Myelin-laden macrophages are anti-inflammatory, consistent with foam cells in multiple sclerosis

Microglial nodules in early multiple sclerosis white matter are associated with degenerating axons

Microglial nodules in the normal-appearing white matter have been suggested as the earliest stage(s) of multiple sclerosis (MS) lesion formation. Such nodules are characterized by an absence of leukocyte infiltration, astrogliosis or demyelination, and may develop into active demyelinating MS lesions. Although the etiology of MS is still not known, inflammation and autoimmunity are considered to be the central components of this disease. Previous studies provide evidence that Wallerian degeneration, occurring as a consequence of structural damage in MS lesions, might be responsible for observed pathological abnormalities in connected normal-appearing white matter. As innate immune cells, microglia/macrophages are the first to react to even minor pathological changes in the CNS. Biopsy tissue from 27 MS patients and autopsy and biopsy tissue from 22 normal and pathological controls were analyzed to determine the incidence of microglial nodules. We assessed MS periplaque white matter tissue from early disease stages to determine whether microglial nodules are associated with altered axons. With immunohistochemical methods, the spatial relation of the two phenomena was visualized using HLA-DR antibody for MHC II expression by activated microglia/macrophages and by applying antibodies against damaged axons, i.e., SMI32 (non-phosphorylated neurofilaments) and amyloid precursor protein as well as neuropeptide Y receptor Y1, which marks axons undergoing Wallerian degeneration. Our data demonstrate that the occurrence of microglial nodules is not specific to MS and is associated with degenerating as well as damaged axons in early MS. In addition, we show that early MS microglial nodules exhibit both pro- and antiinflammatory phenotypes.

Iron is a sensitive biomarker for inflammation in multiple sclerosis lesions

MRI phase imaging in multiple sclerosis (MS) patients and in autopsy tissue have demonstrated the presence of iron depositions in white matter lesions.

The accumulation of iron in some but not all lesions suggests a specific, potentially disease-relevant process, however; its pathophysiological significance remains unknown.

Here, we explore the role of lesional iron in multiple sclerosis using multiple approaches: immunohistochemical examination of autoptic MS tissue, an in vitro model of iron-uptake in human cultured macrophages and ultra-highfield phase imaging of highly active and of secondary progressive MS patients.

Using Perls' stain and immunohistochemistry, iron was detected in MS tissue sections predominantly in non-phagocytosing macrophages/microglia at the edge of established, demyelinated lesions. Moreover, iron-containing macrophages but not myelin-laden macrophages expressed markers of proinflammatory (M1) polarization.

Similarly, in human macrophage cultures, iron was preferentially taken up by non-phagocytosing, M1-polarized macrophages and induced M1 (super) polarization. Iron uptake was minimal in myelin-laden macrophages and active myelin phagocytosis led to depletion of intracellular iron.

Finally, we demonstrated in MS patients using GRE phase imaging with ultra-highfield MRI that phase hypointense lesions were significantly more prevalent in patients with active relapsing than with secondary progressive MS.

Taken together, our data provide a basis to interpret iron-sensitive GRE phase imaging in MS patients: iron is present in non-phagocytosing, M1-polarized microglia/macrophages at the rim of chronic active white matter demyelinating lesions. Phase imaging may therefore visualize specific, chronic proinflammatory activity in established MS lesions and thus provide important clinical information on disease status and treatment efficacy in MS patients.

Selective upregulation of scavenger receptors in and around demyelinating areas in multiple sclerosis

Autoantibodies and complement opsonization have been implicated in the process of demyelination in the major human CNS demyelinating disease multiple sclerosis (MS), but scavenger receptors (SRs) may also play pathogenetic roles. We characterized SR mRNA and protein expression in postmortem brain tissue from 13 MS patients in relation to active demyelination. CD68, chemokine (C-X-C motif) ligand 16 (CXCL16), class A macrophage SR (SR-AI/II), LOX-1 (lectin-like oxidized low-density lipoprotein receptor 1), FcγRIII, and LRP-1 (low-density lipoprotein receptor-related protein 1) mRNA were upregulated in the rims of chronic active MS lesions. CD68 and CXCL16 mRNA were also upregulated around chronic active MS lesions. By immunohistochemistry, CD68, CXCL16, and SR-AI/II were expressed by foamy macrophages in the rim and by ramified microglia around chronic active MS lesions. CXCL16 and SR-AI/II were also expressed by astrocytes in MS lesions and by primary human microglia and astrocytes in vitro. These data suggest that SRs are involved in myelin uptake in MS, and that upregulation of CD68, CXCL16, and SR-AI/II is one of the initial events in microglia as they initiate myelin phagocytosis. As demyelination continues, additional upregulation of LOX-1, FcγRIII, and LRP-1 may facilitate this process.

Recruitment of beneficial M2 macrophages to injured spinal cord is orchestrated by remote brain choroid plexus

Monocyte-derived macrophages are essential for recovery after spinal cord injury, but their homing mechanism is poorly understood. Here, we show that although of common origin, the homing of proinflammatory (M1) and the "alternatively activated" anti-inflammatory (M2) macrophages to traumatized spinal cord (SC) was distinctly regulated, neither being through breached blood-brain barrier. The M1 macrophages (Ly6c(hi)CX3CR1(lo)) derived from monocytes homed in a CCL2 chemokine-dependent manner through the adjacent SC leptomeninges. The resolving M2 macrophages (Ly6c(lo)CX3CR1(hi)) derived from monocytes trafficked through a remote blood-cerebrospinal-fluid (CSF) barrier, the brain-ventricular choroid plexus (CP), via VCAM-1-VLA-4 adhesion molecules and epithelial CD73 enzyme for extravasation and epithelial transmigration. Blockage of these determinants, or mechanical CSF flow obstruction, inhibited M2 macrophage recruitment and impaired motor-function recovery. The CP, along with the CSF and the central canal, provided an anti-inflammatory supporting milieu, potentially priming the trafficking monocytes. Overall, our finding demonstrates that the route of monocyte entry to central nervous system provides an instructional environment to shape their function.

Macrophages in inflammatory multiple sclerosis lesions have an intermediate activation status

Background

Macrophages play a dual role in multiple sclerosis (MS) pathology. They can exert neuroprotective and growth promoting effects but also contribute to tissue damage by production of inflammatory mediators. The effector function of macrophages is determined by the way they are activated. Stimulation of monocyte-derived macrophages in vitro with interferon-γ and lipopolysaccharide results in classically activated (CA/M1) macrophages, and activation with interleukin 4 induces alternatively activated (AA/M2) macrophages.

Methods

For this study, the expression of a panel of typical M1 and M2 markers on human monocyte derived M1 and M2 macrophages was analyzed using flow cytometry. This revealed that CD40 and mannose receptor (MR) were the most distinctive markers for human M1 and M2 macrophages, respectively. Using a panel of M1 and M2 markers we next examined the activation status of macrophages/microglia in MS lesions, normal appearing white matter and healthy control samples.

Results

Our data show that M1 markers, including CD40, CD86, CD64 and CD32 were abundantly expressed by microglia in normal appearing white matter and by activated microglia and macrophages throughout active demyelinating MS lesions. M2 markers, such as MR and CD163 were expressed by myelin-laden macrophages in active lesions and perivascular macrophages. Double staining with anti-CD40 and anti-MR revealed that approximately 70% of the CD40-positive macrophages in MS lesions also expressed MR, indicating that the majority of infiltrating macrophages and activated microglial cells display an intermediate activation status.

Conclusions

Our findings show that, although macrophages in active MS lesions predominantly display M1 characteristics, a major subset of macrophages have an intermediate activation status.

Astrocytes regulate myelin clearance through recruitment of microglia during cuprizone-induced demyelination

Recent evidence suggests that astrocytes play an important role in regulating de- and remyelination in multiple sclerosis. The role of astrocytes is controversial, and both beneficial as well as detrimental effects are being discussed. We performed loss-of-function studies based on astrocyte depletion in a cuprizone-induced rodent model of demyelination. This led to strong astrogliosis accompanied by microgliosis and demyelination in C57BL/6 wild-type mice. Ablation of astrocytes in glial fibrillary acidic protein-thymidine kinase transgenic mice was associated with a failure of damaged myelin removal and a consecutive delay in remyelination. Despite oligodendrocyte death, myelin was still present, but ultrastructual investigations showed that the myelin structure was loosened and this damaged myelin did not protect axons. These alterations were associated with a decrease in microglial activation. Thus, our results show that astrocyte loss does not prevent myelin damage, but clearance of damaged myelin through recruitment of microglia is impaired. Further studies suggest that this process is regulated by the chemokine CXCL10. As a consequence of the delayed removal of myelin debris, remyelination and oligodendrocyte precursor cell proliferation were impaired. Experiments omitting the influence of myelin debris demonstrated an additional beneficial effect of astrocytes on oligodendrocyte regeneration during remyelination. In conclusion, these data demonstrate for the first time in vivo that astrocytes provide the signal environment that forms the basis for the recruitment of microglia to clear myelin debris, a process required for subsequent repair mechanisms. This is of great importance to understanding regenerative processes in demyelinating diseases such as multiple sclerosis.

Glatiramer acetate increases phagocytic activity of human monocytes in vitro and in multiple sclerosis patients

Beside its effects on T cells, a direct influence on cells of the myelo-monocytic lineage by GA becomes evident. Recently, we demonstrated that GA drives microglia to adopt properties of type II antigen presenting cells (APC) and increases their phagocytic activity. In the present work, we focused on human blood monocytes in order to examine whether GA may increase phagocytic activity in vivo and to evaluate the molecular mechanisms explaining this new discovered mode of action.

Peripheral blood mononuclear cells (PBMC) were obtained using a Biocoll-Isopaque gradient and monocytes were subsequently isolated by using CD14 MicroBeads. Phagocytic activity was determined by flow cytometric measurement of the ingestion of fluorescent beads. Flow cytometry was also used to assess monocytic differentiation and expression of phagocytic receptors. Monocytes of GA treated MS patients exhibited a significantly higher phagocytic activity than those of healthy controls or non-treated MS patients. In vitro, a significant phagocytic response was already detectable after 1 h of GA treatment at the concentrations of 62.5 and 125 µg/ml. A significant increase at all concentrations of GA was observed after 3 h and 24 h, respectively. Only monocytes co-expressing CD16, particularly CD14⁺⁺CD16⁺ cells, were observed to phagocytose. Treatment of monocytes with IL-10 and supernatants from GA-treated monocytes did not alter phagocytosis. We observed a decrease in CD11c expression by GA while no changes were found in the expression of CD11b, CD36, CD51/61, CD91, TIM-3, and CD206. In our blocking assays, treatment with anti-CD14, anti-CD16, anti-TIM3, anti-CD210, and particularly anti-CD36 antibodies led to a decrease in phagocytosis.

Our results demonstrate a new mechanism of action of GA treatment that augments phagocytic activity of human monocytes in vivo and in vitro. This activity seems to arise from the CD14⁺⁺CD16⁺ monocyte subset.

Myelin-derived lipids modulate macrophage activity by liver X receptor activation

Multiple sclerosis is a chronic, inflammatory, demyelinating disease of the central nervous system in which macrophages and microglia play a central role. Foamy macrophages and microglia, containing degenerated myelin, are abundantly found in active multiple sclerosis lesions. Recent studies have described an altered macrophage phenotype after myelin internalization. However, it is unclear by which mechanisms myelin affects the phenotype of macrophages and how this phenotype can influence lesion progression. Here we demonstrate, by using genome wide gene expression analysis, that myelin-phagocytosing macrophages have an enhanced expression of genes involved in migration, phagocytosis and inflammation. Interestingly, myelin internalization also induced the expression of genes involved in liver-X-receptor signaling and cholesterol efflux. In vitro validation shows that myelin-phagocytosing macrophages indeed have an increased capacity to dispose intracellular cholesterol. In addition, myelin suppresses the secretion of the pro-inflammatory mediator IL-6 by macrophages, which was mediated by activation of liver-X-receptor β. Our data show that myelin modulates the phenotype of macrophages by nuclear receptor activation, which may subsequently affect lesion progression in demyelinating diseases such as multiple sclerosis.

Current concepts in osteolysis

The most frequent cause of failure after total hip replacement in all reported arthroplasty registries is peri-prosthetic osteolysis. Osteolysis is an active biological process initiated in response to wear debris. The eventual response to this process is the activation of macrophages and loss of bone. Activation of macrophages initiates a complex biological cascade resulting in the final common pathway of an increase in osteolytic activity. The biological initiators, mechanisms for and regulation of this process are beginning to be understood. This article explores current concepts in the causes of, and underlying biological mechanism resulting in peri-prosthetic osteolysis, reviewing the current basic science and clinical literature surrounding the topic.

Harmful and beneficial effects of inflammation after spinal cord injury: potential therapeutic implications

Spinal cord injury (SCI) results in immediate damage followed by a secondary phase of tissue damage that occurs over a period of several weeks. The mechanisms underlying this secondary damage are multiple and not fully understood. A number of studies suggest that the local inflammatory response in the spinal cord that occurs after SCI contributes importantly to secondary damage. This response is mediated by cells normally found in the central nervous system (CNS) as well as infiltrating leukocytes. While the inflammatory response mediated by these cells is required for efficient clearance of tissue debris, and promotes wound healing and tissue repair, they also release various factors that can be detrimental to neurons, glia, axons, and myelin. In this chapter we provide an overview of the inflammatory response at the cell and molecular level after SCI, and review the current state of knowledge about its contribution to tissue damage and repair. Additionally, we discuss how some of this work is leading to the development and testing of drugs that modulate inflammation to treat acute SCI in humans.

The glial scar-monocyte interplay: a pivotal resolution phase in spinal cord repair

The inflammatory response in the injured spinal cord, an immune privileged site, has been mainly associated with the poor prognosis. However, recent data demonstrated that, in fact, some leukocytes, namely monocytes, are pivotal for repair due to their alternative anti-inflammatory phenotype. Given the pro-inflammatory milieu within the traumatized spinal cord, known to skew monocytes towards a classical phenotype, a pertinent question is how parenchymal-invading monocytes acquire resolving properties essential for healing, under such unfavorable conditions. In light of the spatial association between resolving (interleukin (IL)-10 producing) monocytes and the glial scar matrix chondroitin sulfate proteoglycan (CSPG), in this study we examined the mutual relationship between these two components. By inhibiting the de novo production of CSPG following spinal cord injury, we demonstrated that this extracellular matrix, mainly known for its ability to inhibit axonal growth, serves as a critical template skewing the entering monocytes towards the resolving phenotype. In vitro cell culture studies demonstrated that this matrix alone is sufficient to induce such monocyte polarization. Reciprocal conditional ablation of the monocyte-derived macrophages concentrated at the lesion margins, using diphtheria toxin, revealed that these cells have scar matrix-resolving properties. Replenishment of monocytic cell populations to the ablated mice demonstrated that this extracellular remodeling ability of the infiltrating monocytes requires their expression of the matrix-degrading enzyme, matrix metalloproteinase 13 (MMP-13), a property that was found here to be crucial for functional recovery. Altogether, this study demonstrates that the glial scar-matrix, a known obstacle to regeneration, is a critical component skewing the encountering monocytes towards a resolving phenotype. In an apparent feedback loop, monocytes were found to regulate scar resolution. This cross-regulation between the glial scar and monocytes primes the resolution of this interim phase of spinal cord repair, thereby providing a fundamental platform for the dynamic healing response.

Identification of a microglia phenotype supportive of remyelination

In multiple sclerosis, endogenous oligodendrocyte precursor cells (OPCs) attempt to remyelinate areas of myelin damage. During disease progression, however, these attempts fail. It has been suggested that modulating the inflammatory environment of the lesion might provide a promising therapeutic approach to promote endogenous remyelination. Microglia are known to play a central role in neuroinflammatory processes. To investigate the microglia phenotype that supports remyelination, we performed genome-wide gene expression analysis of microglia from the corpus callosum during demyelination and remyelination in the mouse cuprizone model, in which remyelination spontaneously occurs after an episode of toxin-induced primary demyelination. We provide evidence for the existence of a microglia phenotype that supports remyelination already at the onset of demyelination and persists throughout the remyelination process. Our data show that microglia are involved in the phagocytosis of myelin debris and apoptotic cells during demyelination. Furthermore, they express a cytokine and chemokine repertoire enabling them to activate and recruit endogenous OPCs to the lesion site and deliver trophic support during remyelination. This study not only provides a detailed transcriptomic analysis of the remyelination-supportive microglia phenotype but also reinforces the notion that the primary function of microglia is the maintenance of tissue homeostasis and the support of regeneration already at the earliest stages in the development of demyelinating lesions.

Natural recovery from antiglomerular basement membrane glomerulonephritis is associated with glomeruli-infiltrating CD8α+CD11c+MHC class II+ cells

BACKGROUND/AIMS

In an antiglomerular basement membrane glomerulonephritis (GN) model, GN-resistant Lewis (LEW) rats naturally recover from early glomerular inflammation (days 21-23). We have previously identified a glomeruli-infiltrating CD8α(+)CD11(high)MHC II(+) cell (GIL CD8α(+) cell) in GN-prone Wistar Kyoto (WKY) rats, which terminates glomerular inflammation through inducing T cell apoptosis prior to glomerular fibrosis at days 35-40. We investigated if GIL CD8α(+) cells were also associated with the recovery in LEW rats.

METHODS

GIL CD8α(+) cells in LEW rats were characterized; their infiltration was observed in connection with T cell apoptosis in glomeruli.

RESULTS

An influx of GIL CD8α(+) cells into inflamed glomeruli was confirmed in the immunized LEW rats at days 17-22, which was much earlier than days 28-35 in WKY rats. Notably, LEW rats had a GIL CD8α(+)CD11(high) subpopulation after day 17, while WKY rats lacked this population until after day 30. Analyses further revealed a large number of clustered apoptotic CD4(+) or CD3(+) T cells in the glomeruli during recovery (day 23) in LEW rats, as compared to day 35 (transition to fibrosis) in WKY rats. Thus, infiltration of GIL CD8α(+) cells coincided with decline of glomerular inflammation and T cell apoptosis during recovery in LEW rats. Isolated GIL CD8α(+) cells were able to infiltrate glomeruli in both WKY and LEW rats at day 20.

CONCLUSION

Our data revealed a strong association between GIL CD8a+ cells and recovery from early glomerular inflammation. It raises a possibility of involvement of GIL CD8a+ cells in the recovery.

Lipopolysaccharide delays demyelination and promotes oligodendrocyte precursor proliferation in the central nervous system

Systemic infection can influence the course in many diseases of the central nervous system (CNS) such as multiple sclerosis (MS), yet the relationship between infection outside the CNS and potential damage and/or protection within the CNS is still not understood. Activation of microglia is a characteristic feature of most CNS autoimmune disorders, including MS, and both protective and degenerative functions of microglia have been proposed. Hence, we analyzed the effects of a systemic inflammatory reaction induced by peripheral treatment with lipopolysaccharide (LPS) on microglial reaction and cuprizone induced de- and remyelination. We found that LPS administration delayed demyelination, which was linked with inhibition of microglial proliferation and reduced numbers of activated microglia. The phenotype of microglia changed as an increase of Toll-like receptor 4 was found. During remyelination, LPS treatment delayed the onset of myelin protein re-expression, but later there was a beneficial effect via an increase of proliferating oligodendrocyte precursor cells (OPC) and mature oligodendrocytes. Moreover, the expression of ciliary neurotrophic factor was increased in response to LPS, a growth factor known to mediate OPC proliferation. Additional experiments showed that the time window to induce LPS effects was limited and associated with the presence of microglia. In conclusion, LPS delayed demyelination and caused beneficial effects on remyelination via increasing the proliferation of OPC. These differences seem to be an effect of LPS induced microglial modulation and indicate that exposure to certain infectious agents within a given time window may be beneficial in promoting tissue repair.

Biomarkers for microglial activation in Alzheimer's disease

Intensive research over the last decades has provided increasing evidence for neuroinflammation as an integral part in the pathogenesis of neurodegenerative diseases such as Alzheimer's disease (AD). Inflammatory responses in the central nervous system (CNS) are initiated by activated microglia, representing the first line of the innate immune defence of the brain. Therefore, biochemical markers of microglial activation may help us understand the underlying mechanisms of neuroinflammation in AD as well as the double-sided qualities of microglia, namely, neuroprotection and neurotoxicity. In this paper we summarize candidate biomarkers of microglial activation in AD along with a survey of recent neuroimaging techniques.

Myelin-phagocytosing macrophages modulate autoreactive T cell proliferation

Introduction

Multiple sclerosis (MS) is a chronic, inflammatory, demyelinating disease of the central nervous system (CNS) in which macrophages play a central role. Initially, macrophages where thought to be merely detrimental in MS, however, recent evidence suggests that their functional phenotype is altered following myelin phagocytosis. Macrophages that have phagocytosed myelin may be less inflammatory and may exert beneficial effects. The presence of myelin-containing macrophages in CNS-draining lymph nodes and perivascular spaces of MS patients suggests that these cells are ideally positioned to exert an immune regulatory role. Therefore we evaluated in this study the effect of myelin-phagocytosing macrophages on lymphocyte reactivity.

Methods

Thioglycolate-elicited rat peritoneal macrophages were loaded with myelin and cocultured with myelin-basic protein (MBP) or ovalbumin (OVA) reactive lymphocytes. Lymphocyte proliferation was determined by CFSE-labeling. The role of nitric oxide in regulating lymphocyte proliferation was assessed by addition of an inhibitor of inducible nitric oxide synthase to the coculture. In vivo immune regulation was investigated by treating MBP- and OVA-immunized animals subcutaneously with myelin. Cognate antigen specific lymphocyte proliferation and nitric oxide production were determined 9d post-immunization.

Results

In this study we demonstrate that myelin-phagocytosing macrophages inhibit TCR-triggered lymphocyte proliferation in an antigen-independent manner. The observed immune suppression is mediated by an increase in NO production by myelin-phagocytosing macrophages upon contact with lymphocytes. Additionally, myelin delivery to primarily CD169⁺ macrophages in popliteal lymph nodes of OVA-immunized animals results in a reduced cognate antigen specific proliferation. In contrast to OVA-immunized animals, lymphocytes from MBP-immunized animals displayed an increased proliferation after stimulation with their cognate antigen, indicating that myelin-phagocytosing macrophages have dual effects depending on the specificity of surrounding lymphocytes.

Conclusions

Collectively our data show that myelin phagocytosis leads to an altered macrophage function that inhibits lymphocyte proliferation. Additionally, results from this study indicate that myelin-phagocytosing macrophages fulfill a dual role in vivo. On one hand they aggravate autoimmunity by activating myelin-reactive lymphocytes and on the other hand they suppress lymphocyte reactivity by producing NO.

Repertoire of microglial and macrophage responses after spinal cord injury

Macrophages from the peripheral circulation and those derived from resident microglia are among the main effector cells of the inflammatory response that follows spinal cord trauma. There has been considerable debate in the field as to whether the inflammatory response is good or bad for tissue protection and repair. Recent studies on macrophage polarization in non-neural tissues have shed much light on their changing functional states. In the context of this literature, we discuss the activation of macrophages and microglia following spinal cord injury, and their effects on repair. Harnessing their anti-inflammatory properties could pave the way for new therapeutic strategies for spinal cord trauma.

Biomarkers in the diagnosis of lysosomal storage disorders: proteins, lipids, and inhibodies

A biomarker is an analyte indicating the presence of a biological process linked to the clinical manifestations and outcome of a particular disease. In the case of lysosomal storage disorders (LSDs), primary and secondary accumulating metabolites or proteins specifically secreted by storage cells are good candidates for biomarkers. Clinical applications of biomarkers are found in improved diagnosis, monitoring disease progression, and assessing therapeutic correction. These are illustrated by reviewing the discovery and use of biomarkers for Gaucher disease and Fabry disease. In addition, recently developed chemical tools allowing specific visualization of enzymatically active lysosomal glucocerebrosidase are described. Such probes, coined inhibodies, offer entirely new possibilities for more sophisticated molecular diagnosis, enzyme replacement therapy monitoring, and fundamental research.

CCL5 induces a pro-inflammatory profile in microglia in vitro

The chemokine receptors CCR1, CCR2, CCR3, CCR5, and CXCR2 have been found to be expressed on microglia in many neurodegenerative diseases, such as multiple sclerosis and Alzheimer's disease. There is emerging evidence that chemokines, besides chemoattraction, might directly modulate reactive profiles of microglia. To address this hypothesis we have investigated the effects of CCL2, CCL3, CCL5, and CXCL1 on cytokine and growth factor production, NO synthesis, and phagocytosis in non-stimulated and lipopolysaccharide-stimulated primary rat microglia. The respective receptors CCR1, CCR5, and CXCR2 were shown to be functionally expressed on microglia. All tested chemokines stimulated chemotaxis whereas only CCL5 increased NO secretion and attenuated IL-10 as well as IGF-1 production in activated microglia. Based on these findings we propose that besides its chemoattractant function CCL5 has a modulatory effect on activated microglia.

In Vivo imaging reveals distinct inflammatory activity of CNS microglia versus PNS macrophages in a mouse model for ALS

Mutations in the enzyme superoxide dismutase-1 (SOD1) cause hereditary variants of the fatal motor neuronal disease Amyotrophic lateral sclerosis (ALS). Pathophysiology of the disease is non-cell-autonomous: neurotoxicity is derived not only from mutant motor neurons but also from mutant neighbouring non-neuronal cells. In vivo imaging by two-photon laser-scanning microscopy was used to compare the role of microglia/macrophage-related neuroinflammation in the CNS and PNS using ALS-linked transgenic SOD1^G93A mice. These mice contained labeled projection neurons and labeled microglia/macrophages. In the affected lateral spinal cord (in contrast to non-affected dorsal columns), different phases of microglia-mediated inflammation were observed: highly reactive microglial cells in preclinical stages (in 60-day-old mice the reaction to axonal transection was ∼180% of control) and morphologically transformed microglia that have lost their function of tissue surveillance and injury-directed response in clinical stages (reaction to axonal transection was lower than 50% of control). Furthermore, unlike CNS microglia, macrophages of the PNS lack any substantial morphological reaction while preclinical degeneration of peripheral motor axons and neuromuscular junctions was observed. We present in vivo evidence for a different inflammatory activity of microglia and macrophages: an aberrant neuroinflammatory response of microglia in the CNS and an apparently mainly neurodegenerative process in the PNS.

The release of cytokines by macrophages is not affected by myelin ingestion

Macrophages play an important role in demyelination in multiple sclerosis (MS). Activated macrophages ingest myelin particles, thereby acquiring a foamy appearance. Foamy macrophages in MS lesions were described as being anti-inflammatory. Therefore, these cells might play a role in modulating the inflammatory state of an active lesion. Here, we investigated the mechanism by which myelin uptake leads to skewing of macrophages toward an anti-inflammatory phenotype. Macrophages were incubated with myelin, leading to the development of foamy macrophages. Afterwards, the cells were stimulated with the TLR-4 ligand lipopolysaccharide (LPS), and cytokine production was determined. Interestingly, foamy macrophages appeared to have a reduced cytokine secretion and were LPS insensitive only when generated with one of the myelin preparations. The factor responsible for the different outcomes between different myelin batches turned out to be LPS. We demonstrated that LPS contamination induced insensitivity to LPS in foamy macrophages. On the contrary, foamy macrophages generated in the presence of LPS-free myelin were able to secrete cytokines upon activation. To conclude, myelin-laden macrophages were not LPS insensitive, indicating that they had not acquired an anti-inflammatory phenotype.

Adenosine triphosphate-binding cassette transporters mediate chemokine (C-C motif) ligand 2 secretion from reactive astrocytes: relevance to multiple sclerosis pathogenesis

Adenosine triphosphate-binding cassette efflux transporters are highly expressed at the blood-brain barrier and actively hinder passage of harmful compounds, thereby maintaining brain homoeostasis. Since, adenosine triphosphate-binding cassette transporters drive cellular exclusion of potential neurotoxic compounds or inflammatory molecules, alterations in their expression and function at the blood-brain barrier may contribute to the pathogenesis of neuroinflammatory disorders, such as multiple sclerosis. Therefore, we investigated the expression pattern of different adenosine triphosphate-binding cassette efflux transporters, including P-glycoprotein, multidrug resistance-associated proteins-1 and -2 and breast cancer resistance protein in various well-characterized human multiple sclerosis lesions. Cerebrovascular expression of P-glycoprotein was decreased in both active and chronic inactive multiple sclerosis lesions. Interestingly, foamy macrophages in active multiple sclerosis lesions showed enhanced expression of multidrug resistance-associated protein-1 and breast cancer resistance protein, which coincided with their increased function of cultured foamy macrophages. Strikingly, reactive astrocytes display an increased expression of P-glycoprotein and multidrug resistance-associated protein-1 in both active and inactive multiple sclerosis lesions, which correlated with their enhanced in vitro activity on astrocytes derived from multiple sclerosis lesions. To investigate whether adenosine triphosphate-binding cassette transporters on reactive astrocytes can contribute to the inflammatory process, primary cultures of reactive human astrocytes were generated through activation of Toll-like receptor-3 to mimic the astrocytic phenotype as observed in multiple sclerosis lesions. Notably, blocking adenosine triphosphate-binding cassette transporter activity on reactive astrocytes inhibited immune cell migration across a blood-brain barrier model in vitro, which was due to the reduction of astrocytic release of the chemokine (C-C motif) ligand 2. Our data point towards a novel (patho)physiological role for adenosine triphosphate-binding cassette transporters, suggesting that limiting their activity by dampening astrocyte activation may open therapeutic avenues to diminish tissue damage during multiple sclerosis pathogenesis.

Altered M1/M2 activation patterns of monocytes in severe relapsing experimental rat model of multiple sclerosis. Amelioration of clinical status by M2 activated monocyte administration

OBJECTIVES

We investigated proinflammatory M1 and immunomodulatory M2 activation profiles of circulating monocytes in relapsing experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis, and tested whether altered M1/M2 equilibrium promotes CNS inflammation.

RESULTS

Approaches of MRI macrophage tracking with USPIO nanoparticles and expression patterns of M1/M2 macrophages and microglia in brain and M1/M2 monocytes in blood samples at various disease stages revealed that M1/M2 equilibrium in blood and CNS favors mild EAE, while imbalance towards M1 promotes relapsing EAE. We consequently investigated whether M2 activated monocyte restoration in peripheral blood could cure acute clinical EAE disease. Administration of ex vivo activated M2 monocytes both suppressed ongoing severe EAE and increased immunomodulatory expression pattern in lesions, confirming their role in the induction of recovery.

CONCLUSION

We conclude that imbalance of monocyte activation profiles and impaired M2 expression, are key factors in development of relapses. Our study opens new perspectives for therapeutic applications in MS.

Reduced cortisol levels in cerebrospinal fluid and differential distribution of 11beta-hydroxysteroid dehydrogenases in multiple sclerosis: implications for lesion pathogenesis

Relapses during multiple sclerosis (MS) are treated by administration of exogenous corticosteroids. However, little is known about the bioavailability of endogenous steroids in the central nervous system (CNS) of MS patients. We thus determined cortisol and dehydroepiandrosterone (DHEA) levels in serum and cerebrospinal fluid (CSF) samples from 34 MS patients, 28 patients with non-inflammatory neurological diseases (NIND) and 16 patients with other inflammatory neurological diseases (OIND). This revealed that MS patients - in sharp contrast to patients with OIND - show normal cortisol concentrations in serum and lowered cortisol levels in the CSF during acute relapses. This local cortisol deficit may relate to poor local activation of cortisone via 11beta-hydroxysteroid dehydrogenase type 1 (11bHSD1) or to inactivation via 11bHSD2. Accordingly, 11bHSD2 was found to be expressed within active plaques, whereas 11bHSD1 was predominantly detected in surrounding "foamy" macrophages. Our study thus provides new insights into the impaired endogenous CNS cortisol regulation in MS patients and its possible relation to MS lesion pathogenesis. Moreover, an observed upregulation of 11bHSD1 in myelin-loaded macrophages in vitro suggests an intriguing hypothesis for the self-limiting nature of MS lesion development. Finally, our findings provide an attractive explanation for the effectivity of high- vs. low-dose exogenous corticosteroids in the therapy of acute relapses.

Inflammation induced neurological handicap processes in multiple sclerosis: new insights from preclinical studies

Multiple sclerosis (MS) is described as originating from incompletely explained neuroinflammatory processes, dysfunction of neuronal repair mechanisms and chronicity of inflammation events. Blood-borne immune cell infiltration and microglia activation are causing both neuronal destruction and myelin loss, which are responsible for progressive motor deficiencies, organic and cognitive dysfunctions. MRI as a non-invasive imaging method offers various ways to visualise de- and remyelination, neuronal loss, leukocyte infiltration, blood-brain barrier modification and new sensors are emerging to detect inflammatory lesions at an early stage. We describe studies performed on experimental autoimmune encephalomyelitis (EAE) animal models of MS that shed new light on mechanisms of functional impairments to understand the neurological handicap in MS. We focus on examples of neuroinflammation-mediated inhibition of CNS repair involving adult neurogenesis in the sub-ventricular zone and hippocampus and such experimentally observed inhibitions could reflect deficient plasticity and activation of compensatory mechanisms in MS. In parallel with cognitive decline, organic deficits such as bladder dysfunction are described in most of MS patients. Neuropharmacological interventions, electrical stimulation of nerves, MRI and histopathology follow-up studies helped in understanding the operating events to remodel the neurological networks and to compensate the inflammatory lesions both in spinal cord and in cortical regions. At the molecular level, the local production of reactive products is a well-described phenomenon: oxidative species disturb cellular physiology and generate new molecular epitopes that could further promote immune reactions. The translational research from EAE animal models to MS patient cohorts helps in understanding the mechanisms of the neurological handicap and in development of new therapeutic concepts in MS.

T cell recognition of self-antigen presenting cells by protein transfer assay reveals a high frequency of anti-myelin T cells in multiple sclerosis

Although peripheral blood myelin-autoreactive T cells are thought to play a key role in multiple sclerosis, they are generally considered to have qualitative differences rather than quantitative ones when compared to those found in healthy individuals. Here, we revisited the assessment of myelin-autoreactive T cells in a new approach based on their combined ability to acquire membrane proteins from autologous antigen presenting cells, and to respond to whole myelin extract as the stimulating autoantigen. Using this approach, the myelin-autoreactive T cell frequency in patients with multiple sclerosis was found to be unexpectedly high (n = 22, subtracted values median 2.08%, range 0-6%; background median 1%, range 0-4%) and to exceed that of age/gender-matched healthy individuals significantly (n = 18, subtracted values median 0.1%, range 0-5.3%, P < 0.0001; background median 1.45%, range 0.1-4%). Higher anti-myelin autoreactivity was stable in patients with multiple sclerosis after several months. These data correlated with whole myelin-induced gamma interferon-enzyme-linked immunosorbent spot assay performed under the same conditions, although the values obtained with enzyme-linked immunosorbent spot assay under all conditions were 58 times lower than with this new method. The myelin-autoreactive T cells were memory T cells expressing CD40L with a CD62(low) phenotype, suggesting their ability for homing to tissues. Collectively, these new data show a higher frequency of autoreactive T cells during multiple sclerosis than in age/gender-matched healthy individuals, and support an autoimmune aetiology in multiple sclerosis.

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.

Progressive multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory, demyelinating disease of the central nervous system, which starts in the majority of patients with a relapsing/remitting MS (RRMS) course , which after several years of disease duration converts into a progressive disease. Since anti-inflammatory therapies and immune modulation exert a beneficial effect at the relapsing/remitting stage of the disease, but not in the progressive stage, the question was raised whether inflammation drives tissue damage in progressive MS at all. We show here that also in progressive MS, inflammation is the driving force for brain injury and that the discrepancy between inflammation-driven tissue injury and response to immunomodulatory therapies can be explained by different pathomechanisms acting in RRMS and progressive MS.

Microglia in neurodegenerative disease

Microglia, the resident macrophages of the CNS, are exquisitely sensitive to brain injury and disease, altering their morphology and phenotype to adopt a so-called activated state in response to pathophysiological brain insults. Morphologically activated microglia, like other tissue macrophages, exist as many different phenotypes, depending on the nature of the tissue injury. Microglial responsiveness to injury suggests that these cells have the potential to act as diagnostic markers of disease onset or progression, and could contribute to the outcome of neurodegenerative diseases. The persistence of activated microglia long after acute injury and in chronic disease suggests that these cells have an innate immune memory of tissue injury and degeneration. Microglial phenotype is also modified by systemic infection or inflammation. Evidence from some preclinical models shows that systemic manipulations can ameliorate disease progression, although data from other models indicates that systemic inflammation exacerbates disease progression. Systemic inflammation is associated with a decline in function in patients with chronic neurodegenerative disease, both acutely and in the long term. The fact that diseases with a chronic systemic inflammatory component are risk factors for Alzheimer disease implies that crosstalk occurs between systemic inflammation and microglia in the CNS.

Differential expression of the EGF-TM7 family members CD97 and EMR2 in lipid-laden macrophages in atherosclerosis, multiple sclerosis and Gaucher disease

The members of the epidermal growth factor (EGF)-transmembrane (TM)7 family of adhesion class G-protein coupled receptors are abundantly expressed by cells of the myeloid lineage. A detailed investigation of their expression by functional subsets of activated macrophages is still lacking. Therefore, we determined the expression of CD97, EGF module-containing mucin-like receptor (EMR)2 and EMR3 by monocyte-derived macrophages experimentally polarized in vitro. This was compared to three types of disease-associated lipid-laden macrophages displaying an alternatively activated phenotype in situ. Polarization in vitro towards classically activated M1 versus alternatively activated M2 extremes of macrophage activation did not result in a congruent regulation of EGF-TM7 receptor mRNA and protein except for a down-regulation of CD97 by IL-10. In contrast, macrophages handling lipid overload in vivo displayed differences in the expression of CD97 and EMR2. While foamy macrophages in atherosclerotic vessels expressed both CD97 and EMR2, foam cells in multiple sclerosis brain expressed CD97, but only little EMR2. Foam cell formation in vitro by oxidized LDL and myelin did not affect CD97 or EMR2 expression. Gaucher spleen cells accumulating glucosylceramide expressed very high levels of CD97 and EMR2. These findings indicate that complex cellular expression programmes rather than activation modes regulate the expression of EGF-TM7 receptors in macrophages.

Type 3 deiodinase expression in inflammatory spinal cord lesions in rat experimental autoimmune encephalomyelitis

BACKGROUND

We have shown substantial expression of type 3 deiodinase (D3, a major enzyme involved in the inactivation of thyroid hormone) in infiltrating leukocytes in several models of inflammation. Recently, thyroid hormone has been shown to improve remyelination in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. As induction of D3 may play an important role in decreasing local bioavailability of thyroid hormone at inflammation sites, we hypothesized that D3 is induced in spinal cord inflammatory lesions in EAE.

METHODS

The aim of the study was to evaluate D3 expression in spinal cord inflammatory lesions of EAE Dark Agouti rats and to investigate D3 induction in activated monocytes.

RESULTS

Here, we show marked expression of D3 by granulocytes and macrophages in spinal cord inflammatory lesions of EAE rats. We further confirm induction of D3 expression in vitro in monocytes that were activated toward proinflammatory or immunomodulatory phenotypes.

CONCLUSIONS

We observed increased D3 expression both in spinal cord inflammatory lesions during EAE and in activated monocytes. Although increased D3 expression theoretically results in decreased triiodothyronine availability, it is unknown at present whether reduced local triiodothyronine concentrations are involved in impaired remyelination as observed during EAE.

CC-chemokine ligand 18/pulmonary activation-regulated chemokine expression in the CNS with special reference to traumatic brain injuries and neoplastic disorders

Pulmonary activation-regulated chemokine (PARC) now designated CC-chemokine ligand 18 (CCL18) has been shown to play a significant role in the pathogenesis of various tissue injuries and diseases in a proinflammatory or immune suppressive way to limit or support the inflammation or disease. While much is known about the roles of CCL18/PARC in non-neural tissues, its expression in the CNS has remained largely unexplored and controversial. Using reverse transcription polymerase chain reaction (RT-PCR) and double immunohistochemical staining, we analyzed the expression of CCL18/PARC in the human brain with special reference to traumatic brain injuries and tumors. The RT-PCR analysis revealed the expression of CCL18/PARC mRNA both in the traumatic brain and glioma tissues examined. Immunoexpression of CCL18/PARC protein was consistently detected in all cases of traumatic brain injuries examined by immunohistochemical staining. Double immunofluorescence labeling has extended the study that CCL18/PARC positive cells were macrophages/microglia, astrocytes or neurons. The CCL18/PARC expression was localized in macrophage-like cells in two of eight glioblastoma tissues whose cancer cells were CCL18/PARC negative. Unexpectedly, CCL18/PARC mRNA weakly and constitutively expressed by glioblastoma cell line was upregulated after endotoxin stimulation. The present results indicated a significant production of CCL18/PARC in different CNS traumatic and neoplasm tissues by specific cellular elements expressing the chemokine. An anti-inflammatory mechanism jointly exerted by these cells via CCL18/PARC may be involved in the CNS immunity after traumatic injury and tumorigenesis.

Impact of human myelin on the maturation and function of human monocyte-derived dendritic cells

Macrophages and dendritic cells (DC) play an important role in the immunopathology of multiple sclerosis. We analyzed the impact of human myelin on monocyte-derived DC and describe their immunostimulatory capacity. Cells were grown on myelin and stimulated with LPS or a defined maturation cocktail. DC activation was analyzed by the expression of cell surface markers and the secretion of cytokines and chemokines. The immunostimulatory capacity of DC was assessed by allogeneic mixed-leukocyte reactions via proliferation. Additionally, their ability to bias T cells towards Th1, Th17 or Treg differentiation was investigated. We found that phagocytosis of myelin impaired the activation of DC, displayed by an impaired ability to stimulate allogeneic T cells, an increased production of TGF-beta1 and a diminished upregulation of CCR7 but did not affect the differentiation into T helper cell subsets. We hypothesize that myelin influences DC activation and plays a pivotal role in balancing immunity and tolerance.

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.

Preactive lesions in multiple sclerosis

PURPOSE OF REVIEW

Knowledge of the early pathological changes observed in multiple sclerosis (MS) has advanced by implementation of many improved pathological, biochemical and imaging techniques. This review highlights the accumulating evidence for early pathological changes we term 'preactive lesions', characterized by clusters of activated microglia in otherwise normal-appearing white matter.

RECENT FINDINGS

Compelling evidence is accumulating for pathological changes in normal-appearing white matter of MS patients, which occur before the actual development of the active demyelinating lesion. Focal disorder has been documented in normal-appearing white matter of MS months to years before the appearance of gadolinium-enhancing lesions. In these foci, clusters of activated microglia are found in the absence of demyelination and clear leukocyte infiltration, distinguishing them from the traditional demyelinating active and chronic active lesions. Although the events that give rise to preactive lesions are still to be identified, oligodendrocyte abnormalities appear to be crucially involved. Importantly, preactive lesions do not always develop into demyelinating lesions but often appear to resolve without subsequent disorder.

SUMMARY

Preactive lesions in MS represent early stages in the formation of destructive MS lesions. As many of them spontaneously resolve, they are expected to hold important clues to stop the inflammatory process in MS.

The "window of susceptibility" for inflammation in the immature central nervous system is characterized by a leaky blood-brain barrier and the local expression of inflammatory chemokines

Early in postnatal development, the immature central nervous system (CNS) is more susceptible to inflammation than its adult counterpart. We show here that this "window of susceptibility" is characterized by the presence of leaky vessels in the CNS, and by a global chemokine expression profile which is clearly distinct from the one observed in the adult CNS and has three important characteristics. First, it contains chemokines with known roles in the differentiation and maturation of glia and neurons. Secondly, these chemokines have been described before in inflammatory lesions of the CNS, where they are important for the recruitment of monocytes and T cells. Lastly, the chemokine profile is shaped by pathological changes like oligodendrocyte stress and attempts of myelin repair. Changes in the chemokine expression profile along with a leaky blood-brain barrier pave the ground for an accelerated development of CNS inflammation.

Multiple sclerosis - a response-to-damage model

According to a widely supported but unproven concept, the autoimmune mechanisms that drive neuroinflammation in multiple sclerosis (MS) are triggered by virus infection. However, a direct viral trigger of MS has not been identified. MS models in non-human primates suggest that lifelong asymptomatic infection with certain herpesviruses (e.g. cytomegalovirus) creates a repertoire of potentially autoreactive memory T cells. When these are exposed to antigens released after central nervous system injury as a consequence of an unknown pathogenic event, they are reactivated and induce autoimmune neurological disease. This response-to-damage of antiviral memory cells can take place years after the initiating infection. Consequently, elucidating the anti-herpesvirus T-cell repertoire might provide new targets for preventive diagnosis and therapy.

Increased soluble TREM-2 in cerebrospinal fluid from patients with multiple sclerosis and CNS inflammation

Evaluation of: Piccio L, Buonsanti C, Cella M et al.: Identification of soluble TREM-2 in the cerebrospinal fluid and its association with multiple sclerosis and CNS inflammation. Brain 131, 3081–3091 (2008). TREM-2 is a membrane-bound receptor expressed by microglia and macrophages and its engagement reduces inflammation. In this study, a soluble form of TREM-2 (sTREM-2) is identified. Cerebrospinal fluid (CSF) sTREM-2 levels were found to be higher in relapsing–remitting multiple sclerosis patients (n = 52) compared with noninflammatory neurologic diseases cases (n = 41; p = 0.004). Primary-progressive multiple sclerosis patients (n = 21) and other inflammatory neurologic diseases subjects (n = 19) also had high CSF TREM-2 levels (p < 0.001). Furthermore, a subset of CSF monocytes expressed TREM-2, which was also highly expressed on myelin-laden macrophages in active demyelinating lesions. The elevated levels of sTREM-2 in the CSF of multiple sclerosis patients may inhibit the anti-inflammatory function of the membrane-bound receptor. Therefore, sTREM-2 may be a possible target for future therapies.

Dendritic cell differentiation signals induce anti-inflammatory properties in human adult microglia

Microglia are resident cells of the CNS that belong to the myeloid cell lineage. In experimental models of neuroinflammation, they have limited capacity to function as APCs when compared with dendritic cells (DCs). Human peripheral blood monocytes have the plasticity to differentiate into mature DCs when exposed to GM-CSF and IL-4 followed by LPS. In this study we addressed the potential of human microglia to acquire phenotypic and functional properties of mature DCs under similar inducing conditions. Treated adult and fetal microglia became CD14(low) and acquired limited expression of CD209 (DC-SIGN); they remained CD1a(-) and CD83(-), and decreased MHCII expression, suggesting that they had not achieved a complete DC phenotype. The monocyte-derived DCs efficiently promoted CD4 T cell proliferation in an allogeneic MLR, whereas differentiated adult microglia had a decreased ability to stimulate CD4 T cell proliferation compared with their untreated counterparts. Differentiated fetal microglia did support CD4 T cell proliferation, whereas untreated cells could not. Fetal and adult microglia produced significant amounts of IL-10 following differentiation but no detectable IL-12 p70, in contrast to differentiated monocytes that produced IL-12 p70. Our data indicate that neither adult nor fetal microglia acquired the full characteristic phenotype of mature stimulatory DCs when treated with DC-inducing cytokines in vitro. Moreover, such treatment, especially of adult microglia, induces functional responses that could promote an antiinflammatory environment in the CNS.

Severe oxidative damage in multiple sclerosis lesions coincides with enhanced antioxidant enzyme expression

Reactive oxygen species (ROS) and subsequent oxidative damage may contribute to the formation and persistence of multiple sclerosis (MS) lesions by acting on distinct pathological processes. ROS initiate lesion formation by inducing blood-brain barrier disruption, enhance leukocyte migration and myelin phagocytosis, and contribute to lesion persistence by mediating cellular damage to essential biological macromolecules of vulnerable CNS cells. Relatively little is known about which CNS cell types are affected by oxidative injury in MS lesions. Here, we show the presence of extensive oxidative damage to proteins, lipids, and nucleotides occurring in active demyelinating MS lesions, predominantly in reactive astrocytes and myelin-laden macrophages. Oxidative stress can be counteracted by endogenous antioxidant enzymes that confer protection against oxidative damage. Here, we show that antioxidant enzymes, including superoxide dismutase 1 and 2, catalase, and heme oxygenase 1, are markedly upregulated in active demyelinating MS lesions compared to normal-appearing white matter and white matter tissue from nonneurological control brains. Particularly, hypertrophic astrocytes and myelin-laden macrophages expressed an array of antioxidant enzymes. Enhanced antioxidant enzyme production in inflammatory MS lesions may reflect an adaptive defense mechanism to reduce ROS-induced cellular damage.

Brain antigens in functionally distinct antigen-presenting cell populations in cervical lymph nodes in MS and EAE

Drainage of central nervous system (CNS) antigens to the brain-draining cervical lymph nodes (CLN) is likely crucial in the initiation and control of autoimmune responses during multiple sclerosis (MS). We demonstrate neuronal antigens within CLN of MS patients. In monkeys and mice with experimental autoimmune encephalomyelitis (EAE) and in mouse models with non-inflammatory CNS damage, the type and extent of CNS damage was associated with the frequencies of CNS antigens within the cervical lymph nodes. In addition, CNS antigens drained to the spinal-cord-draining lumbar lymph nodes. In human MS CLN, neuronal antigens were present in pro-inflammatory antigen-presenting cells (APC), whereas the majority of myelin-containing cells were anti-inflammatory. This may reflect a different origin of the cells or different drainage mechanisms. Indeed, neuronal antigen-containing cells in human CLN did not express the lymph node homing receptor CCR7, whereas myelin antigen-containing cells in situ and in vitro did. Nevertheless, CLN from EAE-affected CCR7-deficient mice contained equal amounts of myelin and neuronal antigens as wild-type mice. We conclude that the type and frequencies of CNS antigens within the CLN are determined by the type and extent of CNS damage. Furthermore, the presence of myelin and neuronal antigens in functionally distinct APC populations within MS CLN suggests that differential immune responses can be evoked.

CCR5 expression on macrophages/microglia is associated with early remyelination in multiple sclerosis lesions

Remyelination in multiple sclerosis (MS) occurs spontaneously and extensively. The underlying mechanisms, however, are only partly understood. Findings in experimental animal settings suggest that inflammation promotes remyelination and repair. Here, we characterized the chemokine receptor expression profiles of macrophages/microglia in early remyelinating and completely remyelinated lesions compared with active demyelinating and inactive demyelinated MS lesions obtained in the early disease course. Biopsy material consisting of 16 MS cases was available for this study. We found that macrophages/microglia within early remyelinating lesions expressed predominantly CCR5. Our findings implicate a possible role of CCR5(+) cells in initiating remyelination.