Restoring immune suppression in the multiple sclerosis brain

A Pilot Study of Whole-Blood Transcriptomic Analysis to Identify Genes Associated with Repetitive Low-Level Blast Exposure in Career Breachers

Repetitive low-level blast exposure is one of the major occupational health concerns among US military service members and law enforcement. This study seeks to identify gene expression using microRNA and RNA sequencing in whole-blood samples from experienced breachers and unexposed controls. We performed experimental RNA sequencing using Illumina’s HiSeq 2500 Sequencing System, and microRNA analysis using NanoString Technology nCounter miRNA expression panel in whole-blood total RNA samples from 15 experienced breachers and 14 age-, sex-, and race-matched unexposed controls. We identified 10 significantly dysregulated genes between experienced breachers and unexposed controls, with FDR corrected <0.05: One upregulated gene, LINC00996 (long intergenic non-protein coding RNA 996); and nine downregulated genes, IGLV3-16 (immunoglobulin lambda variable 3-16), CD200 (CD200 molecule), LILRB5 (leukocyte immunoglobulin-like receptor B5), ZNF667-AS1 (ZNF667 antisense RNA 1), LMOD1 (leiomodin 1), CNTNAP2 (contactin-associated protein 2), EVPL (envoplakin), DPF3 (double PHD fingers 3), and IGHV4-34 (immunoglobulin heavy variable 4-34). The dysregulated gene expressions reported here have been associated with chronic inflammation and immune response, suggesting that these pathways may relate to the risk of lasting neurological symptoms following high exposures to blast over a career.

CD47 in the Brain and Neurodegeneration: An Update on the Role in Neuroinflammatory Pathways

CD47 is a receptor belonging to the immunoglobulin (Ig) superfamily and broadly expressed on cell membranes. Through interactions with ligands such as SIRPα, TSP-1, integrins, and SH2-domain bearing protein tyrosine phosphatase substrate-1 (SHPS-1), CD47 regulates numerous functions like cell adhesion, proliferation, apoptosis, migration, homeostasis, and the immune system. In this aspect, previous research has shown that CD47 modulates phagocytosis via macrophages, the transmigration of neutrophils, and the activation of T-cells, dendritic cells, and B-cells. Moreover, several studies have reported the increased expression of the CD47 receptor in a variety of diseases, including acute lymphoblastic leukemia (ALL), chronic myeloid leukemia, non-Hodgkin’s lymphoma (NHL), multiple myeloma (MM), bladder cancer, acute myeloid leukemia (AML), Gaucher disease, Multiple Sclerosis and stroke among others. The ubiquitous expression of the CD47 cell receptor on most resident cells of the CNS has previously been established through different methodologies. However, there is little information concerning its precise functions in the development of different neurodegenerative pathologies in the CNS. Consequently, further research pertaining to the specific functions and roles of CD47 and SIRP is required prior to its exploitation as a druggable approach for the targeting of various neurodegenerative diseases that affect the human population. The present review attempts to summarize the role of both CD47 and SIRP and their therapeutic potential in neurodegenerative disorders.

Phloroglucinol derivative compound 21 attenuates cuprizone-induced multiple sclerosis mice through promoting remyelination and inhibiting neuroinflammation

Multiple sclerosis (MS) is a chronic autoimmune demyelinating disease in the central nervous system. The myelin loss is mainly caused by dysfunction of oligodendrocytes and inflammatory responses of microglia and astrocytes further aggravate the demyelination. Current therapies for MS focus on suppressing the overactivated immune response but cannot halt the disease progress, so effective drugs are urgently needed. Compound 21 is a phloroglucinol derivative that has been proved to have an outstanding anti-inflammatory effect. The purpose of the present study is to investigate whether this novel compound is effective in MS. The cuprizone-induced model was used in this study to mimic the pathological progress of MS. The results showed that Compound 21 significantly improved the neurological dysfunction and motor coordination impairment. Luxol Fast Blue staining and myelin basic protein immunostaining demonstrated that Compound 21 remarkably promoted remyelination. In addition, Compound 21 significantly promoted oligodendrocytes differentiation. Furthermore, we found that Compound 21 decreased microglia and astrocytes activities and the subsequent neuroinflammatory response, indicating that the anti-inflammatory effect of Compound 21 was also involved in its neuro-protection. All the data prove that Compound 21 exerts protective effect on MS through promoting remyelination and suppressing neuroinflammation, indicating that Compound 21 might be a potential drug candidate for MS treatment.

Clinical PET Imaging of Microglial Activation: Implications for Microglial Therapeutics in Alzheimer's Disease

In addition to extracellular β-amyloid plaques and intracellular neurofibrillary tangles, neuroinflammation has been identified as a key pathological characteristic of Alzheimer's disease (AD). Once activated, neuroinflammatory cells called microglia acquire different activation phenotypes. At the early stage of AD, activated microglia are mainly dominated by the neuroprotective and anti-inflammatory M2 phenotype. Conversely, in the later stage of AD, the excessive activation of microglia is considered detrimental and pro-inflammatory, turning into the M1 phenotype. Therapeutic strategies targeting the modulation of microglia may regulate their specific phenotype. Fortunately, with the rapid development of in vivo imaging methodologies, visualization of microglial activation has been well-explored. In this review, we summarize the critical role of activated microglia during the pathogenesis of AD and current studies concerning imaging of microglial activation in AD patients. We explore the possibilities for identifying activated microglial phenotypes with imaging techniques and highlight promising therapies that regulate the microglial phenotype in AD mice.

Alterations in CD200-CD200R1 System during EAE Already Manifest at Presymptomatic Stages

In the brain of patients with multiple sclerosis, activated microglia/macrophages appear in active lesions and in normal appearing white matter. However, whether they play a beneficial or a detrimental role in the development of the pathology remains a controversial issue. The production of pro-inflammatory molecules by chronically activated microglial cells is suggested to contribute to the progression of neurodegenerative processes in neurological disease. In the healthy brain, neurons control glial activation through several inhibitory mechanisms, such as the CD200-CD200R1 interaction. Therefore, we studied whether alterations in the CD200-CD200R1 system might underlie the neuroinflammation in an experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis. We determined the time course of CD200 and CD200R1 expression in the brain and spinal cord of an EAE mouse model from presymptomatic to late symptomatic stages. We also assessed the correlation with associated glial activation, inflammatory response and EAE severity. Alterations in CD200 and CD200R1 expression were mainly observed in spinal cord regions in the EAE model, mostly a decrease in CD200 and an increase in CD200R1 expression. A decrease in the expression of the mRNA encoding a full CD200 protein was detected before the onset of clinical signs, and remained thereafter. A decrease in CD200 protein expression was observed from the onset of clinical signs. By contrast, CD200R1 expression increased at EAE onset, when a glial reaction associated with the production of pro- and anti-inflammatory markers occurred, and continued to be elevated during the pathology. Moreover, the magnitude of the alterations correlated with severity of the EAE mainly in spinal cord. These results suggest that neuronal-microglial communication through CD200-CD200R1 interaction is compromised in EAE. The early decreases in CD200 expression in EAE suggest that this downregulation might also occur in the initial phases of multiple sclerosis, and that this early neuronal dysfunction might facilitate the development of neuroinflammation. The increased CD200R1 expression in the EAE model highlights the potential use of targeted agonist molecules as therapeutic tools to control neuroinflammation. In summary, the CD200-CD200R1 system is a potential therapeutic target in multiple sclerosis, and CD200R1 agonists are molecules that may be worth developing in this context.

Interleukin-4 is a participant in the regulation of depressive-like behavior

Inflammatory immune activation has been frequently associated with the development of major depression. Microglia might serve as an important interface in this immune system-to-brain communication. Interleukin-4, the major Th2 type cytokine, might be protective against depression due to its ability to counter-regulate inflammation and to inhibit serotonin transporter activity. By using an Interferon-α mouse model, we show that a decreased IL-4 responsiveness of microglia was specifically related to the development of depressive-like behavior. IL-4 deficient mice in a BALB/cJ background showed a considerable increase of depressive-like behavior in the forced swim (FST) and tail suspension test (TST) and reduced avoidance behavior in an active avoidance task. Prior conditioning with unescapable foot shocks further decreased avoidance behavior (learned helplessness) but to a similar level as in the wild type strain. IFN-α treatment was not able to further enhance the already increased level of depressive-like behavior in the FST and TST. Thus, IL-4 seems to be a critical participant in the regulation of depressive-like behavior in an untreated baseline condition. Increase of depressive-like behavior during inflammation in wild-type mice might be mediated to some extent by a reduction of IL-4 signaling.

Novel CD200 homologues iSEC1 and iSEC2 are gastrointestinal secretory cell-specific ligands of inhibitory receptor CD200R

CD200R is an inhibitory receptor expressed on myeloid cells and some lymphoid cells, and plays important roles in negatively regulating immune responses. CD200 is the only known ligand of CD200R and broadly distributed in a variety of cell types. Here we identified novel CD200 homologues, designated iSEC1 and iSEC2, that are expressed exclusively by secretory cell lineages in the gastrointestinal epithelium while authentic CD200 is expressed by none of epithelial cells including secretory cells. Both iSEC1 and iSEC2 could bind to CD200R but not other members of the CD200R family. Notably, CD200R expression was confined to intraepithelial lymphocytes (IELs) among cells in the gastrointestinal epithelium. Binding of iSEC1 to CD200R on IELs resulted in the suppression of cytokine production and cytolytic activity by activated IELs. Thus, iSEC1 is a previously unappreciated CD200R ligand with restricted expression in gastrointestinal secretory cells and may negatively regulate mucosal immune responses.

Microglia activation is associated with IFN-α induced depressive-like behavior

Inflammatory immune activation has been frequently associated with the development of major depression. This association was confirmed in patients receiving long-term treatment with pro-inflammatory interferon-α (IFN-α). Microglia, the resident immune cells in the brain, might serve as an important interface in this immune system-to-brain communication. The aim of the present study was to investigate the role of microglia in an IFN-α mouse model of immune-mediated depression. Male BALB/c mice were treated with daily injections of IFN-α for two weeks. Depressive-like behavior was analyzed in the forced swim and tail suspension test. Activation of microglia was measured by flow cytometry. Pro-inflammatory M1 type (MHC-II, CD40, CD54, CD80, CD86, CCR7), anti-inflammatory M2 type (CD206, CD200R), and maturation markers (CD11c, CCR7) were tested, as well as the chemokine receptor CCR2. IFN-α led to a significant increase in depressive-like behavior and expression of the pro-inflammatory surface markers MHC-II, CD86, and CD54, indicating M1 polarization. Because IFN-α-treated mice showed great individual variance in the behavioral response to IFN-α, they were further divided into vulnerable and non-vulnerable subgroups. Only IFN-α vulnerable mice (characterized by their development of depressive-like behavior in response to IFN-α) showed an increased expression of MHC-II and CD86, while CD54 was similarly enhanced in both subgroups. Thus, IFN-α-induced activation of microglia was specifically associated with depressive-like behavior.

The immunomodulatory oligodendrocyte

Oligodendrocytes, the myelinating glial cells of the central nervous system (CNS), are due to their high specialization and metabolic needs highly vulnerable to various insults. This led to a general view that oligodendrocytes are defenseless victims during brain damage such as occurs in acute and chronic CNS inflammation. However, this view is challenged by increasing evidence that oligodendrocytes are capable of expressing a wide range of immunomodulatory molecules. They express various cytokines and chemokines (e.g. Il-1β, Il17A, CCL2, CXCL10), antigen presenting molecules (MHC class I and II) and co-stimulatory molecules (e.g. CD9, CD81), complement and complement receptor molecules (e.g. C1s, C2 and C3, C1R), complement regulatory molecules (e.g. CD46, CD55, CD59), tetraspanins (e.g. TSPAN2), neuroimmune regulatory proteins (e.g. CD200, CD47) as well as extracellular matrix proteins (e.g. VCAN) and many others. Their potential immunomodulatory properties can, at specific times and locations, influence ongoing immune processes as shown by numerous publications. Therefore, oligodendrocytes are well capable of immunomodulation, especially during the initiation or resolution of immune processes in which subtle signaling might tip the scale. A better understanding of the immunomodulatory oligodendrocyte can help to invent new, innovative therapeutic interventions in various diseases such as Multiple Sclerosis. This article is part of a Special Issue entitled SI: Myelin Evolution.

Macrophage subsets and microglia in multiple sclerosis

Along with microglia and monocyte-derived macrophages, macrophages in the perivascular space, choroid plexus, and meninges are the principal effector cells in neuroinflammatory and neurodegenerative disorders. These phagocytes are highly heterogeneous cells displaying spatial- and temporal-dependent identities in the healthy, injured, and inflamed CNS. In the last decade, researchers have debated on whether phagocytes subtypes and phenotypes are pathogenic or protective in CNS pathologies. In the context of this dichotomy, we summarize and discuss the current knowledge on the spatiotemporal physiology of macrophage subsets and microglia in the healthy and diseased CNS, and elaborate on factors regulating their behavior. In addition, the impact of macrophages present in lymphoid organs on CNS pathologies is defined. The prime focus of this review is on multiple sclerosis (MS), which is characterized by inflammation, demyelination, neurodegeneration, and CNS repair, and in which microglia and macrophages have been extensively scrutinized. On one hand, microglia and macrophages promote neuroinflammatory and neurodegenerative events in MS by releasing inflammatory mediators and stimulating leukocyte activity and infiltration into the CNS. On the other hand, microglia and macrophages assist in CNS repair through the production of neurotrophic factors and clearance of inhibitory myelin debris. Finally, we define how microglia and macrophage physiology can be harnessed for new therapeutics aimed at suppressing neuroinflammatory and cytodegenerative events, as well as promoting CNS repair. We conclude that microglia and macrophages are highly dynamic cells displaying disease stage and location-specific fates in neurological disorders. Changing the physiology of divergent phagocyte subsets at particular disease stages holds promise for future therapeutics for CNS pathologies.

Myelin antigen load influences antigen presentation and severity of central nervous system autoimmunity

This study was designed to understand the impact of self-antigen load on manifestation of organ specific autoimmunity. Using a transgenic mouse model characterized by CNS hypermyelination, we show that larger myelin content results in greater severity of experimental autoimmune encephalomyelitis attributable to an increased number of microglia within the hypermyelinated brain. We conclude that a larger self-antigen load affects an increase in number of tissue resident antigen presenting cells (APCs) most likely due to compensatory antigen clearance mechanisms thereby enhancing the probability of productive T cell-APC interactions in an antigen abundant environment and results in enhanced severity of autoimmune disease.

Multifaces of neuropeptide Y in the brain--neuroprotection, neurogenesis and neuroinflammation

Neuropeptide Y (NPY) has been implicated in the modulation of important features of neuronal physiology, including calcium homeostasis, neurotransmitter release and excitability. Moreover, NPY has been involved as an important modulator of hippocampal and thalamic circuits, receiving particular attention as an endogenous antiepileptic peptide and as a potential master regulator of feeding behavior. NPY not only inhibits excessive glutamate release (decreasing circuitry hyperexcitability) but also protects neurons from excitotoxic cell death. Furthermore, NPY has been involved in the modulation of the dynamics of dentate gyrus and subventricular zone neural stem cell niches. In both regions, NPY is part of the chemical resource of the neurogenic niche and acts through NPY Y1 receptors to promote neuronal differentiation. Interestingly, NPY is also considered a neuroimmune messenger. In this review, we highlight recent evidences concerning paracrine/autocrine actions of NPY involved in neuroprotection, neurogenesis and neuroinflammation. In summary, the three faces of NPY, discussed in the present review, may contribute to better understand the dynamics and cell fate decision in the brain parenchyma and in restricted areas of neurogenic niches, in health and disease.

The conundrum of iron in multiple sclerosis--time for an individualised approach

Although the involvement of immune mechanisms in multiple sclerosis (MS) is undisputed, some argue that there is insufficient evidence to support the hypothesis that MS is an autoimmune disease, and that the difference between immune- and autoimmune disease mechanisms has yet to be clearly delineated. Uncertainties surrounding MS disease pathogenesis and the modest efficacy of currently used disease modifying treatments (DMTs) in the prevention of disability, warrant the need to explore other possibilities. It is evident from the literature that people diagnosed with MS differ widely in symptoms and clinical outcome--some patients have a benign disease course over many years without requiring any DMTs. Attempting to include all patients into a single entity is an oversimplification and may obscure important observations with therapeutic consequences. In this review we advocate an individualised approach named Pathology Supported Genetic Testing (PSGT), in which genetic tests are combined with biochemical measurements in order to identify subgroups of patients requiring different treatments. Iron dysregulation in MS is used as an example of how this approach may benefit patients. The theory that iron deposition in the brain contributes to MS pathogenesis has caused uncertainty among patients as to whether they should avoid iron. However, the fact that a subgroup of people diagnosed with MS show clinical improvement when they are on iron supplementation emphasises the importance of individualised therapy, based on genetic and biochemical determinations.

1α,25-dihydroxyvitamin D3 promotes CD200 expression by human peripheral and airway-resident T cells

BACKGROUND

CD200, a cell-surface immunoglobulin-like molecule expressed by immune and stromal cells, dampens the pro-inflammatory activity of tissue-resident innate cells via its receptor, CD200R. This interaction appears critical for peripheral immune tolerance, particularly in the airways where excessive inflammation is undesirable. Vitamin D contributes to pulmonary health and promotes regulatory immune pathways, therefore its influence on CD200 and CD200R was investigated.

METHODS

CD200 and CD200R expression were assessed by qPCR and immunoreactivity of human lymphoid, myeloid and epithelial cells following 1α,25-dihydroxyvitamin D3 (1α,25VitD3) exposure in vitro and in peripheral T cells following 1α,25VitD3 oral ingestion in vivo. The effect of 1α25VitD3 was also assessed in human airway-resident cells.

RESULTS

1α25VitD3 potently upregulated CD200 on peripheral human CD4+ T cells in vitro, and in vivo there was a trend towards upregulation in healthy, but not asthmatic individuals. CD200R expression was not modulated in any cells studied. CD200 induction was observed to a lesser extent in CD8+ T cells and not in B cells or airway epithelium. T cells isolated from the human airway also responded strongly to 1α25VitD3 to upregulate CD200.

CONCLUSIONS

The capacity of 1α,25-dihydroxyvitamin D3 to induce CD200 expression by peripheral and respiratory tract T cells identifies an additional pathway via which vitamin D can restrain inflammation in the airways to maintain respiratory health.

The neuroprotective effects of milk fat globule-EGF factor 8 against oligomeric amyloid β toxicity

Background

Phosphatidylserine receptor is a key molecule that mediates the phagocytosis of apoptotic cells. Milk fat globule-EGF factor 8 (MFG-E8) is a phosphatidylserine receptor that is expressed on various macrophage lineage cells, including microglia in the central nervous system (CNS). Targeted clearance of degenerated neurons by microglia is essential to maintain healthy neural networks. We previously showed that the CX3C chemokine fractalkine is secreted from degenerated neurons and accelerates microglial clearance of neuronal debris via inducing the release of MFG-E8. However, the mechanisms by which microglia produce MFG-E8 and the precise functions of MFG-E8 are unknown.

Methods

The release of MFG-E8 from microglia treated with conditioned medium from neurons exposed to neurotoxic substances, glutamate or oligomeric amyloid β (oAβ) was measured by ELISA. The neuroprotective effects of MFG-E8 and MFG-E8 − induced microglial phagocytosis of oAβ were assessed by immunocytochemistry. The effects of MFG-E8 on the production of the anti-oxidative enzyme hemeoxygenase-1 (HO-1) were determined by ELISA and immunocytochemisty.

Results

MFG-E8 was induced in microglia treated with conditioned medium from neurons that had been exposed to neurotoxicants, glutamate or oAβ. MFG-E8 significantly attenuated oAβ-induced neuronal cell death in a primary neuron − microglia coculture system. Microglial phagocytosis of oAβ was accelerated by MFG-E8 treatment due to increased CD47 expression in the absence of neurotoxic molecule production, such as tumor necrosis factor-α, nitric oxide, and glutamate. MFG-E8 − treated microglia induced nuclear factor E(2) − related factor 2 (Nrf2) − mediated HO-1 production, which also contributed to neuroprotection.

Conclusions

These results suggest that microglia release MFG-E8 in response to signals from degenerated neurons and that MFG-E8 protects oAβ-induced neuronal cell death by promoting microglial phagocytic activity and activating the Nrf2-HO-1 pathway. Thus, MFG-E8 may have novel roles as a neuroprotectant in neurodegenerative conditions.

Animal Models of MS Reveal Multiple Roles of Microglia in Disease Pathogenesis

Multiple sclerosis (MS) is a progressive inflammatory and demyelinating disease that affects more than 2.5 million people worldwide every year. Current therapies use mostly disease-modifying drugs, focusing on blocking and regulating systemic functions and the central nervous system (CNS) infiltration of immune cells; however, these therapies only attenuate or delay MS symptoms, but are not effective in halting the disease progression. More recent evidence indicated that regulation of inflammation within the CNS might be a better way to approach the treatment of the disease and microglia, the resident immune cells, may be a promising target of therapeutic studies. Microglia activation classically accompanies MS development, and regulation of microglia function changes the outcome of the disease. In this paper, we review the contributions of microglia to MS pathogenesis and discuss microglial functions in antigen presentation, cytokine release, and phagocytosis. We describe data both from animal and human studies. The significant impact of the timing, intensity, and differentiation fate of activated microglia is discussed, as they can modulate MS outcomes and potentially be critically modified for future therapeutic studies.

CD200-CD200R dysfunction exacerbates microglial activation and dopaminergic neurodegeneration in a rat model of Parkinson's disease

BACKGROUND

Increasing evidence suggests that microglial activation may participate in the aetiology and pathogenesis of Parkinson's disease (PD). CD200-CD200R signalling has been shown to be critical for restraining microglial activation. We have previously shown that expression of CD200R in monocyte-derived macrophages, induced by various stimuli, is impaired in PD patients, implying an intrinsic abnormality of CD200-CD200R signalling in PD brain. Thus, further in vivo evidence is needed to elucidate the role of malfunction of CD200-CD200R signalling in the pathogenesis of PD.

METHODS

6-hydroxydopamine (6-OHDA)-lesioned rats were used as an animal model of PD. CD200R-blocking antibody (BAb) was injected into striatum to block the engagement of CD200 and CD200R. The animals were divided into three groups, which were treated with 6-OHDA/Veh (PBS), 6-OHDA/CAb (isotype control antibody) or 6-OHDA/BAb, respectively. Rotational tests and immunohistochemistry were employed to evaluate motor deficits and dopaminergic neurodegeneration in animals from each group. HPLC analysis was used to measure monoamine levels in striatum. Morphological analysis and quantification of CD11b- (or MHC II-) immunoreactive cells were performed to investigate microglial activation and possible neuroinflammation in the substantia nigra (SN). Finally, ELISA was employed to assay protein levels of proinflammatory cytokines.

RESULTS

Compared with 6-OHDA/CAb or 6-OHDA/Veh groups, rats treated with 6-OHDA/BAb showed a significant increase in counts of contralateral rotation and a significant decrease in TH-immunoreactive (TH-ir) neurons in SN. A marked decrease in monoamine levels was also detected in 6-OHDA/BAb-treated rats, in comparison to 6-OHDA/Veh-treated ones. Furthermore, remarkably increased activation of microglia as well as up-regulation of proinflammatory cytokines was found concomitant with dopaminergic neurodegeneration in 6-OHDA/BAb-treated rats.

CONCLUSIONS

This study shows that deficits in the CD200-CD200R system exacerbate microglial activation and dopaminergic neurodegeneration in a 6-OHDA-induced rat model of PD. Our results suggest that dysfunction of CD200-CD200R signalling may be involved in the aetiopathogenesis of PD.

Cannabidiol inhibits pathogenic T cells, decreases spinal microglial activation and ameliorates multiple sclerosis-like disease in C57BL/6 mice

BACKGROUND AND PURPOSE

Cannabis extracts and several cannabinoids have been shown to exert broad anti-inflammatory activities in experimental models of inflammatory CNS degenerative diseases. Clinical use of many cannabinoids is limited by their psychotropic effects. However, phytocannabinoids like cannabidiol (CBD), devoid of psychoactive activity, are, potentially, safe and effective alternatives for alleviating neuroinflammation and neurodegeneration.

EXPERIMENTAL APPROACH

We used experimental autoimmune encephalomyelitis (EAE) induced by myelin oligodendrocyte glycoprotein (MOG) in C57BL/6 mice, as a model of multiple sclerosis. Using immunocytochemistry and cell proliferation assays we evaluated the effects of CBD on microglial activation in MOG-immunized animals and on MOG-specific T-cell proliferation.

KEY RESULTS

Treatment with CBD during disease onset ameliorated the severity of the clinical signs of EAE. This effect of CBD was accompanied by diminished axonal damage and inflammation as well as microglial activation and T-cell recruitment in the spinal cord of MOG-injected mice. Moreover, CBD inhibited MOG-induced T-cell proliferation in vitro at both low and high concentrations of the myelin antigen. This effect was not mediated via the known cannabinoid CB(1) and CB(2) receptors.

CONCLUSIONS AND IMPLICATIONS

CBD, a non-psychoactive cannabinoid, ameliorates clinical signs of EAE in mice, immunized against MOG. Suppression of microglial activity and T-cell proliferation by CBD appeared to contribute to these beneficial effects.

Dual induction of TREM2 and tolerance-related transcript, Tmem176b, in amyloid transgenic mice: implications for vaccine-based therapies for Alzheimer's disease

Vaccine-based autoimmune (anti-amyloid) treatments are currently being examined for their therapeutic potential in Alzheimer's disease. In the present study we examined, in a transgenic model of amyloid pathology, the expression of two molecules previously implicated in decreasing the severity of autoimmune responses: TREM2 (triggering receptor expressed on myeloid cells 2) and the intracellular tolerance-associated transcript, Tmem176b (transmembrane domain protein 176b). In situ hybridization analysis revealed that both molecules were highly expressed in plaque-associated microglia, but their expression defined two different zones of plaque-associated activation. Tmem176b expression was highest in the inner zone of amyloid plaques, whereas TREM2 expression was highest in the outer zone. Induced expression of TREM2 occurred co-incident with detection of thioflavine-S-positive amyloid deposits. Transfection studies revealed that expression of TREM2 correlated negatively with motility, but correlated positively with the ability of microglia to stimulate CD4⁺ T-cell proliferation, TNF (tumour necrosis factor) and CCL2 (chemokine ligand 2) production, but not IFNγ (interferon γ) production. TREM2 expression also showed a positive correlation with amyloid phagocytosis in unactivated cells. However, activating cells with LPS (lipopolysaccharide), but not IFNγ, reduced the correlation between TREM2 expression and phagocytosis. Transfection of Tmem176b into both microglial and macrophage cell lines increased apoptosis. Taken together, these data suggest that, in vivo, Tmem176b⁺ cells in closest apposition to amyloid may be the least able to clear amyloid. Conversely, the phagocytic TREM2⁺ microglia on the plaque outer zones are positioned to capture and present self-antigens to CNS (central nervous system)-infiltrating lymphocytes without promoting pro-inflammatory lymphocyte responses. Instead, plaque-associated TREM2⁺ microglia have the potential to evoke neuroprotective immune responses that may serve to support CNS function during pro-inflammatory anti-amyloid immune therapies.