature search found that phenotypic changes occur continuously in Alzheimer's disease and that microglia exhibit extensive crosstalk with astrocytes, oligodendrocytes, neurons, and penetrated peripheral innate immune cells via specific signaling pathways and cytokines. Collectively, unlike previous efforts to modulate microglial phenotypes at a single level, targeting the phenotypes of microglia and the crosstalk with other cells in the central nervous system may be more effective in reducing inflammation in the central nervous system in Alzheimer's disease. This would establish a theoretical basis for reducing neuronal death from central nervous system inflammation and provide an appropriate environment to promote neuronal regeneration in the treatment of Alzheimer's disease.

Experimental and Clinical Biomarkers for Progressive Evaluation of Neuropathology and Therapeutic Interventions for Acute and Chronic Neurological Disorders

This article describes commonly used experimental and clinical biomarkers of neuronal injury and neurodegeneration for the evaluation of neuropathology and monitoring of therapeutic interventions. Biomarkers are vital for diagnostics of brain disease and therapeutic monitoring. A biomarker can be objectively measured and evaluated as a proxy indicator for the pathophysiological process or response to therapeutic interventions. There are complex hurdles in understanding the molecular pathophysiology of neurological disorders and the ability to diagnose them at initial stages. Novel biomarkers for neurological diseases may surpass these issues, especially for early identification of disease risk. Validated biomarkers can measure the severity and progression of both acute neuronal injury and chronic neurological diseases such as epilepsy, migraine, Alzheimer's disease, Parkinson's disease, Huntington's disease, traumatic brain injury, amyotrophic lateral sclerosis, multiple sclerosis, and other brain diseases. Biomarkers are deployed to study progression and response to treatment, including noninvasive imaging tools for both acute and chronic brain conditions. Neuronal biomarkers are classified into four core subtypes: blood-based, immunohistochemical-based, neuroimaging-based, and electrophysiological biomarkers. Neuronal conditions have progressive stages, such as acute injury, inflammation, neurodegeneration, and neurogenesis, which can serve as indices of pathological status. Biomarkers are critical for the targeted identification of specific molecules, cells, tissues, or proteins that dramatically alter throughout the progression of brain conditions. There has been tremendous progress with biomarkers in acute conditions and chronic diseases affecting the central nervous system.

The P522R protective variant of PLCG2 promotes the expression of antigen presentation genes by human microglia in an Alzheimer's disease mouse model

The P522R variant of PLCG2, expressed by microglia, is associated with reduced risk of Alzheimer's disease (AD). Yet, the impact of this protective mutation on microglial responses to AD pathology remains unknown. Chimeric AD and wild-type mice were generated by transplanting PLCG2-P522R or isogenic wild-type human induced pluripotent stem cell microglia. At 7 months of age, single-cell and bulk RNA sequencing, and histological analyses were performed. The PLCG2-P522R variant induced a significant increase in microglial human leukocyte antigen (HLA) expression and the induction of antigen presentation, chemokine signaling, and T cell proliferation pathways. Examination of immune-intact AD mice further demonstrated that the PLCG2-P522R variant promotes the recruitment of CD8+ T cells to the brain. These data provide the first evidence that the PLCG2-P522R variant increases the capacity of microglia to recruit T cells and present antigens, promoting a microglial transcriptional state that has recently been shown to be reduced in AD patient brains.

Effects of biological sex mismatch on neural progenitor cell transplantation for spinal cord injury in mice

Despite advancement of neural progenitor cell transplantation to spinal cord injury clinical trials, there remains a lack of understanding of how biological sex of transplanted cells influences outcomes after transplantation. To address this, we transplanted GFP-expressing sex-matched, sex-mismatched, or mixed donor cells into sites of spinal cord injury in adult male and female mice. Biological sex of the donor cells does not influence graft neuron density, glial differentiation, formation of the reactive glial cell border, or graft axon outgrowth. However, male grafts in female hosts feature extensive hypervascularization accompanied by increased vascular diameter and perivascular cell density. We show greater T-cell infiltration within male-to-female grafts than other graft types. Together, these findings indicate a biological sex-specific immune response of female mice to male donor cells. Our work suggests that biological sex should be considered in the design of future clinical trials for cell transplantation in human injury.

In this study, Pitonak et al. report that transplantation of neural progenitor cells derived from male donors trigger an immune rejection response following transplantation into sites of spinal cord injury in female mice.

An opinion on the debatable function of brain resident immune protein, T-cell receptor beta subunit in the central nervous system

In recent years scientific research has established that the nervous and immune systems have shared molecular signaling components. Proteins native to immune cells, which are also found in the brain, have neuronal functions in the nervous system where they affect synaptic plasticity, axonal regeneration, neurogenesis, and neurotransmission. Certain native immune molecules like major histocompatibility complex I (MHC-I), paired immunoglobulin receptor B (PirB), toll-like receptor (TLR), cluster of differentiation-3 zeta (CD3ζ), CD4 co-receptor, and T-cell receptor beta (TCR-β) expression in neurons have been extensively documented. In this review, we provide our opinion and discussed the possible roles of T-cell receptor beta subunits in modulating the function of neurons in the central nervous system. Based on the previous findings of Syken and Shatz., 2003; Nishiyori et al., 2004; Rodriguez et., 1993 and Komal et., 2014; we discuss whether restrictive expression of TCR-β subunits in selected brain regions could be involved in the pathology of neurological disorders and whether their aberrant enhancement in expression may be considered as a suitable biomarker for aging or neurodegenerative diseases like Huntington's disease (HD).

Regenerative Role of T Cells in Nerve Repair and Functional Recovery

The immune system is essential in the process of nerve repair after injury. Successful modulation of the immune response is regarded as an effective approach to improving treatment outcomes. T cells play an important role in the immune response of the nervous system, and their beneficial roles in promoting regeneration have been increasingly recognized. However, the diversity of T-cell subsets also delivers both neuroprotective and neurodegenerative functions. Therefore, this review mainly discusses the beneficial impact of T-cell subsets in the repair of both peripheral nervous system and central nervous system injuries and introduces studies on various therapies based on T-cell regulation. Further discoveries in T-cell mechanisms and multifunctional biomaterials will provide novel strategies for nerve regeneration.

Calpain activation and progression of inflammatory cycles in Parkinson's disease

Parkinson's disease (PD) is a progressive, neurodegenerative condition of the central nervous system (CNS) affecting 6.3 million people worldwide with no curative treatments. Current therapies aim to mitigate PD's effects and offer symptomatic relief for patients. Multiple pathways are involved in the pathogenesis of PD, leading to neuroinflammation and the destruction of dopaminergic neurons in the CNS. This review focuses on PD pathology and the role of calpain, a neutral protease, as a regulator of various immune cells such as T-cells, microglia and astrocytes which lead to persistent neuroinflammatory responses and neuronal loss in both the brain and spinal cord (SC). Calpain plays a significant role in the cleavage and aggregation of toxic α-synuclein (α-syn), a presynaptic neural protein, and other organelles, contributing to mitochondrial dysfunction and oxidative stress. α-Syn aggregation results in the formation of Lewy bodies (LB) that further contribute to neuronal damage through lipid bilayer penetration, calcium ion (Ca2+) influx, oxidative stress and damage to the blood brain barrier (BBB). Dysfunctional mitochondria destabilize cytosolic Ca2+ concentrations, raising intracellular Ca2+; this leads to excessive calpain activation and persistent inflammatory responses. α-Syn aggregation also results in the disruption of dopamine synthesis through phosphorylation of tyrosine hydroxylase (TH), a key enzyme involved in the conversion of tyrosine to levodopa (L-DOPA), the amino acid precursor to dopamine. Decreased dopamine levels result in altered dopamine receptor (DR) signaling, ultimately activating pro-inflammatory T-cells to further contribute to the inflammatory response. All of these processes, together, result in neuroinflammation, degeneration and ultimately neuronal death seen in PD. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP-a prodrug to the neurotoxin 1-methyl-4-phenylpyridinium (MPP+)), rotenone (an environmental neurotoxin), and 6-hydroxydopamine (6-OHDA - a neurotoxic synthetic organic compound) induce PD-like conditions when injected into rodents. All three agents work through similar mechanisms and lead to degeneration of dopaminergic neurons in the substantia nigra (SN) and more recently discovered in motor neurons of the spinal cord (SC). These neurotoxins also increase calpain activity, furthering the neuroinflammatory response. Hence, calpain inhibitors have been posited as potential therapeutics for PD to prevent calpain-related inflammation and neurodegenerative responses in not only the SN but the SC as well.

Autoimmune Epilepsy - Novel Multidisciplinary Analysis, Discoveries and Insights

Epilepsy affects ~50 million people. In ~30% of patients the etiology is unknown, and ~30% are unresponsive to anti-epileptic drugs. Intractable epilepsy often leads to multiple seizures daily or weekly, lasting for years, and accompanied by cognitive, behavioral, and psychiatric problems. This multidisciplinary scientific (not clinical) 'Perspective' article discusses Autoimmune Epilepsy from immunological, neurological and basic-science angles. The article includes summaries and novel discoveries, ideas, insights and recommendations. We summarize the characteristic features of the respective antigens, and the pathological activity in vitro and in animal models of autoimmune antibodies to: Glutamate/AMPA-GluR3, Glutamate/NMDA-NR1, Glutamate/NMDA-NR2, GAD-65, GABA-R, GLY-R, VGKC, LGI1, CASPR2, and β2 GP1, found in subpopulations of epilepsy patients. Glutamate receptor antibodies: AMPA-GluR3B peptide antibodies, seem so far as the most exclusive and pathogenic autoimmune antibodies in Autoimmune Epilepsy. They kill neural cells by three mechanisms: excitotoxicity, Reactive-Oxygen-Species, and complement-fixation, and induce and/or facilitate brain damage, seizures, and behavioral impairments. In this article we raise and discuss many more topics and new insights related to Autoimmune Epilepsy. 1. Few autoimmune antibodies tilt the balance between excitatory Glutamate and inhibitory GABA, thereby promoting neuropathology and epilepsy; 2. Many autoantigens are synaptic, and have extracellular domains. These features increase the likelihood of autoimmunity against them, and the ease with which autoimmune antibodies can reach and harm these self-proteins. 3. Several autoantigens have 'frenetic character'- undergoing dynamic changes that can increase their antigenicity; 4. The mRNAs of the autoantigens are widely expressed in multiple organs outside the brain. If translated by default to proteins, broad spectrum detrimental autoimmunity is expected; 5. The autoimmunity can precede seizures, cause them, and be detrimental whether primary or epiphenomenon; 6. Some autoimmune antibodies induce, and associate with, cognitive, behavioral and psychiatric impairments; 7. There are evidences for epitope spreading in Autoimmune Epilepsy; 8. T cells have different 'faces' in the brain, and in Autoimmune Epilepsy: Normal T cells are needed for the healthy brain. Normal T cells are damaged by autoimmune antibodies to Glutamate/AMPA GluR3, which they express, and maybe by additional autoantibodies to: Dopamine-R, GABA-R, Ach-R, Serotonin-R, and Adrenergic-R, present in various neurological diseases (summarized herein), since T cells express all these Neurotransmitter receptors. However, autoimmune and/or cytotoxic T cells damage the brain; 9. The HLA molecules are important for normal brain function. The HLA haplotype can confer susceptibility or protection from Autoimmune Epilepsy; 10. There are several therapeutic strategies for Autoimmune Epilepsy.

Engineered cells as glioblastoma therapeutics

In spite of significant recent advances in our understanding of the genetics and cell biology of glioblastoma, to date, this has not led to improved treatments for this cancer. In addition to small molecule, antibody, and engineered virus approaches, engineered cells are also being explored as glioblastoma therapeutics. This includes CAR-T cells, CAR-NK cells, as well as engineered neural stem cells and mesenchymal stem cells. Here we review the state of this field, starting with clinical trial studies. These have established the feasibility and safety of engineered cell therapies for glioblastoma and show some evidence for activity. Next, we review the preclinical literature and compare the strengths and weaknesses of various starting cell types for engineered cell therapies. Finally, we discuss future directions for this nascent but promising modality for glioblastoma therapy.

T cells in the brain inflammation

The immune system is deeply involved in autoimmune diseases of the central nervous system (CNS), such as multiple sclerosis, N-methyl-d-aspartate (NMDA) receptor encephalitis, and narcolepsy. Additionally, the immune system is involved in various brain diseases including cerebral infarction and neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). In particular, reports related to T cells are increasing. T cells may also play important roles in brain deterioration and dementia that occur with aging. Our understanding of the role of immune cells in the context of the brain has been greatly improved by the use of acute ischemic brain injury models. Additionally, similar neural damage and repair events are shown to occur in more chronic brain neurodegenerative brain diseases. In this review, we focus on the role of T cells, including CD4⁺ T cells, CD8⁺ T cells and regulatory T cells (Tregs) in cerebral infarction and neurodegenerative diseases.

Immune system challenge improves recognition memory and reverses malaria-induced cognitive impairment in mice

The immune system plays a role in the maintenance of healthy neurocognitive function. Different patterns of immune response triggered by distinct stimuli may affect nervous functions through regulatory or deregulatory signals, depending on the properties of the exogenous immunogens. Here, we investigate the effect of immune stimulation on cognitive-behavioural parameters in healthy mice and its impact on cognitive sequelae resulting from non-severe experimental malaria. We show that immune modulation induced by a specific combination of immune stimuli that induce a type 2 immune response can enhance long-term recognition memory in healthy adult mice subjected to novel object recognition task (NORT) and reverse a lack of recognition ability in NORT and anxiety-like behaviour in a light/dark task that result from a single episode of mild Plasmodium berghei ANKA malaria. Our findings suggest a potential use of immunogens for boosting and recovering recognition memory that may be impaired by chronic and infectious diseases and by the effects of ageing.

Herpesviruses and the hidden links to Multiple Sclerosis neuropathology

Herpesviruses like Epstein-Barr virus, human herpesvirus (HHV)-6, HHV-1, VZV, and human endogenous retroviruses, have an age-old clinical association with multiple sclerosis (MS). MS is an autoimmune disease of the nervous system wherein the myelin sheath deteriorates. The most popular mode of virus mediated immune system manipulation is molecular mimicry. Numerous herpesvirus antigens are similar to myelin proteins. Other mechanisms described here include the activity of cytokines and autoantibodies produced by the autoreactive T and B cells, respectively, viral déjà vu, epitope spreading, CD46 receptor engagement, impaired remyelination etc. Overall, this review addresses the host-parasite association of viruses with MS.

The Role of the Blood Neutrophil-to-Lymphocyte Ratio in Aneurysmal Subarachnoid Hemorrhage

Aneurysmal subarachnoid hemorrhage (aSAH) is an important type of stroke with the highest rates of mortality and disability. Recent evidence indicates that neuroinflammation plays a critical role in both early brain injury and delayed neural deterioration after aSAH, contributing to unfavorable outcomes. The neutrophil-to-lymphocyte ratio (NLR) is a peripheral biomarker that conveys information about the inflammatory burden in terms of both innate and adaptive immunity. This review summarizes relevant studies that associate the NLR with aSAH to evaluate whether the NLR can predict outcomes and serve as an effective biomarker for clinical management. We found that increased NLR is valuable in predicting the clinical outcome of aSAH patients and is related to the risk of complications such as delayed cerebral ischemia (DCI) or rebleeding. Combined with other indicators, the NLR provides improved accuracy for predicting prognosis to stratify patients into different risk categories. The underlying pathophysiology is highlighted to identify new potential targets for neuroprotection and to develop novel therapeutic strategies.

In Vivo T Cell-Targeting Nanoparticle Drug Delivery Systems: Considerations for Rational Design

T cells play an important role in immunity and repair and are implicated in diseases, including blood cancers, viral infections, and inflammation, making them attractive targets for the treatment and prevention of diseases. Over recent years, the advent of nanomedicine has shown an increase in studies that use nanoparticles as carriers to deliver therapeutic cargo to T cells for ex vivo and in vivo applications. Nanoparticle-based delivery has several advantages, including the ability to load and protect a variety of drugs, control drug release, improve drug pharmacokinetics and biodistribution, and site- or cell-specific targeting. However, the delivery of nanoparticles to T cells remains a major technological challenge, which is primarily due to the nonphagocytic nature of T cells. In this review, we discuss the physiological barriers to effective T cell targeting and describe the different approaches used to deliver cargo-loaded nanoparticles to T cells for the treatment of disease such as T cell lymphoma and human immunodeficiency virus (HIV). In particular, engineering strategies that aim to improve nanoparticle internalization by T cells, including ligand-based targeting, will be highlighted. These nanoparticle engineering approaches are expected to inspire the development of effective nanomaterials that can target or manipulate the function of T cells for the treatment of T cell-related diseases.

Common Peripheral Immunity Mechanisms in Multiple Sclerosis and Alzheimer's Disease

Neurodegenerative diseases are closely related to inflammatory and autoimmune events, suggesting that the dysregulation of the immune system is a key pathological factor. Both multiple sclerosis (MS) and Alzheimer's disease (AD) are characterized by infiltrating immune cells, activated microglia, astrocyte proliferation, and neuronal damage. Moreover, MS and AD share a common pro-inflammatory signature, characterized by peripheral leukocyte activation and transmigration to the central nervous system (CNS). MS and AD are both characterized by the accumulation of activated neutrophils in the blood, leading to progressive impairment of the blood–brain barrier. Having migrated to the CNS during the early phases of MS and AD, neutrophils promote local inflammation that contributes to pathogenesis and clinical progression. The role of circulating T cells in MS is well-established, whereas the contribution of adaptive immunity to AD pathogenesis and progression is a more recent discovery. Even so, blocking the transmigration of T cells to the CNS can benefit both MS and AD patients, suggesting that common adaptive immunity mechanisms play a detrimental role in each disease. There is also growing evidence that regulatory T cells are beneficial during the initial stages of MS and AD, supporting the link between the modulatory immune compartments and these neurodegenerative disorders. The number of resting regulatory T cells declines in both diseases, indicating a common pathogenic mechanism involving the dysregulation of these cells, although their precise role in the control of neuroinflammation remains unclear. The modulation of leukocyte functions can benefit MS patients, so more insight into the role of peripheral immune cells may reveal new targets for pharmacological intervention in other neuroinflammatory and neurodegenerative diseases, including AD.

The immune response of T cells and therapeutic targets related to regulating the levels of T helper cells after ischaemic stroke

Through considerable effort in research and clinical studies, the immune system has been identified as a participant in the onset and progression of brain injury after ischaemic stroke. Due to the involvement of all types of immune cells, the roles of the immune system in stroke pathology and associated effects are complicated. Past research concentrated on the functions of monocytes and neutrophils in the pathogenesis of ischaemic stroke and tried to demonstrate the mechanisms of tissue injury and protection involving these immune cells. Within the past several years, an increasing number of studies have elucidated the vital functions of T cells in the innate and adaptive immune responses in both the acute and chronic phases of ischaemic stroke. Recently, the phenotypes of T cells with proinflammatory or anti-inflammatory function have been demonstrated in detail. T cells with distinctive phenotypes can also influence cerebral inflammation through various pathways, such as regulating the immune response, interacting with brain-resident immune cells and modulating neurogenesis and angiogenesis during different phases following stroke. In view of the limited treatment options available following stroke other than tissue plasminogen activator therapy, understanding the function of immune responses, especially T cell responses, in the post-stroke recovery period can provide a new therapeutic direction. Here, we discuss the different functions and temporal evolution of T cells with different phenotypes during the acute and chronic phases of ischaemic stroke. We suggest that modulating the balance between the proinflammatory and anti-inflammatory functions of T cells with distinct phenotypes may become a potential therapeutic approach that reduces the mortality and improves the functional outcomes and prognosis of patients suffering from ischaemic stroke.

CD45RA, CD8β, and IFNγ Are Potential Immune Biomarkers of Human Cognitive Function

There is increasing evidence that in humans the adaptive immunological system can influence cognitive functions of the brain. We have undertaken a comprehensive immunological analysis of lymphocyte and monocyte populations as well as of HLA molecules expression in a cohort of elderly volunteers (age range, 64–101) differing in their cognitive status. Hereby, we report on the identification of a novel signature in cognitively impaired elderly characterized by: (1) elevated percentages of CD8+ T effector-memory cells expressing high levels of the CD45RA phosphate receptor (Temra^hi); (2) high percentages of CD8+ T cells expressing high levels of the CD8β chain (CD8β^hi); (3) augmented production of IFNγ by in vitro activated CD4+ T cells. Noteworthy, CD3+CD8+ Temra^hi and CD3+CD8β^hi cells were associated with impaired cognition. Cytomegalovirus seroprevalence showed that all volunteers studied but one were CMV positive. Finally, we show that some of these phenotypic and functional features are associated with an increased frequency of the HLA-B8 serotype, which belongs to the ancestral haplotype HLA-A1, Cw7, B8, DR3, DQ2, among cognitively impaired volunteers. To our knowledge, this is the first proof in humans linking the amount of cell surface CD45RA and CD8β chain expressed by CD8+ Temra cells, and the amount of IFNγ produced by in vitro activated CD4+ T cells, with impaired cognitive function in the elderly.

Metabolic determinants of leukocyte pathogenicity in neurological diseases

Neuroinflammatory and neurodegenerative diseases are characterized by the recruitment of circulating blood-borne innate and adaptive immune cells into the central nervous system (CNS). These leukocytes sustain the detrimental response in the CNS by releasing pro-inflammatory mediators that induce activation of local glial cells, blood-brain barrier (BBB) dysfunction, and neural cell death. However, infiltrating peripheral immune cells could also dampen CNS inflammation and support tissue repair. Recent advances in the field of immunometabolism demonstrate the importance of metabolic reprogramming for the activation and functionality of such innate and adaptive immune cell populations. In particular, an increasing body of evidence suggests that the activity of metabolites and metabolic enzymes could influence the pathogenic potential of immune cells during neuroinflammatory and neurodegenerative disorders. In this review, we discuss the role of intracellular metabolic cues in regulating leukocyte-mediated CNS damage in Alzheimer's and Parkinson's disease, multiple sclerosis and stroke, highlighting the therapeutic potential of drugs targeting metabolic pathways for the treatment of neurological diseases.

Lesion stage-dependent causes for impaired remyelination in MS

Multiple sclerosis (MS) is the most frequent demyelinating disease and a leading cause for disability in young adults. Despite significant advances in immunotherapies in recent years, disease progression still cannot be prevented. Remyelination, meaning the formation of new myelin sheaths after a demyelinating event, can fail in MS lesions. Impaired differentiation of progenitor cells into myelinating oligodendrocytes may contribute to remyelination failure and, therefore, the development of pharmacological approaches which promote oligodendroglial differentiation and by that remyelination, represents a promising new treatment approach. However, this generally accepted concept has been challenged recently. To further understand mechanisms contributing to remyelination failure in MS, we combined detailed histological analyses assessing oligodendroglial cell numbers, presence of remyelination as well as the inflammatory environment in different MS lesion types in white matter with in vitro experiments using induced-pluripotent stem cell (iPSC)-derived oligodendrocytes (hiOL) and supernatants from polarized human microglia. Our findings suggest that there are multiple reasons for remyelination failure in MS which are dependent on lesion stage. These include lack of myelin sheath formation despite the presence of mature oligodendrocytes in a subset of active lesions as well as oligodendroglial loss and a hostile tissue environment in mixed active/inactive lesions. Therefore, we conclude that better in vivo and in vitro models which mimic the pathological hallmarks of the different MS lesion types are required for the successful development of remyelination promoting drugs.

Eriodictyol suppresses Th17 differentiation and the pathogenesis of experimental autoimmune encephalomyelitis

T helper 17 (Th17) cells that express interleukin-17 (IL-17) play a key role in various inflammatory diseases, such as multiple sclerosis (MS), and its animal model experimental autoimmune encephalomyelitis (EAE). The retinoic acid receptor-related orphan receptors γt (RORγt) have an indispensable effect on the differentiation of this cell type, and are thus considered a valuable target in the treatment of Th17-related disorders. In this study, we found that eriodictyol (EDT), a natural flavonoid abundant in citrus fruits and peanuts, was located directly in the binding pocket of RORγt, and induced a conformational change that resulted in the effective suppression of the receptor's activity, thus offering insight into the transcriptional inhibition of RORγt-dependent genes. Consistent with this, EDT dose-dependently (5-10 μM) blocked murine Th17 differentiation, and markedly reduced IL-17A secretion in vitro. Furthermore, this compound has been found to have novel properties for directly inhibiting Th1 cell development and promoting Treg cell differentiation at high doses (≥10 μM). EDT administration significantly decreased the clinical severity in the EAE model, with inhibited demyelination and reduced inflammatory responses in the periphery and in the central nervous system (CNS). In the adoptive transfer model, EDT also remarkably suppressed the Th17 cell infiltration and pathogenicity. Collectively, our data demonstrated that EDT, as an agent for the pharmacological inhibition of RORγt, has great potential for immunomodulation, and for use in the treatment of Th17-mediated autoimmune disease.

Harnessing regulatory T cell neuroprotective activities for treatment of neurodegenerative disorders

Emerging evidence demonstrates that adaptive immunity influences the pathobiology of neurodegenerative disorders. Misfolded aggregated self-proteins can break immune tolerance leading to the induction of autoreactive effector T cells (Teffs) with associated decreases in anti-inflammatory neuroprotective regulatory T cells (Tregs). An imbalance between Teffs and Tregs leads to microglial activation, inflammation and neuronal injury. The cascade of such a disordered immunity includes the drainage of the aggregated protein antigens into cervical lymph nodes serving to amplify effector immune responses. Both preclinical and clinical studies demonstrate transformation of this altered immunity for therapeutic gain. We posit that the signs and symptoms of common neurodegenerative disorders such as Alzheimer's and Parkinson's diseases, amyotrophic lateral sclerosis, and stroke can be attenuated by boosting Treg activities.