Immune cell trafficking from the brain maintains CNS immune tolerance

Kurarinone regulates Th17/Treg balance and ameliorates autoimmune uveitis via Rac1 inhibition

INTRODUCTION

Autoimmune uveitis (AU) is a severe intraocular autoimmune disorder with a chronic disease course and a high rate of blindness. Kurarinone (KU), a major component of the traditional Chinese medicine Sophorae Flavescentis Radix, possesses a wide spectrum of activities and has been used to treat several inflammation-related diseases.

OBJECTIVE

We aimed to investigate the effects of KU on AU and its modulatory mechanisms.

METHODS

We used an experimental autoimmune uveitis (EAU) animal model and characterized the comprehensive immune landscape of KU-treated EAU mice using single-cell RNA sequencing (scRNA-seq). The retina and lymph nodes were analyzed. The siRNAs and selective inhibitors were used to study the signaling pathway. The effect of KU on peripheral blood mononuclear cells (PBMCs) from uveitis patients was also examined.

RESULTS

We found that KU relieved chorioretinal lesions and immune cell infiltration in EAU model mice. Subsequent single-cell analysis revealed that KU downregulated the EAU-upregulated expression of inflammatory and autoimmune-related genes and suppressed pathways associated with immune cell differentiation, activation, and migration in a cell-specific manner. KU was implicated in restoring T helper 17 (Th17)/regulatory T (Treg) cell balance by alleviating inflammatory injury and elevating the expression of modulatory mediators in Tregs, while simultaneously ameliorating excessive inflammation by Th17 cells. Furthermore, Rac1 and the Id2/Pim1 axis potentiated the pathogenicity of Th17 cells during EAU, which was inhibited by KU treatment, contributing to the amelioration of EAU-induced inflammation and treatment of AU. In addition, KU suppressed inflammatory cytokine production in activated human PBMCs by inhibiting Rac1. Integration of the glucocorticoid-treated transcriptome suggests that KU has immunomodulatory effects on lymphocytes.

CONCLUSION

Our study constructed a high-resolution atlas of the immunoregulatory effects of KU treatment on EAU and identified its potential therapeutic mechanisms, which hold great promise in treating autoimmune disorders.

Olfactory Development and Dysfunction: Involvement of Microglia

Olfactory deficits are increasingly recognized in a variety of neurological, neurodevelopmental, psychiatric, and viral diseases. While the pathology underlying olfactory loss is likely to differ across diseases, one shared feature may be an immune response mediated by microglia. Microglia orchestrate the brain's response to environmental insults and maintain neurodevelopmental homeostasis. Here, we explore the potential involvement of microglia in olfactory development and loss in disease. The effects of microglia-mediated immune response during development may be of special relevance to the olfactory system, which is unique in both its vulnerability to environmental insults as well as its extended period of neurogenesis and neuronal migration.

18 kDa Translocator protein (TSPO) is upregulated in rat brain after peripheral nerve injury and downregulated by diroximel fumarate

Neuroimmune signaling is a key process underlying neuropathic pain. Clinical studies have demonstrated that 18 kDa translocator protein (TSPO), a putative marker of neuroinflammation, is upregulated in discrete brain regions of patients with chronic pain. However, no preclinical studies have investigated TSPO dynamics in the brain in the context of neuropathic pain and in response to analgesic treatments. We used positron emission tomography-computed tomography (PET-CT) and [18F]-PBR06 radioligand to measure TSPO levels in the brain across time after chronic constriction injury (CCI) of the sciatic nerve in both male and female rats. Up to 10 weeks post-CCI, TSPO expression was increased in discrete brain regions, including medial prefrontal cortex, somatosensory cortex, insular cortex, anterior cingulate cortex, motor cortex, ventral tegmental area, amygdala, midbrain, pons, medulla, and nucleus accumbens. TSPO was broadly upregulated across these regions at 4 weeks post CCI in males, and 10 weeks in females, though there were regional differences between the sexes. Using immunohistochemistry, we confirmed TSPO expression in these regions. We further demonstrated that TSPO was upregulated principally in microglia in the nucleus accumbens core, and astrocytes and endothelial cells in the nucleus accumbens shell. Finally, we tested whether TSPO upregulation was sensitive to diroximel fumarate, a drug that induces endogenous antioxidants via nuclear factor E2-related factor 2 (Nrf2). Diroximel fumarate alleviated neuropathic pain and reduced TSPO upregulation. Our findings indicate that TSPO is upregulated over the course of neuropathic pain development and is resolved by an antinociceptive intervention in animals with peripheral nerve injury.

Glymphatic system: a gateway for neuroinflammation

The glymphatic system is a relatively recently identified fluid exchange and transport system in the brain. Accumulating evidence indicates that glymphatic function is impaired not only in central nervous system disorders but also in systemic diseases. Systemic diseases can trigger the inflammatory responses in the central nervous system, occasionally leading to sustained inflammation and functional disturbance of the central nervous system. This review summarizes the current knowledge on the association between glymphatic dysfunction and central nervous system inflammation. In addition, we discuss the hypothesis that disease conditions initially associated with peripheral inflammation overwhelm the performance of the glymphatic system, thereby triggering central nervous system dysfunction, chronic neuroinflammation, and neurodegeneration. Future research investigating the role of the glymphatic system in neuroinflammation may offer innovative therapeutic approaches for central nervous system disorders.

Mononuclear phagocytes in autoimmune neuroinflammation

A healthy mammalian central nervous system (CNS) harbors a diverse population of leukocytes including members of the mononuclear phagocyte system (MPS). Exerting their specific functions, CNS tissue-resident macrophages as well as associated monocytes and dendritic cells (DCs) maintain CNS homeostasis. Under neuroinflammatory conditions, leukocytes from the systemic immune compartment invade the CNS. This review focuses on the newly discovered roles of the MPS in autoimmune neuroinflammation elicited by encephalitogenic T cells. We propose that CNS-associated DCs act as gatekeepers and antigen-presenting cells that guide the adaptive immune response while bone marrow (BM)-derived monocytes contribute to immunopathology and tissue damage. By contrast, CNS-resident macrophages primarily support tissue function and promote the repair and maintenance of CNS functions.

Medulla oblongata and NCCs are central defenders against Streptococcus agalactiae infection of the tilapia brain

Various types of professional immune cells first emerge in fish and likely represent the primordial form and functions. Recent advancements revealed the direct connection between the central nervous system and the immune system in the mammalian brain. However, the specifics of brain-immune networks in the fish and the underlying mechanisms of teleost's brain against pathogen infection have not been fully elucidated. In this study, we investigated the distribution of markers representing cerebral cells associated with protection and professional lymphocytes in the seven major components of the Nile tilapia brain through RNA-Seq assay and observed the most dominant abundance in the medulla oblongata. The subsequent challenge test revealed the non-specific cytotoxic cells (NCCs) exhibited the strongest response against streptococcal infection of the brain. The presence of NCCs in the brain was then confirmed using immunofluorescence and the cytotoxic effects usually induced by NCCs under infection were determined as well. Collectively, these findings contribute significantly to comprehending the mechanism of fish neuroimmune interaction and enhancing our understanding of its evolutionary development.

A Stable Micellar Formulation of RAD001 for Intracerebroventricular Delivery and the Treatment of Alzheimer's Disease and Other Neurological Disorders

A large body of evidence, replicated in many mouse models of Alzheimer's disease (AD), supports the therapeutic efficacy of the oral mammalian target of rapamycin inhibitors (mTOR-Is). Our preliminary data show that intracerebroventricular (ICV) administration of everolimus (RAD001) soon after clinical onset greatly diminished cognitive impairment and the intracellular beta amyloid and neurofibrillary tangle load. However, RAD001 shows >90% degradation after 7 days in solution at body temperature, thus hampering the development of proper therapeutic regimens for patients. To overcome such a drawback, we developed a stable, liquid formulation of mTOR-Is by loading RAD001 into distearoylphosphatidylethanolamine-polyethylene glycol 2000 (DSPE-PEG2000) micelles using the thin layer evaporation method. The formulation showed efficient encapsulation of RAD001 and a homogeneous colloidal size and stabilised RAD001, with over 95% of activity preserved after 14 days at 37 °C with a total decay only occurring after 98 days. RAD001-loaded DSPE-PEG2000 micelles were unchanged when stored at 4 and 25 °C over the time period investigated. The obtained formulation may represent a suitable platform for expedited clinical translation and effective therapeutic regimens in AD and other neurological diseases.

mRNA expression profile reveals differentially expressed genes in splenocytes of experimental autoimmune encephalomyelitis model

Experimental autoimmune encephalomyelitis (EAE) is a mouse model that can be used to investigate aetiology, pathogenesis, and treatment approaches for multiple sclerosis (MS). A novel integrated bioinformatics approach was used to understand the involvement of differentially expressed genes (DEGs) in the spleen of EAE mice through data mining of existing microarray and RNA-seq datasets. We screened differentially expressed mRNAs using mRNA expression profile data of EAE spleens taken from Gene Expression Omnibus (GEO). Functional and pathway enrichment analyses of DEGs were performed by Database for Annotation, Visualization, and Integrated Discovery (DAVID). Subsequently, the DEGs-encoded protein-protein interaction (PPI) network was constructed. The 784 DEGs in GSE99300 A.SW PP-EAE mice spleen mRNA profiles, 859 DEGs in GSE151701 EAE mice spleen mRNA profiles, and 646 DEGs in GSE99300 SJL/J PP-EAE mice spleen mRNA profiles were explored. Functional enrichment of 55 common DEGs among 3 sub-datasets revealed several immune-related terms, such as neutrophil extravasation, leucocyte migration, antimicrobial humoral immune response mediated by an antimicrobial peptide, toll-like receptor 4 bindings, IL-17 signalling pathway, and TGF-beta signalling pathway. In the screening of 10 hub genes, including MPO, ELANE, CTSG, LTF, LCN2, SELP, CAMP, S100A9, ITGA2B, and PRTN3, and in choosing and validating the 5 DEGs, including ANK1, MBOAT2, SLC25A21, SLC43A1, and SOX6, the results showed that SLC43A1 and SOX6 were significantly decreased in EAE mice spleen. Thus this study offers a list of genes expressed in the spleen that might play a key role in the pathogenesis of EAE.

Immune cells as messengers from the CNS to the periphery: the role of the meningeal lymphatic system in immune cell migration from the CNS

In recent decades there has been a large focus on understanding the mechanisms of peripheral immune cell infiltration into the central nervous system (CNS) in neuroinflammatory diseases. This intense research led to several immunomodulatory therapies to attempt to regulate immune cell infiltration at the blood brain barrier (BBB), the choroid plexus (ChP) epithelium, and the glial barrier. The fate of these infiltrating immune cells depends on both the neuroinflammatory environment and their type-specific interactions with innate cells of the CNS. Although the fate of the majority of tissue infiltrating immune cells is death, a percentage of these cells could become tissue resident immune cells. Additionally, key populations of immune cells can possess the ability to "drain" out of the CNS and act as messengers reporting signals from the CNS toward peripheral lymphatics. Recent data supports that the meningeal lymphatic system is involved not just in fluid homeostatic functions in the CNS but also in facilitating immune cell migration, most notably dendritic cell migration from the CNS to the meningeal borders and to the draining cervical lymph nodes. Similar to the peripheral sites, draining immune cells from the CNS during neuroinflammation have the potential to coordinate immunity in the lymph nodes and thus influence disease. Here in this review, we will evaluate evidence of immune cell drainage from the brain via the meningeal lymphatics and establish the importance of this in animal models and humans. We will discuss how targeting immune cells at sites like the meningeal lymphatics could provide a new mechanism to better provide treatment for a variety of neurological conditions.

Dendritic Cells as a Nexus for the Development of Multiple Sclerosis and Models of Disease

Multiple sclerosis (MS) results from an autoimmune attack on the central nervous system (CNS). Dysregulated immune cells invade the CNS, causing demyelination, neuronal and axonal damage, and subsequent neurological disorders. Although antigen-specific T cells mediate the immunopathology of MS, innate myeloid cells have essential contributions to CNS tissue damage. Dendritic cells (DCs) are professional antigen-presenting cells (APCs) that promote inflammation and modulate adaptive immune responses. This review focuses on DCs as critical components of CNS inflammation. Here, evidence from studies is summarized with animal models of MS and MS patients that support the critical role of DCs in orchestrating CNS inflammation.

Autophagy pathways in autoimmune diseases

Autophagy comprises a growing range of cellular pathways, which occupy central roles in response to energy deprivation, organelle turnover and proteostasis. Over the years, autophagy has been increasingly linked to governing several aspects of immunity, including host defence against various pathogens, unconventional secretion of cytokines and antigen presentation. While canonical autophagy-mediated antigen processing in thymic epithelial cells supports the generation of a self-tolerant CD4+ T cell repertoire, mounting evidence suggests that deregulated autophagy pathways contribute to or sustain autoimmune responses. In animal models of multiple sclerosis (MS), non-canonical autophagy pathways such as microtubule-associated protein 1 A/1 B-light chain 3 (LC3)-associated phagocytosis can contribute to major histocompatibility complex (MHC) class II presentation of autoantigen, thereby amplifying autoreactive CD4+ T cell responses. In systemic lupus erythematosus (SLE), increased type 1 interferon production is linked to excessive autophagy in plasmacytoid dendritic cells (DCs). In rheumatoid arthritis (RA), autophagy proteins contribute to pathological citrullination of autoantigen. Immunotherapies effective in autoimmune diseases modulate autophagy functions, and strategies harnessing autophagy pathways to restrain autoimmune responses have been developed. This review illustrates recent insights in how autophagy, distinct autophagy pathways and autophagy protein functions intersect with the evolution and progression of autoimmune diseases, focusing on MS, SLE and RA.

Role of DAMPs and cell death in autoimmune diseases: the example of multiple sclerosis

Multiple sclerosis is a chronic neuroinflammatory demyelinating disease of the central nervous system (CNS) of unknown etiology and still incompletely clarified pathogenesis. The disease is generally considered a disorder resulting from a complex interplay between environmental risk factors and predisposing causal genetic variants. To examine the etiopathogenesis of the disease, two complementary pre-clinical models are currently discussed: the "outside-in" model proposing a peripherally elicited inflammatory/autoimmune attack against degraded myelin as the cause of the disease, and the "inside-out" paradigm implying a primary cytodegenerative process of cells in the CNS that triggers secondary reactive inflammatory/autoimmune responses against myelin debris. In this review, the integrating pathogenetic role of damage-associated molecular patterns (DAMPs) in these two scenario models is examined by focusing on the origin and sources of these molecules, which are known to promote neuroinflammation and, via activation of pattern recognition receptor-bearing antigen-presenting cells, drive and shape autoimmune responses. In particular, environmental factors are discussed that are conceptually defined as agents which produce endogenous DAMPs via induction of regulated cell death (RCD) or act themselves as exogenous DAMPs. Indeed, in the field of autoimmune diseases, including multiple sclerosis, recent research has focused on environmental triggers that cause secondary events in terms of subroutines of RCD, which have been identified as prolific sources of DAMPs. Finally, a model of a DAMP-driven positive feed-forward loop of chronic inflammatory demyelinating processes is proposed, aimed at reconciling the competing "inside-out" and "outside-in" paradigms.

The Role of Hypoxia in Brain Tumor Immune Responses

Oxygen is a vital component of living cells. Low levels of oxygen in body tissues, known as hypoxia, can affect multiple cellular functions across a variety of cell types and are a hallmark of brain tumors. In the tumor microenvironment, abnormal vasculature and enhanced oxygen consumption by tumor cells induce broad hypoxia that affects not only tumor cell characteristics but also the antitumor immune system. Although some immune reactions require hypoxia, hypoxia generally negatively affects immunity. Hypoxia induces tumor cell invasion, cellular adaptations to hypoxia, and tumor cell radioresistance. In addition, hypoxia limits the efficacy of immunotherapy and hinders antitumor responses. Therefore, understanding the role of hypoxia in the brain tumor, which usually does not respond to immunotherapy alone is important for the development of effective anti-tumor therapies. In this review, we discuss recent evidence supporting the role of hypoxia in the context of brain tumors.

The complex role of inflammation and gliotransmitters in Parkinson's disease

Our understanding of the role of innate and adaptive immune cell function in brain health and how it goes awry during aging and neurodegenerative diseases is still in its infancy. Inflammation and immunological dysfunction are common components of Parkinson's disease (PD), both in terms of motor and non-motor components of PD. In recent decades, the antiquated notion that the central nervous system (CNS) in disease states is an immune-privileged organ, has been debunked. The immune landscape in the CNS influences peripheral systems, and peripheral immunological changes can alter the CNS in health and disease. Identifying immune and inflammatory pathways that compromise neuronal health and survival is critical in designing innovative and effective strategies to limit their untoward effects on neuronal health.

Neural precursor cells tune striatal connectivity through the release of IGFBPL1

The adult brain retains over life endogenous neural stem/precursor cells (eNPCs) within the subventricular zone (SVZ). Whether or not these cells exert physiological functions is still unclear. In the present work, we provide evidence that SVZ-eNPCs tune structural, electrophysiological, and behavioural aspects of striatal function via secretion of insulin-like growth factor binding protein-like 1 (IGFBPL1). In mice, selective ablation of SVZ-eNPCs or selective abrogation of IGFBPL1 determined an impairment of striatal medium spiny neuron morphology, a higher failure rate in GABAergic transmission mediated by fast-spiking interneurons, and striatum-related behavioural dysfunctions. We also found IGFBPL1 expression in the human SVZ, foetal and induced-pluripotent stem cell-derived NPCs. Finally, we found a significant correlation between SVZ damage, reduction of striatum volume, and impairment of information processing speed in neurological patients. Our results highlight the physiological role of adult SVZ-eNPCs in supporting cognitive functions by regulating striatal neuronal activity.

The CNS mononuclear phagocyte system in health and disease

CNS-resident macrophages-including parenchymal microglia and border-associated macrophages (BAMs)-contribute to neuronal development and health, vascularization, and tissue integrity at steady state. Border-patrolling mononuclear phagocytes such as dendritic cells and monocytes confer important immune functions to the CNS, protecting it from pathogenic threats including aberrant cell growth and brain malignancies. Even though we have learned much about the contribution of lymphocytes to CNS pathologies, a better understanding of differential roles of tissue-resident and -invading phagocytes is slowly emerging. In this perspective, we propose that in CNS neuroinflammatory diseases, tissue-resident macrophages (TRMs) contribute to the clearing of debris and resolution of inflammation, whereas blood-borne phagocytes are drivers of immunopathology. We discuss the remaining challenges to resolve which specialized mononuclear phagocyte populations are driving or suppressing immune effector function, thereby potentially dictating the outcome of autoimmunity or brain cancer.

The lymphatic system: a therapeutic target for central nervous system disorders

The lymphatic vasculature forms an organized network that covers the whole body and is involved in fluid homeostasis, metabolite clearance, and immune surveillance. The recent identification of functional lymphatic vessels in the meninges of the brain and the spinal cord has provided novel insights into neurophysiology. They emerge as major pathways for fluid exchange. The abundance of immune cells in lymphatic vessels and meninges also suggests that lymphatic vessels are actively involved in neuroimmunity. The lymphatic system, through its role in the clearance of neurotoxic proteins, autoimmune cell infiltration, and the transmission of pro-inflammatory signals, participates in the pathogenesis of a variety of neurological disorders, including neurodegenerative and neuroinflammatory diseases and traumatic injury. Vascular endothelial growth factor C is the master regulator of lymphangiogenesis, a process that is critical for the maintenance of central nervous system homeostasis. In this review, we summarize current knowledge and recent advances relating to the anatomical features and immunological functions of the lymphatic system of the central nervous system and highlight its potential as a therapeutic target for neurological disorders and central nervous system repair.

The Interplay of Tumor Vessels and Immune Cells Affects Immunotherapy of Glioblastoma

Immunotherapies with immune checkpoint inhibitors or adoptive cell transfer have become powerful tools to treat cancer. These treatments act via overcoming or alleviating tumor-induced immunosuppression, thereby enabling effective tumor clearance. Glioblastoma (GBM) represents the most aggressive, primary brain tumor that remains refractory to the benefits of immunotherapy. The immunosuppressive immune tumor microenvironment (TME), genetic and cellular heterogeneity, and disorganized vasculature hinder drug delivery and block effector immune cell trafficking and activation, consequently rendering immunotherapy ineffective. Within the TME, the mutual interactions between tumor, immune and endothelial cells result in the generation of positive feedback loops, which intensify immunosuppression and support tumor progression. We focus here on the role of aberrant tumor vasculature and how it can mediate hypoxia and immunosuppression. We discuss how immune cells use immunosuppressive signaling for tumor progression and contribute to the development of resistance to immunotherapy. Finally, we assess how a positive feedback loop between vascular normalization and immune cells, including myeloid cells, could be targeted by combinatorial therapies with immune checkpoint blockers and sensitize the tumor to immunotherapy.

Meningeal lymphatic drainage promotes T cell responses against Toxoplasma gondii but is dispensable for parasite control in the brain

The discovery of meningeal lymphatic vessels that drain the CNS has prompted new insights into how immune responses develop in the brain. In this study, we examined how T cell responses against CNS-derived antigen develop in the context of infection. We found that meningeal lymphatic drainage promotes CD4⁺ and CD8⁺ T cell responses against the neurotropic parasite Toxoplasma gondii in mice, and we observed changes in the dendritic cell compartment of the dural meninges that may support this process. Indeed, we found that mice chronically, but not acutely, infected with T. gondii exhibited a significant expansion and activation of type 1 and type 2 conventional dendritic cells (cDC) in the dural meninges. cDC1s and cDC2s were both capable of sampling cerebrospinal fluid (CSF)-derived protein and were found to harbor processed CSF-derived protein in the draining deep cervical lymph nodes. Disrupting meningeal lymphatic drainage via ligation surgery led to a reduction in CD103⁺ cDC1 and cDC2 number in the deep cervical lymph nodes and caused an impairment in cDC1 and cDC2 maturation. Concomitantly, lymphatic vessel ligation impaired CD4⁺ and CD8⁺ T cell activation, proliferation, and IFN-γ production at this site. Surprisingly, however, parasite-specific T cell responses in the brain remained intact following ligation, which may be due to concurrent activation of T cells at non-CNS-draining sites during chronic infection. Collectively, our work reveals that CNS lymphatic drainage supports the development of peripheral T cell responses against T. gondii but remains dispensable for immune protection of the brain.

Dendritic Cell-Targeted Therapies to Treat Neurological Disorders

Dendritic cells (DCs) are the immune system's highly specialized antigen-presenting cells. When DCs are sluggish and mature, self-antigen presentation results in tolerance; however, when pathogen-associated molecular patterns stimulate mature DCs, antigen presentation results in the development of antigen-specific immunity. DCs have been identified in various vital organs of mammals (e.g., the skin, heart, lungs, intestines, and spleen), but the brain has long been thought to be devoid of DCs in the absence of neuroinflammation. However, neuroinflammation is becoming more recognized as a factor in a variety of brain illnesses. DCs are present in the brain parenchyma in trace amounts under healthy circumstances, but their numbers rise during neuroinflammation. New therapeutics are being developed that can reduce dendritic cell immunogenicity by inhibiting pro-inflammatory cytokine production and T cell co-stimulatory pathways. Additionally, innovative ways of regulating dendritic cell growth and differentiation and harnessing their tolerogenic capability are being explored. Herein, we described the function of dendritic cells in neurological disorders and discussed the potential for future therapeutic techniques that target dendritic cells and dendritic cell-related targets in the treatment of neurological disorders.

Meningeal Lymphatics: An Immune Gateway for the Central Nervous System

The recent (re)discovery of the meningeal lymphatic system has opened new theories as to how immune cells traffic and interact with the central nervous system (CNS). While evidence is accumulating on the contribution of the meningeal lymphatic system in both homeostatic and disease conditions, a lot remains unknown about the mechanisms that allow for interaction between the meningeal lymphatic system and immune cells. In this review, we synthesize the knowledge about the lymphatic immune interaction in the CNS and highlight the important questions that remain to be answered.

PD-L1 blockade exhibits anti-tumor effect on brain metastasis by activating CD8+ T cells in hematogenous metastasis model with lymphocyte infusion

Brain metastases are common complication in cancer patients. Immune checkpoint inhibitors show therapeutic benefits also in patients with central nervous system (CNS) metastases. However, their antitumor effects on metastatic tumors and their underlying mechanisms are still poorly understood. In this study we investigated the antitumor effect of anti-programmed death-ligand 1 (PD-L1) antibody on metastatic brain tumors and evaluated immune responses during treatment. We employed a hematogenous brain metastasis xenograft model using immunodeficient mice with murine lymphocyte infusions. A human non-small-cell lung cancer (NSCLC) cell line stably expressing NanoLuc^® reporter (Nluc-H1915) was inoculated from the internal carotid artery of SCID mice. After metastases were established (24 days after inoculation), splenocytes prepared from H1915-immunized BALB/c mice were injected intravenously and mouse IgG or anti-PD-L1 antibody treatment was started (day 1). Evaluated by Nluc activity, tumor volume in the brain on day 14 was significantly lower in anti-PD-L1-treated mice than in mouse IgG-treated mice. Furthermore CD8⁺ cells were primarily infiltrated intratumorally and peritumorally and anti-PD-L1 treatment induced a significantly higher proportion of Granzyme B (GzmB)⁺ cells among CD8⁺ T cells. The antitumor effect of anti-PD-L1 antibody on brain metastasis is thought to be achieved by the enhanced activation of infiltrated CD8⁺ T cells into metastatic brain tumor. These results suggest that anti-PD-L1 antibody-containing regimens may be promising treatment options for cancer patients with brain metastases.

Low tumour-infiltrating lymphocyte density in primary and recurrent glioblastoma

Immunotherapies targeting tumour-infiltrating lymphocytes (TILs) that express the immune checkpoint molecule programmed cell death-1 (PD-1) have shown promise in preclinical glioblastoma models but have had limited success in clinical trials. To assess when glioblastoma is most likely to benefit from immune checkpoint inhibitors we determined the density of TILs in primary and recurrent glioblastoma. Thirteen cases of matched primary and recurrent glioblastoma tissue were immunohistochemically labelled for CD3, CD8, CD4 and PD-1, and TIL density assessed. CD3+ TILs were observed in all cases, with the majority of both primary (69.2%) and recurrent (61.5%) tumours having low density of TILs present. CD8+ TILs were observed at higher densities than CD4+ TILs in both tumour groups. PD-1+ TILs were sparse and present in only 25% of primary and 50% of recurrent tumours. Quantitative analysis of TILs demonstrated significantly higher CD8+ TIL density at recurrence (p = 0.040). No difference was observed in CD3+ (p = 0.191), CD4+ (p = 0.607) and PD-1+ (p = 0.070) TIL density between primary and recurrent groups. This study shows that TILs are present at low densities in both primary and recurrent glioblastoma. Furthermore, PD-1+ TILs were frequently absent, which may provide evidence as to why anti-PD-1 immunotherapy trials have been largely unsuccessful in glioblastoma.

Current concepts on communication between the central nervous system and peripheral immunity via lymphatics: what roles do lymphatics play in brain and spinal cord disease pathogenesis?

The central nervous system (CNS) lacks conventional lymphatics within the CNS parenchyma, yet still maintains fluid homeostasis and immunosurveillance. How the CNS communicates with systemic immunity has thus been a topic of interest for scientists in the past century, which has led to several theories of CNS drainage routes. In addition to perineural routes, rediscoveries of lymphatics surrounding the CNS in the meninges revealed an extensive network of lymphatics, which we now know play a significant role in fluid homeostasis and immunosurveillance. These meningeal lymphatic networks exist along the superior sagittal sinus and transverse sinus dorsal to the brain, near the cribriform plate below the olfactory bulbs, at the base of the brain, and surrounding the spinal cord. Inhibition of one or all of these lymphatic networks can reduce CNS autoimmunity in a mouse model of multiple sclerosis (MS), while augmenting these lymphatic networks can improve immunosurveillance, immunotherapy, and clearance in glioblastoma, Alzheimer's disease, traumatic brain injury, and cerebrovascular injury. In this review, we will provide historical context of how CNS drainage contributes to immune surveillance, how more recently published studies fit meningeal lymphatics into the context of CNS homeostasis and neuroinflammation, identify the complex dualities of lymphatic function during neuroinflammation and how therapeutics targeting lymphatic function may be more complicated than currently appreciated, and conclude by identifying some unresolved questions and controversies that may guide future research.

A Microfluidic 3D Endothelium-on-a-Chip Model to Study Transendothelial Migration of T Cells in Health and Disease

The recruitment of T cells is a crucial component in the inflammatory cascade of the body. The process involves the transport of T cells through the vascular system and their stable arrest to vessel walls at the site of inflammation, followed by extravasation and subsequent infiltration into tissue. Here, we describe an assay to study 3D T cell dynamics under flow in real time using a high-throughput, artificial membrane-free microfluidic platform that allows unimpeded extravasation of T cells. We show that primary human T cells adhere to endothelial vessel walls upon perfusion of microvessels and can be stimulated to undergo transendothelial migration (TEM) by TNFα-mediated vascular inflammation and the presence of CXCL12 gradients or ECM-embedded melanoma cells. Notably, migratory behavior was found to differ depending on T cell activation states. The assay is unique in its comprehensiveness for modelling T cell trafficking, arrest, extravasation and migration, all in one system, combined with its throughput, quality of imaging and ease of use. We envision routine use of this assay to study immunological processes and expect it to spur research in the fields of immunological disorders, immuno-oncology and the development of novel immunotherapeutics.

Neuroinflammation-Driven Lymphangiogenesis in CNS Diseases

The central nervous system (CNS) undergoes immunosurveillance despite the lack of conventional antigen presenting cells and lymphatic vessels in the CNS parenchyma. Additionally, the CNS is bathed in a cerebrospinal fluid (CSF). CSF is continuously produced, and consequently must continuously clear to maintain fluid homeostasis despite the lack of conventional lymphatics. During neuroinflammation, there is often an accumulation of fluid, antigens, and immune cells to affected areas of the brain parenchyma. Failure to effectively drain these factors may result in edema, prolonged immune response, and adverse clinical outcome as observed in conditions including traumatic brain injury, ischemic and hypoxic brain injury, CNS infection, multiple sclerosis (MS), and brain cancer. Consequently, there has been renewed interest surrounding the expansion of lymphatic vessels adjacent to the CNS which are now thought to be central in regulating the drainage of fluid, cells, and waste out of the CNS. These lymphatic vessels, found at the cribriform plate, dorsal dural meninges, base of the brain, and around the spinal cord have each been implicated to have important roles in various CNS diseases. In this review, we discuss the contribution of meningeal lymphatics to these processes during both steady-state conditions and neuroinflammation, as well as discuss some of the many still unknown aspects regarding the role of meningeal lymphatics in neuroinflammation. Specifically, we focus on the observed phenomenon of lymphangiogenesis by a subset of meningeal lymphatics near the cribriform plate during neuroinflammation, and discuss their potential roles in immunosurveillance, fluid clearance, and access to the CSF and CNS compartments. We propose that manipulating CNS lymphatics may be a new therapeutic way to treat CNS infections, stroke, and autoimmunity.

T cell transgressions: Tales of T cell form and function in diverse disease states

Insights into T cell form, function, and dysfunction are rapidly evolving. T cells have remarkably varied effector functions including protecting the host from infection, activating cells of the innate immune system, releasing cytokines and chemokines, and heavily contributing to immunological memory. Under healthy conditions, T cells orchestrate a finely tuned attack on invading pathogens while minimizing damage to the host. The dark side of T cells is that they also exhibit autoreactivity and inflict harm to host cells, creating autoimmunity. The mechanisms of T cell autoreactivity are complex and dynamic. Emerging research is elucidating the mechanisms leading T cells to become autoreactive and how such responses cause or contribute to diverse disease states, both peripherally and within the central nervous system. This review provides foundational information on T cell development, differentiation, and functions. Key T cell subtypes, cytokines that create their effector roles, and sex differences are highlighted. Pathological T cell contributions to diverse peripheral and central disease states, arising from errors in reactivity, are highlighted, with a focus on multiple sclerosis, rheumatoid arthritis, osteoarthritis, neuropathic pain, and type 1 diabetes.

Rescue of maternal immune activation-induced behavioral abnormalities in adult mouse offspring by pathogen-activated maternal Treg cells

Maternal immune activation (MIA) induced by lipopolysaccharides or polyinosinic:polycytidylic acid injections can induce behavioral abnormalities in adult mouse offspring. Here, we used the soluble tachyzoite antigen from Toxoplasma gondii, a parasite that infects approximately two billion people, to induce MIA in mice. The adult male offspring showed autism-relevant behaviors and abnormal brain microstructure, along with a pro-inflammatory T-cell immune profile in the periphery and upregulation of interleukin-6 in brain astrocytes. We show that adoptive transfer of regulatory T (T_reg) cells largely reversed these MIA-induced phenotypes. Notably, pathogen-activated maternal T_reg cells showed greater rescue efficacy than those from control donors. Single-cell RNA sequencing identified and characterized a unique group of pathogen-activated T_reg cells that constitute 32.6% of the pathogen-activated maternal T_reg population. Our study establishes a new preclinical parasite-mimicking MIA model and suggests therapeutic potential of adoptive T_reg cell transfer in neuropsychiatric disorders associated with immune alterations.

New strategy for MS treatment with autoantigen-modified liposomes and their therapeutic effect

As current treatments for multiple sclerosis (MS) remain chemotherapeutic ones directed toward symptoms, the development of a curative treatment is urgently required. Herein, we show an autoreactive immune cell-targetable approach using autoantigen-modified liposomes for the curative treatment of MS. In these experiments, experimental autoimmune encephalomyelitis (EAE) induced by autoantigenic myelin oligodendrocyte glycoprotein (MOG) peptide was used as a model of primary progressive MS, and MOG-modified liposomes encapsulating doxorubicin (MOG-LipDOX) were used as a therapeutic drug. The results showed that the progression of encephalomyelitis symptoms was significantly suppressed by MOG-LipDOX injection, whereas the other samples failed to show any effect. Additionally, invasion of inflammatory immune cells into the spinal cord and demyelination of neurons were clearly suppressed in the MOG-LipDOX-treated mice. FACS analysis revealed that the number of both MOG-recognizable CD4⁺ T cells in the spleen was obviously decreased after MOG-LipDOX treatment. Furthermore, the number of effector Th17 cells in the spleen was significantly decreased and that of regulatory Treg cells was concomitantly increased. Finally, we demonstrated that myelin proteolipid protein (PLP)-modified liposomes encapsulating DOX (PLP-LipDOX) also showed the therapeutic effect on relapsing-remitting EAE. These findings indicate that autoantigen-modified liposomal drug produced a highly therapeutic effect on EAE by delivering the encapsulated drug to autoantigen-recognizable CD4⁺ T cells and thus suppressing autoreactive immune responses. The present study suggests that the use of these autoantigen-modified liposomes promises to be a suitable therapeutic approach for the cure of MS.

Apolipoprotein E4 and meningeal lymphatics in Alzheimer disease: a conceptual framework

The potential existence and roles of the meningeal lymphatic system in normal and pathological brain function have been a long-standing enigma. Recent evidence suggests that meningeal lymphatic vessels are present in both the mouse and human brain; in mice, they seem to play a role in clearing toxic amyloid-beta peptides, which have been connected with Alzheimer disease (AD). Here, we review the evidence linking the meningeal lymphatic system with human AD. Novel findings suggest that the recently described meningeal lymphatic vessels could be linked to, and possibly drain, the efferent paravascular glial lymphatic (glymphatic) system carrying cerebrospinal fluid, after solute and immune cell exchange with brain interstitial fluid. In so doing, the glymphatic system could contribute to the export of toxic solutes and immune cells from the brain (an exported fluid we wish to describe as glymph, similarly to lymph) to the meningeal lymphatic system; the latter, by being connected with downstream anatomic regions, carries the glymph to the conventional cervical lymphatic vessels and nodes. Thus, abnormal function in the meningeal lymphatic system could, in theory, lead to the accumulation, in the brain, of amyloid-beta, cellular debris, and inflammatory mediators, as well as immune cells, resulting in damage of the brain parenchyma and, in turn, cognitive and other neurologic dysfunctions. In addition, we provide novel insights into APOE4-the leading genetic risk factor for AD-and its relation to the meningeal lymphatic system. In this regard, we have reanalyzed previously published RNA-Seq data to show that induced pluripotent stem cells (iPSCs) carrying the APOE4 allele (either as APOE4 knock-in or stemming from APOE4 patients) express lower levels of (a) genes associated with lymphatic markers, and (b) genes for which well-characterized missense mutations have been linked to peripheral lymphedema. Taking into account this evidence, we propose a new conceptual framework, according to which APOE4 could play a novel role in the premature shrinkage of meningeal lymphatic vessels (meningeal lymphosclerosis), leading to abnormal meningeal lymphatic functions (meningeal lymphedema), and, in turn, reduction in the clearance of amyloid-beta and other macromolecules and inflammatory mediators, as well as immune cells, from the brain, exacerbation of AD manifestations, and progression of the disease. Altogether, these findings and their potential interpretations may herald novel diagnostic tools and therapeutic approaches in patients with AD.

Neuroimmunological therapies for treating spinal cord injury: Evidence and future perspectives

Spinal cord injury (SCI) has a complex pathophysiology. Following the initial physical trauma to the spinal cord, which may cause vascular disruption, hemorrhage, mechanical injury to neural structures and necrosis, a series of biomolecular cascades is triggered to evoke secondary injury. Neuroinflammation plays a major role in the secondary injury after traumatic SCI. To date, the administration of systemic immunosuppressive medications, in particular methylprednisolone sodium succinate, has been the primary pharmacological treatment. This medication is given as a complement to surgical decompression of the spinal cord and maintenance of spinal cord perfusion through hemodynamic augmentation. However, the impact of neuroinflammation is complex with harmful and beneficial effects. The use of systemic immunosuppressants is further complicated by the natural onset of post-injury immunosuppression, which many patients with SCI develop. It has been hypothesized that immunomodulation to attenuate detrimental aspects of neuroinflammation after SCI, while avoiding systemic immunosuppression, may be a superior approach. To accomplish this, a detailed understanding of neuroinflammation and the systemic immune responses after SCI is required. Our review will strive to achieve this goal by first giving an overview of SCI from a clinical and basic science context. The role that neuroinflammation plays in the pathophysiology of SCI will be discussed. Next, the positive and negative attributes of the innate and adaptive immune systems in neuroinflammation after SCI will be described. With this background established, the currently existing immunosuppressive and immunomodulatory therapies for treating SCI will be explored. We will conclude with a summary of topics that can be explored by neuroimmunology research. These concepts will be complemented by points to be considered by neuroscientists developing therapies for SCI and other injuries to the central nervous system.

The glymphatic system and meningeal lymphatics of the brain: new understanding of brain clearance

The glymphatic system and meningeal lymphatics have recently been characterized. Glymphatic system is a glia-dependent system of perivascular channels, and it plays an important role in the removal of interstitial metabolic waste products. The meningeal lymphatics may be a key drainage route for cerebrospinal fluid into the peripheral blood, may contribute to inflammatory reaction and central nervous system (CNS) immune surveillance. Breakdowns and dysfunction of the glymphatic system and meningeal lymphatics play a crucial role in age-related brain changes, the pathogenesis of neurovascular and neurodegenerative diseases, as well as in brain injuries and tumors. This review discusses the relationship recently characterized meningeal lymphatic vessels with the glymphatic system, which provides perfusion of the CNS with cerebrospinal and interstitial fluids. The review also presents the results of human studies concerning both the presence of meningeal lymphatics and the glymphatic system. A new understanding of how aging, medications, sleep and wake cycles, genetic predisposition, and even body posture affect the brain drainage system has not only changed the idea of brain fluid circulation but has also contributed to an understanding of the pathology and mechanisms of neurodegenerative diseases.

FTY720 Reduces Endothelial Cell Apoptosis and Remodels Neurovascular Unit after Experimental Traumatic Brain Injury

Traumatic brain injury (TBI) is a major cause of death and disability worldwide. A sequence of pathological processes occurred when there is TBI. Previous studies showed that sphingosine-1-phosphate receptor 1 (S1PR1) played a critical role in inflammatory response in the brain after TBI. Thus, the present study was designed to evaluate the effects of the S1PR1 modulator FTY720 on neurovascular unit (NVU) after experimental TBI in mice. The weight-drop TBI method was used to induce TBI. Western blot (WB) was performed to determine the levels of SIPR1, claudin-5 and occludin at different time points. FTY720 was intraperitoneally administered to mice after TBI was induced. The terminal deoxynucleotidyl transferase-dUTP nick end labeling (TUNEL) assay was used to assess endothelial cell apoptosis. Immunofluorescence and WB were performed to measure the expression of tight junction proteins: claudin-5 and occludin. Evans blue (EB) permeability assay and brain water content were applied to evaluate the blood-brain barrier (BBB) permeability and brain edema. Immunohistochemistry was performed to assess the activation of astrocytes and microglia. The results showed that FTY720 administration reduced endothelial cell apoptosis and improved BBB permeability. FTY720 also attenuated astrocytes and microglia activation. Furthermore, treatment with FTY720 not only improved neurological function, but also increased the survival rate of mice significantly. These findings suggest that FTY720 administration restored the structure of the NVU after experimental TBI by decreasing endothelial cell apoptosis and attenuating the activation of astrocytes. Moreover, FTY720 might reduce inflammation in the brain by reducing the activation of microglia in TBI mice.

Feasibility of dendritic cell-based vaccine against glioblastoma by using cytoplasmic transduction peptide (CTP)-fused protein antigens combined with anti-PD1

Recent clinical trials utilizing antigen-pulsed dendritic cells (DCs) have demonstrated increased survival of vaccinated cancer patients. Besides, the cytoplasmic transduction peptide (CTP) not only has an excellent transcellular efficiency but also shows a strong tendency to remain in the cytoplasm after transduction, without migrating into the nucleus. In this study, we investigated the effectiveness of immunotherapy against malignant gliomas using DCs pulsed with CTP-fused protein antigens combined with programmed cell death protein 1 blockade (anti-PD1). The expression of tumor associated antigen (WT1 and BIRC5) and PDL1 on glioblastoma (GBM) target cells was confirmed by western blot. The effect of CTP-fused protein antigens on mature DCs (VaxDCs) was determined. The immunophenotypes of VaxDCs pulsed with CTP-fused protein antigens was confirmed by flow cytometry and the cytokine production levels of T helper polarization were measured by enzyme-linked immunosorbent (ELISA) assay. The IFN-γ-enzyme linked immunospot and lactate dehydrogenase release assays were performed to estimate the cytotoxic activity of antigen-specific cytotoxic T lymphocytes (CTLs), stimulated by VaxDCs pulsed with CTP-fused protein antigens and anti-PD1, against malignant glioma cells expressing target antigens. VaxDCs pulsed with CTP-fused protein antigens showed enhanced expression of major histocompatibility complex (MHC) and co-stimulatory markers of DCs and resulted in Th1 cytokine polarization. The increase in the number of IFN-γ+ effector T cells paralleled with the enhanced percent specific lysis of GBM targets cells by antigen-specific CTLs. Our study suggested that using CTP-fused protein antigens for DC vaccine preparation along with PD1 blockade could be an effective immunotherapy strategy for GBM.

Glioblastoma Immune Landscape and the Potential of New Immunotherapies

Glioblastoma (GBM) are the most common tumors of the central nervous system and among the deadliest cancers in adults. GBM overall survival has not improved over the last decade despite optimization of therapeutic standard-of-care. While immune checkpoint inhibitors (ICI) have revolutionized cancer care, they unfortunately have little therapeutic success in GBM. Here, we elaborate on normal brain and GBM-associated immune landscapes. We describe the role of microglia and tumor-associated macrophages (TAMs) in immune suppression and highlight the impact of energy metabolism in immune evasion. We also describe the challenges and opportunities of immunotherapies in GBM and discuss new avenues based on harnessing the anti-tumor activity of myeloid cells, vaccines, chimeric antigen receptors (CAR)-T and -NK cells, oncolytic viruses, nanocarriers, and combination therapies.

Dendritic Cells and Microglia Have Non-redundant Functions in the Inflamed Brain with Protective Effects of Type 1 cDCs

Brain CD11c⁺ cells share features with microglia and dendritic cells (DCs). Sterile inflammation increases brain CD11c⁺ cells, but their phenotype, origin, and functions remain largely unknown. We report that, after cerebral ischemia, microglia attract DCs to the inflamed brain, and astroglia produce Flt3 ligand, supporting development and expansion of CD11c⁺ cells. CD11c⁺ cells in the inflamed brain are a complex population derived from proliferating microglia and infiltrating DCs, including a major subset of OX40L⁺ conventional cDC2, and also cDC1, plasmacytoid, and monocyte-derived DCs. Despite sharing certain morphological features and markers, CD11c⁺ microglia and DCs display differential expression of pattern recognition receptors and chemokine receptors. DCs excel CD11c^- and CD11c⁺ microglia in the capacity to present antigen through MHCI and MHCII. Of note, cDC1s protect from brain injury after ischemia. We thus reveal aspects of the dynamics and functions of brain DCs in the regulation of inflammation and immunity.

Molecular Heterogeneity and Immunosuppressive Microenvironment in Glioblastoma

Glioblastoma (GBM) is the most aggressive primary brain tumor in adults, with a poor prognosis, despite surgical resection combined with radio- and chemotherapy. The major clinical obstacles contributing to poor GBM prognosis are late diagnosis, diffuse infiltration, pseudo-palisading necrosis, microvascular proliferation, and resistance to conventional therapy. These challenges are further compounded by extensive inter- and intra-tumor heterogeneity and the dynamic plasticity of GBM cells. The complex heterogeneous nature of GBM cells is facilitated by the local inflammatory tumor microenvironment, which mostly induces tumor aggressiveness and drug resistance. An immunosuppressive tumor microenvironment of GBM provides multiple pathways for tumor immune evasion. Infiltrating immune cells, mostly tumor-associated macrophages, comprise much of the non-neoplastic population in GBM. Further understanding of the immune microenvironment of GBM is essential to make advances in the development of immunotherapeutics. Recently, whole-genome sequencing, epigenomics and transcriptional profiling have significantly helped improve the prognostic and therapeutic outcomes of GBM patients. Here, we discuss recent genomic advances, the role of innate and adaptive immune mechanisms, and the presence of an established immunosuppressive GBM microenvironment that suppresses and/or prevents the anti-tumor host response.

Leptomeningeal disease in melanoma patients: An update to treatment, challenges, and future directions

In February 2018, the Melanoma Research Foundation and the Moffitt Cancer Center hosted the Second Summit on Melanoma Central Nervous System Metastases in Tampa, Florida. The meeting included investigators from multiple academic centers and disciplines. A consensus summary of the progress and challenges in melanoma parenchymal brain metastases was published (Eroglu et al., Pigment Cell & Melanoma Research, 2019, 32, 458). Here, we will describe the current state of basic, translational, clinical research, and therapeutic management, for melanoma patients with leptomeningeal disease. We also outline key challenges and barriers to be overcome to make progress in this deadly disease.

Meningeal Immunity and Its Function in Maintenance of the Central Nervous System in Health and Disease

Neuroimmunology, albeit a relatively established discipline, has recently sparked numerous exciting findings on microglia, the resident macrophages of the central nervous system (CNS). This review addresses meningeal immunity, a less-studied aspect of neuroimmune interactions. The meninges, a triple layer of membranes—the pia mater, arachnoid mater, and dura mater—surround the CNS, encompassing the cerebrospinal fluid produced by the choroid plexus epithelium. Unlike the adjacent brain parenchyma, the meninges contain a wide repertoire of immune cells. These constitute meningeal immunity, which is primarily concerned with immune surveillance of the CNS, and—according to recent evidence—also participates in postinjury CNS recovery, chronic neurodegenerative conditions, and even higher brain function. Meningeal immunity has recently come under the spotlight owing to the characterization of meningeal lymphatic vessels draining the CNS. Here, we review the current state of our understanding of meningeal immunity and its effects on healthy and diseased brains.

Mechanisms of cognitive dysfunction in CKD

Cognitive impairment is an increasingly recognized major cause of chronic disability and is commonly found in patients with chronic kidney disease (CKD). Knowledge of the relationship between kidney dysfunction and impaired cognition may improve our understanding of other forms of cognitive dysfunction. Patients with CKD are at an increased risk (compared with the general population) of both dementia and its prodrome, mild cognitive impairment (MCI), which are characterized by deficits in executive functions, memory and attention. Brain imaging in patients with CKD has revealed damage to white matter in the prefrontal cortex and, in animal models, in the subcortical monoaminergic and cholinergic systems, accompanied by widespread macrovascular and microvascular damage. Unfortunately, current interventions that target cardiovascular risk factors (such as anti-hypertensive drugs, anti-platelet agents and statins) seem to have little or no effect on CKD-associated MCI, suggesting that the accumulation of uraemic neurotoxins may be more important than disturbed haemodynamic factors or lipid metabolism in MCI pathogenesis. Experimental models show that the brain monoaminergic system is susceptible to uraemic neurotoxins and that this system is responsible for the altered sleep pattern commonly observed in patients with CKD. Neural progenitor cells and the glymphatic system, which are important in Alzheimer disease pathogenesis, may also be involved in CKD-associated MCI. More detailed study of CKD-associated MCI is needed to fully understand its clinical relevance, underlying pathophysiology, possible means of early diagnosis and prevention, and whether there may be novel approaches and potential therapies with wider application to this and other forms of cognitive decline.

Endogenous neural precursor cells in health and disease

Neurogenesis persists in the adult brain of mammals in the subventricular zone (SVZ) of the lateral ventricles and in the subgranular zone (SGZ) of the dentate gyrus (DG). The complex interactions between intrinsic and extrinsic signals provided by cells in the niche but also from distant sources regulate the fate of neural stem/progenitor cells (NPCs) in these sites. This fine regulation is perturbed in aging and in pathological conditions leading to a different NPC behavior, tailored to the specific physio-pathological features. Indeed, NPCs exert in physiological and pathological conditions important neurogenic and non-neurogenic regulatory functions and participate in maintaining and protecting brain tissue homeostasis. In this review, we discuss intrinsic and extrinsic signals that regulate NPC activation and NPC functional role in various homeostatic and non-homeostatic conditions.

Peripheral Immunity, Immunoaging and Neuroinflammation in Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder among elderly population, characterized by the progressive degeneration of dopaminergic neurons in the midbrain. To date, exact cause remains unknown and the mechanism of neurons death uncertain. It is typically considered as a disease of central nervous system (CNS). Nevertheless, numerous evidence has been accumulated in several past years testifying undoubtedly about the principal role of neuroinflammation in progression of PD. Neuroinflammation is mainly associated with presence of activated microglia in brain and elevated levels of cytokine levels in CNS. Nevertheless, active participation of immune system as well has been noted, such as, elevated levels of cytokine levels in blood, the presence of auto antibodies, and the infiltration of T cell in CNS. Moreover, infiltration and reactivation of those T cells could exacerbate neuroinflammation to greater neurotoxic levels. Hence, peripheral inflammation is able to prime microglia into pro-inflammatory phenotype, which can trigger stronger response in CNS further perpetuating the on-going neurodegenerative process. In the present review, the interplay between neuroinflammation and the peripheral immune response in the pathobiology of PD will be discussed. First of all, an overview of regulation of microglial activation and neuroinflammation is summarized and discussed. Afterwards, we try to collectively analyze changes that occurs in peripheral immune system of PD patients, suggesting that these peripheral immune challenges can exacerbate the process of neuroinflammation and hence the symptoms of the disease. In the end, we summarize some of proposed immunotherapies for treatment of PD.

MiRNA-210 induces microglial activation and regulates microglia-mediated neuroinflammation in neonatal hypoxic-ischemic encephalopathy

Neuroinflammation is a major contributor to secondary neuronal injury that accounts for a significant proportion of final brain cell loss in neonatal hypoxic-ischemic encephalopathy (HIE). However, the immunological mechanisms that underlie HIE remain unclear. MicroRNA-210 (miR-210) is the master "hypoxamir" and plays a key role in hypoxic-ischemic tissue damage. Herein, we report in an animal model of neonatal rats that HIE significantly upregulated miR-210 expression in microglia in the neonatal brain and strongly induced activated microglia. Intracerebroventricular administration of miR-210 antagomir effectively suppressed microglia-mediated neuroinflammation and significantly reduced brain injury caused by HIE. We demonstrated that miR-210 induced microglial M1 activation partly by targeting SIRT1, thereby reducing the deacetylation of the NF-κB subunit p65 and increasing NF-κB signaling activity. Thus, our study identified miR-210 as a novel regulator of microglial activation in neonatal HIE, highlighting a potential therapeutic target in the treatment of infants with hypoxic-ischemic brain injury.

To the Brain and Back: Migratory Paths of Dendritic Cells in Multiple Sclerosis

Migration of dendritic cells (DC) to the central nervous system (CNS) is a critical event in the pathogenesis of multiple sclerosis (MS). While up until now, research has mainly focused on the transmigration of DC through the blood-brain barrier, experimental evidence points out that also the choroid plexus and meningeal vessels represent important gateways to the CNS, especially in early disease stages. On the other hand, DC can exit the CNS to maintain immunological tolerance to patterns expressed in the CNS, a process that is perturbed in MS. Targeting trafficking of immune cells, including DC, to the CNS has demonstrated to be a successful strategy to treat MS. However, this approach is known to compromise protective immune surveillance of the brain. Unravelling the migratory paths of regulatory and pathogenic DC within the CNS may ultimately lead to the design of new therapeutic strategies able to selectively interfere with the recruitment of pathogenic DC to the CNS, while leaving host protective mechanisms intact.

Neuroinflammation-induced lymphangiogenesis near the cribriform plate contributes to drainage of CNS-derived antigens and immune cells

There are no conventional lymphatic vessels within the CNS parenchyma, although it has been hypothesized that lymphatics near the cribriform plate or dura maintain fluid homeostasis and immune surveillance during steady-state conditions. However, the role of these lymphatic vessels during neuroinflammation is not well understood. We report that lymphatic vessels near the cribriform plate undergo lymphangiogenesis in a VEGFC – VEGFR3 dependent manner during experimental autoimmune encephalomyelitis (EAE) and drain both CSF and cells that were once in the CNS parenchyma. Lymphangiogenesis also contributes to the drainage of CNS derived antigens that leads to antigen specific T cell proliferation in the draining lymph nodes during EAE. In contrast, meningeal lymphatics do not undergo lymphangiogenesis during EAE, suggesting heterogeneity in CNS lymphatics. We conclude that increased lymphangiogenesis near the cribriform plate can contribute to the management of neuroinflammation-induced fluid accumulation and immune surveillance.

Lymphangiogenesis occurs in the context of systemic inflammation and development but has not been reported for the lymphatics that surround the CNS. Here the authors show that in the context of experimental autoimmune encephatlitis, lymphangiogenesis occurs at the cribriform plate, but not the meninges, and contributes to immune cell and antigen drainage.

The role of neutrophil granulocytes in immune-to-brain communication

Immune-to-brain communication has been studied in a variety of experimental models. Crucial insights into signalling and mechanisms were previously revealed in studies investigating fever induction pathways. The scientific community has primarily focused on neuronal and humoral pathways in the manifestation of this response. Emerging evidence has now shown that immune-to-brain signalling via immune cells is pivotal for normal brain function and brain pathology. The present manuscript aims to provide a brief overview on the current understanding of how immune cells signal to the brain. Insights are summarized on the potential physiological significance of some immune cells signalling from the periphery to the brain. A particular focus is laid on the role of neutrophil granulocytes. As such, IL-1β expressing neutrophil granulocytes have been shown to transfer inflammatory information to the brain and contribute to prolonged behavioural changes due to septic encephalopathy in rats during severe systemic inflammation induced by the bacterial component and TLR4 agonist lipopolysaccharide. Modulation of immune cell recruitment to the brain is discussed by various confounding factors including sleep, exercise, the nutritional status e.g. obesity, leptin and omega 3 fatty acids, and psychological or inflammatory stressors. The physiological significance of immune cell mediated communication between the immune system and the brain is highlighted by the fact that systemic inflammatory insults can exacerbate ongoing brain pathologies via immune cell trafficking. New insights into mechanisms and mediators of immune cell mediated immune-to-brain communication are important for the development of new therapeutic strategies and the better understanding of existing ones. Abbreviations: ACTH: adrenocorticotropic hormone; BBB: blood-brain barrier; BBI: blood-brain interface; CD: cluster of differentiation; CINC: cytokine-induced neutrophil chemoattractant; CRH: corticotropin releasing hormone; CVOs: circumventricular organs; CXCR: chemokine receptor; DAPI: 40:6-diamidino-2-phenylindole dilactate; DHA: docosahexaenoid acid; ICAM: intracellular adhesion molecule; IL: interleukin; i.p.: intraperitoneal; i.v.: intravenous; KC: keratinocytes-derived chemokine; LPS: lipopolysaccharide; MIP: macrophage inflammatory protein; MS: multiple sclerosis; NFκB: nuclear factor kappa B; NF-IL6: nuclear factor IL-6; PCTR: protectin conjugates in tissue regeneration; PG: prostaglandin; p.i.: post injection; PVN: paraventricular nucleus; ra: receptor antagonist; STAT3: signal transducer and activator of transcription 3; TIMP: tissue inhibitors of metalloproteinases; TLR: toll-like receptor; TNFα: tumor necrosis factor alpha.

Promises and limitations of immune cell-based therapies in neurological disorders

The healthy immune system has natural checkpoints that temper pernicious inflammation. Cells mediating these checkpoints include regulatory T cells, regulatory B cells, regulatory dendritic cells, microglia, macrophages and monocytes. Here, we highlight discoveries on the beneficial functions of regulatory immune cells and their mechanisms of action and evaluate their potential use as novel cell-based therapies for brain disorders. Regulatory immune cell therapies have the potential not only to mitigate the exacerbation of brain injury by inflammation but also to promote an active post-injury brain repair programme. By harnessing the reparative properties of these cells, we can reduce over-reliance on medications that mask clinical symptoms but fail to impede or reverse the progression of brain disorders. Although these discoveries encourage further testing and genetic engineering of regulatory immune cells for the clinical management of neurological disorders, a number of challenges must be surmounted to improve their safety and efficacy in humans.

Resident brain neural precursor cells develop age-dependent loss of therapeutic functions in Alzheimer's mice

There is vast knowledge on pathogenic mechanisms in Alzheimer's disease but very little on means by which the brain protects itself from disease. A major candidate in providing neuroprotection is the resident brain neural precursor/stem cell (NPC) pool. Transplanted NPCs possess powerful immune-modulatory and trophic properties in vivo and in vitro, underscoring the question whether resident brain NPCs have any role in regulating disease pathology in Alzheimer's disease, and particularly whether they fail to protect the brain from degeneration. To evaluate brain NPC function in relation to disease pathology, we first characterized the pathological properties of 5xFAD transgenic mouse model of Alzheimer's disease at different ages. We found that age 7 months is a critical time point of heavy amyloid deposition and gliosis but before neurodegeneration and a normal basal rate of NPC turnover in the subventricular zone (SVZ) of 5xFAD mice as compared to wild-type mice. Analysis of NPC functional properties showed that despite preserved rate of turnover, there was substantial SVZ NPC dysfunction as indicated by both ex vivo and in vivo assays. Freshly isolated NPCs from 7-month-old 5xFAD mice exhibited reduced expansion rate and diminished immune-modulatory and trophic properties. Moreover, there was slowed recovery of SVZ NPCs after cytosine-arabinoside insult and markedly reduced migratory response following a lysolecithin-induced lesion in the corpus callosum in vivo. Importantly, these functions were fully preserved in 2-month-old 5xFAD mice, a time point before Alzheimer's disease-specific pathological changes. There was reduced expression of key genes involved in NPC proliferative and migratory response in NPCs derived from 7-month-old 5xFAD mice. The dysfunctional properties and downregulation of gene expression were reversible in NPCs derived from 7-month-old 5xFAD mice following in vitro expansion and were reproduced in wild-type NPC by addition of amyloid beta peptide. Thus, there is age-dependent acquired NPC dysfunction, with loss of immune-modulatory and neurotrophic properties, which is induced by the pathological Alzheimer's brain environment at a critical time point before neurodegeneration. We suggest that failure of resident NPC to provide tissue support may be involved in promoting neurodegeneration.

Advances in NKT cell Immunotherapy for Glioblastoma

Type I or invariant natural killer T cells belong to a unique lineage of innate T cells, which express markers of both T lymphocytes and NK cells, namely T cell receptor (TCR) and NK1.1 (CD161C), respectively. Thus, apart from direct killing of target cells like NK cells, and they also produce a myriad of cytokines which modulate the adaptive immune responses. Unlike traditional T cells which carry a conventional αβ TCR, NKT cells express semi-invariant TCR - Vα14-Jα18, coupled with Vβ8, Vβ7 and Vβ2 in mice. In humans, the invariant TCR is composed of Vα24-Jα18, coupled with Vβ11.