Downregulation of macrophage inhibitory molecules in multiple sclerosis lesions

Inhibition of 26S protease regulatory subunit 7 (MSS1) suppresses neuroinflammation

Recently, researchers have focused on immunosuppression induced by rifampicin. Our previous investigation found that rifampicin was neuroprotective by inhibiting the production of pro-inflammatory mediators, thereby suppressing microglial activation. In this study, using 2-dimensional gel electrophoresis (2-DE) and mass spectrometry (MS), we discovered that 26S protease regulatory subunit 7 (MSS1) was decreased in rifampicin-treated microglia. Western blot analysis verified the downregulation of MSS1 expression by rifampicin. As it is indicated that the modulation of the ubiquitin-26S proteasome system (UPS) with proteasome inhibitors is efficacious for the treatment of neuro-inflammatory disorders, we next hypothesized that silencing MSS1 gene expression might inhibit microglial inflammation. Using RNA interference (RNAi), we showed significant reduction of IkBα degradation and NF-kB activation. The production of lipopolysaccharides-induced pro-inflammatory mediators such as inducible nitric oxide synthase (iNOS), nitric oxide, cyclooxygenase-2, and prostaglandin E₂ were also reduced by MSS1 gene knockdown. Taken together, our findings suggested that rifampicin inhibited microglial inflammation by suppressing MSS1 protein production. Silencing MSS1 gene expression decreased neuroinflammation. We concluded that MSS1 inhibition, in addition to anti-inflammatory rifampicin, might represent a novel mechanism for the treatment of neuroinflammatory disorders.

Artemisinin attenuates lipopolysaccharide-stimulated proinflammatory responses by inhibiting NF-κB pathway in microglia cells

Microglial activation plays an important role in neuroinflammation, which contributes to neuronal damage, and inhibition of microglial activation may have therapeutic benefits that could alleviate the progression of neurodegeneration. Recent studies have indicated that the antimalarial agent artemisinin has the ability to inhibit NF-κB activation. In this study, the inhibitory effects of artemisinin on the production of proinflammatory mediators were investigated in lipopolysaccharide (LPS)-stimulated primary microglia. Our results show that artemisinin significantly inhibited LPS-induced production of tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), monocyte chemotactic protein-1 (MCP-1) and nitric oxide (NO). Artemisinin significantly decreased both the mRNA and the protein levels of these pro-inflammatory cytokines and inducible nitric oxide synthase (iNOS) and increased the protein levels of IκB-α, which forms a cytoplasmic inactive complex with the p65-p50 heterodimeric complex. Artemisinin treatment significantly inhibited basal and LPS-induced migration of BV-2 microglia. Electrophoretic mobility shift assays revealed increased NF-κB binding activity in LPS-stimulated primary microglia, and this increase could be prevented by artemisinin. The inhibitory effects of artemisinin on LPS-stimulated microglia were blocked after IκB-α was silenced with IκB-α siRNA. Our results suggest that artemisinin is able to inhibit neuroinflammation by interfering with NF-κB signaling. The data provide direct evidence of the potential application of artemisinin for the treatment of neuroinflammatory diseases.

C3-dependent mechanism of microglial priming relevant to multiple sclerosis

Microglial priming predisposes the brain to neurodegeneration and affects disease progression. The signal to switch from the quiescent to the primed state is unknown. We show that deleting the C3 convertase regulator complement receptor 1-related protein y (Crry) induces microglial priming. Mice that were double-knockout for Crry and either C3 or factor B did not show priming, demonstrating dependence on alternative pathway activation. Colocalization of C3b/iC3b and CR3 implicated the CR3/iC3b interaction in priming. Systemic lipopolysaccharide challenge overactivated primed microglia with florid expression of proinflammatory molecules, which were blocked by complement inhibition. Relevance for neurodegenerative disease is exemplified by human multiple sclerosis (MS) and by experimental autoimmune encephalomyelitis (EAE), a model of MS. In human MS, microglial priming was evident in perilesional white matter, in close proximity to C3b/iC3b deposits. EAE was accelerated and exacerbated in Crry-deficient mice, and was dependent on C activation. In summary, C3-dependent microglial priming confers susceptibility to other challenges. Our observations are relevant to progression in MS and other neurological diseases exacerbated by acute insults.

FGF-2 and Anosmin-1 are selectively expressed in different types of multiple sclerosis lesions

Multiple sclerosis is a demyelinating disease that affects ≈ 2,000,000 people worldwide. In the advanced stages of the disease, endogenous oligodendrocyte precursors cannot colonize the lesions or differentiate into myelinating oligodendrocytes. During development, both FGF-2 and Anosmin-1 participate in oligodendrocyte precursor cell migration, acting via the FGF receptor 1 (FGFR1). Hence, we performed a histopathological and molecular analysis of these developmental modulators in postmortem tissue blocks from multiple sclerosis patients. Accordingly, we demonstrate that the distribution of FGF-2 and Anosmin-1 varies between the different types of multiple sclerosis lesions: FGF-2 is expressed only within active lesions and in the periplaque of chronic lesions, whereas Anosmin-1 is upregulated within chronic lesions and is totally absent in active lesions. We show that the endogenous oligodendrocyte precursor cells recruited toward chronic-active lesions express FGFR1, possibly in response to the FGF-2 produced by microglial cells in the periplaque. Also in human tissue, FGF-2 is upregulated in perivascular astrocytes in regions of the normal-appearing gray matter, where the integrity of the blood-brain barrier is compromised. In culture, FGF-2 and Anosmin-1 influence adult mouse oligodendrocyte precursor cell migration in the same manner as at embryonic stages, providing an explanation for the histopathological observations: FGF-2 attracts/enhances its migration, which is hindered by Anosmin-1. We propose that FGF-2 and Anosmin-1 are markers for the histopathological type and the level of inflammation of multiple sclerosis lesions, and that they may serve as novel pharmacogenetic targets to design future therapies that favor effective remyelination and protect the blood-brain barrier.

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.

Potential role of IL-13 in neuroprotection and cortical excitability regulation in multiple sclerosis

BACKGROUND

Inflammation triggers secondary neurodegeneration in multiple sclerosis (MS).

OBJECTIVES

It is unclear whether classical anti-inflammatory cytokines have the potential to interfere with synaptic transmission and neuronal survival in MS.

METHODS

Correlation analyses between cerebrospinal fluid (CSF) contents of anti-inflammatory cytokines and molecular, imaging, clinical, and neurophysiological measures of neuronal alterations were performed.

RESULTS

Our data suggest that interleukin-13 (IL-13) plays a neuroprotective role in MS brains. We found, in fact, that the levels of IL-13 in the CSF of MS patients were correlated with the contents of amyloid-β(1-42). Correlations were also found between IL-13 and imaging indexes of axonal and neuronal integrity, such as the retinal nerve fibre layer thickness and the macular volume evaluated by optical coherence tomography. Furthermore, the levels of IL-13 were related to better performance in the low-contrast acuity test and Multiple Sclerosis Functional Composite scoring. Finally, by means of transcranial magnetic stimulation, we have shown that GABAA-mediated cortical inhibition was more pronounced in patients with high IL-13 levels in the CSF, as expected for a neuroprotective, anti-excitotoxic effect.

CONCLUSIONS

The present correlation study provides some evidence for the involvement of IL-13 in the modulation of neuronal integrity and synaptic function in patients with MS.

Rifampicin inhibits microglial inflammation and improves neuron survival against inflammation

Microglial activation plays an important role in the pathophysiology of neurodegenerative diseases, and suppression of microglial activation prevents the progression of neurodegeneration. Rifampicin, a bacteriocidal antibiotic, induces immunosuppression. We hypothesized that rifampicin might be neuroprotective by inhibiting the production of pro-inflammatory mediators, thereby suppressing microglial activation. In the present study, we examined the effects of rifampicin on the production of lipopolysaccharide (LPS)-induced pro-inflammatory mediators and their signaling pathways in BV2 microglia. We also assessed the neuroprotective effects of rifampicin using a co-culture of microglia and neurons. Our results showed that rifampicin inhibited the LPS-stimulated expression of inducible nitric oxide synthase, cyclooxygenase-2, tumor necrosis factor-α, and interleukin-1β, as well as the production of nitric oxide and prostaglandin E₂. Moreover, rifampicin suppressed LPS-induced nuclear factor-kappa B activation by blocking the degradation of the inhibitor of the nuclear transcription factor NF-kappa B. Rifampicin inhibited the phosphorylation of mitogen activated protein kinases, although protein kinase B was not inhibited. Preincubation of microglia with rifampicin reduced neurotoxicity and improved neuron survival in a microglia-neuronal co-culture system. Taken together, these findings suggest that rifampicin, with its anti-inflammatory properties, might be a novel treatment for neurodegenerative diseases.

Neurosteroid and GABA-A receptor alterations in Alzheimer's disease, Parkinson's disease and multiple sclerosis

Steroid hormones (e.g. estrogens, androgens, progestagens) which are synthesized de novo or metabolized within the CNS are called neurosteroids. There is substantial evidence from animal studies suggesting that these steroids can affect brain function by modulating neurotransmission, and influence neuronal survival, neuronal and glial differentiation and myelination in the CNS by regulating gene expression of neurotrophic factors and anti-inflammatory molecules. Indeed, evidence is emerging that expression of the enzymes responsible for the synthesis of neurosteroids changes in neurodegenerative diseases. Some of these changes may contribute to the pathology, while others, conversely, may represent an attempted rescue program in the diseased brain. Here we review the data on changes in neurosteroid levels and neurosteroid synthesis pathways in the human brain in three neurodegenerative conditions, Alzheimers's (AD) and Parkinson's (PD) diseases and Multiple Sclerosis (MS) and the extent to which these findings may implicate protective or pathological roles for neurosteroids in the course of these diseases.Some neurosteroids can modulate neurotransmitter activity, for example, the pregnane steroids allopregnanolone and 3α5α-tetrahydro-deoxycorticosterone which are potent positive allosteric modulators of ionotropic GABA-A receptors. Therefore, neurosteroid-modulated GABA-A receptor subunit alterations found in AD and PD will also be discussed. These data imply an involvement of neurosteroid changes in the neurodegenerative and neuroinflammatory processes and suggest that they may deserve further investigation as potential therapeutic agents in AD, PD and MS. Finally, suggestions for therapeutic strategies will be included. This article is part of a Special Issue entitled: Neuroactive Steroids: Focus on Human Brain.

Novel distribution of cluster of differentiation 200 adhesion molecule in glial cells of the peripheral nervous system of rats and its modulation after nerve injury

This study examined CD200 expression in different peripheral nerves and ganglia. Intense CD200 immunoreactivity was consistently localized in unmyelinated nerve fibers as opposed to a faint immunostaining in the myelinated nerve fibers. By light microscopy, structures resembling the node of Ranvier and Schmidt-Lanterman incisures in the myelinated nerve fibers displayed CD200 immunoreactivity. Ultrastructural study revealed CD200 expression on the neurilemma of Schwann cells whose microvilli and paranodal loops at the node of Ranvier were immunoreactive. The CD200 immunoexpression was also localized in the satellite glial cells of sensory and autonomic ganglia and in the enteric glial cells. Double labeling of CD200 with specific antigens of satellite glia or Schwann cells in the primary cultures of dorsal root ganglia had shown a differential expression of CD200 in the peripheral glial cells. The existence of CD200 in glial cells in the peripheral nervous system (PNS) was corroborated by the expression of CD200 mRNA and protein in a rat Schwann cell line RSC96. Using the model of crush or transected sciatic nerve, it was found that CD200 expression was attenuated or diminished at the site of lesion. A remarkable feature, however, was an increase in incidence of CD200-labelled Schmidt-Lanterman incisures proximal to the injured site at 7 days postlesion. Because CD200 has been reported to impart immunosuppressive signal, we suggest that its localization in PNS glial cells may play a novel inhibitory role in immune homeostasis in both normal and pathological conditions.

Pathophysiology of translational regulation by microRNAs in multiple sclerosis

MicroRNAs (miRNAs) comprise a group of several hundred, small non-coding RNA molecules with a fundamental influence on the regulation of gene expression. Certain miRNAs are altered in blood cells of multiple sclerosis (MS), and active and inactive MS brain lesions have distinct miRNA expression profiles. Several miRNAs such as miR-155 or miR-326 are considerably overexpressed in active MS lesions versus controls, and mice lacking these miRNAs either through knock-out (miR-155) or by in vivo silencing (miR-326) show a reduction of symptoms in experimental autoimmune encephalomyelitis (EAE), a model system for multiple sclerosis. This review describes miRNAs regulated in the blood or in brain lesions of MS patients in the context of their previously described functions in physiology and pathophysiology.

The emerging role of microRNAs in multiple sclerosis

Several hundred microRNAs (miRNAs) fine-tune the expression of approximately half of all human genes. Recent studies have revealed that miRNA profiles in blood cells become altered in multiple sclerosis (MS), and that active and inactive MS lesions have distinct miRNA expression patterns. The dysregulated miRNAs in MS lesions seem to be associated with astrocytes and infiltrating immune cells, and might unleash local macrophages through downregulation of the self-recognition signal CD47. The expression of miRNA-326 in blood cells has been reported to increase during relapses. This miRNA promotes T helper 17 cell differentiation and is highly abundant in active MS lesions. miRNAs are needed for maintenance of the myelin sheath, and the absence of such molecules results in axonal damage in mice. miRNA-219 and other miRNAs promote oligodendrocyte differentiation. Here, we discuss the possible contribution of miRNAs to MS pathogenesis. An improved understanding of this contribution should help to identify novel therapeutic targets and biomarkers for this disease.

Dysregulated neuronal-microglial cross-talk during aging, stress and inflammation

Communication between neurons and microglia is essential for maintaining homeostasis in the central nervous system (CNS) during both physiological and inflammatory conditions. While microglial activation is necessary and beneficial in response to injury or disease, excessive or prolonged activation can have deleterious effects on brain function and behavior. To prevent inflammation-associated damage, microglia reactivity is actively modulated by neurons in the healthy brain. Age or stress-induced disruption of normal neuronal-microglial communication could lead to an aberrant central immune response when additional stressors are applied. Recent work suggests that both aging and stress shift the CNS microenvironment to a pro-inflammatory state characterized by increased microglial reactivity and a reduction in anti-inflammatory and immunoregulatory factors. This review will discuss how heightened neuroinflammation associated with aging and stress may be compounded by the concomitant loss of neuronally derived factors that control microglial activation, leaving the brain vulnerable to excessive inflammation and neurobehavioral complications upon subsequent immune challenge.

Microglia: key innate immune cells of the brain

Microglia are the histiocytes of the central nervous system. These long-lived cells undergo very little turnover in normal physiological states; however, in pathological conditions, increased egress from the bone marrow and chemoattractive signals in the brain can substantially modulate the indigenous population. Although they were initially conceived of as "resting" cells, recent data suggest that they would be more aptly described as "surveillance" cells. Microglia are specifically adapted to sense various types of danger and differentially react with a classical or alternative reparative response. Our understanding of macrophage function has shifted away from focusing on cell lineage to a more systems-based biology of gene networks accomplishing the detoxification and immune functions. With our greater appreciation of microglial involvement in the innate immune response, we have entered a new era in which the modulation of microglia can be proposed as a means of modulating neurological disease.

MicroRNAs and Multiple Sclerosis

MicroRNAs (miRNAs) have recently emerged as a new class of modulators of gene expression. miRNAs control protein synthesis by targeting mRNAs for translational repression or degradation at the posttranscriptional level. These noncoding RNAs are endogenous, single-stranded molecules approximately 22 nucleotides in length and have roles in multiple facets of immunity, from regulation of development of key cellular players to activation and function in immune responses. Recent studies have shown that dysregulation of miRNAs involved in immune responses leads to autoimmunity. Multiple sclerosis (MS) serves as an example of a chronic and organ-specific autoimmune disease in which miRNAs modulate immune responses in the peripheral immune compartment and the neuroinflammatory process in the brain. For MS, miRNAs have the potential to serve as modifying drugs. In this review, we summarize current knowledge of miRNA biogenesis and mode of action and the diverse roles of miRNAs in modulating the immune and inflammatory responses. We also review the role of miRNAs in autoimmunity, focusing on emerging data regarding miRNA expression patterns in MS. Finally, we discuss the potential of miRNAs as a disease marker and a novel therapeutic target in MS. Better understanding of the role of miRNAs in MS will improve our knowledge of the pathogenesis of this disease.

The regulation of the CNS innate immune response is vital for the restoration of tissue homeostasis (repair) after acute brain injury: a brief review

Neurons and glia respond to acute injury by participating in the CNS innate immune response. This involves the recognition and clearance of "not self " pathogens and "altered self " apoptotic cells. Phagocytic receptors (CD14, CD36, TLR-4) clear "not self" pathogens; neurons and glia express "death signals" to initiate apoptosis in T cells.The complement opsonins C1q, C3, and iC3b facilitate the clearance of apoptotic cells by interacting with CR3 and CR4 receptors. Apoptotic cells are also cleared by the scavenger receptors CD14, Prs-R, TREM expressed by glia. Serpins also expressed by glia counter the neurotoxic effects of thrombin and other systemic proteins that gain entry to the CNS following injury. Complement pathway and T cell activation are both regulated by complement regulatory proteins expressed by glia and neurons. CD200 and CD47 are NIRegs expressed by neurons as "don't eat me" signals and they inhibit microglial activity preventing host cell attack. Neural stem cells regulate T cell activation, increase the Treg population, and suppress proinflammatory cytokine expression. Stem cells also interact with the chemoattractants C3a, C5a, SDF-1, and thrombin to promote stem cell migration into damaged tissue to support tissue homeostasis.

Dendritic cell nuclear protein-1, a novel depression-related protein, upregulates corticotropin-releasing hormone expression

The recently discovered dendritic cell nuclear protein-1 is the product of a novel candidate gene for major depression. The A allele encodes full-length dendritic cell nuclear protein-1, while the T allele encodes a premature termination of translation at codon number 117 on chromosome 5. In the present study we investigate whether the two forms of dendritic cell nuclear protein-1 might act on corticotropin-releasing hormone, which plays a crucial role in the stress response and in the pathogenesis of depression. The messenger RNA expression of dendritic cell nuclear protein-1 appeared to be increased in the laser micro-dissected paraventricular nucleus of patients with depression compared with control subjects. Dendritic cell nuclear protein-1 was also found to be co-localized with corticotropin-releasing hormone in paraventricular nucleus neurons. Moreover, full-length dendritic cell nucleus protein-1 bound to and transactivated the promoter of corticotropin-releasing hormone in human embryonic kidney 293 cells. We propose that full-length dendritic cell nucleus protein-1 may play a role in the pathogenesis of depressive disorders by enhancing corticotropin-releasing hormone expression in the hypothalamic paraventricular nucleus.

Altered regulation of CD200 receptor in monocyte-derived macrophages from individuals with Parkinson's disease

Microglia are the representative myeloid cells in the brain, and their over-activation plays an important role in the pathogenesis of Parkinson's disease (PD). Microglia activation is believed to be regulated by the CD200-CD200R signaling. As the peripheral counterpart of microglia, monocyte-derived macrophages (MDMs) share the same progenitor and antigen markers, and they have similar biological behaviors and mirror microglial function in the brain. Here, we studied CD200R expression and its regulation in MDMs from 32 PD cases, 27 age-matched old controls, and 28 young controls. We found that the basal CD200R expression is similar in MDMs from young control, old control and PD patients. However, the induction of CD200R expression in MDMs under various conditions is impaired in the old groups, especially in PD patients. There was a selective decrease in CD200R expression induced by co-culture with dying PC12 cells in MDMs from PD cases, as compared with MDMs from the age-matched controls. We also found that the inducible CD200R expression correlated inversely with the onset age of PD and to tumor necrosis factor-alpha (TNF-alpha) released from MDMs. These results suggest an intrinsic abnormality in the CD200-CD200R signaling in MDMs during aging and, especially, in PD. We speculate that in the PD brain,microglia might undergo abnormalities similar to MDMs.

Cleavage of osteopontin by matrix metalloproteinase-12 modulates experimental autoimmune encephalomyelitis disease in C57BL/6 mice

A role for osteopontin (OPN) in promoting disease activity of multiple sclerosis or its animal model experimental autoimmune encephalomyelitis (EAE) has recently been suggested. As the biological activity of OPN is heavily influenced by posttranslational processing, we investigated the capacity of matrix metalloproteinase (MMP)-12 to cleave OPN and determined whether this influenced disease activity. We found that OPN mRNA and protein expression in the spinal cord increased with EAE disease in C57BL/6 mice concurrently with MMP-12 expression. A Western blot of EAE and control spinal cords revealed different OPN-immunoreactive bands, with a pattern that was similar to MMP-12 cleavage of recombinant OPN in vitro. In addition, OPN fragments in the spinal cord of EAE-afflicted mice were reduced in MMP-12(-/-) mice compared with wild-type controls. However, examination of OPN(-/-) mice in short- and long-term experiments revealed no difference in EAE outcomes from wild-type animals. OPN/MMP-12 double null mice were generated, and it was revealed that MMP-12(-/-) mice had a worsening of disease compared with wild-type mice, which returned to wild-type levels in the OPN/MMP-12 double null mice. These results suggest that EAE disease activity may be modulated by the cleavage of OPN by MMP-12.

Disruption of central nervous system barriers in multiple sclerosis

The delicate microenvironment of the central nervous system (CNS) is protected by the blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCB). These barriers function in distinct CNS compartments and their anatomical basis lay on the junctional proteins present in endothelial cells for the BBB and in the choroidal epithelium for the BCB. During neuroinflammatory conditions like multiple sclerosis (MS) and its murine model experimental autoimmune encephalomyelitis (EAE), activation or damage of the various cellular components of these barriers facilitate leukocyte infiltration leading to oligodendrocyte death, axonal damage, demyelination and lesion development. This manuscript will review in detail the features of these barriers under physiological and pathological conditions, particularly when focal immune activation promotes the loss of the BBB and BCB phenotype, the upregulation of cell adhesion molecules (CAMs) and the recruitment of immune cells.

Gene expression analysis of the microvascular compartment in multiple sclerosis using laser microdissected blood vessels

The blood brain barrier (BBB) is formed by capillary endothelial cells with inter-endothelial cell tight junctions and other cells such as pericytes and astrocytes present. Previous studies have shown a role for tight junction abnormalities in BBB leakage in multiple sclerosis (MS) brain. This marks a key stage in the development of inflammatory demyelination in MS. The aim of this study was to identify aberrantly expressed genes involved in BBB changes in MS lesions. A focused endothelial cell biology microarray, capable of detecting changes in expression of 113 endothelial cell-specific genes, was employed to analyse endothelial cell mRNA extracted from post-mortem control white matter, MS normal appearing white matter (NAWM), chronic active or inactive lesions by laser capture microdissection. Microarray analysis found 52 genes out of 113 analysed, predominantly in the activation functional group, to be differentially expressed in lesions compared to control or NAWM (p < 0.01). The majority of the differentially expressed genes were validated by quantitative real time PCR. In addition, the protein expression profiles of ICAM2, MMP2, and VEGFR1 were examined by immunofluorescent staining of selected tissue blocks. ICAM-2 was expressed at a higher level in chronic inactive lesions than control or NAWM, corresponding with the increased mRNA measured by microarray and real time PCR. The data shown, presenting a number of differentially expressed genes in the microvascular compartment of MS lesions, may shed light on the molecular mechanisms that are involved in the breakdown of the BBB. This moves us a step closer to the identification of potential therapeutic targets for repair of the compromised BBB.

Neuroinflammation responses and neurodegeneration in multiple sclerosis

Diffuse neurodegeneration is now considered to be the main cause of irreversible neurological disability in multiple sclerosis (MS). Demonstration of a diffuse inflammatory reaction in the MS brain led to the assumption that diffuse neuroinflammation induces diffuse neurodegeneration. Macrophages/microglia accumulate throughout the MS brain and are, therefore, considered the main culprits implicated in the development of neurodegeneration. However, recent advances in the understanding of macrophage/microglia functions and origins have now challenged that view. This report is a summary of these advances, and discusses their contribution to the perception of macrophage/microglia functions in MS-associated neurodegeneration.

CD200R1 agonist attenuates mechanisms of chronic disease in a murine model of multiple sclerosis

To assess the effects and mechanisms of a CD200R1 agonist administered during the progressive stage of a multiple sclerosis model, we administered CD200R1 agonist (CD200Fc) or control IgG2a during the chronic phase of disease (days 10-30) in mice with experimental autoimmune encephalomyelitis (EAE), induced using myelin oligodendrocyte glycoprotein peptide 35-55 (MOG35-55) peptide. We found that administration of CD200Fc during the chronic stages of EAE reduced disease severity, demyelination, and axonal damage, through the modulation of several key disease mechanisms. CD200Fc treatment suppressed macrophage and microglial accumulation within the CNS, in part through downregulation of adhesion molecules VLA-4 and LFA-1, which are necessary for macrophage migration. Additionally, expression of activation markers MHC-II and CD80 and production of proinflammatory cytokines IL-6, tumor necrosis factor-alpha, and nitric oxide by CD11b(+) cells were decreased in both the spleen and CNS in CD200Fc-treated animals. Antigen-presenting cell function in the spleen and CNS was suppressed in CD200Fc-treated mice, but there were no significant alterations on T cell activation or phenotype. CD200Fc increased apoptosis of CD11b(+) cells but not astrocytes. In contrast, addition of CD200Fc treatment protected oligodendrocytes from apoptosis in vitro and in vivo. Our results demonstrate that CD200R1 agonists modulate both myeloid- and non-myeloid-related mechanisms of chronic disease in the EAE model and may be effective in the treatment of progressive multiple sclerosis and other neurodegenerative diseases.

Microglia activation and anti-inflammatory regulation in Alzheimer's disease

Inflammatory regulators, including endogenous anti-inflammatory systems, can down-regulate inflammation thus providing negative feedback. Chronic inflammation can result from imbalance between levels of inflammatory mediators and regulators during immune responses. As a consequence, there are heightened inflammatory responses and irreversible tissue damage associated with many age-related chronic diseases. Alzheimer's disease (AD) brain is marked by prominent inflammatory features, in which microglial activation is the driving force for the elaboration of an inflammatory cascade. How the regulation of inflammation loses its effectiveness during AD pathogenesis remains largely unclear. In this article, we will first review current knowledge of microglial activation and its association with AD pathology. We then discuss four examples of anti-inflammatory systems that could play a role in regulating microglial activation: CD200/CD200 receptor, vitamin D receptor, peroxisome proliferator-activated receptors, and soluble receptor for advanced glycation end products. Through this, we hope to illustrate the diverse aspects of inflammatory regulatory systems in brain and neurodegenerative diseases such as AD. We also propose the importance of neuronal defense systems, because they are part of the integral inflammatory and anti-inflammatory systems. Augmenting the anti-inflammatory defenses of neurons can be included in the strategy for restoration of balanced immune responses during aging and neurodegenerative diseases.

Myelin activates FAK/Akt/NF-kappaB pathways and provokes CR3-dependent inflammatory response in murine system

Inflammatory response following central nervous system (CNS) injury contributes to progressive neuropathology and reduction in functional recovery. Axons are sensitive to mechanical injury and toxic inflammatory mediators, which may lead to demyelination. Although it is well documented that degenerated myelin triggers undesirable inflammatory responses in autoimmune diseases such as multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE), there has been very little study of the direct inflammatory consequences of damaged myelin in spinal cord injury (SCI), i.e., there is no direct evidence to show that myelin debris from injured spinal cord can trigger undesirable inflammation in vitro and in vivo. Our data showed that myelin can initiate inflammatory responses in vivo, which is complement receptor 3 (CR3)-dependent via stimulating macrophages to express pro-inflammatory molecules and down-regulates expression of anti-inflammatory cytokines. Mechanism study revealed that myelin-increased cytokine expression is through activation of FAK/PI3K/Akt/NF-kappaB signaling pathways and CR3 contributes to myelin-induced PI3K/Akt/NF-kappaB activation and cytokine production. The myelin induced inflammatory response is myelin specific as sphingomyelin (the major lipid of myelin) and myelin basic protein (MBP, one of the major proteins of myelin) are not able to activate NF-kappaB signaling pathway. In conclusion, our results demonstrate a crucial role of myelin as an endogenous inflammatory stimulus that induces pro-inflammatory responses and suggest that blocking myelin-CR3 interaction and enhancing myelin debris clearance may be effective interventions for treating SCI.

MicroRNA profiling of multiple sclerosis lesions identifies modulators of the regulatory protein CD47

We established microRNA profiles from active and inactive multiple sclerosis lesions. Using laser capture microdissection from multiple sclerosis lesions to pool single cells and in vitro cultures, we assigned differentially expressed microRNA to specific cell types. Astrocytes contained all 10 microRNA that were most strongly upregulated in active multiple sclerosis lesions, including microRNA-155, which is known to modulate immune responses in different ways but so far had not been assigned to central nervous system resident cells. MicroRNA-155 was expressed in human astrocytes in situ, and further induced with cytokines in human astrocytes in vitro. This was confirmed with astrocyte cultures from microRNA-155-|-lacZ mice. We matched microRNA upregulated in phagocytically active multiple sclerosis lesions with downregulated protein coding transcripts. This converged on CD47, which functions as a 'don't eat me' signal inhibiting macrophage activity. Three microRNA upregulated in active multiple sclerosis lesions (microRNA-34a, microRNA-155 and microRNA-326) targeted the 3'-untranslated region of CD47 in reporter assays, with microRNA-155 even at two distinct sites. Our findings suggest that microRNA dysregulated in multiple sclerosis lesions reduce CD47 in brain resident cells, releasing macrophages from inhibitory control, thereby promoting phagocytosis of myelin. This mechanism may have broad implications for microRNA-regulated macrophage activation in inflammatory diseases.

Distribution and expression of CD200 in the rat respiratory system under normal and endotoxin-induced pathological conditions

In vivo and in vitro studies have clearly demonstrated that signaling mediated by the interaction of CD200 and its cognate receptor, CD200R, results in an attenuation of inflammatory or autoimmune responses through multiple mechanisms. The present results have shown a differential expression of CD200 in the respiratory tract of intact rats. Along the respiratory passage, CD200 was specifically distributed at the bronchiolar epithelia with intense CD200 immunoreactivity localized at the apical surface of some ciliated epithelial cells; only a limited expression was detected on the Clara cells extending into the alveolar duct. In the alveolar septum, double immunofluorescence showed intense CD200 immunolabeling on the capillary endothelia. A moderate CD200 labeling was observed on the alveolar type II epithelial cells. It was, however, absent in the alveolar type I epithelial cells and the alveolar macrophages. Immunoelectron microscopic study has revealed a specific distribution of CD200 on the luminal front of the thin portion of alveolar endothelia. During endotoxemia, the injured lungs showed a dose- and time-dependent decline of CD200 expression accompanied by a vigorous infiltration of immune cells, some of them expressing ionized calcium binding adapter protein 1 or CD200. Ultrastructural examination further showed that the marked reduction of CD200 expression was mainly attributable to the loss of alveolar endothelial CD200. It is therefore suggested that CD200 expressed by different lung cells may play diverse roles in immune homeostasis of normal lung, in particular, the molecules on alveolar endothelia that may control regular recruitment of immune cells via CD200-CD200R interaction. Additionally, it may contribute to intense infiltration of immune cells following the loss or inefficiency of CD200 under pathological conditions.

Immune activation in brain aging and neurodegeneration: too much or too little?

Until recently, the brain was studied almost exclusively by neuroscientists and the immune system by immunologists, fuelling the notion that these systems represented two isolated entities. However, as more data suggest an important role of the immune system in regulating the progression of brain aging and neurodegenerative disease, it has become clear that the crosstalk between these systems can no longer be ignored and a new interdisciplinary approach is necessary. A central question that emerges is whether immune and inflammatory pathways become hyperactivated with age and promote degeneration or whether insufficient immune responses, which fail to cope with age-related stress, may contribute to disease. We try to explore here the consequences of gain versus loss of function with an emphasis on microglia as sensors and effectors of immune function in the brain, and we discuss the potential role of the peripheral environment in neurodegenerative diseases.

Restoring immune suppression in the multiple sclerosis brain

Multiple sclerosis is a very disabling inflammatory demyelinating disease of the brain of unknown etiology. Current therapies can reduce new lesion development and partially prevent clinical disease activity, but none can halt the progression, or cure the disease. We will review current therapeutic strategies, which are mostly discussed in literature in terms of their effective inhibition of T cells. However, we argue that many of these treatments also influence the myeloid compartment. Interestingly, recent evidence indicates that myelin phagocytosis by infiltrated macrophages and activated microglia is not just a hallmark of multiple sclerosis, but also a key determinant of lesion development and disease progression. We reason that severe side effects and/or insufficient effectiveness of current treatments necessitates the search for novel therapeutic targets, and postulate that these should aim at manipulation of the activation and phagocytic capacity of macrophages and microglia. We will discuss three candidate targets with high potential, namely the complement receptor 3, CD47-SIRPalpha interaction as well as CD200-CD200R interaction. Blocking the actions of complement receptor 3 could inhibit myelin phagocytosis, as well as migration of myeloid cells into the brain. CD47 and CD200 are known to inhibit macrophage/microglia activation through binding to their receptors SIRPalpha and CD200R, expressed on phagocytes. Triggering these receptors may thus dampen the inflammatory response. Our recent findings indicate that the CD200-CD200R interaction is the most specific and hence probably best-suited target to suppress excessive macrophage and microglia activation, and restore immune suppression in the brain of patients with multiple sclerosis.

CD8+ T cells and neuronal damage: direct and collateral mechanisms of cytotoxicity and impaired electrical excitability

Cytotoxic CD8(+) T cells are increasingly recognized as key players in various inflammatory and degenerative central nervous system (CNS) disorders. CD8(+) T cells are believed to actively contribute to neural damage in these CNS conditions. Conceptually, one can separate two possible ways that CD8(+) T cells harm neuronal function or integrity: CD8(+) T cells either directly target neurons and their neurites in an antigen- or contact-dependent fashion, or exert their action via "collateral" mechanisms of neuronal damage that might follow destruction of the myelin sheath or glial cells in both the CNS gray and white matter. After introducing clinical examples, in which the putative relevance CD8(+) T cells has been demonstrated, we summarize knowledge on the sequence of initiation and execution of CD8(+) T-cell responses in the CNS. This includes the initial antigen cross-presentation and priming of naive CD8(+) T cells, followed by the invasion, migration, and target-cell recognition of CD8(+) effector T cells in the CNS parenchyma. Moreover, we discuss mechanisms of impaired electrical signaling and cell death of neurons as direct and collateral targets of CD8(+) T cells in the CNS.

The multiple roles of the innate immune system in the regulation of apoptosis and inflammation in the brain

Central nervous system (CNS) tissues contain cells (i.e. glia and neurons) that have innate immune functions. These cells express a range of receptors that are capable of detecting and clearing apoptotic cells and regulating inflammatory responses. Phagocytosis of apoptotic cells is a nonphlogistic (i.e. noninflammatory) process that provides immune regulation through anti-inflammatory cytokines andregulatory T cells. Neurons and glia express cellular death signals, including CD95Fas/CD95L, FasL, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and tumor necrosis factor receptor 1 (TNFR), through which they can trigger apoptosis in T cells and other infiltrating cells. Microglia, astrocytes, ependymal cells, and neurons express defense collagens and scavenger and phagocytic receptors that recognize apoptotic cells displaying apoptotic cell-associated molecular patterns, which serve as markers of "altered self." Glia also express pentraxins and complement proteins (C1q, C3b, and iC3b) that opsonize apoptotic cells, making them targets for the phagocytic receptors CR3 and CR4. Immunoregulatory molecules such as the complement regulator CD46 are lost from apoptotic cells and stimulate phagocytosis, whereas the expression of CD47 and CD200 is upregulated during apoptosis; this inhibits proinflammatory microglial cytokine expression, thereby reducing the severity of inflammation. This review outlines the cellular pathways used for the detection and phagocytosis of apoptotic cells in vitro and in experimental models of CNS inflammation.

Distribution of the immune inhibitory molecules CD200 and CD200R in the normal central nervous system and multiple sclerosis lesions suggests neuron-glia and glia-glia interactions

CD200 is a membrane glycoprotein that suppresses immune activity via its receptor, CD200R. CD200-CD200R interactions have recently been considered to contribute to the "immune privileged" status of the central nervous system (CNS). The mechanisms by which these interactions take place are not well understood in part because there is limited detailed information on the distribution of CD200 and CD200R in the CNS. Here, we used immunohistochemistry to characterize the distinct anatomical and cellular distribution of these molecules in multiple sclerosis (MS) lesions and controls. CD200 was robustly expressed in gray matter areas including the cerebral cortex, hippocampus, striatum, cerebellum, and spinal cord, where neurons appeared immunopositive. CD200 expression was also detected in oligodendrocytes, but not in astrocytes or microglia. In CNS samples from MS patients, CD200 expression was additionally observed on reactive astrocytes in chronic active plaque centers, despite our previous finding of an overall decrease ofCD200 expression in MS lesions. In contrast to CD200, the immunolocalization pattern of CD200R was very distinct, showing high expression on perivascular macrophages in both gray and white matter. Using flow cytometry, we also found that human primary microglia express low levels of CD200R. These data suggest that CD200-mediated immune suppression may occur not only via neuron-microglia interactions, but also via glia-glia interactions, especially in inflammatory conditions in which an immune-suppressive environment needs to be restored; this may occur as a result of increased CD200 expression on reactive astrocytes.

Neuronal regulation of immune responses in the central nervous system

The central nervous system (CNS) has traditionally been considered to be immunologically privileged, but over the years there has been a re-evaluation of this dogma. To date, studies have tended to focus on the immune functions of glial cells, whereas the roles of neurons have been regarded as passive and their immune-regulatory properties have been less examined. However, recent findings indicate that CNS neurons actively participate in immune regulation by controlling their glial cell counterparts and infiltrated T cells. Here, we describe the immune-regulatory roles of CNS neurons by both contact-dependent and contact-independent mechanisms. In addition, we specifically deal with the immune functions of neuronal cell adhesion molecules, many of which are key modulators of neuronal synaptic formation and plasticity.

Blueberry opposes beta-amyloid peptide-induced microglial activation via inhibition of p44/42 mitogen-activation protein kinase

Alzheimer's Disease (AD) is the most common age-related dementia, with a current prevalence in excess of five million individuals in the United States. The aggregation of amyloid-beta (A beta) into fibrillar amyloid plaques is a key pathological event in the development of the disease. Microglial proinflammatory activation is widely known to cause neuronal and synaptic damage that correlates with cognitive impairment in AD. However, current pharmacological attempts at reducing neuroinflammation mediated via microglial activation have been largely negative in terms of slowing AD progression. Previously, we have shown that microglia express proinflammatory cytokines and a reduced capacity to phagocytose A beta in the context of CD40, A beta peptides and/or lipopolysaccharide (LPS) stimulation, a phenomenon that can be opposed by attenuation of p44/42 mitogen-activated protein kinase (MAPK) signaling. Other groups have found that blueberry (BB) extract both inhibits phosphorylation of this MAPK module and also improves cognitive deficits in AD model mice. Given these considerations and the lack of reduced A beta quantities in behaviorally improved BB-fed mice, we wished to determine whether BB supplementation would alter the microglial proinflammatory activation state in response to A beta. We found that BB significantly enhances microglial clearance of A beta, inhibits aggregation of A beta(1-42), and suppresses microglial activation, all via suppression of the p44/42 MAPK module. Thus, these data may explain the previously observed behavioral recovery in PSAPP mice and suggest a means by which dietary supplementation could mitigate an undesirable microglial response toward fibrillar A beta.

Decreased expression of CD200 and CD200 receptor in Alzheimer's disease: a potential mechanism leading to chronic inflammation

Inflammatory activation of microglia in response to neurodegenerative changes in diseases such as Alzheimer's disease (AD) and Parkinson's disease has been extensively described. These observations have suggested that inflammation could be contributing to disease progression. In this paper, the potential role of CD200 and CD200 receptor (CD200R), whose known functions are to activate anti-inflammatory pathways and induce immune tolerance through binding of CD200 to CD200 receptor (CD200R), was studied in AD. Quantitative studies showed a significant decrease in CD200 protein and mRNA in AD hippocampus and inferior temporal gyrus, but not cerebellum. Immunohistochemistry of brain tissue sections of hippocampus, superior frontal gyrus, inferior temporal gyrus and cerebellum from AD and non-demented cases demonstrated a predominant, though heterogeneous, neuronal localization for CD200. Decreased neuronal expression was apparent in brain regions affected by AD pathology. There was also a significant decrease in CD200R mRNA expression in AD hippocampus and inferior temporal gyrus, but not cerebellum. Low expression of CD200R by microglia was confirmed at the mRNA and protein level using cultured human microglia compared to blood-derived macrophages. Treatment of microglia and macrophages with interleukin-4 and interleukin-13 significantly increased expression of CD200R. Expression of these cytokines was not generally detectable in brain. These data indicate that the anti-inflammatory CD200/CD200R system may be deficient in AD brains. Mechanisms aimed at increasing levels of CD200 and CD200R could have therapeutic potential for controlling inflammation in human neurodegenerative diseases.

Identification of soluble TREM-2 in the cerebrospinal fluid and its association with multiple sclerosis and CNS inflammation

Triggering receptor expressed on myeloid cells 2 (TREM-2) is a membrane-bound receptor expressed by microglia and macrophages. Engagement of TREM-2 on these cells has been reported to reduce inflammatory responses and, in microglial cells, to promote phagocytosis. TREM-2 function is critical within the CNS, as its genetic deficiency in humans causes neurodegeneration with myelin and axonal loss. Blockade of TREM-2 worsened the mouse model for multiple sclerosis. In the present study, a soluble form of TREM-2 protein has been identified by immunoprecipitation and by ELISA. Soluble TREM-2 protein (sTREM-2) was detected in human CSF, and was compared among subjects with relapsing-remitting multiple sclerosis (RR-MS; n = 52), primary progressive multiple sclerosis (PP-MS; n = 21), other inflammatory neurologic diseases (OIND; n = 19), and non-inflammatory neurologic diseases (NIND; n = 41). Compared to NIND subjects, CSF sTREM-2 levels were significantly higher in RR-MS (P = 0.004 by ANOVA) and PP-MS (P < 0.001) subjects, as well as in OIND (P < 0.001) subjects. In contrast, levels of sTREM-2 in blood did not differ among the groups. Furthermore, TREM-2 was detected on a subset of CSF monocytes by flow cytometry, and was also highly expressed on myelin-laden macrophages in eight active demyelinating lesions from four autopsied multiple sclerosis subjects. The elevated levels of sTREM-2 in CSF of multiple sclerosis patients may inhibit the anti-inflammatory function of the membrane-bound receptor suggesting sTREM-2 to be a possible target for future therapies.

Gene expression analysis in the human hypothalamus in depression by laser microdissection and real-time PCR: the presence of multiple receptor imbalances

Hyperactivity of corticotropin-releasing factor (CRF) neurons in the paraventricular nucleus (PVN) of the hypothalamus is a prominent feature in depression and may be important in the etiology of this disease. The activity of the CRF neurons in the stress response is modulated by a number of factors that stimulate or inhibit CRF expression, including (1) corticosteroid receptors and their chaperones, heat shock proteins 70 and 90, (2) sex hormone receptors, (3) CRF receptors 1 (CRFR1) and 2, (4) cytokines interleukin 1-beta and tumor necrosis factor-alpha, (5) neuropeptides and receptors, vasopressin (AVP), AVP receptor 1a (AVPR1A) and oxytocin and (6) transcription factor cAMP-response element-binding protein. We hypothesized that, in depression, the transcript levels of those genes that are involved in the activation of the hypothalamo-pituitary-adrenal (HPA) axis are upregulated, whereas the transcript levels of the genes involved in the inhibition of the HPA axis are downregulated. We performed laser microdissection and real-time PCR in the PVN and as a control in the supraoptic nucleus. Snap-frozen post-mortem hypothalami of seven depressed and seven matched controls were used. We found significantly increased CRF mRNA levels in the PVN of the depressed patients. This was accompanied by a significantly increased expression of four genes that are involved in the activation of CRF neurons, that is, CRFR1, estrogen receptor-alpha, AVPR1A and mineralocorticoid receptor, while the expression of the androgen receptor mRNA involved in the inhibition of CRF neurons was decreased significantly. These findings raise the possibility that a disturbed balance in the production of receptors may contribute to the activation of the HPA axis in depression.

CNS inflammation and neuronal degeneration is aggravated by impaired CD200-CD200R-mediated macrophage silencing

Multiple sclerosis is a chronic disabling CNS disorder, characterized by autoimmune inflammatory demyelination and neurodegeneration. CD200, broadly expressed on neurons and endothelial cells, mediates inhibitory signals through its receptor, CD200R, on cells of myeloid origin. Antibody-mediated blockade of CD200R leads to an aggravated clinical course of rodent experimental autoimmune encephalomyelitis in vivo, accompanied by profoundly augmented cellular infiltrates consisting of T cells and activated iNOS(+) macrophages in inflammatory spinal cord lesions. In vitro blockade of CD200R on macrophages leads to enhanced IFN-gamma-induced release of IL6 and neuronal cell death in co-cultures with hippocampal neurons expressing CD200. CD200 and its receptor could also be detected on neurons and macrophages in human MS plaques. Therefore the CD200-CD200R pathway seems of critical relevance for macrophage-mediated damage in autoimmune inflammation of the CNS.

Depletion of autoreactive B-lymphocytes by a recombinant myelin oligodendrocyte glycoprotein-based immunotoxin

We report the construction of a fusion protein comprising the extracellular domain of myelin oligodendrocyte glycoprotein (MOG) and a truncated version of Pseudomonas aeruginosa exotoxin A (ETA'). The chimeric immunotoxin targeted MOG-reactive B-lymphocytes by binding selectively to the appropriate receptors, leading to internalization and apoptosis of the target cells. The functionality of the immunotoxin was tested on a MOG-sensitive murine hybridoma cell line and ex vivo on freshly isolated splenocytes from transgenic IgH(MOG) mice. These data demonstrate, for the first time, the specific cytotoxicity of a MOG-containing recombinant immunotoxin expressed in bacteria towards MOG-reactive B-lymphocytes.