Loss of Allograft Inflammatory Factor-1 Ameliorates Experimental Autoimmune Encephalomyelitis by Limiting Encephalitogenic CD4 T-Cell Expansion.

Experimental autoimmune encephalomyelitis (EAE), an animal model of human multiple sclerosis (MS), is mediated by myelin-specific autoreactive T cells that cause inflammation and demyelination in the central nervous system (CNS), with significant contributions from activated microglia and macrophages. The molecular bases for expansion and activation of these cells, plus trafficking to the CNS for peripheral cells, are not fully understood. Allograft inflammatory factor-1 (Aif-1) (also known as ionized Ca(2+) binding adapter-1 [Iba-1]) is induced in leukocytes in MS and EAE; here we provide the first assessment of Aif-1 function in this setting. After myelin oligodendrocyte glycoprotein peptide (MOG35-55) immunization, Aif-1-deficient mice were less likely than controls to develop EAE and had less CNS leukocyte infiltration and demyelination; their spinal cords contained fewer CD4 T cells and microglia and more CD8 T cells. These mice also showed significantly less splenic CD4 T-cell expansion and activation, plus decreased proinflammatory cytokine expression. These findings identify Aif-1 as a potent molecule that promotes expansion and activation of CD4 T cells, plus elaboration of a proinflammatory cytokine milieu, in MOG35-55-induced EAE and as a potential therapeutic target in MS.

The astrocyte in multiple sclerosis revisited.

Among the constituent cell types of the multiple sclerosis (MS) plaque, the astrocyte has been the least considered as a player in the pathogenesis of the lesion. Traditionally, it has been assigned a secondary scarring role with little or no role in lesion formation or repair. However, the recent upsurge of interest in the demyelinating condition neuromyelitis optica (NMO) has resulted in NMO being identified as the first disease of myelin in which primary damage to astrocytes, resulting from a humoral immune response that forms against the water channel aquaporin-4, has been documented. This finding in NMO prompted us to re-examine data and material from cases of MS displaying active lesions. Our reappraisal revealed unambiguous early damage to perivascular astrocyte end-feet and to hypertrophic astrocytes in the adjacent parenchyma, but whether this was a primary event was difficult to evaluate due to concomitant edema and inflammation in these acute lesions. The astrocyte damage was long-lasting since resolving lesions displaying remyelination also showed defects in the integrity of the astrocytic covering around blood vessels. Analysis of our findings and of the astrocytic literature supports multiple roles for the astrocyte in the evolution of changes encountered in MS depending upon lesion stage and lesion topography. At variance with the somewhat inhibitory role of the astrocyte is the abundant and growing evidence for this cell to actively participate in both lesion development and repair. We propose that the unequivocal selective early involvement of the astrocyte in MS lesions may have therapeutic relevance

Revisiting Notch in remyelination of multiple sclerosis lesions.

MS results from destruction of the protective myelin sheath surrounding axons, which prevents the transmission of nerve impulses. Precursors of oligodendrocytes, the cells capable of myelinating axons, are preserved in demyelinating lesions; however, why these precursors do not differentiate into mature oligodendrocytes and remyelinate axons is unknown. Contactin is a noncanonical Notch receptor ligand that mediates oligodendrocyte differentiation. In this issue of the JCI, Nakahara et al. show that Contactin is abundantly expressed on demyelinated axons in human chronic MS lesions and that Notch1 is activated in oligodendrocyte precursor cells (see the related article beginning on page 169). However, Notch1 intracellular domain coassociates with the nuclear transporter Importin beta but fails to show evidence of nuclear translocation. These cytoplasmic aggregates also contain TAT-interacting protein 30 kDa (TIP30), a proapoptotic factor, which inhibits nuclear transport and, consequently, Notch1-mediated oligodendrocyte differentiation and remyelination. These data target TIP30 as a new pathogenic factor in MS.

Transcriptional profiling of microdissected areas of active multiple sclerosis lesions reveals activation of heat shock protein genes.

Heat shock proteins (HSPs) are stress-responsive proteins that serve as important molecules contributing to cellular "protein triage." We and others have reported an increase of selected HSPs in multiple sclerosis (MS) lesions. However, the exact expression pattern of HSP family genes in MS is not known. The aim of our research was to assess global transcriptional changes of all gene members of the HSP families within MS lesions and associated normal-appearing white matter (NAWM). To this end, we used laser capture microdissection (LCM) to isolate defined regions of chronic-active MS lesions (n = 5), one of the most common types of MS lesions. To identify changes in HSP genes in relation to different areas of the plaque, we used genome-wide microarray analysis. We detected a significant change in the transcriptional profile of the demyelinated region compared with NAWM. In particular, overall expression of different HSP genes was upregulated in different areas of chronic-active lesion. These changes were linked to an upregulation of heat shock factor 4 (HSF4). This is the first global analysis of transcriptional changes in HSPs in the central nervous system during MS. The results support a relationship between HSP activation and lesion activity.

Notch1 signaling plays a role in regulating precursor differentiation during CNS remyelination.

In the developing CNS, Notch1 and its ligand, Jagged1, regulate oligodendrocyte differentiation and myelin formation, but their role in repair of demyelinating lesions in diseases such as multiple sclerosis remains unresolved. To address this question, we generated a mouse model in which we targeted Notch1 inactivation to oligodendrocyte progenitor cells (OPCs) using Olig1Cre and a floxed Notch1 allele, Notch1(12f). During CNS development, OPC differentiation was potentiated in Olig1Cre:Notch1(12f/12f) mice. Importantly, in adults, remyelination of demyelinating lesions was also accelerated, at the expense of proliferation within the progenitor population. Experiments in vitro confirmed that Notch1 signaling was permissive for OPC expansion but inhibited differentiation and myelin formation. These studies also revealed that astrocytes exposed to TGF-beta1 restricted OPC maturation via Jagged1-Notch1 signaling. These data suggest that Notch1 signaling is one of the mechanisms regulating OPC differentiation during CNS remyelination. Thus, Notch1 may represent a potential therapeutical avenue for lesion repair in demyelinating disease.

Loss of the receptor tyrosine kinase Axl leads to enhanced inflammation in the CNS and delayed removal of myelin debris during experimental autoimmune encephalomyelitis.

BACKGROUND: Axl, together with Tyro3 and Mer, constitute the TAM family of receptor tyrosine kinases. In the nervous system, Axl and its ligand Growth-arrest-specific protein 6 (Gas6) are expressed on multiple cell types. Axl functions in dampening the immune response, regulating cytokine secretion, clearing apoptotic cells and debris, and maintaining cell survival. Axl is upregulated in various disease states, such as in the cuprizone toxicity-induced model of demyelination and in multiple sclerosis (MS) lesions, suggesting that it plays a role in disease pathogenesis. To test for this, we studied the susceptibility of Axl-/- mice to experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis. METHODS: WT and Axl-/- mice were immunized with myelin oligodendrocyte glycoprotein (MOG)35-55 peptide emulsified in complete Freund's adjuvant and injected with pertussis toxin on day 0 and day 2. Mice were monitored daily for clinical signs of disease and analyzed for pathology during the acute phase of disease. Immunological responses were monitored by flow cytometry, cytokine analysis and proliferation assays. RESULTS: Axl-/- mice had a significantly more severe acute phase of EAE than WT mice. Axl-/- mice had more spinal cord lesions with larger inflammatory cuffs, more demyelination, and more axonal damage than WT mice during EAE. Strikingly, lesions in Axl-/- mice had more intense Oil-Red-O staining indicative of inefficient clearance of myelin debris. Fewer activated microglia/macrophages (Iba1+) were found in and/or surrounding lesions in Axl-/- mice relative to WT mice. In contrast, no significant differences were noted in immune cell responses between naïve and sensitized animals. CONCLUSIONS: These data show that Axl alleviates EAE disease progression and suggests that in EAE Axl functions in the recruitment of microglia/macrophages and in the clearance of debris following demyelination. In addition, these data provide further support that administration of the Axl ligand Gas6 could be therapeutic for immune-mediated demyelinating diseases.

Multiple sclerosis: re-expression of a developmental pathway that restricts oligodendrocyte maturation.

During mammalian central nervous system (CNS) development, contact-mediated activation of Notch1 receptors on oligodendrocyte precursors by the ligand Jagged1 induces Hes5, which inhibits maturation of these cells. Here we tested whether the Notch pathway is re-expressed in the adult CNS in multiple sclerosis (MS), an inflammatory demyelinating disease in which remyelination is typically limited. We found that transforming growth factor-beta 1 (TGF-beta 1), a cytokine upregulated in MS, specifically re-induced Jagged1 in primary cultures of human astrocytes. Within and around active MS plaques lacking remyelination, Jagged1 was expressed at high levels by hypertrophic astrocytes, whereas Notch1 and Hes5 localized to cells with an immature oligodendrocyte phenotype, and TGF-beta 1 was associated with perivascular extracellular matrix in the same areas. In contrast, there was negligible Jagged1 expression in remyelinated lesions. Experiments in vitro showed that Jagged1 signaling inhibited process outgrowth from primary human oligodendrocytes. These data are the first to implicate the Notch pathway in the limited remyelination in MS. Thus, Notch may represent a potential target for therapeutic intervention in this disease.

Deletion of astrocyte connexins 43 and 30 leads to a dysmyelinating phenotype and hippocampal CA1 vacuolation.

Astrocytes are coupled via gap junctions (GJs) comprising connexin 43 (Cx43) (Gja1) and Cx30 (Gjb6), which facilitate intercellular exchange of ions. Astrocyte connexins also form heterotypic GJs with oligodendrocytic somata and lamellae. Loss of oligodendrocyte gap junctions results in oligodendrocyte and myelin pathology. However, whether loss of astrocyte GJs affects oligodendrocytes and myelin is not known. To address this question, mice with astrocyte-targeted deletion of Cx43 and global loss of Cx30 [double knock-out (dKO)] were studied using Western blotting, immunohistochemistry, electron microscopy, and functional assays. Commencing around postnatal day 23 and persisting into old age, we found widespread pathology of white matter tracts comprising vacuolated oligodendrocytes and intramyelinic edema. In contrast, gray matter pathology was restricted to the CA1 region of the hippocampus, and consisted of edematous astrocytes. No differences were observed in synaptic density or total NeuN(+) cells in the hippocampus, or olig2(+) cells in the corpus callosum. However, in dKO mice, fewer CC1-positive mature oligodendrocytes were detected, and Western blotting indicated reduced myelin basic protein. Pathology was not noted in mice expressing a single allele of either Cx43 or Cx30. When compared with single connexin knock-outs, dKO mice were impaired in sensorimotor (rotarod, balance beam assays) and spatial memory tasks (object recognition assays). We conclude that loss of astrocytic GJs can result in white matter pathology that has functional consequences.

TGFbeta1 induces Jagged1 expression in astrocytes via ALK5 and Smad3 and regulates the balance between oligodendrocyte progenitor proliferation and differentiation.

Notch1 receptor signaling regulates oligodendrocyte progenitor differentiation and myelin formation in development, and during remyelination in the adult CNS. In active multiple sclerosis lesions, Notch1 localizes to oligodendrocyte lineage cells, and its ligand Jagged1 is expressed by reactive astrocytes. Here, we examined induction of Jagged1 in human astrocytes, and its impact on oligodendrocyte differentiation. In human astrocyte cultures, the cytokine TGFbeta1 induced Jagged1 expression and blockade of the TGFbeta1 receptor kinase ALK5 abrogated Jagged1 induction. TGFbeta2 and beta3 had similar effects, but induction was not observed in response to the TGFbeta family member activin A or other cytokines. Downstream, TGFbeta1 activated Smad-dependent signaling, and Smad-independent pathways that included PI3 kinase, p38, and JNK MAP kinase, but only inhibition of the Smad-dependent pathway blocked Jagged1 expression. SiRNA inhibition of Smad3 downregulated induction of Jagged1, and this was potentiated by Smad2 siRNA. Purified oligodendrocyte progenitor cells (OPCs) nucleofected with Notch1 intracellular signaling domain displayed a shift towards proliferation at the expense of differentiation, demonstrating functional relevance of Notch1 signaling in OPCs. Furthermore, human OPCs plated onto Jagged1-expressing astrocytes exhibited restricted differentiation. Collectively, these data illustrate the mechanisms underlying Jagged1 induction in human astrocytes, and suggest that TGFbeta1-induced activation of Jagged1-Notch1 signaling may impact the size and differentiation of the OPC pool in the human CNS.

Toll-like receptors in CNS viral infections.

Protection against viral infections is critically dependent upon the early production of significant levels of type 1 interferons and the expression of interferon-stimulated genes that function as the effectors of innate antiviral immunity. Activation of Toll-like receptors on cells of the immune system is known to play an important role in this process. In this chapter we review evidence for a role of TLRs in innate immune responses against viral infections of the central nervous system. By far the most extensive literature pertains to TLR3. Data from various laboratories have shown that TLR3 is expressed in cells endogenous to the CNS, particularly in astrocytes and microglia. Triggering TLR3 by synthetic dsRNA, poly I:C effectively induces innate antiviral responses as well as boosts adaptive immune responses. Additional experiments show cooperative responses between TLRs (3, 7/8 and 9) in mounting an effective antiviral immune response in the periphery. Perhaps the most exciting data are from patient populations that document the critical role that specific TLRs play in specific CNS infections. Studies also suggest that inappropriate activation of the TLRs can result in a pathogenic outcome rather than a protective one. Since TLR ligands are being actively considered for their antiviral and potential adjuvant effects, this will be an important issue to address in the context of the CNS environment.

P2X7 receptors mediate ATP release and amplification of astrocytic intercellular Ca2+ signaling.

Modulation of synaptic transmission and brain microcirculation are new roles ascribed to astrocytes in CNS function. A mechanism by which astrocytes modify neuronal activity in the healthy brain depends on fluctuations of cytosolic Ca2+ levels, which regulate the release of "gliotransmitters" via an exocytic pathway. Under pathological conditions, however, the participation of other pathways, including connexin hemichannels and the pore-forming P2X7R, have been proposed but remain controversial. Through the use of genetically modified 1321N1 human astrocytoma cells and of spinal cord astrocytes derived from neonatal Cx43- and P2X7R-null mice, we provide strong evidence that P2X7Rs, but not Cx43 hemichannels, are sites of ATP release that promote the amplification of Ca2+ signal transmission within the astrocytic network after exposure to low divalent cation solution. Moreover, our results showing that gap junction channel blockers (heptanol, octanol, carbenoxolone, flufenamic acid, and mefloquine) are antagonists of the P2X7R indicate the inadequacy of using these compounds as evidence for the participation of connexin hemichannels as sites of gliotransmitter release.

Gas6/Axl signaling activates the phosphatidylinositol 3-kinase/Akt1 survival pathway to protect oligodendrocytes from tumor necrosis factor alpha-induced apoptosis.

Growth arrest-specific protein 6 (gas6) activity is mediated through the receptor tyrosine kinase family members Axl, Rse, and Mer, all of which are expressed in human oligodendrocytes. In this study, we examined whether recombinant human (rh) gas6 protects oligodendrocytes from growth factor (insulin) withdrawal or tumor necrosis factor-alpha (TNFalpha) cytotoxicity. In addition, we examined whether the effect was caspase-dependent, which receptor mediated the protective effect, and whether survival required Akt1 activation. Oligodendrocyte viability was assessed by O4 staining and terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling. Addition of rhgas6 to insulin-depleted cultures resulted in a significant increase in oligodendrocyte viability. Rhgas6 and caspase inhibitors also reduced active caspase-3 immunoreactivity relative to TNFalpha-only-treated cultures. In cultures treated with TNFalpha (100 ng/ml), the oligodendrocyte survival rate was 18% compared with cultures treated with TNFalpha and rhgas6 (64%) or the caspase inhibitors IETD-fmk [z-Ile-Glu(OMe)-Thr-Asp(OMe)-fluoromethyl ketone] (65%) and zVAD-fmk (N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone) (63%). Increased phosphoAkt (Ser473) immunoreactivity was detected 15 min after administration of gas6 and TNFalpha to oligodendrocyte cultures but not in TNFalpha-treated cultures. The gas6 protective effect was abrogated by the Axl decoy receptor Axl-Fc, by the phosphatidylinositol 3 (PI3) kinase inhibitor LY294002 [2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one], and in Akt1(-/-) oligodendrocytes. Oligodendrocyte cultures established from wild-type and Rse(-/-) mice, but not from Axl(-/-) mice, were also protected from TNFalpha-induced cell death when maintained in rhgas6. We conclude that gas6 signaling through the Axl receptor and the PI3 kinase/Akt1 survival pathway protects oligodendrocytes from growth factor withdrawal and TNFalpha-mediated cell death.

Interleukin-11 potentiates oligodendrocyte survival and maturation, and myelin formation.

Mechanisms that regulate oligodendrocyte survival and myelin formation are an intense focus of research into myelin repair in the lesions of multiple sclerosis (MS). Although demyelination and oligodendrocyte loss are pathological hallmarks of the disease, increased oligodendrocyte numbers and remyelination are frequently observed in early lesions, but these diminish as the disease course progresses. In the current study, we used a microarray-based approach to investigate genes regulating repair in MS lesions, and identified interleukin-11 (IL-11) as an astrocyte-derived factor that potentiates oligodendrocyte survival and maturation, and myelin formation. IL-11 was induced in human astrocyte cultures by the cytokines IL-1beta and TGFbeta1, which are both prominently expressed in MS plaques. In MS tissue samples, IL-11 was expressed by reactive astrocytes, with expression particularly localized at the myelinated border of both active and silent lesions. Its receptor, IL-11R alpha, was expressed by oligodendrocytes. In experiments in human cultures in vitro, IL-11R alpha localized to immature oligodendrocytes, and its expression decreased during maturation. In cultures treated with IL-11, we observed a significant increase in oligodendrocyte number, and this was associated with enhanced oligodendrocyte survival and maturation. Importantly, we also found that IL-11 treatment was associated with significantly increased myelin formation in rodent CNS cocultures. These data are the first to implicate IL-11 in oligodendrocyte viability, maturation, and myelination. We suggest that this pathway may represent a potential therapeutic target for oligodendrocyte protection and remyelination in MS.

Novel synthetic amino acid copolymers that inhibit autoantigen-specific T cell responses and suppress experimental autoimmune encephalomyelitis.

Copolymer 1 (Cop 1, Copaxone [Teva Marion Partners, Kansas City, Missouri, USA]), a random amino acid copolymer of tyrosine (Y), glutamic acid (E), alanine (A), and lysine (K), reduces the frequency of relapses by 30% in relapsing-remitting multiple sclerosis (MS) patients. In the present study, novel random four-amino acid copolymers, whose design was based on the nature of the anchor residues of the immunodominant epitope of myelin basic protein (MBP) 85-99 and of the binding pockets of MS-associated HLA-DR2 (DRB1*1501), have been synthesized by solid-phase chemistry. Poly (Y, F, A, K) (YFAK) inhibited binding of the biotinylated MBP 86-100 epitope to HLA-DR2 molecules more efficiently than did either unlabeled MBP 85-99 or any other copolymer including Cop 1. Moreover, YFAK and poly (F, A, K) (FAK) were much more effective than Cop 1 in inhibition of MBP 85-99-specific HLA-DR2-restricted T cell clones. Most importantly, these novel copolymers suppressed experimental autoimmune encephalomyelitis, induced in the susceptible SJL/J (H-2(s)) strain of mice with the encephalitogenic epitope PLP 139-151, more efficiently than did Cop 1. Thus, random synthetic copolymers designed according to the binding motif of the human immunodominant epitope MBP 85-99 and the binding pockets of HLA-DR2 might be more beneficial than Cop 1 in treatment of MS.

Regulation of immune response by P2X7 receptor.

The P2X7 receptor is an ATP-gated cation channel that is widely expressed in cells of the immune system. Signal transduction is accompanied by fast influx of Ca2+ and Na+, and efflux of K+. This receptor differs from other members of the P2X family in its relatively low affinity for ATP, the presence of a long C-terminal region that contains several protein-protein interaction motifs, and the activation of two membrane conductance states following receptor ligation. In the immune system, this receptor has been implicated in the processing and release of cytokines such as IL-1 beta, and in the initiation of cell death via both apoptotic and necrotic pathways. As such, it has been proposed to function as a major regulator of inflammation. Consistent with this hypothesis, inactivation of this receptor in mice modulates disease pathogenesis in several animal models of inflammatory and autoimmune diseases. Loss-of-function polymorphisms have also been noted in the human population, and there is accumulating evidence that these polymorphisms are linked to certain diseases. In this article, we review the current status of research in this field, with particular emphasis on the signaling pathways activated by this receptor, the mechanisms involved in the initiation of cell death, and associations with disease states in mice and humans.

New possible roles for aquaporin-4 in astrocytes: cell cytoskeleton and functional relationship with connexin43.

Aquaporin-4 (AQP4), the main water channel in the brain, is expressed in the perivascular membranes of mouse, rat, and human astrocytes. In a previous study, we used small interfering RNA (siRNA) to specifically knock down AQP4 in rat astrocyte primary cultures and found that together with reduced osmotic permeability, AQP4 knockdown (KD) led to altered cell morphology. However, a recent report on primary cultured astrocytes from AQP4 null mice (KO) showed no morphological differences compared with wild types. In this study, we compared the effect of AQP4 KD in mouse, rat, and human astrocyte primary cultures and found that AQP4 KD in human astrocytes resulted in a morphological phenotype similar to that found in rat. In contrast, AQP4 KD in mouse astrocytes caused only very mild morphological changes. The actin cytoskeleton of untreated astrocytes exhibited strong species-specific differences, with F-actin being organized in cortical bands in mouse and in stress fibers in rat and human astrocytes. Surprisingly, as a consequence of AQP4 KD, F-actin cytoskeleton was depolymerized in rat and human whereas it was completely rearranged in mouse astrocytes. Although AQP4 KD induced alterations of the cell cytoskeleton, we found that the expression of dystrophin (DP71), beta-dystroglycan, and alpha-syntrophin was not altered. AQP4 KD in cultured mouse astrocytes produced strong down-regulation of connexin43 (Cx43) with a concomitant reduction in cell coupling while no major alterations in Cx43 expression were found in rat and human cells. Taken together, these results demonstrate that with regard to these properties, human astrocytes in culture are more similar to rat than to mouse astrocytes. Moreover, even though AQP4 KD in mouse astrocytes did not result in a dramatic morphological phenotype, it induced a remarkable rearrangement of F-actin, not related to disruption of the dystrophin complex, indicating a primary role of this water channel in the cytoskeleton changes observed. Finally, the strong down-regulation of Cx43 and cell coupling in AQP4 KD mouse astrocytes indicate that a functional relationship likely exists between water channels and gap junctions in brain astrocytes.

Interleukin-1beta induces a reactive astroglial phenotype via deactivation of the Rho GTPase-Rock axis.

The cytokine interleukin-1beta (IL-1beta) is critical to the formation of an astrocytic scar after CNS injury, but the mechanisms by which it induces a reactive phenotype remain unresolved. Here, we show that IL-1beta regulates the phenotype of astrocytes via deactivation of the Rho GTPase-Rho kinase (ROCK) pathway, which governs cellular morphology and migration via effects on F-actin and its interactions with focal adhesions, nonmuscle myosin, and microvillar adapter proteins of the ezrin-radixin-moesin (ERM) family. We found that IL-1beta induced cortical reorganization of F-actin and dephosphorylation of focal adhesion kinase, myosin light chain 2, and myosin phosphatase targeting subunit 1 in primary human astrocytes, and that all of these effects were mimicked by Rho-ROCK pathway blockade. We also found that IL-1beta conversely potentiated ERM phosphorylation, and that this effect was mediated via a Rho-ROCK-independent mechanism. Next, we used a rhotekin pulldown assay to confirm directly that IL-1beta deactivates Rho, and further demonstrated that a constitutively active Rho construct rescued astrocytes from developing an IL-1beta-induced reactive phenotype. These data implicate cytokine regulation of the Rho-ROCK pathway in the generation of a reactive astrogliosis, and we suggest that interventions targeted at this level may facilitate manipulation of the glial scar in inflammatory disorders of the human CNS.

Upregulation of group 1 CD1 antigen presenting molecules in guinea pigs with experimental autoimmune encephalomyelitis: an immunohistochemical study.

In humans, group 1 CD1 glycoproteins present foreign and self lipid and glycolipid antigens to T-cells. Homologues of these molecules are not found in mice or rats but are present in guinea pigs (GPs). We examined CD1 and MHC class II expression in the central nervous system (CNS) of GPs sensitized for experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. In normal GPs and the uninflamed CNS, low-level MHC class II (MHC II) immunoreactivity occurred on vascular elements, meningeal macrophages and parenchymal microglial cells, whereas immunoreactivity for CD1 was absent. In the inflamed CNS, the majority of infiltrating cells were MHC II+ and microglia showed increased expression. CD1 immunoreactivity was detected on astrocytes and subsets of inflammatory cells Including B cells and macrophages. Minimal CD1 and MHC II co-expression was noted on inflammatory cells or glia. We conclude that group 1 CD1 molecules are strongly upregulated in the inflamed CNS on subsets of cells distinct from the majority of MHC II bearing cells. The expression of CD1 proteins in such lesions broadens the potential repertoire of antigens recognized at these sites and highlights the value of the GP as a model for studies of the relevance of CD1 molecules in host defense and autoimmune diseases.

Cytokines: powerful regulators of glial cell activation.

It is now clear that cytokines function as powerful regulators of glial cell function in the central nervous system (CNS), either inhibiting or promoting their contribution to CNS pathology. Although these interactions are complex, the availability of animals with targeted deletions of these genes and/or their receptors, as well as transgenic mice in which cytokine expression has been targeted to specific cell types, and the availability of purified populations of glia that can be studied in vitro, has provided a wealth of interesting and frequently surprising data relevant to this activity. A particular feature of many of these studies is that it is the nature of the receptor that is expressed, rather than the cytokine itself, that regulates the functional properties of these cytokines. Because cytokine receptors are themselves modulated by cytokines, it becomes evident that the effects of these cytokines may change dramatically depending upon the cytokine milieu present in the immediate environment. An additional exciting aspect of these studies is the previously underappreciated role of these factors in repair to the CNS. In this review, we focus on current information that has helped to define the role of cytokines in regulating glial cell function as it relates to the properties of microglia and astrocytes.

15-deoxy-delta (12,14)-PGJ2 inhibits astrocyte IL-1 signaling: inhibition of NF-kappaB and MAP kinase pathways and suppression of cytokine and chemokine expression.

We studied the role of 15-deoxy-delta (12,14)-PGJ2 (15d-PGJ2), a macrophage inhibitor with reported therapeutic effects on experimental allergic encephalomyelitis, in human astrocyte activation in vitro. 15d-PGJ2 inhibited a broad range of astrocyte inflammatory gene expression induced by IL-1, including cytokines (TNFalpha and IL-6), chemokines (RANTES/CCL5 and IP-10/CXCL10) and inducible nitric oxide synthase. 15d-PGJ2 inhibited transactivation of NF-kappaB-dependent promoters, as well as p38 and JNK MAPK phosphorylation induced by IL-1, while having no inhibitory effect on IFN-induced Stat signaling pathways. Our results demonstrating 15d-PGJ2-mediated astrocyte deactivation through inhibition of NF-kappaB are similar to those described for macrophages, and add astrocytes as additional targets for this prostaglandin (PG).