Biomedical subjects

Tim Magnus

Publications and source records attributed to Tim Magnus.

At least 19 recordsLinked to original sources

PubMed2007

Autoimmune modulation of astrocyte-mediated homeostasis.

Astrocytes are principal mediators of homeostasis in the central nervous system (CNS). They supply neurons and oligodendrocytes with substrates for energy metabolism and clear the extracellular space of excess neurotransmitters. In neuroinflammation, astrocytes have classically been regarded as unimportant since their capacity to present antigen to T cells is limited and has been questioned in vivo. However, it is an evolving concept that autoimmunity in the CNS has a profound impact on astrocytes. In this review, we focus on the alterations in astrocyte functions that occur during an autoimmune attack of the CNS.

Animals↗

PubMed2006

Cytoplasmic translocation of Olig2 in adult glial progenitors marks the generation of reactive astrocytes following autoimmune inflammation.

The injury response in the brain involves complex interplay between neural and immune components. Following inflammatory insults to the adult CNS, formation of an astroglial scar often impedes functional repair. Glial progenitor cells expressing the nuclear transcription factor Olig2 possibly generate astrocytes in response to various types of injuries; however, the mechanisms underlying this differentiation are unclear. In a model of immune-mediated injury (MOG(35-55)-experimental autoimmune encephalomyelitis), we show that the conversion from progenitor to reactive astrocyte is marked by the translocation of Olig2 into the cytoplasm. Evidence of this process is found for months after disease initiation in the absence of new inflammatory infiltrates. A proportion of cells with cytoplasmic Olig2 was found to express NG2 or Nkx2.2, but only Nkx2.2 was occasionally retained by GFAP+ cells. We further show that differentiation to astrocytes is induced in glial progenitors in vitro through exposure to the pro-inflammatory cytokine IFN-gamma, but not to TNF-alpha. Together, these data ascribe a pivotal role to Olig2+ glial precursor cells in the adult CNS, linking autoimmune inflammation and glial scar formation.

Animals↗

PubMed2006

Complement mediators in ischemia-reperfusion injury.

BACKGROUND: Ischemia-reperfusion (I/R) injury occurs when a tissue is temporarily deprived of blood supply and the return of the blood supply triggers an intense inflammatory response. Pathologically, increased complement activity can cause substantial damage to blood vessels, tissues and also facilitate leukocyte activation and recruitment following I/R injury. Herein, previously published studies are reported and critically reviewed. METHODS: Medline and the World Wide Web were searched and the relevant literature was classified under the following categories: (1) Complement pathways; (2) The complement system and the inflammatory response; (3) Complement in ischemia-reperfusion injuries; and (4) Therapeutic approaches against complement in I/R injuries. RESULTS AND CONCLUSIONS: I/R injury is a common clinical event with the potential to seriously affect, and sometimes kill, the patient and is a potent inducer of complement activation that results in the production of a number of inflammatory mediators. Complement activation leads to the release of biologically active potent inflammatory complement substances including the anaphylatoxins (C3a and C5a) and the cytolytic terminal membrane attack complement complex C5b-9 (MAC). The use of specific complement inhibitors to block complement activation at various levels of the cascade has been shown to prevent or reduce local tissue injury after I/R. Several agents that inhibit all or part of the complement system, such as soluble complement receptor type 1 (sCR1), C1 inhibitor (C1-INH), C5a monoclonal antibodies, a C5a receptor antagonist and soluble CD59 (sCD59) have been shown to reduce I/R injury of various organs. The novel inhibitors of complement products may eventually find wide clinical application because there are no effective drug therapies currently available to treat I/R injuries.

Animals↗

PubMed2006

Gamma secretase-mediated Notch signaling worsens brain damage and functional outcome in ischemic stroke.

Mice transgenic for antisense Notch and normal mice treated with inhibitors of the Notch-activating enzyme gamma-secretase showed reduced damage to brain cells and improved functional outcome in a model of focal ischemic stroke. Notch endangers neurons by modulating pathways that increase their vulnerability to apoptosis, and by activating microglial cells and stimulating the infiltration of proinflammatory leukocytes. These findings suggest that Notch signaling may be a therapeutic target for treatment of stroke and related neurodegenerative conditions.

Amyloid Precursor Protein Secretases↗

PubMed2006

Ageing and neuronal vulnerability.

Everyone ages, but only some will develop a neurodegenerative disorder in the process. Disease might occur when cells fail to respond adaptively to age-related increases in oxidative, metabolic and ionic stress, thereby resulting in the accumulation of damaged proteins, DNA and membranes. Determinants of neuronal vulnerability might include cell size and location, metabolism of disease-specific proteins and a repertoire of signal transduction pathways and stress resistance mechanisms. Emerging evidence on protein interaction networks that monitor and respond to the normal ageing process suggests that successful neural ageing is possible for most people, but also cautions that cures for neurodegenerative disorders are unlikely in the near future.

Aging↗

PubMed2006

Borrelia burgdorferi Induces TLR1 and TLR2 in human microglia and peripheral blood monocytes but differentially regulates HLA-class II expression.

The spirochete Borrelia burgdorferi is the agent of Lyme disease, which causes central nervous system manifestations in up to 20% of patients. We investigated the response of human brain microglial cells, glial progenitors, neurons, astrocytes, as well as peripheral blood monocytes to stimulation with B. burgdorferi. We used oligoarrays to detect changes in the expression of genes important for shaping adaptive and innate immune responses. We found that stimulation with B. burgdorferi lysate increased the expression of Toll-like receptors (TLRs) 1 and 2 in all cell types except neurons. However, despite similarities in global gene profiles of monocytes and microglia, only microglial cells responded to the stimulation with a robust increase in HLA-DR, HLA-DQ, and also coexpressed CD11-c, a dendritic cell marker. In contrast, a large number of HLA-related molecules were repressed at both the RNA and the protein levels in stimulated monocytes, whereas secretion of IL-10 and TNF-alpha was strongly induced. These results show that signaling through TLR1/2 in response to B. burgdorferi can elicit opposite immunoregulatory effects in blood and in brain immune cells, which could play a role in the different susceptibility of these compartments to infection.

Borrelia burgdorferi↗

PubMed2005

Neurogenesis in Talpha-1 tubulin transgenic mice during development and after injury.

Talpha-1 tubulin promoter-driven EYFP expression is seen in murine neurons born as early as E9.5. Double labeling with markers for stem cells (Sox 1, Sox 2, nestin), glial progenitors (S100beta, NG2, Olig2), and neuronal progenitors (doublecortin, betaIII-tubulin, PSA-NCAM) show that Talpha-1 tubulin expression is limited to early born neurons. BrdU uptake and double labeling with neuronal progenitor markers in vivo and in vitro show that EYFP-expressing cells are postmitotic and Talpha-1 tubulin EYFP precedes the expression of MAP-2 and NeuN, and follows the expression of PSA-NCAM, doublecortin (Dcx), and betaIII-tubulin. Talpha-1 tubulin promoter-driven EYFP expression is transient and disappears in most neurons by P0. Persistent EYFP expression is mainly limited to scattered cells in the subventricular zone (SVZ), rostral migratory stream, and hippocampus. However, there are some areas that continue to express Talpha-1 tubulin in the adult without apparent neurogenesis. The number of EYFP-expressing cells declines with age indicating that Talpha-1 tubulin accurately identifies early born postmitotic neurons throughout development but less clearly in the adult. Assessment of neurogenesis after stab wound injuries in the cortex, cerebellum and spinal cord of adult animals shows no neurogenesis in most areas with an increase in BrdU incorporation in glial and other non neuronal populations. An up-regulation of Talpha-1 tubulin can be seen in certain areas unaccompanied by new neurogenesis. Our results suggest that even if stem cells proliferate their ability to generate neurons is limited and caution is warranted in attributing increased BrdU incorporation to stem cells or cells fated to be neurons even in neurogenic areas.

Animals↗

PubMed2005

Autoantigen specific T cells inhibit glutamate uptake in astrocytes by decreasing expression of astrocytic glutamate transporter GLAST: a mechanism mediated by tumor necrosis factor-alpha.

Glutamate excitotoxicity is increasingly being recognized as a pathogenic mechanism in autoimmune inflammatory disorders of the central nervous system (CNS). Astrocytes are the predominant players in clearing the extracellular space from glutamate and normally have extensive spare capacities in terms of glutamate uptake. We asked what might be the basis of glutamate accumulation in T cell triggered autoimmune inflammation. In vitro, coculture of primary rat astrocytes with activated myelin basic protein (MBP)-specific T cells resulted in a decrease of astrocytic glutamate uptake rates (Vmax). In parallel, the amount of the Na+-dependent glutamate transporter GLAST was reduced within 48-60 h. Significant decreases of GLAST protein were observed in astrocytes harvested after incubation with T cells activated by MBP during coculture or after incubation with T cell blasts preactivated in the presence of splenocytes beforehand. Since exposure of astrocytes to cell-free supernatant of MBP-activated T cells also resulted in reduced expression of GLAST, a humoral factor appeared to be the driving agent. In blocking experiments using neutralizing antibodies and by incubation of astrocytes with recombinant cytokines, tumor necrosis factor-alpha (TNF-alpha) was identified as being responsible for the down-modulation of GLAST. GLAST was also down-regulated in the CNS of autoimmune encephalomyelitic rats but not in animals suffering from systemic inflammation. Since the loss of GLAST was not confined to inflammatory infiltrates, here too, a humoral factor seemed to be causative. In conclusion, T cell derived TNF-alpha impairs glutamate clearance capacity of astrocytes in vitro and probably also in vivo providing a pathogenic link to glutamate excitotoxicity that may contribute to early axonal dysfunction remote from active autoimmune inflammatory demyelination.

Amino Acid Transport System X-AG↗

PubMed2005

Microglial expression of the B7 family member B7 homolog 1 confers strong immune inhibition: implications for immune responses and autoimmunity in the CNS.

Inflammation of the CNS is usually locally limited to avoid devastating consequences. Critical players involved in this immune regulatory process are the resident immune cells of the brain, the microglia. Interactions between the growing family of B7 costimulatory ligands and their receptors are increasingly recognized as important pathways for costimulation and/or inhibition of immune responses. Human and mouse microglial cells constitutively express B7 homolog 1 (B7-H1) in vitro. However, under inflammatory conditions [presence of interferon-gamma (IFN-gamma) or T-helper 1 supernatants], a significant upregulation of B7-H1 was detectable. Expression levels of B7-H1 protein on microglial cells were substantially higher compared with astrocytes or splenocytes. Coculture experiments of major histocompatibility complex class II-positive antigen-presenting cells (APC) with syngeneic T cells in the presence of antigen demonstrated the functional consequences of B7-H1 expression on T-cell activation. In the presence of a neutralizing anti-B7-H1 antibody, both the production of inflammatory cytokines (IFN-gamma and interleukin-2) and the upregulation of activation markers (inducible costimulatory signal) by T cells were markedly enhanced. Interestingly, this effect was clearly more pronounced when microglial cells were used as APC, compared with astrocytes or splenocytes. Furthermore, B7-H1 was highly upregulated during the course of myelin oligodendrocyte glycoprotein-induced and proteolipid protein-induced experimental allergic encephalomyelitis in vivo. Expression was predominantly localized to areas of strongest inflammation and could be colocalized with microglial cells/macrophages as well as T cells. Together, our data propose microglial B7-H1 as an important immune inhibitory molecule capable of downregulating T-cell activation in the CNS and thus confining immunopathological damage.

Animals↗

PubMed2005

Interaction with antigen-specific T cells regulates expression of the lactate transporter MCT1 in primary rat astrocytes: specific link between immunity and homeostasis.

Monocarboxylates like lactate are provided by astrocytes and can be used as fuel by neurons and oligodendrocytes. In an autoimmune inflammatory environment, homeostatic functions of astrocytes are incompletely understood. In primary Lewis rat astrocytes, co-culture with MHC class II-restricted myelin basic protein (MBP)-specific T cells in the presence of MBP resulted in a marked upregulation of the astrocytic lactate transporter MCT1 that is to export lactate into the extracellular space. It was evident that the increase in MCT1 was triggered by T cells in an antigen-dependent manner. The glial isoform of the glucose transporter GLUT1 was not regulated under these conditions. T-cell blasts that had been pre-activated by antigen and splenic antigen-presenting cells (APCs) beforehand also led to an increase in the expression of astrocytic MCT1 after co-culture. Resting T cells did not induce a relevant upregulation of MCT1 in astrocytes. However, resting T cells stimulated the expression of MCT1 when anti-MHC class II antibodies, but not when anti-MHC class I antibodies, were added to the co-culture. Therefore, even in the presence of inactive T cells, complexation of MHC class II molecules on astrocytes might lead to the regulation of certain astrocytic transport proteins. Consistent with the in vitro experiments, an upregulation of MCT1 was observed in the spinal cord of autoimmune encephalitic rats while GLUT1 expression appeared to be unchanged. This T-cell-mediated regulation of MCT1 might contribute to a compensatory or protective mechanism in order to guarantee substrate pools for neurons and oligodendrocytes under inflammatory conditions.

Adoptive Transfer↗

PubMed2005

Autonomic dysfunction in ALS: a preliminary study on the effects of intrathecal BDNF.

This pilot study aimed at exploring the effects of intrathecally administered brain derived neurotrophic factor (BDNF) on autonomic functions in patients with ALS. A battery of autonomic sympathetic and parasympathetic tests was performed at baseline and after nine months of treatment in 10 ALS patients participating in a double-blind placebo-controlled phase II/III study of intrathecally administered BDNF. Results of patients treated with BDNF (25 or 150 microg/day) were compared to those receiving placebo. Sudomotor function and blood pressure response to handgrip significantly worsened during the treatment period (55.4+/-26.1 vs. 38.9+/-23.9 g/m(2)h, p<0.05; 20+/-6 vs. 13+/-4 microHg, p<0.05) whereas other sympathetic and all parasympathetic function tests only tended to be more abnormal at follow-up. Serum norepinephrine levels increased significantly during the nine-months observation period. The results of autonomic function tests were not different between patients treated with BDNF and placebo, but norepinephrine levels were higher in the BDNF group. We conclude that autonomic nervous system function deteriorates along with poorer motor performance independently from treatment with BDNF. The elevation of norepinephrine levels might reflect a non-specific up-regulation, and its association with BDNF an autocrine effect.

Adult↗

PubMed2004

Modulation of effector cell functions in experimental autoimmune encephalomyelitis by leflunomide--mechanisms independent of pyrimidine depletion.

Leflunomide inhibits de novo pyrimidine synthesis and is a novel, immunosuppressive agent that has been successfully used to treat rheumatoid arthritis. Here, we investigated the efficacy of leflunomide and its mode of action in experimental autoimmune encephalomyelitis (EAE), which is a T helper cell type 1 cell-borne disease model to simulate inflammatory aspects of multiple sclerosis and was induced in Lewis rats by adoptive transfer of myelin basic protein (MBP)-specific T line cells. Given in vivo for 7 days after cell transfer, leflunomide suppressed clinical signs of disease even in uridine-substituted animals. MBP-specific T line cells that had been antigen-activated in vitro in the presence of A77 1726 (active metabolite of leflunomide) produced less interferon-gamma, whereas interleukin (IL)-10 secretion had a tendency to be increased without changes in signal transducer and activator of transcription 6 trafficking. Furthermore, these T cells exhibited reduced chemotaxis and induced a significantly mitigated disease course upon transfer into naive rats. The effects of leflunomide on MBP-specific memory type T line cells in vitro may not be mediated by pyrimidine depletion, as they were not reversible by exogenous uridine. Moreover, A77 1726 led to increased expression of CD86 (B7-2) and secretion of IL-10 in cultured microglial cells in vitro, strengthening their down-modulatory impact on activated, autoantigen-specific T cells. In conclusion, our observations underline that the immunomodulatory potential of leflunomide in effector cells of EAE is clinically relevant and is not exclusively dependent on the depletion of cellular pyrimidine pools.

Adoptive Transfer↗

PubMed2004

Induction of IL-10 in rat peritoneal macrophages and dendritic cells by glatiramer acetate.

Glatiramer acetate (GLAT) is a mixture of basic polypeptides that have been shown to suppress experimental autoimmune encephalomyelitis (EAE). As Copaxone, GLAT is approved for the treatment of relapsing-remitting multiple sclerosis (MS). Different immunomechanisms have been suggested to contribute to the beneficial effects of GLAT which rely on blockade of MHC class II molecules or cross-recognition with myelin basic protein (MBP). Because GLAT could also inhibit experimental autoimmunity not related to myelin proteins, we searched for additional, less-restricted immunomodulatory actions of GLAT. Using freshly isolated resident peritoneal macrophages from naive Lewis rats, it is shown that GLAT profoundly modulates cytokine secretion of the cells. In unseparated macrophages (MPhi) and MPhi of low density, GLAT enhanced constitutive and LPS-induced production of interleukin 10 (IL-10) while LPS-induced synthesis of tumor necrosis factor-alpha (TNF-alpha) was dose-dependently suppressed by GLAT. Although both basic proteins GLAT and MBP facilitated adherence of MPhi, MBP had opposite effects on cytokine production suggesting unique properties of GLAT. In contrast to MPhi, peritoneal mast cells produced only little amounts of cytokines. The inductive effect of GLAT on IL-10 production by antigen-presenting cells was also observed in bone marrow-derived rat dendritic cells (DCs) which, unlike MPhi, were not suppressed in their production of TNF-alpha. Induction of IL-10 in different antigen-presenting cells is a new immunomodulatory mechanism of GLAT. In part, it goes along with the inhibition of TNF-alpha and may be a common basis for the known beneficial effects of GLAT on various cellular autoimmune responses including MS.

Animals↗

PubMed2004

Chronically stimulated microglial cells do no longer alter their immune functions in response to the phagocytosis of apoptotic cells.

In an autoimmune inflammatory setting, ingestion of apoptotic T cells leads to a down-regulation of microglial immune functions. Recent studies have indicated that microglia can be matured by exposure to GM-CSF. GM-CSF stimulation led to a differentiated microglial phenotype and enhanced antigen-presenting capabilities. The secretion of TNF-alpha was significantly decreased by the uptake of apoptotic cells in unstimulated microglia, but not in GM-CSF-differentiated microglia. IL-10 secretion was unaffected. After ingestion of apoptotic cells, only previously unstimulated, but not GM-CSF-differentiated microglial cells decreased their T cell-activating potential as measured by IFN-gamma secretion in antigen-activated MBP-specific T cells. Thus, GM-CSF stimulation reduces the immunomodulatory functions of microglial cells.

Adjuvants, Immunologic↗

PubMed2003

Phagocytosis of apoptotic inflammatory cells by microglia and its therapeutic implications: termination of CNS autoimmune inflammation and modulation by interferon-beta.

Apoptosis of autoaggressive T-cells in the CNS is an effective, noninflammatory mechanism for the resolution of T-cell infiltrates, contributing to clinical recovery in T-cell-mediated neuroinflammatory diseases. The clearance of apoptotic leukocytes by tissue-specific phagocytes is critical in the resolution of the inflammatory infiltrate and leads to a profound downregulation of phagocyte immune functions. Adult human microglia from surgically removed normal brain tissue was used in a standardized, light-microscopic in vitro phagocytosis assay of apoptotic autologous peripheral blood-derived mononuclear cells (MNCs). Microglia from five different patients had a high capacity for the uptake of apoptotic MNCs in contrast to nonapoptotic target cells with the phagocytosis rate for nonapoptotic MNCs amounting to only 61.6% of the apoptotic MNCs. A newly described phosphatidylserine receptor, critical in the phagocytosis of apoptotic cells by macrophages, is also expressed at similar levels on human microglia. The effects of the therapeutically used immunomodulatory agent interferon-beta (IFNbeta) were investigated using Lewis rat microglia and apoptotic, encephalitogenic, myelin basic protein-specific autologous T-cells. Also, rat microglia had a high capacity to phagocytose apoptotic T-cells specifically. IFNbeta increased the phagocytosis of apoptotic T-cells to 36.8% above the untreated controls. The enhanced phagocytic activity was selective for apoptotic T-cells and was not mediated by increased IL-10 secretion. Apoptotic inflammatory cells may be efficiently and rapidly removed by microglial cells in the autoimmune-inflamed human CNS. The in vitro increase of phagocytosis by IFNbeta merits further investigations whether this mechanism could also be therapeutically exploited.

Animals↗

PubMed2003

Transient dystonia following magnetic resonance imaging in a patient with deep brain stimulation electrodes for the treatment of Parkinson disease. Case report.

Data from previous studies have shown that magnetic resonance (MR) imaging of the head can be performed safely in patients with deep brain stimulators. The authors report on a 73-year-old patient with bilaterally implanted deep brain electrodes for the treatment of Parkinson disease, who exhibited dystonic and partially ballistic movements of the left leg immediately after an MR imaging session. Such dystonic or ballistic movements had not been previously observed in this patient. In the following months, this focal movement disorder resolved completely. This case demonstrates the possible risks of MR imaging in patients with deep brain stimulators.

Aged↗

PubMed2002

Truncation of the neuritogenic peptide bP2(60-70) results in the generation of altered peptide ligands with the potential to interfere with T cell activation.

Due to the central role of T cells in the pathogenesis of inflammatory diseases of the peripheral nervous system like the Guillain-Barré syndrome, specific immunotherapies aim at modifying T cell responses. Use of truncated mutants of the neuritogenic peptide of myelin basic protein (MBP) has been shown to anergize autoreactive T cells and to reverse experimental autoimmune encephalitis (EAE). To establish a rationale basis for the use of altered peptide ligands (APLs) in the treatment of autoimmune diseases we designed a set of N- and C-terminally truncated mutants of the minimal experimental autoimmune neuritis (EAN) inducing bovine P2 (bP2) (60-70) peptide and compared them for the ability to induce immune responses and T cell receptor (TCR) cell signaling. Truncated peptides bound to MHC class II molecules and induced TCR internalization and expression of interferon gamma (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha) with decreasing potency. None of the shortened mutants elicited a proliferative response in P2-specific T cells. Stimulation of these antigen-specific T cells with peptide bP2(62-69) using antigen presenting cells (APCs) prepulsed with bP2(60-70) resulted in a significant decrease of the proliferative response. In agreement with the observed effects on T cell activation, analysis of TCR signaling demonstrated a lack of CD3 epsilon phosphorylation and MAPK activation. Moreover, repeated injection of bP2(62-69) significantly slowed progression of adoptive transfer EAN (AT-EAN). Taken together, these findings strongly suggest that peptide bP2(62-69) can favorably modulate the antigen-induced response of neuritogenic T cells.

Animals↗

PubMed2002

Phagocytotic removal of apoptotic, inflammatory lymphocytes in the central nervous system by microglia and its functional implications.

Apoptotic cell death of inflammatory T cells is an established mechanism to terminate an autoimmune inflammatory response in the rodent and human central nervous system (CNS). The efficient clearance of apoptotic cells protects the tissue from leakage of potentially harmful substances from secondary necrotic cells. As the resident phagocyte, the microglial cell is the primary candidate for the clearance of apoptotic lymphocytes. Furthermore, the phagocytosis of apoptotic cells is accompanied by a spectrum of anti-inflammatory effects. In this review, we focus on the mechanisms for removal of apoptotic inflammatory cells by microglia in the central nervous system and their functional consequences.

Animals↗