Microglial cell activation and proliferation precedes the onset of CNS autoimmunity

Different peripheral tissue injury induces differential phenotypic changes of spinal activated microglia

The purpose of this study is to investigate the possible different cellular marker expression associated with spinal cord microglial activation in different pain models. Immunohistochemistry and western blotting analysis of CD45, CD68, and MHC class I antigen as well as CD11b and Iba-1 in the spinal cord were quantitatively compared among widely used three pain animal models, complete Freund's adjuvant (CFA) injection, formalin injection, and chronic constriction injury (CCI) models. The results showed that significant upregulated expressions of CD45 and MHC class I antigen in spinal microglia as well as morphological changes with increased staining with CD11b and Iba-1 were seen in CCI and formalin models and not found in CFA-induced inflammatory pain model. CD68 expression was only detected in CCI model. Our findings suggested that different peripheral tissue injuries produced differential phenotypic changes associated with spinal microglial activation; peripheral nerve injury might induce spinal microglia to acquire these immunomolecular phenotypic changes.

Functional diversity of microglia - how heterogeneous are they to begin with?

Microglia serve in the surveillance and maintenance, protection and restoration of the central nervous system (CNS) homeostasis. By their parenchymal location they differ from other CNS-associated myeloid cells, and by origin as well as functional characteristics they are also–at least in part–distinct from extraneural tissue macrophages. Nevertheless, microglia themselves may not comprise a uniform cell type. CNS regions vary by cellular and chemical composition, including white matter (myelin) content, blood–brain barrier properties or prevailing neurotransmitters. Such a micromilieu could instruct as well as require local adaptions of microglial features. Yet even cells within circumscribed populations may reveal some specialization by subtypes, regarding house-keeping duties and functional capacities upon challenges. While diversity of reactive phenotypes has been established still little is known as to whether all activated cells would respond with the same program of induced genes and functions or whether responder subsets have individual contributions. Preferential synthesis of a key cytokine could asign a master control to certain cells among a pool of activated microglia. Critical functions could be sequestered to discrete microglial subtypes in order to avoid interference, such as clearance of endogenous material and presentation of antigens. Indeed, several and especially a number of recent studies provide evidence for the constitutive and reactive heterogeneity of microglia by and within CNS regions. While such a principle of “division of labor” would influence the basic notion of “the” microglia, it could come with the practival value of addressing separate microglia types in experimental and therapeutic manipulations.

All-trans-retinoic acid ameliorates experimental allergic encephalomyelitis by affecting dendritic cell and monocyte development

Experimental allergic encephalomyelitis (EAE) can be induced in animal models by injecting the MOG35-55 peptide subcutaneously. Dendritic cells (DCs) that are located at the immunization site phagocytose the MOG35-55 peptide. These DCs mature and migrate into the nearest draining lymph nodes (dLNs), then present antigen, resulting in the activation of naive T cells. T helper type 1 (Th1) and Th17 cells are the primary cells involved in EAE progression. All-trans-retinoic acid (AT-RA) has been shown to have beneficial effects on EAE progression; however, whether AT-RA influences DC maturation or mediates other functions is unclear. In the present study, we showed that AT-RA led to the down-regulation of MHC class II, CD80 (B7-1) and CD86 (B7-2) expressed on the surface of DCs that were isolated from dLNs or spleen 3 days post-immunization in an EAE model. Changes to DC function influenced Th1/Th17 subset polarization. Furthermore, the number of CD44(+) monocytes (which might trigger EAE progression) was also significantly decreased in dLNs, spleen, subarachnoid space and the spinal cord parenchyma after AT-RA treatment. These findings are the first to demonstrate that AT-RA impairs the antigen-presenting capacity of DCs, leading to down-regulation of pathogenic Th1 and Th17 inflammatory cell responses and reducing EAE severity.

Dynamic cross-regulation of antigen-specific effector and regulatory T cell subpopulations and microglia in brain autoimmunity

Background

Multiple Sclerosis (MS) is considered a T-cell-mediated autoimmune disease with a prototypical oscillatory behavior, as evidenced by the presence of clinical relapses. Understanding the dynamics of immune cells governing the course of MS, therefore, has many implications for immunotherapy. Here, we used flow cytometry to analyze the time-dependent behavior of antigen-specific effector (T_eff) and regulatory (T_reg) T cells and microglia in mice model of MS, Experimental Autoimmune Encephalomyelitis (EAE), and compared the observations with a mathematical cross-regulation model of T-cell dynamics in autoimmune disease.

Results

We found that T_eff and T_reg cells specific to myelin olygodendrocyte glycoprotein (MOG) developed coupled oscillatory dynamics with a 4- to 5-day period and decreasing amplitude that was always higher for the T_eff populations, in agreement with the mathematical model. Microglia activation followed the oscillations of MOG-specific T_eff cells in the secondary lymphoid organs, but they were activated before MOG-specific T-cell peaks in the CNS. Finally, we assessed the role of B-cell depletion induced by anti-CD20 therapy in the dynamics of T cells in an EAE model with more severe disease after therapy. We observed that B-cell depletion decreases T_eff expansion, although its oscillatory behavior persists. However, the effect of B cell depletion was more significant in the T_reg population within the CNS, which matched with activation of microglia and worsening of the disease. Mathematical modeling of T-cell cross-regulation after anti-CD20 therapy suggests that B-cell depletion may influence the dynamics of T cells by fine-tuning their activation.

Conclusions

The oscillatory dynamics of T-cells have an intrinsic origin in the physiological regulation of the adaptive immune response, which influences both disease phenotype and response to immunotherapy.

Peli1 promotes microglia-mediated CNS inflammation by regulating Traf3 degradation

Microglia are crucial for the pathogenesis of multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE). Here we show that the E3 ubiquitin ligase Peli1 is abundantly expressed in microglia and promotes microglial activation during the course of EAE induction. Peli1 mediates the induction of chemokines and proinflammatory cytokines in microglia and thereby promotes recruitment of T cells into the central nervous system. The severity of EAE is reduced in Peli1-deficient mice despite their competent induction of inflammatory T cells in the peripheral lymphoid organs. Notably, Peli1 regulates Toll-like receptor (TLR) pathway signaling by promoting degradation of TNF receptor-associated factor 3 (Traf3), a potent inhibitor of mitogen-activated protein kinase (MAPK) activation and gene induction. Ablation of Traf3 restores microglial activation and CNS inflammation after the induction of EAE in Peli1-deficient mice. These findings establish Peli1 as a microglia-specific mediator of autoimmune neuroinflammation and suggest a previously unknown signaling mechanism of Peli1 function.

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.

Efficiently stimulated adult microglia cross-prime naive CD8+ T cells injected in the brain

Microglia are the major myeloid-immune cells of the brain parenchyma. In a steady state, microglia monitor their environment for pathogens or damaged cells. In response to neural injury or inflammation, microglia become competent APCs able to prime CD4(+) and CD8(+) T lymphocytes. We previously demonstrated that neonatal and adult microglia cross-present exogenous soluble Ags in vitro. However, whether microglia are able to cross-present Ag to naive CD8(+) T cells in vivo, within the brain microenvironment, remains undetermined. Here, we have designed an original protocol in order to exclude the involvement in cross-presentation activity of peripheral migrating APCs and of CNS-associated APCs. In C57Bl/6 mice, in which the body but not the head has been properly irradiated, we analyzed the ability of resident microglia to stimulate intracerebrally injected CD8(+) T cells in vivo. This study demonstrates for the first time that adult microglia cross-present Ag to naive CD8(+) T cells in vivo and that full microglia activation is required to overcome the inhibitory constrains of the brain and to render microglia able to cross-prime naive CD8(+) T cells injected in the brain. These observations offer new insights in brain-tumor immunotherapy based on the induction of cytotoxic antitumoral T cells.

Adaptive immune responses in CNS autoimmune disease: mechanisms and therapeutic opportunities

The processes underlying autoimmune CNS inflammation are complex, but key roles for autoimmune lymphocytes seem inevitable, based on clinical investigations in multiple sclerosis (MS) and related diseases such as neuromyelitis optica, together with the known pathogenic activity of T cells in experimental autoimmune encephalomyelitis (EAE) models. Despite intense investigation, the details of etiopathology in these diseases have been elusive. Here we describe recent advances in the rodent models that begin to allow a map of pathogenic and protective immunity to be drawn. This map might illuminate previous successful and unsuccessful therapeutic strategies targeting particular pathways, whilst also providing better opportunities for the future, leading to tailored intervention based on understanding the quality of each individual's autoimmune response.

Regulation of microglial proliferation during chronic neurodegeneration

An important component of chronic neurodegenerative diseases is the generation of an innate inflammatory response within the CNS. Microglial and astroglial cells play a key role in the development and maintenance of this inflammatory response, showing enhanced proliferation and activation. We studied the time course and regulation of microglial proliferation, using a mouse model of prion disease. Our results show that the proliferation of resident microglial cells accounts for the expansion of the population during the development of the disease. We identify the pathway regulated by the activation of CSF1R and the transcription factors PU.1 and C/EBPα as the molecular regulators of the proliferative response, correlating with the chronic human neurodegenerative conditions variant Creutzfeldt-Jakob disease and Alzheimer's disease. We show that targeting the activity of CSF1R inhibits microglial proliferation and slows neuronal damage and disease progression. Our results demonstrate that microglial proliferation is a major component in the evolution of chronic neurodegeneration, with direct implications for understanding the contribution of the CNS innate immune response to disease progression.

C16 peptide shown to prevent leukocyte infiltration and alleviate detrimental inflammation in acute allergic encephalomyelitis model

Integrins are important adhesion receptors for leukocytes binding to endothelial cellular adhesion molecules. Previous studies have suggested that blocking relevant integrins might prevent leukocyte infiltration and suppress clinical and pathological features of neuroinflammatory disease. Experimental autoimmune encephalomyelitis (EAE), a rodent model of Multiple sclerosis (MS), is characterized by chronic inflammatory disorder of the central nervous system in which circulating leukocytes enter the brain and spinal cord leading to inflammation, myelin damage and subsequent paralysis. To prove this hypothesis and explore a promising application for MS treatment, the effects of C16, an ανβ3 integrin-binding peptide, were tested in vitro and in vivo by transendothelial assay, electron microscopy observation, multiple histological and immunohistochemical staining. The results showed C16 inhibited transendothelial migration of the C8166-CD4 lymphoblast cells, and alleviated extensive spinal cord and brain infiltration of leukocytes and macrophages in the EAE model. Furthermore, a significant amelioration of astrogliosis and a dramatic decrease in demyelination and axonal loss were observed in C16 treated animals. The attenuating inflammatory progression may improve the regional environment and trigger further neuroprotective effects on myelin and axons, all this suggests that C16 peptide may be a promising therapeutic agent for multiple sclerosis.

MicroRNAs in the brain: it's regulatory role in neuroinflammation

MicroRNAs (miRNAs) are single-stranded noncoding regions of approximately 21 nucleotides that regulate protein synthesis by targeting mRNAs for translational repression or degradation at the post-transcriptional level. These classes of RNAs are highly conserved across species and are known to regulate several protein-coding genes in humans. Therefore, their dysregulation is synonymous with inflammation, autoimmunity, neurodegeneration, viral infections, heart diseases, and cancer, among other conditions. Recent years have witnessed considerable amount of research interest in studies on miRNA-mediated modulation of gene function during neuroinflammation. This review is a meticulous compilation of information on biogenesis of miRNAs and their role in neuroinflammatory diseases. Further, their potential as markers of inflammatory diseases or novel therapeutic agents against neuroinflammation has also been discussed in detail.

Differential lumbar spinal cord responses among wild type, CD4 knockout, and CD40 knockout mice in spinal nerve L5 transection-induced neuropathic pain

BACKGROUND

Our previous studies have indicated that both lumbar spinal cord-infiltrating CD4+ T cells and microglial CD40 contribute to the maintenance of mechanical hypersensitivity in a murine model of neuropathic pain spinal nerve L5 transection (L5Tx). To further delineate the CD4 and CD40-mediated mechanisms involved in the development of L5Tx-induced neuropathic pain behaviors, we examined the lumbar spinal cord mononuclear cells of wild type (WT) BALB/c, BALB/c-CD4 knockout (KO), and BALB/c-CD40 KO mice via flow cytometry.

RESULTS

In WT mice, L5Tx induced significant but transient (at day 3 and/or day 7) increases of the total numbers of mononuclear cells, microglial cells (CD45loCD11b+), and infiltrating leukocytes (CD45hi) in the ipsilateral side of the spinal cord. In CD4 KO mice, significant elevation of microglia was detected only on day 7 post-L5Tx, while no significant increase in infiltrating leukocytes post-L5Tx was observed. CD40 KO mice did not exhibit any of the changes observed in WT mice. Furthermore, neutralizing CD40 antibody treatment indicated an early involvement of CD40 signaling in the development of L5Tx-induced mechanical hypersensitivity.

CONCLUSIONS

Altogether, data indicate that both CD4 and CD40 play a role in L5Tx-induced leukocyte infiltration into the lumbar spinal cord but have differential contributions to spinal cord microglial activation following peripheral nerve injury.

Monocyte-derived cells of the brain and malignant gliomas: the double face of Janus

OBJECTIVE

Monocyte-derived cells of the brain (MDCB) are a diverse group of functional immune cells that are also highly abundant in gliomas. There is growing evidence that MDCB play essential roles in the pathogenesis of gliomas. The aim of this review was to collate and systematize contemporary knowledge about these cells as they relate to glioma progression and antiglioblastoma therapeutic modalities with a view toward improved effectiveness of therapy.

METHODS

We reviewed relevant studies to construct a summary of different MDCB subpopulations in steady state and in malignant gliomas and discuss their role in the development of malignant gliomas and potential future therapies.

RESULTS

Current studies suggest that MDCB subsets display different phenotypes and differentiation potentials depending on their milieu in the brain and exposure to tumoral influences. MDCB possess specific and unique functions, including those that are protumoral and those that are antitumoral.

CONCLUSIONS

Elucidating the role of mononuclear-derived cells associated with gliomas is crucial in designing novel immunotherapy strategies. Much progress is needed to characterize markers to identify cell subsets and their specific regulatory roles. Investigation of MDCB can be clinically relevant. Specific MDCB populations potentially can be used for glioma therapy as a target or as cell vehicles that might deliver cytotoxic substances or processes to the glioma microenvironment.

Monocyte galactose/N-acetylgalactosamine-specific C-type lectin receptor stimulant immunotherapy of an experimental glioma. Part II: combination with external radiation improves survival

Background

A peptide mimetic of a ligand for the galactose/N-acetylgalactosamine-specific C-type lectin receptors (GCLR) exhibited monocyte-stimulating activity, but did not extend survival when applied alone against a syngeneic murine malignant glioma. In this study, the combined effect of GCLRP with radiation was investigated.

Methods

C57BL/6 mice underwent stereotactic intracranial implantation of GL261 glioma cells. Animals were grouped based on randomized tumor size by magnetic resonance imaging on day seven. One group that received cranial radiation (4 Gy on days seven and nine) only were compared with animals treated with radiation and GCLRP (4 Gy on days seven and nine combined with subcutaneous injection of 1 nmol/g on alternative days beginning on day seven). Magnetic resonance imaging was used to assess tumor growth and correlated with survival rate. Blood and brain tissues were analyzed with regard to tumor and contralateral hemisphere using fluorescence-activated cell sorting analysis, histology, and enzyme-linked immunosorbent assay.

Results

GCLRP activated peripheral monocytes and was associated with increased blood precursors of dendritic cells. Mean survival increased (P < 0.001) and tumor size was smaller (P < 0.02) in the GCLRP + radiation group compared to the radiation-only group. Accumulation of dendritic cells in both the tumoral hemisphere (P < 0.005) and contralateral tumor-free hemisphere (P < 0.01) was associated with treatment.

Conclusion

Specific populations of monocyte-derived brain cells develop critical relationships with malignant gliomas. The biological effect of GCLRP in combination with radiation may be more successful because of the damage incurred by tumor cells by radiation and the enhanced or preserved presentation of tumor cell antigens by GCLRP-activated immune cells. Monocyte-derived brain cells may be important targets for creating effective immunological modalities such as employing the receptor system described in this study.

Brain conditioning is instrumental for successful microglia reconstitution following hematopoietic stem cell transplantation

The recent hypothesis that postnatal microglia are maintained independently of circulating monocytes by local precursors that colonize the brain before birth has relevant implications for the treatment of various neurological diseases, including lysosomal storage disorders (LSDs), for which hematopoietic cell transplantation (HCT) is applied to repopulate the recipient myeloid compartment, including microglia, with cells expressing the defective functional hydrolase. By studying wild-type and LSD mice at diverse time-points after HCT, we showed the occurrence of a short-term wave of brain infiltration by a fraction of the transplanted hematopoietic progenitors, independently from the administration of a preparatory regimen and from the presence of a disease state in the brain. However, only the use of a conditioning regimen capable of ablating functionally defined brain-resident myeloid precursors allowed turnover of microglia with the donor, mediated by local proliferation of early immigrants rather than entrance of mature cells from the circulation.

Detection of microRNAs in microglia by real-time PCR in normal CNS and during neuroinflammation

Microglia are cells of the myeloid lineage that reside in the central nervous system (CNS)(1). These cells play an important role in pathologies of many diseases associated with neuroinflammation such as multiple sclerosis (MS)(2). Microglia in a normal CNS express macrophage marker CD11b and exhibit a resting phenotype by expressing low levels of activation markers such as CD45. During pathological events in the CNS, microglia become activated as determined by upregulation of CD45 and other markers(3). The factors that affect microglia phenotype and functions in the CNS are not well studied. MicroRNAs (miRNAs) are a growing family of conserved molecules (~22 nucleotides long) that are involved in many normal physiological processes such as cell growth and differentiation(4) and pathologies such as inflammation(5). MiRNAs downregulate the expression of certain target genes by binding complementary sequences of their mRNAs and play an important role in the activation of innate immune cells including macrophages(6) and microglia(7). In order to investigate miRNA-mediated pathways that define the microglial phenotype, biological function, and to distinguish microglia from other types of macrophages, it is important to quantitatively assess the expression of particular microRNAs in distinct subsets of CNS-resident microglia. Common methods for measuring the expression of miRNAs in the CNS include quantitative PCR from whole neuronal tissue and in situ hybridization. However, quantitative PCR from whole tissue homogenate does not allow the assessment of the expression of miRNA in microglia, which represent only 5-15% of the cells of neuronal tissue. Hybridization in situ allows the assessment of the expression of microRNA in specific cell types in the tissue sections, but this method is not entirely quantitative. In this report we describe a quantitative and sensitive method for the detection of miRNA by real-time PCR in microglia isolated from normal CNS or during neuroinflammation using experimental autoimmune encephalomyelitis (EAE), a mouse model for MS. The described method will be useful to measure the level of expression of microRNAs in microglia in normal CNS or during neuroinflammation associated with various pathologies including MS, stroke, traumatic injury, Alzheimer's disease and brain tumors.

Age related changes in microglial phenotype vary between CNS regions: grey versus white matter differences

Subtle regional differences in microglial phenotype exist in the adult mouse brain. We investigated whether these differences were amplified during ageing and following systemic challenge with lipopolysaccharide (LPS). We studied microglial morphology and phenotype in young (4mo) and aged (21mo) C57/BL6 mice using immunohistochemistry and quantified the expression levels of surface molecules on microglia in white and grey matter along the rostral-caudal neuraxis. We detected significant regional, age dependent differences in microglial phenotypes, with the microglia of white matter and caudal areas of the CNS exhibiting greater upregulation of CD11b, CD68, CD11c, F4/80 and FcγRI than grey matter and rostral CNS areas. Upregulation of CD11c with age was restricted to the white matter, as was the appearance of multinucleated giant cells. Systemic LPS caused a subtle upregulation of FcγRI after 24 h, but the other markers examined were not affected. Burrowing behaviour and static rod assays were used to assess hippocampal and cerebellar integrity. Aged mice exhibited exaggerated and prolonged burrowing deficits following systemic LPS injection, while in the absence of an inflammatory challenge aged mice performed significantly worse than young mice in the static rod test. Taken together, these findings show that the effects of age on microglial phenotype and functional integrity vary significantly between CNS compartments, as do, albeit to a lesser extent, the effects of systemic LPS.

MicroRNAs are universal regulators of differentiation, activation, and polarization of microglia and macrophages in normal and diseased CNS

MicroRNAs (miRNAs) are a class of small (∼22 nucleotides) noncoding RNAs involved in the regulation of gene expression at the post-translational level. It is estimated that 30-90% of human genes are regulated by miRNAs, which makes these molecules of great importance for cell growth, activation, and differentiation. Microglia is CNS-resident cells of a myeloid lineage that play an important role in immune surveillance and are actively involved in many neurologic pathologies. Although the exact origin of microglia remains enigmatic, it is established that primitive macrophages from a yolk sac populate the brain and spinal cord in normal conditions throughout development. During various pathological events such as neuroinflammation, bone marrow derived myeloid cells also migrate into the CNS. Within the CNS, both primitive macrophages from the yolk sac and bone marrow derived myeloid cells acquire a specific phenotype upon interaction with other cell types within the CNS microenvironment. The factors that drive differentiation of progenitors into microglia and control the state of activation of microglia and bone marrow-derived myeloid cells within the CNS are not well understood. In this review we will summarize the role of miRNAs during activation and differentiation of myeloid cells. The role of miR-124 in the adaptation of microglia and macrophages to the CNS microenvironment will be further discussed. We will also summarize the role of miRNAs as modulators of activation of microglia and microphages. Finally, we will describe the role of miR-155 and miR-124 in the polarization of macrophages towards classically and alternatively activated phenotypes.

Early activation of microglia triggers long-lasting impairment of adult neurogenesis in the olfactory bulb

Microglia, the innate immune cells of the brain, engulf and eliminate cellular debris during brain injury and disease. Recent observations have extended their roles to the healthy brain, but the functional impact of activated microglia on neural plasticity has so far been elusive. To explore this issue, we investigated the role of microglia in the function of the adult olfactory bulb network in which both sensory afferents and local microcircuits are continuously molded by the arrival of adult-born neurons. We show here that the adult olfactory bulb hosts a large population of resident microglial cells. Deafferentation of the olfactory bulb resulted in a transient activation of microglia and a concomitant reduction of adult olfactory bulb neurogenesis. One day after sensory deafferentation, microglial cells proliferate in the olfactory bulb, and their numbers peaked at day 3, and reversed at day 7 after lesion. Similar lesions performed on immunodeficient mice demonstrate that the both innate and adaptive lymphocyte responses are dispensable for the lesion-induced microglial proliferation and activation. In contrast, when mice were treated with an antiinflammatory drug to prevent microglial activation, olfactory deafferentation did not reduce adult neurogenesis, showing that activated microglial cells per se, and not the lack of sensory experience, relates to the survival of adult-born neurons. We conclude that the status of the resident microglia in the olfactory bulb is an important factor directly regulating the survival of immature adult-born neurons.

Platelets contribute to the pathogenesis of experimental autoimmune encephalomyelitis

RATIONALE

Multiple sclerosis (MS) and its mouse model, experimental autoimmune encephalomyelitis (EAE), are inflammatory disorders of the central nervous system (CNS). The function of platelets in inflammatory and autoimmune pathologies is thus far poorly defined.

OBJECTIVE

We addressed the role of platelets in mediating CNS inflammation in EAE.

METHODS AND RESULTS

We found that platelets were present in human MS lesions as well as in the CNS of mice subjected to EAE but not in the CNS from control nondiseased mice. Platelet depletion at the effector-inflammatory phase of EAE in mice resulted in significantly ameliorated disease development and progression. EAE suppression on platelet depletion was associated with reduced recruitment of leukocytes to the inflamed CNS, as assessed by intravital microscopy, and with a blunted inflammatory response. The platelet-specific receptor glycoprotein Ibα (GPIbα) promotes both platelet adhesion and inflammatory actions of platelets and targeting of GPIbα attenuated EAE in mice. Moreover, targeting another platelet adhesion receptor, glycoprotein IIb/IIIa (GPIIb/IIIa), also reduced EAE severity in mice.

CONCLUSIONS

Platelets contribute to the pathogenesis of EAE by promoting CNS inflammation. Targeting platelets may therefore represent an important new therapeutic approach for MS treatment.

Magnetic nanoparticles in primary neural cell cultures are mainly taken up by microglia

Background

Magnetic nanoparticles (MNPs) offer a large range of applications in life sciences. Applications in neurosciences are one focus of interest. Unfortunately, not all groups have access to nanoparticles or the possibility to develop and produce them for their applications. Hence, they have to focus on commercially available particles. Little is known about the uptake of nanoparticles in primary cells. Previously studies mostly reported cellular uptake in cell lines. Here we present a systematic study on the uptake of magnetic nanoparticles (MNPs) by primary cells of the nervous system.

Results

We assessed the internalization in different cell types with confocal and electron microscopy. The analysis confirmed the uptake of MNPs in the cells, probably with endocytotic mechanisms. Furthermore, we compared the uptake in PC12 cells, a rat pheochromocytoma cell line, which is often used as a neuronal cell model, with primary neuronal cells. It was found that the percentage of PC12 cells loaded with MNPs was significantly higher than for neurons. Uptake studies in primary mixed neuronal/glial cultures revealed predominant uptake of MNPs by microglia and an increase in their number. The number of astroglia and oligodendroglia which incorporated MNPs was lower and stable. Primary mixed Schwann cell/fibroblast cultures showed similar MNP uptake of both cell types, but the Schwann cell number decreased after MNP incubation. Organotypic co-cultures of spinal cord slices and peripheral nerve grafts resembled the results of the dispersed primary cell cultures.

Conclusions

The commercial MNPs used activated microglial phagocytosis in both disperse and organotypic culture systems. It can be assumed that in vivo application would induce immune system reactivity, too. Because of this, their usefulness for in vivo neuroscientific implementations can be questioned. Future studies will need to overcome this issue with the use of cell-specific targeting strategies. Additionally, we found that PC12 cells took up significantly more MNPs than primary neurons. This difference indicates that PC12 cells are not a suitable model for natural neuronal uptake of nanoparticles and qualify previous results in PC12 cells.

Signal transducer and activator of transcription-3/suppressor of cytokine signaling-3 (STAT3/SOCS3) axis in myeloid cells regulates neuroinflammation

Suppressor of cytokine signaling (SOCS) proteins are feedback inhibitors of the JAK/STAT pathway. SOCS3 has a crucial role in inhibiting STAT3 activation, cytokine signaling, and inflammatory gene expression in macrophages/microglia. To determine the role of SOCS3 in myeloid cells in neuroinflammation, mice with conditional SOCS3 deletion in myeloid cells (LysMCre-SOCS3(fl/fl)) were tested for experimental autoimmune encephalomyelitis (EAE). The myeloid-specific SOCS3-deficient mice are vulnerable to myelin oligodendrocyte glycoprotein (MOG)-induced EAE, with a severe, nonresolving atypical form of disease. In vivo, enhanced infiltration of inflammatory cells and demyelination is prominent in the cerebellum of myeloid-specific SOCS3-deficient mice, as is enhanced STAT3 signaling and expression of inflammatory cytokines/chemokines and an immune response dominated by Th1 and Th17 cells. In vitro, SOCS3-deficient macrophages exhibit heightened STAT3 activation and are polarized toward the classical M1 phenotype. SOCS3-deficient M1 macrophages provide the microenvironment to polarize Th1 and Th17 cells and induce neuronal death. Furthermore, adoptive transfer of M2 macrophages into myeloid SOCS3-deficient mice leads to delayed onset and reduced severity of atypical EAE by decreasing STAT3 activation, Th1/Th17 cells, and proinflammatory mediators in the cerebellum. These findings indicate that myeloid cell SOCS3 provides protection from EAE through deactivation of neuroinflammatory responses.

Involvement of calcitonin gene-related peptide and CCL2 production in CD40-mediated behavioral hypersensitivity in a model of neuropathic pain

The neuropeptide calcitonin gene-related peptide (CGRP) is known to play a pro-nociceptive role after peripheral nerve injury upon its release from primary afferent neurons in preclinical models of neuropathic pain. We previously demonstrated a critical role for spinal cord microglial CD40 in the development of spinal nerve L5 transection (L5Tx)-induced mechanical hypersensitivity. Herein, we investigated whether CGRP is involved in the CD40-mediated behavioral hypersensitivity. First, L5Tx was found to significantly induce CGRP expression in wild-type (WT) mice up to 14 days post-L5Tx. This increase in CGRP expression was reduced in CD40 knockout (KO) mice at day 14 post-L5Tx. Intrathecal injection of the CGRP antagonist CGRP8-37 significantly blocked L5Tx-induced mechanical hypersensitivity. In vitro, CGRP induced glial IL-6 and CCL2 production, and CD40 stimulation added to the effects of CGRP in neonatal glia. Further, there was decreased CCL2 production in CD40 KO mice compared to WT mice 21 days post-L5Tx. However, CGRP8-37 did not significantly affect spinal cord CCL2 production following L5Tx in WT mice. Altogether, these data suggest that CD40 contributes to the maintenance of behavioral hypersensitivity following peripheral nerve injury in part through two distinct pathways, the enhancement of CGRP expression and spinal cord CCL2 production.

GABAergic signaling and connectivity on Purkinje cells are impaired in experimental autoimmune encephalomyelitis

A significant proportion of multiple sclerosis (MS) patients have functionally relevant cerebellar deficits, which significantly contribute to disability. Although clinical and experimental studies have been conducted to understand the pathophysiology of cerebellar dysfunction in MS, no electrophysiological and morphological studies have investigated potential alterations of synaptic connections of cerebellar Purkinje cells (PC). For this reason we analyzed cerebellar PC GABAergic connectivity in mice with MOG((35-55))-induced experimental autoimmune encephalomyelitis (EAE), a mouse model of MS. We observed a strong reduction in the frequency of the spontaneous inhibitory post-synaptic currents (IPSCs) recorded from PCs during the symptomatic phase of the disease, and in presence of prominent microglia activation not only in the white matter (WM) but also in the molecular layer (ML). The massive GABAergic innervation on PCs from basket and stellate cells was reduced and associated to a decrease of the number of these inhibitory interneurons. On the contrary no significant loss of the PCs could be detected. Incubation of interleukin-1beta (IL-1β) was sufficient to mimic the electrophysiological alterations observed in EAE mice. We thus suggest that microglia and pro-inflammatory cytokines, together with a degeneration of basket and stellate cells and their synaptic terminals, contribute to impair GABAergic transmission on PCs during EAE. Our results support a growing body of evidence that GABAergic signaling is compromised in EAE and in MS, and show a selective susceptibility to neuronal and synaptic degeneration of cerebellar inhibitory interneurons.

Role of Ninjurin-1 in the migration of myeloid cells to central nervous system inflammatory lesions

OBJECTIVE

Blood-derived myeloid antigen-presenting cells (APCs) account for a significant proportion of the leukocytes found within lesions of multiple sclerosis (MS) and experimental allergic encephalomyelitis (EAE). These APCs along with activated microglia are thought to be pivotal in the initiation of the central nervous system (CNS)-targeted immune response in MS and EAE. However, the exact molecules that direct the migration of myeloid cells from the periphery across the blood-brain barrier (BBB) remain largely unknown.

METHODS

We identified Ninjurin-1 in a proteomic screen of human BBB endothelial cells (ECs). We assessed the expression of Ninjurin-1 by BBB-ECs and immune cells, and we determined the role of Ninjurin-1 in immune cell migration to the CNS in vivo in EAE mice.

RESULTS

Ninjurin-1 was found to be weakly expressed in the healthy human and mouse CNS but upregulated on BBB-ECs and on infiltrating APCs during the course of EAE and in active MS lesions. In human peripheral blood, Ninjurin-1 was predominantly expressed by monocytes, whereas it was barely detectable on T and B lymphocytes. Moreover, Ninjurin-1 neutralization specifically abrogated the adhesion and migration of human monocytes across BBB-ECs, without affecting lymphocyte recruitment. Finally, Ninjurin-1 blockade reduced clinical disease activity and histopathological indices of EAE and decreased infiltration of macrophages, dendritic cells, and APCs into the CNS.

INTERPRETATION

Our study uncovers an important cell-specific role for Ninjurin-1 in the transmigration of inflammatory APCs across the BBB and further emphasizes the importance of myeloid cell recruitment during the development of neuroinflammatory lesions.

Aminoguanidine and N-acetyl-cysteine supress oxidative and nitrosative stress in EAE rat brains

Experimental autoimmune encephalomyelitis (EAE) is a well-established animal model of human multiple sclerosis (MS). We have evaluated the role of oxidative and nitrosative stress, as the causal factors in the development of EAE, responsible for the damage of cardinal cellular components, such as lipids, proteins and nucleic acids, resulting in demyelination, axonal damage, and neuronal death. EAE was induced in female Sprague-Dawley rats, 3 months old (300±20 g), by immunization with myelin basic protein in combination with Complete Freund's adjuvant (CFA). The animals were divided into seven groups: control, EAE, CFA, EAE+aminoguanidine (AG), AG, EAE+N-acetyl-L-cysteine (NAC) and NAC. The animals were sacrificed 15 days after EAE induction, and the levels of nitrosative and oxidative stress were determined in 10% homogenate of the whole encephalitic mass. In EAE rats, brain NO production and MDA level were significantly increased (P<0.001) compared to the control values, whereas AG and NAC treatment decreased both parameters in EAE rats compared to EAE group (P<0.001). Glutathione (GSH) was reduced (P<0.001) in EAE rats in comparison with the control and CFA groups, but increased in EAE+AG and EAE+NAC group compared to the EAE group (P<0.01). Superoxide dismutase (SOD) activity was significantly decreased (P<0.001) in the EAE group compared to all other experimental groups. The clinical expression of EAE was significantly decreased (P<0.05) in the EAE groups treated with AG and NAC compared to EAE rats, during disease development. The obtained results prove an important role of oxidative and nitrosative stress in the pathogenesis of EAE, whereas AG and NAC protective effects offer new possibilities for a modified combined approach in MS therapy.

Inhibition of TLR ligand- and interferon gamma-induced murine microglial activation by Panax notoginseng

Among the many products which influence microglial activation and resulting neuroinflammation, herbal medicine has recently drawn much attention due to its immunomodulatory and neuroprotective activities. The purpose of the current study was to investigate the effects of an extract of Panax notoginseng (NotoG™) on TLR ligand- and IFNγ-induced activation in N9 and EOC20 microglial cells lines. NotoG suppressed microglial activation as measured by reduced expression of accessory molecules (CD40 and CD86), decreased production of inflammatory mediators (IL-6 and TNFα), and diminished release of antibacterial products (nitric oxide). Furthermore, this immunosuppressive activity was neither dependent on the glucocorticoid receptor, nor the result of a single ginsenosides (Rb1, Rg1, or Re), which are the major active constituents of the whole extract. NotoG and select ginsenosides may therefore be of therapeutic benefit in treating or preventing neurodegenerative diseases such as multiple sclerosis and parkinson's disease.

The fractalkine receptor but not CCR2 is present on microglia from embryonic development throughout adulthood

Microglial cells are difficult to track during development because of the lack of specific reagents for myeloid subpopulations. To further understand how myeloid lineages differentiate during development to create microglial cells, we investigated CX3CR1 and CCR2 transcription unit activation in Cx3cr1(+/GFP)CCR2(+/RFP) knockin fluorescent protein reporter mice. The principal findings include: 1) CX3CR1(+) cells localized to the aorta-gonad-mesonephros region, and visualized at embryonic day (E)9.0 in the yolk sac and neuroectoderm; 2) at E10.5, CX3CR1 single-positive microglial cells were visualized penetrating the neuroepithelium; and 3) CX3CR1 and CCR2 distinguished infiltrating macrophages from resident surveillant or activated microglia within tissue sections and by flow cytometric analyses. Our results support the contribution of the yolk sac as a source of microglial precursors. We provide a novel model to monitor chemokine receptor expression changes in microglia and myeloid cells early (E8.0-E10.5) in development and during inflammatory conditions, which have been challenging to visualize in mammalian tissues.

The critical role of antigen-presentation-induced cytokine crosstalk in the central nervous system in multiple sclerosis and experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is a debilitating disease of the central nervous system (CNS) that has been extensively studied using the animal model experimental autoimmune encephalomyelitis (EAE). It is believed that CD4(+) T lymphocytes play an important role in the pathogenesis of this disease by mediating the demyelination of neuronal axons via secretion of proinflammatory cytokines resulting in the clinical manifestations. Although a great deal of information has been gained in the last several decades about the cells involved in the inflammatory and disease mediating process, important questions have remained unanswered. It has long been held that initial neuroantigen presentation and T cell activation events occur in the immune periphery and then translocate to the CNS. However, an increasing body of evidence suggests that antigen (Ag) presentation might initiate within the CNS itself. Importantly, it has remained unresolved which antigen presenting cells (APCs) in the CNS are the first to acquire and present neuroantigens during EAE/MS to T cells, and what the conditions are under which this takes place, ie, whether this occurs in the healthy CNS or only during inflammatory conditions and what the related cytokine microenvironment is comprised of. In particular, the central role of interferon-γ as a primary mediator of CNS pathology during EAE has been challenged by the emergence of Th17 cells producing interleukin-17. This review describes our current understanding of potential APCs in the CNS and the contribution of these and other CNS-resident cells to disease pathology. Additionally, we discuss the question of where Ag presentation is initiated and under what conditions neuroantigens are made available to APCs with special emphasis on which cytokines may be important in this process.

Organ-specific features of natural killer cells

Natural killer (NK) cells can be swiftly mobilized by danger signals and are among the earliest arrivals in target organs of disease. However, the role of NK cells in regulating inflammatory responses is far from completely understood in different organs. It is often complex and sometimes paradoxical.

The phenotypes and functions of NK cells in the liver, mucosal tissues, uterus, pancreas, joints and brain are influenced by the unique cellular interactions and the local microenvironment within each organ.

Hepatic NK cells exhibit an activated phenotype with high levels of cytotoxic effector molecules. These cells have been implicated in promoting liver injury and inhibiting liver fibrosis and regeneration. The liver is also enriched in NK cells with memory-like adaptive immune features.

NK cells are detected in healthy lymphoid tissues of the lung, skin and gut, and are recruited to these tissues during infection or inflammation. In the gastrointestinal tract, classical NK cells and a variety of innate lymphoid cells, such as the family of lymphoid tissue-inducer (LTi) cells, are likely to have crucial roles in controlling inflammatory responses.

NK cells represent the major lymphocyte subset in the pregnant uterus, with a unique phenotype resembling an early developmental state. Emerging evidence indicates that these cells play a crucial part in mediating the uterine vascular adaptations to pregnancy and promoting the maintenance of healthy pregnancy.

In non-obese diabetic (NOD) mice, NK cells are recruited early to the pancreas, become locally activated and then adopt a hyporesponsive phenotype. Although NK cells have a pathogenic role in the natural progression of diabetes in NOD mice, they contribute to diabetes protection induced by complete Freund's adjuvant and to islet allograft tolerance induced by co-stimulatory blockade.

NK cells in the inflamed joint uniquely express receptor activator of NF-κB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF), which promote osteoclast differentiation. Although NK cells have a pathogenic role in collagen-induced arthritis in mice, they are also crucial for protection against antibody-induced arthritis mediated by CpG oligonucleotides.

Studies in a mouse model of multiple sclerosis have shown that NK cells arrive in the central nervous system (CNS) before pathogenic T cells and have a protective role in the development of CNS inflammation, probably by killing CNS-resident microglia that prime effector T cells.

During evolution, different organs might have evolved distinct ways to recruit and influence the effector functions of NK cells. Once we understand these mechanisms, the next challenge will be to exploit this information for harnessing NK cells to develop prophylactic and therapeutic measures against infectious agents, tumours and inflammatory diseases.

Each tissue in our body contains a unique microenvironment that can differentially shape immune reactivity. In this Review article, Shiet al. describe how organ-specific factors influence natural killer cell homing and phenotype, and discuss the local molecular and cellular interactions that determine the protective or pathogenic functions of natural killer cells in the different tissues.

Natural killer (NK) cells can be swiftly mobilized by danger signals and are among the earliest arrivals at target organs of disease. However, the role of NK cells in mounting inflammatory responses is often complex and sometimes paradoxical. Here, we examine the divergent phenotypic and functional features of NK cells, as deduced largely from experimental mouse models of pathophysiological responses in the liver, mucosal tissues, uterus, pancreas, joints and brain. Moreover, we discuss how organ-specific factors, the local microenvironment and unique cellular interactions may influence the organ-specific properties of NK cells.

Analysis of behavior and trafficking of dendritic cells within the brain during toxoplasmic encephalitis

Under normal conditions the immune system has limited access to the brain; however, during toxoplasmic encephalitis (TE), large numbers of T cells and APCs accumulate within this site. A combination of real time imaging, transgenic reporter mice, and recombinant parasites allowed a comprehensive analysis of CD11c⁺ cells during TE. These studies reveal that the CNS CD11c⁺ cells consist of a mixture of microglia and dendritic cells (DCs) with distinct behavior associated with their ability to interact with parasites or effector T cells. The CNS DCs upregulated several chemokine receptors during TE, but none of these individual receptors tested was required for migration of DCs into the brain. However, this process was pertussis toxin sensitive and dependent on the integrin LFA-1, suggesting that the synergistic effect of signaling through multiple chemokine receptors, possibly leading to changes in the affinity of LFA-1, is involved in the recruitment/retention of DCs to the CNS and thus provides new insights into how the immune system accesses this unique site.

Toxoplasmic encephalitis (TE), caused by the protozoan parasite Toxoplasma gondii, can be potentially life threatening especially in immuno-compromised individuals. Immune cells including dendritic cells have been shown to accumulate in the brain during chronic toxoplasmosis; however, little is known about their function, their behavior in vivo, and the mechanisms by which they migrate into the brain. In the present studies, we utilize a combination of real time imaging, transgenic reporter mice, and recombinant parasites to reveal the distinct behavior and morphologies of dendritic cells within the brain and their ability to interact with parasites and effector T cells during TE. The CNS DCs were also found to exhibit a unique chemokine receptor expression pattern during infection, and the migration of DCs into the brain was mediated through a pertussis toxin (which blocks signaling downstream of several chemokine receptors) sensitive process and dependent on the integrin LFA-1. There is currently a poor understanding of the events that lead to DC recruitment to the CNS during inflammation in general, and our studies provide new insights into the mechanisms by which antigen-presenting cells gain access to the brain during infection.

How to get from here to there: macrophage recruitment in Alzheimer's disease

Alzheimer's disease (AD) is pathologically defined by presence of intracellular neurofibrillary tangles and extracellular amyloid plaques comprised of amyoid-β (Aβ) peptides. Despite local recruitment of brain microglia to sites of amyloid deposition, these mononuclear phagocytes ultimately fail at restricting β-amyloid plaque formation. On the other hand, it is becoming increasingly clear that professional phagocytes from the periphery possess Aβ clearance aptitude. Yet, in order to harness this beneficial innate immune response, effective strategies must be developed to coax monocytes/macrophages from the periphery into the brain. It has previously been suggested that Aβ 'immunotherapy' clears cerebral Aβ deposits via mononuclear phagocytes, and recent evidence suggests that targeting transforming growth factor-β-Smad 2/3 signaling and chemokine pathways such as Ccr2 impacts blood-to-brain trafficking of these cells in transgenic mouse models of AD. It has also been shown that the fractalkine receptor (Cx3cr1) pathway plays a critical role in chemotaxis of mononuclear phagocytes toward neurons destined for death in AD model mice. In order to translate these basic science findings into AD treatments, a key challenge will be to develop a new generation of pharmacotherapeutics that safely and effectively promote recruitment of peripheral amyloid phagocytes into the AD brain.

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.

Infiltrating monocytes trigger EAE progression, but do not contribute to the resident microglia pool

In multiple sclerosis and the experimental autoimmune encephalitis (EAE) mouse model, two pools of morphologically indistinguishable phagocytic cells, microglia and inflammatory macrophages, accrue from proliferating resident precursors and recruitment of blood-borne progenitors, respectively. Whether these cell types are functionally equivalent is hotly debated, but is challenging to address experimentally. Using a combination of parabiosis and myeloablation to replace circulating progenitors without affecting CNS-resident microglia, we found a strong correlation between monocyte infiltration and progression to the paralytic stage of EAE. Inhibition of chemokine receptor-dependent recruitment of monocytes to the CNS blocked EAE progression, suggesting that these infiltrating cells are essential for pathogenesis. Finally, we found that, although microglia can enter the cell cycle and return to quiescence following remission, recruited monocytes vanish, and therefore do not ultimately contribute to the resident microglial pool. In conclusion, we identified two distinct subsets of myelomonocytic cells with distinct roles in neuroinflammation and disease progression.

Interleukin-6, produced by resident cells of the central nervous system and infiltrating cells, contributes to the development of seizures following viral infection

Cells that can participate in an innate immune response within the central nervous system (CNS) include infiltrating cells (polymorphonuclear leukocytes [PMNs], macrophages, and natural killer [NK] cells) and resident cells (microglia and sometimes astrocytes). The proinflammatory cytokine interleukin-6 (IL-6) is produced by all of these cells and has been implicated in the development of behavioral seizures in the Theiler's murine encephalomyelitis virus (TMEV)-induced seizure model. The assessment, via PCR arrays, of the mRNA expression levels of a large number of chemokines (ligands and receptors) in TMEV-infected and mock-infected C57BL/6 mice both with and without seizures did not clearly demonstrate the involvement of PMNs, monocytes/macrophages, or NK cells in the development of seizures, possibly due to overlapping function of the chemokines. Additionally, C57BL/6 mice unable to recruit or depleted of infiltrating PMNs and NK cells had seizure rates comparable to those of controls following TMEV infection, and therefore PMNs and NK cells do not significantly contribute to seizure development. In contrast, C57BL/6 mice treated with minocycline, which affects monocytes/macrophages, microglial cells, and PMNs, had significantly fewer seizures than controls following TMEV infection, indicating monocytes/macrophages and resident microglial cells are important in seizure development. Irradiated bone marrow chimeric mice that were either IL-6-deficient mice reconstituted with wild-type bone marrow cells or wild-type mice reconstituted with IL-6-deficient bone marrow cells developed significantly fewer behavioral seizures following TMEV infection. Therefore, both resident CNS cells and infiltrating cells are necessary for seizure development.

Elevated blood levels of inflammatory monocytes (CD14+ CD16+ ) in patients with complex regional pain syndrome

Complex regional pain syndrome (CRPS) is a chronic pain disorder. Although its pathophysiology is not completely understood, neurogenic inflammation is thought to play a significant role. Microglia and astrocytes are activated following tissue injury or inflammation and have been reported to be both necessary and sufficient for enhanced nociception. Blood-borne monocytes/macrophages can infiltrate the central nervous system (CNS) and differentiate into microglia resulting in hypersensitivity and chronic pain. The primary aim of this study was to evaluate the proportion of the proinflammatory CD14(+) CD16(+) monocytes as well as plasma cytokine levels in blood from CRPS patients compared to age- and gender-matched healthy control individuals. Forty-six subjects (25 CRPS, 21 controls) were recruited for this study. The percentage of monocytes, T, B or natural killer (NK) cells did not differ between CRPS and controls. However, the percentage of the CD14(+) CD16(+) monocyte/macrophage subgroup was elevated significantly (P<0·01) in CRPS compared to controls. Individuals with high percentage of CD14(+) CD16(+) demonstrated significantly lower (P<0·05) plasma levels on the anti-inflammatory cytokine interleukin (IL)-10. Our data cannot determine whether CD14(+) CD16(+) monocytes became elevated prior to or after developing CRPS. In either case, the elevation of blood proinflammatoty monocytes prior to the initiating event may predispose individuals for developing the syndrome whereas the elevation of blood proinflammatory monocytes following the development of CRPS may be relevant for its maintenance. Further evaluation of the role the immune system plays in the pathogenesis of CRPS may aid in elucidating disease mechanisms as well as the development of novel therapies for its treatment.

Isolation of brain and spinal cord mononuclear cells using percoll gradients

Isolation of immune cells that infiltrate the central nervous system (CNS) during infection, trauma, autoimmunity or neurodegeneration, is often required to define their phenotype and effector functions. Histochemical approaches are instrumental to determine the location of the infiltrating cells and to analyze the associated CNS pathology. However, in-situ histochemistry and immunofluorescent staining techniques are limited by the number of antibodies that can be used at a single time to characterize immune cell subtypes in a particular tissue. Therefore, histological approaches in conjunction with immune-phenotyping by flow cytometry are critical to fully characterize the composition of local CNS infiltration. This protocol is based on the separation of CNS cellular suspensions over discontinous percoll gradients. The current article describes a rapid protocol to efficiently isolate mononuclear cells from brain and spinal cord tissues that can be effectively utilized for identification of various immune cell populations in a single sample by flow cytometry.

MicroRNA-124 promotes microglia quiescence and suppresses EAE by deactivating macrophages via the C/EBP-α-PU.1 pathway

MicroRNAs are a family of regulatory molecules involved in many physiological processes, including differentiation and activation of cells of the immune system. We found that brain-specific miR-124 is expressed in microglia but not in peripheral monocytes or macrophages. When overexpressed in macrophages, miR-124 directly inhibited the transcription factor CCAAT/enhancer-binding protein-α (C/EBP-α) and its downstream target PU.1, resulting in transformation of these cells from an activated phenotype into a quiescent CD45(low), major histocompatibility complex (MHC) class II(low) phenotype resembling resting microglia. During experimental autoimmune encephalomyelitis (EAE), miR-124 was downregulated in activated microglia. Peripheral administration of miR-124 in EAE caused systemic deactivation of macrophages, reduced activation of myelin-specific T cells and marked suppression of disease. Conversely, knockdown of miR-124 in microglia and macrophages resulted in activation of these cells in vitro and in vivo. These findings identify miR-124 both as a key regulator of microglia quiescence in the central nervous system and as a previously unknown modulator of monocyte and macrophage activation.

Limited sufficiency of antigen presentation by dendritic cells in models of central nervous system autoimmunity

Experimental autoimmune encephalomyelitis (EAE), a model for the human disease multiple sclerosis (MS), is dependent upon the activation and effector functions of autoreactive CD4 T cells. Multiple interactions between CD4 T cells and major histocompatibility class II (MHCII)+ antigen presenting cells (APCs) must occur in both the periphery and central nervous system (CNS) to elicit autoimmunity. The identity of the MHCII+ APCs involved throughout this process remains in question. We investigated which APC in the periphery and CNS mediates disease using transgenic mice with MHCII expression restricted to dendritic cells (DCs). MHCII expression restricted to DCs results in normal susceptibility to peptide-mediated EAE. Indeed, radiation-sensitive bone marrow-derived DCs were sufficient for all APC functions during peptide-induced disease. However, DCs alone were inefficient at promoting disease after immunization with the myelin protein myelin oligodendrocyte glycoprotein (MOG), even in the presence of MHCII-deficient B cells. Consistent with a defect in disease induction following protein immunization, antigen presentation by DCs alone was incapable of mediating spontaneous optic neuritis. These results indicate that DCs are capable of perpetuating CNS-targeted autoimmunity when antigens are readily available, but other APCs are required to efficiently initiate pathogenic cognate CD4 T cell responses.

Attenuation of CNS inflammatory responses by nicotine involves α7 and non-α7 nicotinic receptors

A considerable number of in vivo studies have demonstrated that the cholinergic system can dampen the peripheral immune response, and it is thought that the α7-nicotinic acetylcholine receptor (nAChR) subtype is a key mediator of this process. The goal of the present study was to determine if nicotine modulates immunological mechanisms known to be involved in the development of experimental autoimmune encephalomyelitis (EAE), a mouse model for CNS autoimmune disease, via α7-nAChRs. Here we show that nicotine exposure attenuates EAE severity and that this effect is largely abolished in nAChR α7 subunit knock-out mice. However, nicotine exposure partially retains the ability to reduce lymphocyte infiltration into the CNS, inhibit auto-reactive T cell proliferation and helper T cell cytokine production, down-regulate co-stimulatory protein expression on myeloid cells, and increase the differentiation and recruitment of regulatory T cells, even in the absence of α7-nAChRs. Diverse effects of nicotine on effector and regulatory T cells, as well as antigen-presenting cells, may be linked to differential expression patterns of nAChR subunits across these cell types. Taken together, our data show that although α7-nAChRs indeed seem to play an important role in nicotine-conferred reduction of the CNS inflammatory response and protection against EAE, other nAChR subtypes also are involved in the anti-inflammatory properties of the cholinergic system.

A genetic mouse model of adult-onset, pervasive central nervous system demyelination with robust remyelination

Adult-onset demyelinating disorders of the central nervous system represent the most common neurological abnormalities in young adults. Nevertheless, our understanding of disease pathogenesis and recovery in demyelinating disorders remains incomplete. To facilitate investigation into these processes, we have developed a new mouse model system that allows for the induction of dipththeria toxin A subunit expression in adult oligodendrocytes, resulting in widespread oligodendrocyte loss and demyelination of the central nervous system. These mice develop severe ataxia and tremor that correlates with impaired axonal conduction in the spinal cord. Strikingly, these animals fully recover from their motor and physiological defects and display extensive oligodendrocyte replenishment and widespread remyelination. This model system demonstrates the robust reparative potential of myelin in the central nervous system and provides a promising model for the quantitative assessment of therapeutic interventions that promote remyelination.

Bone marrow-derived mesenchymal stem cells modulate BV2 microglia responses to lipopolysaccharide

The immunoregulatory properties of mesenchymal stem cells (MSC) have been demonstrated on a wide range of cells. Here, we describe the modulatory effects of mouse bone marrow-derived MSC on BV2 microglia proliferation rate, nitric oxide (NO) production and CD40 expression. Mouse bone marrow MSC were co-cultured with BV2 cells at various seeding density ratios and activated with lipopolysaccharide (LPS). We show that MSC exert an anti-proliferative effect on microglia and are potent producers of NO when stimulated by soluble factors released by LPS-activated BV2. MSC suppressed proliferation of both untreated and LPS-treated microglia in a dose-dependent manner, significantly reducing BV2 proliferation at seeding density ratios of 1:0.2 and 1:0.1 (p<.05). Co-culturing MSC with BV2 cells at different ratios revealed interesting dynamics in NO production. A high number of MSC significantly increases NO in co-cultures whilst a lower number reduces NO. The increased NO levels in co-cultures may be MSC-derived, as we also show that activated BV2 cells stimulate MSC to produce NO. Cell-cell interaction is not a requirement for this effect as soluble factors released by activated BV2 cells alone do stimulate MSC to produce high levels of NO. Although NO is implicated as a mediator for T cell proliferation, it does not appear to play a major role in the suppression of microglia proliferation. Additionally, MSC reduced the expression of the microglial co-stimulator molecule, CD40. Collectively, these regulatory effects of MSC on microglia offer insight into the potential moderating properties of MSC on inflammatory responses within the CNS.