MHC antigen expression on bulk isolated macrophage-microglia from newborn mouse brain: induction of Ia antigen expression by gamma-interferon

Class II transactivator and class II MHC gene expression in microglia: modulation by the cytokines TGF-beta, IL-4, IL-13 and IL-10

Microglia are the resident macrophages of the brain, and when activated, have functions including cytokine production, phagocytosis and antigen presentation. The class II MHC genes encode proteins that present antigenic peptides to helper T cells, leading to T cell activation and the development of an antigen-specific immune response. Class II MHC gene expression is strictly regulated by the class II transactivator (CIITA) transcription factor. In this study, we investigated the effects of various immunomodulatory cytokines on IFN-gamma induction of class II MHC and CIITA gene expression in microglia, both primary microglia and a murine microglial cell line, EOC 20. By flow cytometry analysis we show that IFN-gamma-induced surface expression of class II MHC molecules on EOC 20 cells can be inhibited by the cytokines TGF-beta1, IL-4 and IL-10, but not IL-13. Using a ribonuclease protection assay, we have found that TGF-beta1, IL-4 and IL-10 act by inhibiting the expression of IFN-gamma-induced CIITA mRNA and, in turn, class II MHC mRNA. TGF-beta1, IL-4, and IL-10 inhibition of IFN-gamma-induced CIITA mRNA accumulation was not due to destabilization of CIITA mRNA, suggesting an effect at the level of transcription. In primary murine microglia, IL-10 and TGF-beta1 inhibited IFN-gamma-induced CIITA and class II MHC expression. However, a discordant effect of IL-4 was noted in that IL-4 enhanced IFN-gamma-induced CIITA and class II MHC expression in primary microglia. Although some differences are observed between EOC 20 cells and primary microglia in terms of responsiveness to TGF-beta, IL-4 and IL-10, CIITA and class II MHC gene expression are coordinately modulated.

Effects of phosphodiesterase inhibitors on cytokine production by microglia

Type III and IV phosphodiesterase inhibitors (PDEIs) have recently been shown to suppress the production of TNF-alpha in several types of cells. In the present study, we have shown that all the types of PDEIs, from type I- to V-specific and non-specific, suppress the production of TNF-alpha by mouse microglia stimulated with lipopolysaccharide (LPS) in a dose-dependent manner. Certain combinations of three different types of PDEIs synergistically suppressed TNF-alpha production by microglia at a very low concentration (1 microM). Since some PDEIs reportedly pass through the blood-brain barrier (BBB), the combination of three PDEIs may be worth trying in neurological diseases, such as multiple sclerosis and HIV-related neurological diseases in which TNF-alpha may play a critical role. Some PDEIs also suppressed interleukin-I (IL-I) and IL-6 production by mouse microglia stimulated with LPS. In contrast, the production of IL-10, which is known to be an inhibitory cytokine, was upregulated by certain PDEIs. The suppression of TNF-alpha and induction of IL-10 were confirmed at the mRNA level by RT-PCR. PDEIs may be useful anti-inflammatory agents by downregulating inflammatory cytokines and upregulating inhibitory cytokines in the central nervous system. (CNS).

Murine MHC class II locus control region drives expression of human beta-glucocerebrosidase in antigen presenting cells of transgenic mice

Gaucher disease is the most prevalent lysosomal storage disorder in humans, resulting from an inherited deficiency of the enzyme glucocerebrosidase. Although the enzyme is ubiquitously expressed, cells of the reticuloendothelial system are particularly affected since they accumulate the undigested glucosylceramide substrate through their role in scavenging and breaking down cell debris. Gaucher disease is an attractive target for somatic gene therapy. To test the ability to express the enzyme in the affected cell types we have generated transgenic mice expressing human glucocerebrosidase under the control of the murine major histocompatibility complex (MHC) class II Ead locus control region (LCR). The four transgenic lines express the human enzyme in a copy number-dependent manner, independent of the integration site of the transgene. Over-expression of the human enzyme in mice did not result in any abnormal phenotype or pathology during the period of observation (> 2 years). The enzyme is expressed in B cells, monocytes, dendritic cells, thymic epithelial cells, and macrophages in various tissues: the peritoneal cavity, bone marrow, spleen, kidney, gastrointestinal tract, Kupffer cells in the liver and alveolar macrophages in lungs. Expression in the brain was limited to perivascular macrophages and was not seen in microglial cells. Therefore, the MHC class II LCR could potentially be of use in somatic gene therapy for type 1 Gaucher disease.

Interferon-gamma plus lipopolysaccharide induction of delayed neuronal apoptosis in rat hippocampus

Interferon-gamma and lipopolysaccharide (IFN-gamma/LPS) induce expression of inducible nitric oxide synthase (iNOS) protein both in cells in vitro and in the brain in vivo. In cultured cells, excessive production of nitric oxide (NO) induces neuronal cell death. However, it is still unclear whether IFN-gamma and LPS might induce neuronal cell death in vivo. In this study, we examined the neuronal cell death and induction of major histocompatibility complex (MHC) antigens after microinjection of IFN-gamma/LPS into the rat hippocampus. Although microglia appeared morphologically ramified in the normal and vehicle-injected hippocampus, microinjection of IFN-gamma/LPS immediately induced the ameboid type. From days 1-7, iNOS was expressed in ameboid microglia surrounding the site of the microinjection. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive cells appeared among the granular neurons of the dentate gyrus on day 3 and peaked about 7 days after microinjection. When the NOS inhibitor N(G)-nitro-L-arginine (L-NA) was intraperitoneally administered prior to the microinjection, the number of TUNEL-positive neurons decreased in a L-NA dose-dependent manner. These results suggest that IFN-gamma/LPS induces delayed neuronal apoptosis in the hippocampus in vivo, and it possibly involves excessive NO production by iNOS. Thus, this animal model may be one of neurodegenerative with extensive inflammatory activation in the hippocampus.

Separate precursor cells for macrophages and microglia in mouse brain: immunophenotypic and immunoregulatory properties of the progeny

The brain contains two populations of macrophages: the microglia of brain parenchyma, and the central nervous system (CNS) macrophages located in the perivascular spaces, the leptomeninges and the choroid plexus. The microglia are characterized, in part, by their paucity of major histocompatibility complex (MHC) molecules and lack of constitutive antigen (Ag)-presenting activity for naïve CD4+ T-cells. Some CNS macrophages, on the other hand, constitutively express MHC molecules and present Ag to naïve CD4+ T-cells. We have reported that mouse brain contains precursor cells that, in the presence of colony-stimulating factor-1, the macrophage growth factor, give rise to clones of cells that differ in their ability to constitutively present Ag to naive CD4+ T cells. Here we report that this population of precursor cells can be separated into two discrete subpopulations based on differences in cell density and that the two cell populations give rise to progeny that differ in their content of cells constitutively expressing MHC class II and CD86 molecules, and the ability to present Ag to naïve CD4+ T-cells. A comparison of the level of CD45 staining of the progeny, an indication of a microglial or a CNS macrophage origin, suggests that one population of precursor cells yields immunologically immature microglia and the other CNS macrophages.

Antigen presenting capacity of brain microvasculature in altered peptide ligand modulation of experimental allergic encephalomyelitis

Co-immunization with an altered peptide ligand (LR) partially protects SJL mice from proteolipid protein peptide 139-151-induced experimental allergic encephalomyelitis [Kuchroo, V.K., Greer, J.M., Kaul, D., Ishioka, G.Y., Franco, A., Sette, A., Sobel, R.A., Lees, M.B., 1994. A single TCR antagonist peptide inhibits experimental allergic encephalomyelitis mediated by a diverse T cell repertoire. J. Immunol. 153, 3326-3336; Santambrogio, L., Lees, M.B., Sobel, R.A., 1998. Altered peptide ligand modulation of experimental allergic encephalomyelitis: immune responses within the CNS. J. Neuroimmunol. 81, 1-13]. Clinical protection was noted despite extensive central nervous system inflammation observed after co-immunization with native and altered peptides. To extend our previous reports on this model, we now compare MHC class II expression and antigen presenting cell activity of cells associated with the blood-brain barrier in diseased and protected mice. Immunohistochemical studies identified MHC class II products on both the endothelial and microglial/macrophage populations. Ex vivo experiments suggested a correlation between the reduced clinical disease observed in the co-immunized mice and the antigen presenting activity of cells at the blood-brain barrier. The results suggest that antigen presenting activity is primarily mediated by macrophage-lineage cells of the central nervous system.

Neurons induce the activation of microglial cells in vitro

Although microglial cells are well known to become activated in the pathological brain, mechanisms underlying the microglial activation are not fully understood. In the present study, with an aim to elucidate whether neurons are involved in the microglial activation, we compared the morphology and the superoxide anion (O2-)-generating activity of rat microglial cells in pure culture with those of cells cocultured with rat primary cortical neurons. Microglial cells in pure culture in serum-free Eagle's minimum essential medium on poly-L-lysine-coated coverslips displayed ramified morphology and suppressed activity of O2- generation. In contrast, microglial cells in neuron-microglia coculture under the same conditions as those for the pure culture displayed ameboid shape and upregulated activity of O2- generation. Electron microscopic observation revealed that microglial cells in coculture were more abundant in Golgi apparatus and secretory granules than those in pure culture and that some of microglial cells in the vicinity of neurites exhibited membrane specialization reminiscent of a junctional apparatus with high electron density between a microglial soma and a neurite. Microglial cells in coculture tended to tie neurites in bundles by extending processes. Medium conditioned by neurons significantly enhanced O2- generation by microglia, but microglial cells in contact with or in close apposition to cocultured neurons were much more intensely activated than those remote from the neurons. Furthermore, the membrane fraction of cortical neurons activated microglial cells, and this effect was abolished by treating the neuronal membrane with trypsin or neuraminidase. In conclusion, neuronal-microglial contact may be necessary to mediate microglial activation. The present findings suggest that the contact of microglia with damaged neurons in the brain is a plausible cause to activate microglia in the neuropathological processes.

Microglia in cell culture and in transplantation therapy for central nervous system disease

The central nervous system (CNS) is host to a significant population of macrophage-like cells known as microglia. In addition to these cells which reside within the parenchyma, a diverse array of macrophages are present in meningeal, perivascular, and other peripheral locations. The role that microglia and other CNS macrophages play in disease and injury is under intensive investigation, and functions in development and in the normal adult are just beginning to be explored. At present the biology of these cells represents one of the most fertile areas of CNS research. This article describes methodology for the isolation and maintenance of microglia in cell cultures prepared from murine and feline animals. Various approaches to identify microglia are provided, using antibody, lectin, or scavenger receptor ligand. Assays to confirm macrophage-like functional activity, including phagocytosis, lysosomal enzyme activity, and motility, are described. Findings regarding the origin and development of microglia and results of transplantation studies are reviewed. Based on these data, a strategy is presented that proposes to use the microglial cell lineage to effectively deliver therapeutic compounds to the CNS from the peripheral circulation.

Regulation of beta-chemokine mRNA expression in adult rat astrocytes by lipopolysaccharide, proinflammatory and immunoregulatory cytokines

Astrocytes constitute a part of the blood-brain barrier. Chemokine expression by astrocytes may contribute to leucocyte infiltration within the central nervous system (CNS) during inflammation. To investigate factor(s) regulating chemokine expression by astrocytes, we studied the induction of beta-chemokine mRNA expression in adult rat astrocytes. Astrocyte-derived monocyte chemoattractant protein- (MCP-1), RANTES, macrophage inflammatory protein (MIP)-1alpha and MIP-1beta mRNA were induced by interferon-gamma (IFN-gamma). Tumour necrosis factor-alpha (TNF-alpha) induced MCP-1, RANTES and MIP-1beta mRNA expression, and lipopolysaccharide (LPS) induced MCP-1, MIP-1alpha and MIP-1beta mRNA expression in astrocytes. LPS-induced MCP-1, MIP-1alpha and MIP-1beta mRNA expression by astrocytes was antagonized by transforming growth factor (TGF)-beta1 and interleukin (IL)-10. TGF-beta1 and IL-10 also down-regulated MCP-1 and RANTES mRNA expression induced by TNF-alpha. IL-10, but not TGF-beta1, inhibited MIP-1beta mRNA expression induced by TNF-alpha. The results of this in vitro study suggest that beta-chemokine mRNA expression by adult rat astrocytes can be induced by LPS or proinflammatory cytokines, while regulatory cytokines, such as TGF-beta1 and IL-10, down-regulate astrocyte-derived beta-family chemokine mRNA expression induced by LPS, IFN-gamma and TNF-alpha. Further study of CNS chemokines will enhance our understanding of leucocyte recruitment to the CNS and suggest therapeutic strategies for neurological disorders.

Astrocytes modulate nitric oxide production by microglial cells through secretion of serine and glycine

We investigated lipopolysaccharide (LPS)-induced nitric oxide (NO) production by rat microglia in neuron-microglia and astrocyte-microglia cocultures to evaluate the influence of neurons and astrocytes on microglial activity. Microglial cells solely cultured in medium devoid of serine (Ser), glycine (Gly) hardly expressed inducible NO synthase (iNOS), while those cocultured with neurons and astrocytes expressed iNOS. When microglial cells and astrocytes were separately cultured by using tissue culture inserts, which allowed the microglial cells to be exposed to only diffusible factors arising from astrocytes, NO production was significantly enhanced. On the other hand, neurons, when separated from microglial cells by the inserts, could not activate microglial cells possibly due to lacking of direct contact between neurons and microglial cells. NO production in pure microglial cultures was significantly enhanced in the presence of Ser/Gly at concentrations higher than 25 microM. Conditioned media obtained from microglia culture and neuron-microglia coculture contained less than 10 microM of Ser and Gly, while media from astrocyte culture and astrocyte-microglia coculture contained 33-41 microM Ser and 20-26 microM Gly. Accordingly, astrocytes modulate the activity of microglial cells by secreting Ser and Gly. The present study proposes a novel metabolic coupling between astrocytes and microglial cells via amino acids.

Cytokine actions in the central nervous system

Cytokines and chemokines have been implicated in contributing to the initiation, propagation and regulation of immune and inflammatory responses. Also, these soluble mediators have important roles in contributing to a wide array of neurological diseases such as multiple sclerosis, AIDS Dementia Complex, stroke and Alzheimer's disease. Cytokines and chemokines are synthesized within the central nervous system by glial cells and neurons, and have modulatory functions on these same cells via interactions with specific cell-surface receptors. In this article, I will discuss the ability of glial cells and neurons to both respond to, and synthesize, a variety of cytokines. The emphasize will be on three select cytokines; interferon-gamma (IFN-gamma), a cytokine with predominantly proinflammatory effects; interleukin-6 (IL-6), a cytokine with both pro- and anti-inflammatory properties; and transforming growth factor-beta (TGF-beta), a cytokine with predominantly immunosuppressive actions. The significance of these cytokines to neurological diseases with an immunological component will be discussed.

Brain-specific gene expression by immortalized microglial cell-mediated gene transfer in the mammalian brain

The intra-arterial injection of immortalized microglia transfected with the lacZ gene, resulted in the expression of beta-galactosidase in the rat brain at 48 h and the activity of -galactosidase was detected for up to 3 weeks post-injection. More than 30-fold higher activity of beta-galactosidase was detected in the brain than in the liver, lung or spleen at 48 h post-injection. This method allows us to easily deliver the gene of interest to the brain without influencing other organs. Our brain-targeting gene delivery system can facilitate gene therapy of several brain disorders, including brain tumor, metabolic disorders, and degenerative disorders, as well as investigation into the roles of particular genes in brain function and development.

Linomide-mediated protection of oligodendrocytes is associated with inhibition of nitric oxide production and IL-1beta expression in Lewis rat glial cells

Linomide is a synthetic immunomodulator that down-regulates autoimmune response without inducing systemic immunosuppression. Linomide effectively inhibits severe experimental autoimmune diseases, like experimental allergic encephalomyelitis (EAE), a model of multiple sclerosis (MS). Here we report that Linomide suppresses nitric oxide (NO) production by microglia and astrocytes derived from newborn rats and prevented oligodendrocyte damage. Linomide strongly inhibited interleukin (IL) 1 betamRNA expression on glial cells, suggesting a potential mechanism for inhibition of NO production by Linomide. These results demonstrate that Linomide-mediated inhibition of NO production by glial cells could explain the preventive and therapeutic effects of Linomide in EAE and perhaps also MS. However, Linomide at higher dose [correction of doss] (10(-5) M) resulted in direct oligodendrocyte damage.

Production of interleukin-12 and expression of its receptors by murine microglia

Production of interleukin-12 (IL-12) by cultured murine microglia and astrocytes was examined, by means of ELISA to detect heterodimeric p70 and RT-PCR to analyze the expression of mRNA encoding p35 and p40. Microglia, but not astrocytes, produced IL-12 p70 in response to lipopolysaccharide and interferon-gamma. The microglial cell line, Ra2, produced only p40, but not p35, upon above stimulation. Thus, it is possible that some population of microglia induce helper 1 type T cell response via producing IL-12 in the CNS. Microglia were induced to express mRNA encoding IL-12 receptors which were exclusively expressed in activated T and NK cells.

Activation of outward current by pituitary adenylate cyclase activating polypeptide in mouse microglial cells

In order to investigate the interaction between the nervous and immune systems, we have analyzed the effect of one of the neuropeptides, pituitary adenylate cyclase activating polypeptide (PACAP), on microglia cells by the patch-clamp method. Puff application of PACAP38 onto mouse microglial cells induced an outward current in a dose-dependent manner. Reversal potentials of the outward current were dependent on external K+ concentrations ([K+]0) and independent of [Cl-]0. Ion channel blockers of potassium currents, quinine (1 mM), tetraethylammonium (TEA, 20 mM) and 4-aminopyridine (4-AP, 5 mM), suppressed the outward current with a potency order of quinine>TEA>4-AP. PACAP27 also induced outward current less effectively than PACAP38. A fragment of PACAP38 [PACAP(6-38)], known as an inhibitor for PACAP38, suppressed the outward current. These data suggest that PACAP38 activates a quinine-sensitive K+ outward current and modulates activities in microglia. They indicate that the immune system in the brain can be modulated by neurotransmitters, the mediators of neurons.

Lipopolysaccharide enhances synthesis of brain-derived neurotrophic factor in cultured rat microglia

Expression of neurotrophins in pure microglia cultured from embryonic rat brain and the effects of lipopolysaccharide (LPS) on the expression were investigated. In untreated cultures, nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin (NT)-4/5 mRNAs were detected by use of reverse transcriptase-polymerase chain reaction but NT-3 mRNA was not. LPS stimulation caused a marked increase in BDNF mRNA expression in addition to a slight increment of the NT-4/5 mRNA level; however, the NGF mRNA level was not affected. LPS also increased BDNF-like immunoreactivity in cultured microglia, an action consistent with an elevation of BDNF mRNA. These results demonstrate that LPS stimulates synthesis of BDNF and probably NT-4/5, specific ligands for tyrosine kinase receptor TrkB, suggesting that activated microglia, which appear in the damaged brain, participate in neuronal regeneration via production of such neurotrophins.

Migration activity of microglia and macrophages into rat brain

We examined the entry of intra-arterially injected microglia and macrophages into the brain using a rat muscle graft model to compare their respective abilities to invade the brain parenchyma. Isolated microglia without any activation treatment entered into the brain with or without the muscle graft, while macrophages activated by phorbol 12-myristate-13-acetate (PMA) entered the brain only in the presence of the muscle graft. These results suggest that microglia have a higher affinity for the brain than macrophages.

Transforming growth factor-beta1 in adult human microglia and its stimulated production by interleukin-1

Ameboid microglia express human immunodeficiency virus 1 (HIV-1) more frequently than do ramified microglia. These two microglial subtypes might also differ in the frequency with which they express transforming growth factor-beta1 (TGF-beta1), a cytokine that regulates HIV-1 expression in monocytes. Results described here show that ameboid and ramified microglia express TGF-beta1. In brain tissues from HIV-1-infected individuals as compared with seronegative controls, ameboid rather than ramified microglia more frequently expressed TGF-beta1. Ameboid microglia, isolated and cultured from postmortem adult human brain more frequently expressed TGF-beta1 in presence of interleukin-1(IL-1), a cytokine that is elevated in brains of HIV-1-infected individuals when compared with seronegative controls. The stimulation of TGF-beta1 by IL-1 was dose and time dependent, occurring with ameboid microglia isolated from either frontal cortex or globus pallidus but not midbrain pons. Ameboid microglia are similar to the RCA-1-positive cells that form clusters, called microglial nodules, in the brain of HIV-1-infected individuals. Pathologic conditions, such as disseminated microglial nodules, are associated with HIV-1 encephalitis, direct infection of the brain, and moderate to severe neurologic impairment. TGF-beta1 expression in ameboid microglia may play a role in HIV-1 neuropathogenesis.

Ia expression and antigen presentation by glia: strain and cell type-specific differences among rat astrocytes and microglia

Astrocytes from experimental allergic encephalomyelitis (EAE)-susceptible Lewis rats expressed higher levels of Interferon-gamma-inducible Ia than astrocytes from EAE-resistant Brown Norway (BN) rats, whereas BN microglia expressed higher Ia than Lewis at both mRNA and protein levels. Lewis astrocytes induced proliferation of MBP-specific T cells selected on Lewis background as efficiently as Lewis thymocytes, whereas BN astrocytes were much less efficient in stimulating T cells selected in the presence of BN thymocytes. Microglia, irrespective of strain, induced only weak proliferative responses of these T cells despite the high expression of Ia. Antigen-stimulated T cells underwent apoptosis in the presence of microglia but not astrocytes. Thus, astrocyte-mediated proliferation of MBP-specific T cells may contribute to the development of EAE, while microglia-induced T cell apoptosis may downregulate immunopathological processes in the brain.

Protein tyrosine kinase inhibitors decrease lipopolysaccharide-induced proinflammatory cytokine production in mixed glia, microglia-enriched or astrocyte-enriched cultures

Proinflammatory cytokines, tumor necrosis factor-alpha (TNF alpha), interleukin-1 (IL-1), and interleukin-6 (IL-6), produced by glial cells have been implicated in the neuropathogenesis of various diseases. However, the signal transduction pathway(s) for the production of these cytokines in glial cells are not well understood. This study examined the effects of two potent protein tyrosine kinase inhibitors, genistein and tyrphostin A25, on lipopolysaccharide (LPS)-induced production of TNF alpha, IL-1 alpha, and IL-6 in mouse primary mixed glia, microglia- or astrocyte-enriched cultures. LPS dose-dependently increased the production of TNF alpha, IL-1 alpha, and IL-6 from the mixed glia cultures. Genistein or tyrphostin A25 significantly inhibited the LPS-induced production of these cytokines. The LPS-induced TNF alpha, IL-1 alpha, and IL-6 production in microglia- or astrocyte-enriched cultures were also inhibited by tyrphostin A25. These results demonstrate that protein tyrosine kinases are involved in the signaling events of the LPS-induced production of TNF alpha, IL-1 alpha, or IL-6 in microglia or astrocytes, which may provide insights into therapeutic interventions in the pathway for cytokine production in the brain.

Differential regulation of cytokine-induced major histocompatibility complex class II expression and nitric oxide release in rat microglia and astrocytes by effectors of tyrosine kinase, protein kinase C, and cAMP

Two glial cell populations of the CNS, astrocytes and microglia, were examined for expression of two immunologically important molecules, MHC class II and nitric oxide (NO), following treatment with cytokines. IFN-gamma induced both molecules in microglia at substantially higher levels than astrocytes. The addition of TNF-alpha to IFN-gamma elevated class II expression and NO in both cells. Genistein, an inhibitor of tyrosine kinases, and calphostin, an inhibitor of protein kinase C, diminished cytokine induction of class II MHC and NO in both glial populations. Forskolin was most effective in inhibiting class II MHC expression, but had little inhibitory effect on NO production. These results indicate microglia are more effective than astrocytes in producing cell-associated and secreted immune mediators in response to IFN-gamma and or TNF-alpha and multiple parallel, but distinct, signaling events are required for cytokine induced class II MHC or NO production.

Addition of allogeneic spleen cells causes rejection of intrastriatal embryonic mesencephalic allografts in the rat

To address the importance of antigen-presenting cells for the survival of intracerebral neural allografts, allogeneic spleen cells were added to the graft tissue before transplantation. Dissociated embryonic, dopamine-rich mesencephalic and adult spleen tissues were prepared from either inbred Lewis or Sprague-Dawley rats. A mixture of neural and spleen cells was sterotaxically transplanted into the right striatum of adult Sprague-Dawley rats. Controls were neural allografts without addition of allogeneic spleen cells and syngeneic neural grafts with or without the addition of syngeneic spleen cells. Six weeks after transplantation, brain sections were processed immunocytochemically for tyrosine hydroxylase, specific for grafted dopamine neurons, and a bank of markers for various components in the immune and inflammatory responses. The neural allografts which were mixed with allogeneic spleen cells were rejected. In these rats, there were high levels of expression of major histocompatibility complex class I and II antigens, intense cellular infiltration including macrophages and activated microglial cells, and a presence of cluster of differentiation 4- and 8-immunoreactive cells in the graft sites. Moreover, there were increased levels of intercellular adhesion molecule-1, tumour necrosis factor-alpha and interleukin-6 in and around the grafts which were undergoing rejection. In contrast, syngeneic neural grafts survived well regardless of whether they were mixed with syngeneic spleen cells or not, and control neural allografts also exhibited unimpaired survival. No significant difference was observed in the number of grafted dopamine neurons among these three latter groups. The levels of expression of the different markers for inflammation and rejection were generally lower in these grafts than in implants of combined allogeneic neural and spleen cells. In summary, intrastriatal neural allografts, which normally survive well in our animal model, were rejected if allogeneic spleen cells from the same donor were added to the graft tissue. The added spleen cells caused strong host immune and inflammatory responses. The study gave support to the notion that immunological privilege of the brain does not provide absolute protection to immunogenetically histoincompatible neural grafts.

Activation of microglial and endothelial cells in the rat brain after treatment with interferon-gamma in vivo

Activation of microglial cells occurs during the pathogenesis of various neurologic diseases. However, the mechanisms of activation in vivo are still elusive. We infused adult rats intravenously with interferon-gamma and demonstrated microglial cell activation after three days of treatment. We show for the first time that microglial cells proliferate inside the brain in response to a circulating cytokine. Microglial cells were induced to express major histocompatibility (MHC) class I and class II antigens and small amounts of leukocyte function-associated molecule 1 (LFA-1, CD11a). On endothelial cells of the brain, MHC class I and class II antigens and intercellular adhesion molecule 1 (ICAM-1, CD54) were enhanced.

Microglia from the developing rat medial septal area can affect cholinergic and GABAergic neuronal differentiation in vitro

The normal development of the central nervous system is regulated by glia. In this regard, we have reported that astrocytes, stimulated by epidermal growth factor or transforming growth factor alpha, suppress the biochemical differentiation of rat medial septal cholinergic neurons in vitro, as evidenced by a decrease in choline acetyltransferase activity. In this study, we found that, in contrast to astrocytes, microglia enhance rather than suppress this aspect of cholinergic cell expression. When in excess, microglia can revert the effects of epidermal growth factor on the septal cholinergic neurons without altering the astroglial proliferative response to this growth factor. In the absence of growth factors or other glial cell types, microglia increase choline acetyltransferase activity above control levels and thus, may be a source of cholinergic differentiating activity. The increase in enzyme activity induced by microglia is rapid in onset, detected as early as 2 h after their addition to the septal neurons and maintained up to six or seven days in vitro. Furthermore, in the absence or presence of other glial cell types, microglia also influence septal GABAergic neurons by significantly increasing glutamate decarboxylase activity. As microglia affect neither septal cholinergic nor GABAergic neuronal cell survival, they appear to enhance the biochemical differentiation of these two neuronal cell types. Specific immunoneutralizing antibodies were used to identify the microglia-derived factors affecting these two neuronal types. In this regard, we found that the microglia-derived cholinergic differentiating activity is significantly suppressed by antibodies raised against interleukin-3. Furthermore, interleukin-3 was detected in both conditioned media and cell homogenates from septal neuronal-microglial co-cultures by western blotting. Finally, although basic fibroblast growth factor and interleukin-3 significantly increase septal glutamate decarboxylase activity, neither appears to be implicated in the GABAergic cell response to the microglia. In conclusion, these results demonstrate that microglia can enhance the biochemical differentiation of developing cholinergic and GABAergic neurons in vitro.

Reduction of the microglial cell number in rat primary glial cell cultures by exogenous addition of dibutyryl cyclic adenosine monophosphate

The present work examined the effects induced by dibutyryl cyclic adenosine monophosphate (dB-cAMP) on microglial cells in primary glial cell cultures from newborn rats. Microglial cells were identified by OX42 immunohistochemistry and nucleoside diphosphatase histochemistry. Double staining for astrocytes was carried out by combination with glial fibrillary acidic protein immunolabeling. Addition of 0.25 mM dB-cAMP to the cultures decreased the microglial cell number about sixfold. The findings suggest that the effect of dB-cAMP on the microglial cells might be either a direct action of dB-cAMP on the microglial cells or an indirect effect mediated by the astroglial cells.

Systemic high-dose recombinant-alpha-2a-interferon therapy modulates lymphokine production in multiple sclerosis

Chronic systemic high-dose recombinant alpha 2a-interferon (rIFNA) therapy reduces exacerbation rate and MRI signs of disease activity in relapsing/remitting multiple sclerosis (RR MS) patients. In order to clarify the possible mechanisms underlying the clinical efficacy of rIFNA in MS, several immunologic studies were performed as a part of a pilot clinical trial. Twenty RR MS patients were treated with 9 x 10(6) IU of rIFNA (n = 12) or placebo (n = 8) intramuscularly every other day for 6 months. Cytokine production by cultured lymphocytes, major histocompatibility complex class II (MHC-II) antigen expression on cultured macrophages, peripheral blood (PB) and cerebrospinal fluid (CSF) lymphocyte phenotype, and IgG and beta 2 microglobulin levels were studied before therapy, after 6 months of therapy, and 6 months after stopping therapy. rIFNA therapy was associated with reduction of interferon-gamma and tumor necrosis factor-alpha production by PB lymphocytes (p < 0.04), and with slight, not significant, increase of transforming growth factor-beta 2 or interleukin (IL)-10 production. IL-4 was undetectable in the culture supernatants both before and after therapy. rIFNA therapy had no effect on macrophage MHC-II molecule expression. An increased percentage of CD8+, CD8+ high CD11b+ low, and CD3- CD16+ CD56+ cells, and of CD4+ absolute cell number was observed in CSF after rIFNA therapy. After rIFNA administration, IgG level significantly increased both systemically (p < 0.02) and intrathecally (p < 0.001). Serum beta 2 microglobulin level increased (p < 0.01), as well. Only 1 out of the 12 rIFNA treated patients developed neutralizing antibodies against rIFNA during therapy. Six months after stopping therapy all the immunologic changes returned to baseline. These data suggest that the beneficial effect of rIFNA therapy on MS disease activity is probably mediated by a downregulation of proinflammatory cytokine synthesis by PB lymphocytes rather than by macrophage MHC-II antigen expression. The immunologic effects of high-dose systemic rIFNA therapy are temporary and restricted to the period of drug administration.

In vivo induction of inducible nitric oxide synthase by microinjection with interferon-gamma and lipopolysaccharide in rat hippocampus

To clarify whether the inducible nitric oxide synthase (iNOS) protein can be induced in in vivo brain, we examined the influence of direct intrahippocampal injection with interferon-gamma (IFN-gamma) plus lipopolysaccharide (LPS) in the rat. In the area surrounding the microinjection site, NOS activity (NO2- accumulation) was enhanced 24 h after injection with IFN-gamma plus LPS. Although the level of 160-kDa nNOS protein was not changed, the 130-kDa iNOS protein was induced 12 h after the injection. On the other hand, iNOS mRNA could be detected at 6 and 12 h but not at 24 h. iNOS immunoreactivity was observed in CD11b-immunopositive microglia in close proximity to the injection site, but the immunoreactivity was not colocalized with glial fibrillary acidic protein-immunopositive astrocytes. Although CD11b-immunopositive microglia were of the ramified type even after injection with vehicle after 24 h, injection with IFN-gamma plus LPS caused numerous microglia to change to the ameboid type and to express major histocompatibility complex (MHC) class II antigens. In some of these ameboidal microglia, iNOS immunoreactivity was observed. These results suggest that intrahippocampal injection with IFN-gamma plus LPS induced iNOS mRNA after 6 h and iNOS protein after 12 h in some of the ameboidal microglia that expressed MHC class II antigens in in vivo rat brain.

Role of muIP-10 in interferon-gamma induction of Ia in rat astrocytes

Interferon-gamma, (IFNgamma) is a potent inducer of class II MHC (Ia) in rat astrocytes and microglia which are immunocompetent cells of the central nervous system (CNS). muIP-10, a member of the alpha-chemokine family, is also induced by IFNgamma in these cells. The induction of muIP-10 mRNA occurred in an immediate early manner, while Ia mRNA-induction was delayed and required new protein synthesis. We studied the possible role of muIP-10 in IFNgamma-mediated induction of Ia in astrocytes. Antibodies to muIP-10 protein significantly inhibited the expression of surface Ia molecules by astrocytes. Incubation of astrocytes with antisense-oligonucleotides against muIP-10 mRNA also reduced the number of Ia positive cells inducible by IFNgamma. Neither the number of IFNgamma-inducible class I MHC positive cells nor the number of class I molecules expressed per cell were affected by antisense-oligonucleotides against muIP-10, indicating the specificity of the oligonucleotide and the selective requirement of muIP-10 for Ia induction by IFNgamma. Transient transfection of astrocytes with plasmids expressing muIP-10 in the antisense orientation also reduced the number of Ia positive astrocytes. These studies suggest a role for muIP-10 protein as an autocrine factor that enhances the expression of IFNgamma-inducible Ia on astrocytes. This could create focal areas rich in Ia expressing cells which could more efficiently present antigens to T cells, leading to immune-mediated inflammation such as in multiple sclerosis.

Inhibitory effect of interferon-gamma on LPS-induced interleukin 1 beta production by isolated adult rat brain microglia

The effect of interferon-gamma (IFN-gamma) on lipopolysaccharide (LPS)-induced cytokine production has been examined in adult rat brain microglia. Following treatment of isolated cells in vitro with LPS, interleukin-1 (IL-1) and interleukin-6 (IL-6) levels in culture supernatants, determined by bioassay, were increased in a dose-dependent manner. IL-6 was particularly sensitive to LPS-stimulation. Using in situ hybridisation techniques, the induction by LPS of IL-1 and IL-6 mRNA in cultured microglia has been demonstrated. When IFN-gamma was included, LPS-induced production of both IL-1 and IL-6 by microglia was significantly reduced and this effect was particularly marked in the case of IL-1. Comparisons with peritoneal macrophages demonstrate that whilst both cell types produce IL-1 and IL-6 in response to LPS, IFN-gamma had no significant effect on this response in peritoneal macrophages. This suggests potential control mechanisms which may be effective in down-regulating cytokine production by microglia in vivo.

Reversible inhibitory effects of interferon-gamma and tumour necrosis factor-alpha on oligodendroglial lineage cell proliferation and differentiation in vitro

We have investigated the effects of the two prominent inflammatory cytokines, interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha), on oligodendroglial lineage cell development and survival. Purified oligodendrocytes and oligodendrocyte precursors obtained from neonatal rat brain primary cultures were subcultured in a defined, serum-free medium and exposed to IFN-gamma (1-100 U/ml, TNF-alpha (25-100 ng/ml) or both (100 U/ml and 50 ng/ml respectively) from day 1 to day 3 or from day 3 to day 6. While cell survival was not affected in any of the conditions tested, IFN-gamma dose-dependently inhibited [3H]thymidine or bromodeoxyuridine incorporation (by up to 50%) and the reduction of the tetrazolium salt 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT; by up to 33%). TNF-alpha synergized with IFN-gamma, but was ineffective by itself. Moreover, IFN-gamma totally antagonized the induction by basic fibroblast growth factor and platelet-derived growth factor of the proliferation of the oligodendroglial lineage cell population under study. IFN-gamma also blocked the differentiation of oligodendrocyte precursors, as evidenced by cell morphology, immunostaining for early and late differentiation markers (galactocerebroside and myelin basic protein respectively) and activity of ceramide galactosyl transferase. Again, the effect of IFN-gamma was potentiated by TNF-alpha, which was ineffective when tested alone. The inhibitory activity of IFN-gamma was rapidly reversible: 3 days after removal of the cytokine, administered from day 1 to day 3, complete recovery of cll proliferation and differentiation could be documented. The cytokine-induced arrest in the expression of differentiation antigens was accompanied by perturbations in the expression of the corresponding mRNAs, revealed by a semiquantitative reverse transcription-polymerase chain reaction method. In particular, the message for myelin basic protein (and, in the case of treatment from days 3 to 6, also that for myelin associated glycoprotein) was decreased in cultures exposed to IFN-gamma, and further depressed in cultures treated with IFN-gamma and TNF-alpha, while TNF-alpha alone was ineffective. The above observations may help explain the role of IFN-gamma and TNF-alpha in the pathogenesis of inflammatory demyelinating diseases, in which increases in the levels of these substances have been described. In particular, in the case of multiple sclerosis, our results may bear on the problem of defective remyelination and are consistent with the frequent relapsing-remitting course of the disease.

Apoptosis of cultured microglia by the deprivation of macrophage colony-stimulating factor

Promotion of microglial proliferation and differentiation by colony-stimulating factors (CSFs) and disappearances of microglia at the late neonatal stage by decreasing of CSFs have been reported. In this study, the effects of the deprivation of macrophage CSF (M-CSF) on enriched microglia in cultures were examined by cytochemical methods including in situ nick-end labeling for DNA fragmentation, and Carrazi's hematoxylin nuclear staining. When M-CSF was deprived from the culture medium: (1) at least 40% of the cells were weakly labeled by nick-end within 3 h and more than 70% of the cells were clearly labeled by 16 h; and (2) nuclear condensation or fragmentation, and formation of apoptotic bodies were observed within 48 h. LeY-positive immunoreactivity, identified as a characteristic of cells undergoing apoptosis, was observed on cells positively labeled by nick-end and condensed nucleus, and ones budding apoptotic bodies. From these results, it is conceivable that microglia undergo apoptosis when M-CSF is deprived from the culture medium and, therefore, require CSFs for their survival. This in vitro phenomenon suggests that one of the mechanisms of microglial disappearance in vivo after synaptogenesis may be due to apoptosis by decreasing level of CSFs.

Selective induction of interleukin-6 in mouse microglia by granulocyte-macrophage colony-stimulating factor

Astrocytes produce granulocyte/macrophage colony-stimulating factor (GM-CSF) and support the survival and proliferation of microglia. To study the functions of GM-CSF in the central nervous system (CNS), we examined the effects of GM-CSF on cytokine production by glial cells. GM-CSF induced interleukin-6 (IL-6) production by microglia, but not by astrocytes, in a dose-dependent manner as assessed by bioassay and the detection of IL-6 mRNA by reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. GM-CSF did not induce tumor necrosis factor (TNF) alpha or IL-1 in microglia and astrocytes, whereas lipopolysaccharide induced all these cytokines. The induction of IL-6 by GM-CSF in microglia was completely inhibited by antibodies to GM-CSF. Neither IL-3 nor macrophage-CSF (M-CSF) induced IL-6 production in microglia. Given that IL-1 and TNF alpha, monokines derived from microglia, induce IL-6 production in astrocytes, but not in microglia, results indicate that astrocytes and microglia may mutually regulate IL-6 production by different cytokines.

Methylprednisolone prevents rejection of intrastriatal grafts of xenogeneic embryonic neural tissue in adult rats

We studied the effects of high-dose methylprednisolone on the survival of intrastriatal neural xenografts and the host responses against them. Dissociated mesencephalic tissue from inbred mouse (CBA-strain) embryos was transplanted to the intact striatum of adult Sprague-Dawley rats. The rats received either daily injections of methylprednisolone (30 mg/kg), or cyclosporin A (10 mg/kg), or no immunosuppressive treatment. Two or six weeks after transplantation, there was good survival of xenografts in both the methylprednisolone- and cyclosporin A-treated rats. In contrast, the xenografts in untreated control rats were all rejected by six weeks. There was no marked difference in the degree of expression of MHC class I and II antigens and the accumulation of activated astrocytes and microglial cells/macrophages between the three groups. However, both methylprednisolone and cyclosporin A reduced infiltration of T lymphocytes to the transplantation sites. The expression of pro-inflammatory cytokines (interferon-gamma, tumour necrosis factor-alpha, interleukin-6) in and around the grafts was lower in the methylprednisolone- and cyclosporin A-treated groups than in untreated control rats. Although high-dose methylprednisolone caused significant body weight loss, we conclude that this treatment can prevent rejection of intrastriatal grafts of xenogeneic embryonic neural tissue in the adult.

Transforming growth factor-beta 1 (TGF-beta1)-mediated inhibition of glial cell proliferation and down-regulation of intercellular adhesion molecule-1 (ICAM-1) are interrupted by interferon-gamma (IFN-gamma)

We utilized a model of myelin basic protein (MBP) activation in vivo and MBP-stimulated cultures in vitro to study the influence of TGF-beta1 on glial cell proliferation and ICAM-1/leucocyte function-associated antigen-1 (LFA-1) expression, and to observe the antagonistic effects of TGF-beta1 and IFN-gamma. TGF-beta1 inhibited MBP-stimulated and MBP-activated glial cell proliferation, especially in MBP-stimulated separated microglia and astrocytes, and down-regulated the expression of ICAM-1 on MBP-stimulated glial cells and separated microglia. ICAM-1 expression on MBP-activated glial cells was intensely suppressed, whereas its expression on MBP-stimulated astrocytes was not influenced. TGF-beta1 had no effect on LFA-1 expression. In contrast, IFN-gamma up-regulated ICAM-1 expression, but inhibited proliferative response on MBP-stimulated glial cells when cultured without TGF-beta1. Examination of TGF-beta1 and IFN-gamma interactions revealed that TGF-beta1-mediated inhibition of proliferation and down-regulation of ICAM-1 on glial cells were prevented by IFN-gamma. The suppressive effect was re-established with high doses of TGF-beta1 in cultures, indicating that biological effects of TGF-beta1 vary depending on nitric oxide (NO) production, its concentration in the microenvironment and regulation of the cytokine network.

The role of macrophage subpopulations in autoimmune disease of the central nervous system

In this review the role of various subpopulations of macrophages in the pathogenesis of experimental autoimmune encephalomyetitis is discussed. Immunohistochemistry with macrophage markers shows that in this disease different populations of macrophages (i.e. perivascular cells, microglia and infiltrating blood-borne macrophages) are present in the central nervous system. These subpopulations partially overlap in some functional activity while other activities seem to be restricted to a distinct subpopulation, indicating that these subpopulations have different roles in the pathogenesis of encephalomyelitis. The studies discussed in this review reveal that immunocytochemical and morphological studies, combined with new techniques such as in situ nick translation and experimental approaches like the use of bone marrow chimeras and macrophage depletion techniques, give valuable information about the types and functions of cells involved in central nervous system inflammation. The review is divided in three parts. In the first part the experimental autoimmune encephalomyelitis model is introduced. The second part gives an overview of the origin, morphology and functions of the various subpopulations. In the third part the role of these subpopulations is discussed in relation to the various stages (i.e. preclinical, clinical and recovery) of the experimental disease.

Monoclonal autoantibody SCH94.03, which promotes central nervous system remyelination, recognizes an antigen on the surface of oligodendrocytes

A monoclonal antibody SCH94.03, made in syngeneic mice by injection of spinal cord homogenate, promotes central nervous system remyelination when injected into SJL/J mice chronically infected with Theiler's virus. To elucidate the mechanism of antibody-mediated remyelination, SCH94.03 was investigated by immunocytochemistry, flow cytometry, immunoelectron microscopy, Western blotting, and immuno-thin layer chromatography. All cell types investigated in vitro showed strong cytoplasmic staining with a pattern resembling a cytoskeletal protein. In contrast, among the primary cultured cells studied, only oligodendrocytes showed strong surface reactivity. Other cell types, including astrocytes, microglia, Schwann cells, myoblasts, and T and B lymphocytes, were negative. Mouse and rat oligodendrocytes which showed strong surface reactivity exhibited a well-differentiated morphology, and approximately 50% expressed myelin basic protein. Since oligodendrocyte progenitors were negative for surface staining, the expression of the antigens recognized by this monoclonal antibody appears to be developmentally regulated, i.e., transiently expressed on younger, terminally differentiating oligodendrocytes. Among the cell lines studied, only two rat oligodendrocyte lineage cell lines showed surface reactivity with SCH 94.03. Western blotting of secondary isolated oligodendrocytes lysates revealed reactivity with multiple protein bands of 27, 32, 50, 100, and 106 kDa, whereas there was no reactivity to lipid antigens by immuno-thin layer chromatography. These results raise the possibility that SCH94.03 recognizes a novel oligodendrocyte-specific surface antigen, and may act directly on oligodendrocytes to promote remyelination.

Biomolecular events involved in the establishment of brain anticandidal resistance

Using a murine model, we have demonstrated the establishment of cerebral resistance to local lethal challenge with Candida albicans strain CA-6, by previous intracerebral (i.c.) infection with the low-virulent strain PCA-2. Here we show that i.c. infection with PCA-2 is effective in drastically reducing brain colonization following secondary infection with CA-6. As assessed by colony forming unit assay and histopathological analysis, microbial counts are impaired, granuloma formation and hyphal growth are also reduced in brains of PCA-2- and CA-6-infected mice with respect to CA-6-challenged mice. Furthermore, using PCR studies, we found that, while PCA-2 (i.e. healing infection) induces transient cytokine gene expression in the mouse brain, CA-6 lethal challenge results in long-lasting (until mouse death) high levels of all cytokine gene transcripts assessed. Finally brains from mice that will resist CA-6 challenge, because of previous infection with PCA-2, also exhibit a transient induction of all cytokine genes. Only IL-1 beta remains highly expressed at all time- points tested. Overall, these results provide evidence that healing and non-healing C. albicans i.c. infections differ in the immune reaction(s) locally evoked, at least in terms of cytokine gene expression, strongly suggesting cytokine involvement in the establishment of brain anticandidal resistance.

Human microglia cultures: a powerful model to study their origin and immunoreactive capacity

In this paper, we report that pure cultures of human microglia were obtained from long-term astrocytic cultures of human fetal brain. After five to six months and repeated cell passages, macrophage-like cells started to spontaneously form in vitro, so that in two to three weeks the whole culture was populated by them. These cells were grown up to over 50 passages in culture and analyzed for morphology, specific marker positivity, growth rate and major histocompatibility complex (MHC) antigen expression with or without gamma-interferon (IFN) stimulation. We found that, regardless of embryonic age of original cultures (10-15 weeks of gestation), cultures showed a remarkable homogeneity and purity and over 90 stained for typical microglial markers. Under basal conditions, two cell subpopulations similar to those described in vivo, we observed: the reactive 'ameboid' type and the resting 'ramified' one, the latter increasing with time in vitro and cell passages. Both cell subpopulations were capable of active phagocytosis and of high-rate proliferation. They spontaneously expressed low levels of MHC class II antigens, but were negative for MHC class I. Stimulation with gamma-interferon lymphokine upregulated the MHC class II expression as well as the MHC class I heavy chain form in ameboid, 'reactive' cells but not in the ramified ones. We also found that beta 2 microglobulin, already expressed in basal conditions, was dissociated from HLA A-B-C molecules in lymphokine-stimulated cells at early passages. The physiological significance of these data, as well as the possible correlation with in vivo ontogenetic modifications, are also discussed.

Modulatory effects of [Met5]-enkephalin on interleukin-1 beta secretion from microglia in mixed brain cell cultures

In the present study, functional interactions between [Met5]-enkephalin (ME), naloxone and lipopolysaccharide (LPS) on interleukin-1 beta (IL-1 beta) immunostaining and secretion have been assessed in mixed brain cell cultures from embryonic day 17 mice. Adding ME alone or together with LPS to the culture increased the release of IL-1 beta after 48 h in a concentration-dependent fashion. In situ hybridization studies showed that LPS, but not ME, increased the abundance of IL-1 beta mRNA. The enhanced release of IL-1 beta caused by ME or LPS was partially blocked by naloxone. LPS induced concentration-dependent morphological changes in microglia in mixed brain cell cultures, identified by a monoclonal antibody F4/80 which is specific for macrophages/microglia. Despite increasing IL-1 beta release into the media, ME (10(-8) M) did not induce morphological changes in microglia. Naloxone alone also had no effect on glial morphology; however, the LPS-induced morphological changes were blocked by naloxone. Our data indicate that both exogenous and endogenous opioids regulate IL-1 beta production by microglial cells in the mixed brain cell cultures.

Identification of glial cell types involved in mediating epidermal growth factor's effects on septal cholinergic neurons

We found previously that epidermal growth factor (EGF) decreases choline acetyltransferase (ChAT) activity in forebrain cholinergic neurons in vitro indirectly via glia (Kenigsberg et al.: Neuroscience 50: 85-97, 1992). However, which glial type(s) are implicated in this response remained to be determined. Here we report that in primary cultures from the fetal rat medial septal area the complete elimination of oligodendrocytes or partial elimination of microglia from these cultures does not change the cholinergic cell response to EGF. However, the elimination of astroglia in our cultures by alpha-aminoadipic acid treatment blocks EGF's effects on the cholinergic neurons. Co-culture experiments using pure neuronal and purified glial cells from the medial septum further demonstrate that the cholinergic cell response to EGF can be maintained in the presence of astroglia only. In addition, it appears that EGF regulates the release of soluble factors from pure astroglia cultures following their peak mitotic response to EGF that decreases ChAT enzymatic activity. This soluble cholinergic neuromodulatory activity found in conditioned media from EGF-treated astrocytes has a molecular weight greater than or equal to 10 kD and loses potency following multiple freeze-thaw cycles. These results suggest that a direct glial cell response to a specific glial growth factor like EGF may have an important impact on the expression of local neurons, like the cholinergic in the forebrain.

Participation of cAMP and cAMP-dependent protein kinase in beta-adrenoceptor-mediated interleukin-1 beta mRNA induction in cultured microglia

We previously reported evidence of beta-adrenoceptor-mediated induction of IL-1 beta mRNA in the rat hypothalamus. The present in vitro studies using northern blot analysis showed that the beta-adrenoceptor agonist isoproterenol (1 x 10(-8) to 1 x 10(-5) M) caused a marked induction of IL-1 beta mRNA in microglia, but not in astrocytes. This induction was remarkably suppressed by pretreatment of cells with the beta-adrenoceptor antagonist propranolol. These phenomena were confirmed by in situ hybridization with digoxigenin-labelled IL-1 beta RNA probe. Furthermore, dibutyryl cyclicAMP (dbcAMP) (5 x 10(-4) and 5 x 10(-5) M) markedly induced IL-1 beta mRNA in microglia. The intracellular level of cAMP in microglia was elevated in a dose-dependent manner when they were treated with isoproterenol, and this elevation was completely blocked by propranolol. The induction of IL-1 beta mRNA by either isoproterenol or dbcAMP was strongly inhibited by a cAMP-dependent protein kinase inhibitor, H8. These results, taken together, suggest that (1) microglia primarily induce IL-1 beta mRNA by stimulation of beta-adrenoceptors, and (2) cAMP and cAMP-dependent protein kinase presumably participate in a signal transduction mechanism involved in the induction of IL-1 beta mRNA via beta-adrenoceptors.

Mechanisms of damage and repair in multiple sclerosis--a review

Pathological features of MS include perivascular inflammation and demyelination with oligodendrocyte loss; in addition, attempts at remyelination are often unsuccessful and may culminate in astrocytic scarring. One approach to investigating the biological principles underlying these processes is to use in vitro systems to analyse single-cell behaviour as well as cell-cell interactions. This paper reviews such data concerned with cell injury and repair which illuminate both demyelination and remyelination. In tissue culture oligodendrocytes are susceptible to injury via cell-mediated and humoral mechanisms. Substances including complement and tumour necrosis factor are capable of killing rat oligodendrocytes in vitro; surface complement activation also initiates a number of intracellular processes within oligodendrocytes as well as providing ligands for phagocytic interactions. The reasons for oligodendrocyte complement activation are discussed, but it appears that species differences exist when extrapolating these data to humans. Myelination and remyelination can also be studied both in vitro and in vivo using defined cell populations. Results from these studies may eventually help to explain some pathological features of MS, including astrocytosis and factors governing the limits of remyelination.

Activated microglia cause superoxide-mediated release of iron from ferritin

Ferritin contains the greatest part of the iron found in the brain, and the release of iron stores from ferritin has an essential role in iron-dependent lipid peroxidation. We examined the effect of cultured microglia on iron mobilization from ferritin. Microglia stimulated by phorbol myristate acetate caused the release of iron from ferritin, which was detected by monitoring iron-ferrozine complex formation. This iron mobilization was mediated by microglial superoxide production, as evidenced by the significant inhibitory effect of superoxide dismutase. The role of superoxide was also supported by the close correspondence of cumulative microglial superoxide production, as demonstrated by the MCLA (Cypridina luciferin analogue)-dependent chemiluminescence assay, to the time course of iron release from ferritin. Iron release induced by activated microglia may be partly responsible for the oxidative damage that is thought to occur in Parkinson's disease and other neurodegenerative disorders.