Immunocompetent cell markers in human fetal astrocytes and neurons in culture

Differentiation of Glial Cells From hiPSCs: Potential Applications in Neurological Diseases and Cell Replacement Therapy

Glial cells are the most abundant cell type in the central nervous system (CNS) and play essential roles in maintaining brain homeostasis, forming myelin, and providing support and protection for neurons, etc. Over the past decade, significant progress has been made in the reprogramming field. Given the limited accessibility of human glial cells, in vitro differentiation of human induced pluripotent stem cells (hiPSCs) into glia may provide not only a valuable research tool for a better understanding of the functions of glia in the CNS but also a potential cellular source for clinical therapeutic purposes. In this review, we will summarize up-to-date novel strategies for the committed differentiation into the three major glial cell types, i.e., astrocyte, oligodendrocyte, and microglia, from hiPSCs, focusing on the non-neuronal cell effects on the pathology of some representative neurological diseases. Furthermore, the application of hiPSC-derived glial cells in neurological disease modeling will be discussed, so as to gain further insights into the development of new therapeutic targets for treatment of neurological disorders.

Differentiation of Inflammation-Responsive Astrocytes from Glial Progenitors Generated from Human Induced Pluripotent Stem Cells

Astrocyte dysfunction and neuroinflammation are detrimental features in multiple pathologies of the CNS. Therefore, the development of methods that produce functional human astrocytes represents an advance in the study of neurological diseases. Here we report an efficient method for inflammation-responsive astrocyte generation from induced pluripotent stem cells (iPSCs) and embryonic stem cells. This protocol uses an intermediate glial progenitor stage and generates functional astrocytes that show levels of glutamate uptake and calcium activation comparable with those observed in human primary astrocytes. Stimulation of stem cell-derived astrocytes with interleukin-1β or tumor necrosis factor α elicits a strong and rapid pro-inflammatory response. RNA-sequencing transcriptome profiling confirmed that similar gene expression changes occurred in iPSC-derived and primary astrocytes upon stimulation with interleukin-1β. This protocol represents an important tool for modeling in-a-dish neurological diseases with an inflammatory component, allowing for the investigation of the role of diseased astrocytes in neuronal degeneration.

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Reliable method for generation of astrocytes from human iPSCs and ESCs

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Generated astrocytes are functional and inflammation-responsive

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Generated astrocytes share properties with primary astrocytes in vitro

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This method is a valuable tool for disease modeling of neuroinflammation

Downregulation of inflammatory markers by conjugated linoleic acid isomers in human cultured astrocytes

OBJECTIVES

Conjugated linoleic acid (CLA) isomers have been shown to possess anti-inflammatory activity in the central nervous system. In this study, we aimed to evaluate whether modulation of the fatty acid profile by the CLA isomers c9,t11 or t10,c12CLA was associated with changes in the expression of pro-inflammatory molecules in human astrocytes.

METHODS

Cultured astrocytes were treated for 6 days with 100 µM fatty acids (c9,t11CLA or t10,c12CLA or oleic acid). Following the treatment, the fatty acid profile of the cell and pro-inflammatory molecule expression were assessed.

RESULTS

Only the t10,c12CLA isomer induced a significant decrease in arachidonic acid and increased the ratio of docosahexaenoic acid/eicosapentaenoic acid, which constitutes indirect evidence of peroxisome proliferator-activated receptor alpha activation. Inhibition of tumour necrosis factor-α, interleukin-1β, and RANTES expression was observed in astrocytes treated with c9,t11CLA and t10,c12CLA.

DISCUSSION

Current data demonstrate that CLA isomers, particularly t10,c12, may affect neuroinflammation by reducing the pro-inflammatory molecules in cultured astrocytes, suggesting a potential nutritional role of CLA isomers in modulating the astrocyte inflammatory response.

The CD24 surface antigen in neural development and disease

A cell's surface molecular signature enables its reciprocal interactions with the associated microenvironments in development, tissue homeostasis and pathological processes. The CD24 surface antigen (heat-stable antigen, nectadrin; small cell lung cancer antigen cluster-4) represents a prime example of a neural surface molecule that has long been known, but whose diverse molecular functions in intercellular communication we have only begun to unravel. Here, we briefly summarize the molecular fundamentals of CD24 structure and provide a comprehensive review of CD24 expression and functional studies in mammalian neural developmental systems and disease models (rodent, human). Striving for an integrated view of the intracellular signaling processes involved, we discuss the most pertinent routes of CD24-mediated signaling pathways and functional networks in neurobiology (neural migration, neurite extension, neurogenesis) and pathology (tumorigenesis, multiple sclerosis).

Astrocyte Differentiation of Human Pluripotent Stem Cells: New Tools for Neurological Disorder Research

Astrocytes have a central role in brain development and function, and so have gained increasing attention over the past two decades. Consequently, our knowledge about their origin, differentiation and function has increased significantly, with new research showing that astrocytes cultured alone or co-cultured with neurons have the potential to improve our understanding of various central nervous system diseases, such as amyotrophic lateral sclerosis, Alzheimer’s disease, or Alexander disease. The generation of astrocytes derived from pluripotent stem cells (PSCs) opens up a new area for studying neurologic diseases in vitro; these models could be exploited to identify and validate potential drugs by detecting adverse effects in the early stages of drug development. However, as it is now known that a range of astrocyte populations exist in the brain, it will be important in vitro to develop standardized protocols for the in vitro generation of astrocyte subsets with defined maturity status and phenotypic properties. This will then open new possibilities for co-cultures with neurons and the generation of neural organoids for research purposes. The aim of this review article is to compare and summarize the currently available protocols and their strategies to generate human astrocytes from PSCs. Furthermore, we discuss the potential role of human-induced PSCs derived astrocytes in disease modeling.

Antidepressant imipramine induces human astrocytes to differentiate into cells with neuronal phenotype

Several recent studies have expanded our conception of the role of astrocytes in neurogenesis, proposing that these cells may contribute to this phenomenon not only as a source of trophic substances, but also as stem cells themselves. We recently observed in vitro that human mature astrocytes can be induced to differentiate into cells with a neuronal phenotype. Antidepressant drugs have been shown to increase neurogenesis in the adult rodent hippocampus. In order to better understand the role of astroglia in antidepressant-induced neurogenesis, primary astrocyte cultures were treated with the antidepressant imipramine. Cell morphology was rapidly modified by treatment. In fact, whereas untreated astrocytes showed large, flat morphology, after a few hours of treatment cells exhibited a round-shaped cell body with long, thin processes. The expression of neuronal markers was analysed by immunocytochemistry, Western Blot and RT-PCR at different treatment times. Results showed an increase in neuronal markers such as neurofilament and neuron-specific enolase (NSE), whereas glial fibrillary acidic protein (GFAP) and nestin expression were not significantly modified by treatment. Similar results were obtained with fluoxetine and venlafaxine. Hes1 mRNA significantly increased after 2 h of treatment, suggesting involvement of this transcription factor in this process. These results confirm the role of astrocytes in neurogenesis and suggest that these cells may represent one of the targets of antidepressants.

O-glycosylation pattern of CD24 from mouse brain

The cell adhesion molecule CD24 is a highly glycosylated glycoprotein that plays important roles in the central nervous system, the immune system and in tumor biology. Since CD24 comprises only a short protein core of approximately 30 amino acids and low conservation among species, it has been proposed that the functions of CD24 are mediated by its glycosylation pattern. Our present study provides evidence that interaction of CD24 with the cell adhesion molecule L1 is mediated by O-linked glycans carrying alpha2,3-linked sialic acid. Furthermore, de-N-glycosylated CD24 was shown to promote or inhibit neurite outgrowth of cerebellar neurons or dorsal root ganglion neurons, respectively, to the same extent as untreated CD24. Therefore, this study is focused on the structural elucidation of the chemically released, permethylated CD24 O-glycans by electrospray ionization ion trap mass spectrometry. Our analyses revealed the occurrence of a diverse mixture of mucin-type and O-mannosyl glycans carrying, in part, functionally relevant epitopes, such as 3-linked sialic acid, disialyl motifs, Le(X), sialyl-Le(X) or HNK-1 units. Hence, our data provide the basis for further studies on the contribution of carbohydrate determinants to CD24-mediated biological activities.

Complement factor H, a marker of self protects against experimental autoimmune encephalomyelitis

The CNS innate immune response is a "double-edged sword" representing a fine balance between protective antipathogen responses and detrimental neurocytotoxic effects. Hence, it is important to identify the key regulatory mechanisms involved in the control of CNS innate immunity and which could be harnessed to explore novel therapeutic avenues. In analogy to the newly described neuroimmune regulatory proteins also known as "don't eat me" signals (CD200, CD47, CD22, fractalkine, semaphorins), we herein identify the key role of complement regulator factor H (fH) in controlling neuroinflammation initiated in an acute mouse model of Ab-dependent experimental autoimmune encephalomyelitis. Mouse fH was found to be abundantly expressed by primary cultured neurons and neuronal cell lines (N1E115 and Neuro2a) at a level comparable to BV2 microglia and CLTT astrocytes. Mouse neurons expressed other complement regulators crry and low levels of CD55. In the brain, the expression of fH was localized to neuronal bodies and axons, endothelial cells, microglia but not oligodendrocytes and myelin sheaths and was dramatically reduced in inflammatory experimental autoimmune encephalomyelitis settings. When exogenous human fH was administered to disease Ab-dependent experimental autoimmune encephalomyelitis animals, there was a significant decrease in clinical score, inflammation, and demyelination, as compared with PBS-injected animals. We found that the accumulation of human fH in the brain parenchyma protected neurons from complement opsonization, axonal injury, and leukocyte infiltration. Our data argue for a key regulatory activity of fH in neuroprotection and provide novel therapeutic avenues for CNS chronic inflammatory diseases.

Glycomic analysis of N-linked carbohydrate epitopes from CD24 of mouse brain

Murine CD24 is an abundantly glycosylated glycoprotein that plays important roles in the central nervous system and the immune system. It has been proposed that the functions of CD24 are primarily mediated by its N- and/or O-linked glycans. Applying a highly sensitive glycomics approach which included matrix-assisted laser-desorption ionization and electrospray ionization ion trap mass spectrometry, we have performed a detailed analysis of the N-linked glycans of CD24. Our data revealed a highly heterogeneous pattern of mainly complex type glycans expressing distinct carbohydrate epitopes, like 3-linked sialic acid, Le(X) or blood group H antigens, bisecting N-acetylglucosamine residues and N-acetyllactosamine repeats as well as high-mannose and hybrid type species.

Human astrocytes can be induced to differentiate into cells with neuronal phenotype

Several recent studies have proposed that astrocytes may contribute to neurogenesis, not only as a source of trophic substances regulating it, but also as stem cells themselves. In order to better understand these mechanisms, primary astrocyte cultures were established from human fetal brain. After 3-4 weeks in culture, astrocytes (about 95% GFAP+; neurofilament, NF-; neuro-specific enolase, NSE-) were treated with a cocktail of protein kinase activators and FGF-1. After 5 h of treatment, most cells showed morphological changes that increased progressively up to 24-48 h, exhibiting a round cell body with long processes. Immunocytochemistry showed that treatment-induced NF and NSE expression in about 40% of cells. Nestin expression increased after treatment, whereas GFAP immunostaining was not significantly modified. Western blot and RT-PCR confirmed the results. No neuronal electrophysiological properties were observed after treatment, suggesting an incomplete maturation under these experimental conditions. Understanding the regenerative capability and neurogenic potential of astrocytes might be useful in devising therapeutic approaches for a variety of neurological disorders.

Differentiation of human adult CD34+ stem cells into cells with a neural phenotype: role of astrocytes

It has recently been reported that adult hematopoietic stem cells can differentiate into neural cells, opening new frontiers in therapy for neurodegenerative diseases. In this study, adult human hematopoietic stem cells (HSCs) were isolated via magnetic bead sorting, using a specific CD34 antibody and cultured with human astrocyte culture conditioned medium (ACM). In order to evaluate their differentiation into neurons and/or astrocytes, ACM-treated cultures were probed for the expression of several neural markers. We observed morphological modifications and, after 20 days of treatment, cell morphology displayed extending processes. Immunocytochemistry, Western blotting and RT-PCR showed the expression of neuronal markers such as neurofilaments, neuron specific enolase (NSE) and NeuN in ACM-treated HSCs cultured in poly-L-lysine-coated dishes. On the contrary, when the same ACM-treated cells were grown on a plastic substrate, they expressed high levels of glial fibrillary acidic protein (GFAP), with only weak expression of neuronal markers. Nestin, a neural progenitor cell marker, was present in treated cells, regardless of the substrate. These results demonstrate that astrocytes can generate a suitable microenvironment for inducing HSCs to differentiate into neural cells. Therefore, adult bone marrow may represent a readily accessible source of cells for treating neurodegenerative diseases.

Identification of Epstein-Barr virus proteins as putative targets of the immune response in multiple sclerosis

MS is a chronic inflammatory and demyelinating disease of the CNS with as yet unknown etiology. A hallmark of this disease is the occurrence of oligoclonal IgG antibodies in the cerebrospinal fluid (CSF). To assess the specificity of these antibodies, we screened protein expression arrays containing 37,000 tagged proteins. The 2 most frequent MS-specific reactivities were further mapped to identify the underlying high-affinity epitopes. In both cases, we identified peptide sequences derived from EBV proteins expressed in latently infected cells. Immunoreactivities to these EBV proteins, BRRF2 and EBNA-1, were significantly higher in the serum and CSF of MS patients than in those of control donors. Oligoclonal CSF IgG from MS patients specifically bound both EBV proteins. Also, CD8(+) T cell responses to latent EBV proteins were higher in MS patients than in controls. In summary, these findings demonstrate an increased immune response to EBV in MS patients, which suggests that the virus plays an important role in the pathogenesis of disease.

S100b counteracts effects of the neurotoxicant trimethyltin on astrocytes and microglia

Central nervous system degenerative diseases are often characterized by an early, strong reaction of astrocytes and microglia. Both these cell types can play a double role, protecting neurons against degeneration through the synthesis and secretion of trophic factors or inducing degeneration through the secretion of toxic molecules. Therefore, we studied the effects of S100B and trimethyltin (TMT) on human astrocytes and microglia with two glial models, primary cultures of human fetal astrocytes and a microglia cell line. After treatment with 10(-5) M TMT, astrocytes showed morphological alterations associated with an increase in glial fibrillary acidic protein (GFAP) expression and changes in GFAP filament organization. Administration of S100B before TMT treatment prevented TMT-induced changes in morphology and GFAP expression. A decrease in inducible nitric oxide synthase expression was observed in astrocytes treated with TMT, whereas the same treatment induced iNOS expression in microglia. In both cases, S100B prevented TMT-induced changes. Tumor necrosis factor-alpha mRNA expression in astrocytes was not modified by TMT treatment, whereas it was increased in microglia cells. S100B pretreatment blocked the TMT-induced increase in TNF-alpha expression in microglia. To trace the mechanisms involved in S100B activity, the effect of BAY 11-7082, an inhibitor of nuclear factor-kappaB (NF-kappaB) activation, and of PD98059, an inhibitor of MEK-ERK1/2, were investigated. Results showed that the protective effects of S100B against TMT toxicity in astrocytes depend on NF-kappaB, but not on ERK1/2 activation. These results might help in understanding the role played by glial cells in brain injury after exposure to chemical neurotoxicants and support the view that S100B may protect brain cells in case of injury. (c) 2005 Wiley-Liss, Inc.

Dystrophin antisense oligonucleotides decrease expression of nNOS in human neurons

Nitric oxide (NO) plays an important role in the pathogenesis of neurodegenerative disease. It has been shown that neuronal NO synthase (nNOS), the enzyme that constitutively produces NO in brain, is a component of the dystrophin-associated protein complex. The absence of dystrophin causes Duchenne muscular dystrophy. Thus, we attempted to study whether or not a decrease of dystrophin expression would induce a modification in nNOS expression in cultured human neurons. Human fetal neuronal cultures were treated with antisense oligonucleotides against different isoforms of dystrophin and the expression of nNOS tested by RT-PCR and immunocytochemistry. Results showed that nNOS mRNA was significantly decreased by about 35% in neurons treated with brain-specific dystrophin (brain Dp427) antisense, whereas iNOS expression was not affected. Accordingly, a decrease in immunostaining for nNOS was observed in antisense treated neurons compared to controls. Expression of neuronal markers, such as bFGF or synaptophysin, was not affected by the same antisense treatment. Astrocytes were not affected by treatment, as shown by utrophin expression, a dystrophin-like protein that was not modified in pure astrocytic cultures. Thus, we conclude that a decrease of dystrophin in human neurons is associated with a decrease of nNOS expression.

Expression of CD137 and its ligand in human neurons, astrocytes, and microglia: modulation by FGF-2

CD137 (ILA, 4-1BB), a member of the tumor necrosis factor receptor family, and its ligand CD137-L were assayed by RT-PCR and immunocytochemistry in cultured human brain cells. Results demonstrated that both neurons and astrocytes expressed specific RNA for CD137 and its protein, which was found both on the plasma membrane and in the cytoplasm. Surprisingly, microglia, which also expressed CD137 mRNA, showed negative immunostaining. CD137-L-specific RNA was detected only in astrocytes and neurons. When brain cells were treated with fibroblast growth factor-2 (FGF-2), upregulation of CD137 but not of its ligand was observed in neurons and astrocytes. Protein localization was also affected. In microglia, an inhibition of RNA expression was induced by treatment, whereas CD137-L remained negative. Our data are the first demonstration that human brain cells express a protein found thus far in activated immunocompetent cells and epithelia. Moreover, they suggest not only that CD137 and CD137-L might play a role in interaction among human brain cells, but also that FGF-2 might have an immunoregulatory function in brain, modulating interaction of the central nervous system with peripheral immunocompetent cells.

Cultured astrocytes react to LPS with increased cyclooxygenase activity and phagocytosis

Phagocytosis and prostaglandin E(2) production were investigated in purified cultures of perinatal rat forebrain astrocytes. Light and electron microscopic data indicated that astrocytes respond to bacterial endotoxin, lipopolysaccharide (LPS) by increased phagocytosis and by activating the cyclooxygenase enzyme-pathway. LPS-inducible phagocytosis of astrocytes was demonstrated by electron microscopic studies on colloidal gold uptake and by photometric determination of fluorescent bead ingestion. The internalisation of fragments of the plasma membrane was shown by histochemical detection of membrane-bound ecto-ATPase activity within intracellular vesicles. Activation of the cyclooxygenase pathway, a characteristic reaction of immune cells under inflammatory conditions, was also detected in astroglial cells upon treatment with LPS. The increased prostaglandin E(2) (PGE(2)) production by astrocytes in response to LPS was reduced by the non-steroid anti-inflammatory drug, indomethacin. Our data indicate that astrocytes display some tissue-protective reactions in response to inflammation inducing factors, even in the absence of peripheral immune cells or central microglia. The role of inducible astrocytic phagocytosis in a non-immune protection-pathway is discussed.

Interleukin-1beta induces expression of neuropeptide Y in primary astrocyte cultures in a cytokine-specific manner: induction in human but not rat astrocytes

Previous studies have demonstrated that astrocyte cultures express neuropeptide Y (NPY) in a regulated manner, namely, phorbol ester leads to an increase in proNPY-mRNA and NPY production. In this respect, the behavior of astrocytes derived from the human fetal or rat neonatal brain is similar (Regul. Pept. 75 (1998) 293). Since astrocytes can be exposed to high levels of IL-1beta, we addressed the question: Does IL-1beta regulate NPY expression by the astrocytes? Primary astrocytes derived from the human fetal or rat neonatal cortex were cultured in serum-free medium. IL-1beta, but not IL-6 or TNF-alpha, led to an increase in NPY production dose-dependently. IL-1beta action manifested in the human but not in the rat astrocytes and it was completely abolished by IL-1 receptor antagonist. The responsiveness to IL-1beta did not diminish upon sub-culture of the astrocytes (five passages). In addition, IL-1beta led to an increase in the abundance of proNPY-mRNA, which was preceded by a rapid and transient increase in cFos-mRNA and a rapid and sustained increase in JunB-mRNA. In contrast to cFos/JunB, IL-1beta did not alter the abundance of cJun-mRNA. In summary, we demonstrate that IL-1beta induction of NPY expression in astrocytes is species- and cytokine-specific and that IL-1 receptor is involved. Moreover, induction of NPY expression is preceded by a rapid increase in the expression of two transcription factors (cFos, JunB) that have been previously (Oncogene 9 (1994) 2369; J. Neurochem. 70 (1998) 1887) implicated in transcriptional regulation of the human NPY gene.

Evidence for regulated expression of neuropeptide Y gene by rat and human cultured astrocytes

A series of studies from our laboratory have established that fetal rat and human neuropeptide Y (NPY) cortical neurons in aggregate cultures are differentially regulated. In a preliminary study we found that primary astrocytes produce substantial amounts of immunoreactive (IR) NPY. We addressed the question: Is astrocyte production of NPY-IR a regulated process? The effects of brain-derived neurotrophic factor (BDNF, 50 ng/ml), basic fibroblast growth factor (bFGF), substance P (1 microM), forskolin (10 microM), or phorbol 12-myristate-13-acetate (PMA, 20 nM) on NPY-IR production was tested on rat and human primary astrocyte cultures. Of these agents, PMA and bFGF markedly induced NPY-IR production by rat as well as human astrocytes, forskolin induced NPY-IR production by human but not rat astrocytes, and neither BDNF nor substance P induced NPY-IR production by rat or human astrocytes. The molecular size of PMA-induced NPY-IR was found to be consistent with that of proNPY. Moreover, PMA induced the accumulation of mRNA corresponding in size to the neuronal NPY-mRNA. Immunocytochemical analysis of human post-mortem neocortex revealed co-existence of NPY-IR with astrocyte markers. These results indicate that cultured astrocytes express NPY gene in a regulated manner and they support our proposition that in situ reactive astrocytes may express NPY gene under some physiological/pathological conditions.

Complement receptors in HIV infection

The complement system plays an important role in the antimicrobial defense of the organism. Its components recognize a large variety of pathogens and target them for destruction, either directly by formation of a membrane attack complex or indirectly by recruiting phagocytic cells. In addition, it has several functions in cell activation, clearance of immune complexes, control of inflammatory reactions, chemotaxis and autoimmunity. For mediation of all these tasks of the complement system, complement receptor molecules on the cell surface play a key role. Current knowledge on structure, function, signal transduction and associated molecules is briefly summarized here. The role of complement receptors for human immunodeficiency virus (HIV)-associated pathogenesis is ambiguous and varies depending on cell type. On the one hand, complement receptors support the infected host to manage HIV infection and to defend itself, at least partially, against viral spreading throughout the organism. Such complement receptor-mediated supporting mechanisms are activation of immune cells and lysis of viral particles and infected host cells. On the other hand, HIV employs complement receptors to intrude more easily into various cell types, to become localized into lymph follicles and to activate viral replication in latently infected cells. This review summarizes the complex interaction of virus and complement receptors in HIV infection for different cell types.

Effect of dystrophin antisense oligonucleotides on cultured human neurons

Antisense oligonucleotides offer the potential to block the expression of specific molecules within the cell, thus providing a useful tool in cell function studies. In this paper, we tested the possibility to block dystrophin expression in in vitro cultured neurons with antisense oligonucleotides administration. Human fetal neuronal cultures were treated with different doses of antisense oligonucleotides against dystrophin, the protein coded by the Duchenne muscular dystrophy gene. Results showed that labelled oligonucleotides rapidly accumulated into cultured neurons, but were discarded 15-24 h after treatment. However, no effects could be observed until 3-4 days after treatment, when immunocytochemical staining for dystrophin was significantly decreased in treated neurons. This result was confirmed by polymerase chain reaction assay which showed a significantly lower expression of the dystrophin specific mRNA. Electron microscope observations confirmed that neurons were affected. Large inclusions or packed granules were detectable in their cytoplasm and in terminal endings. Neuronal nuclear membrane was sometimes shredded, so that nuclear shape was altered. These phenomena were dose-dependent, further substantiating the hypothesis of a specific effect of antisense treatment. This interpretation was supported by the absence of alterations when cultures were treated with mismatch or non specific antisenses. Since the function of dystrophin is still unknown, these data might help in understanding the role played by this protein in the developing brain.

Characterization of glial cultures from rapid autopsies of Alzheimer's and control patients

We have developed isolated and mixed cultures of microglia, astrocytes, and oligodendrocytes from rapid (mean of 2 h 55 min) autopsies of nondemented elderly patients and patients with Alzheimer's disease, Parkinson's disease, and multiple sclerosis. Cultures were derived from both the corpus callosum (CC) and superior frontal gyrus (SFG). Cultured microglia phagocytosed latex beads, were reactive for Dil-acetylated low density lipoprotein, were immunoreactive for CD68 and major histocompatibility complex II markers, and were not immunoreactive for fibroblast, astrocyte, or oligodendrocyte markers. Cultured astrocytes included fibrous and protoplasmic types, were immunoreactive for GFAP, and were not immunoreactive for fibroblast, microglia, or oligodendrocyte markers. Cultured oligodendrocytes were poorly adherent, were slow to develop, were immunoreactive for galactocerebroside, and were not immunoreactive for fibroblast, microglia, or astrocyte markers. Because they are readily manipulated under controlled experimental conditions, and because they permit immediate access to individual cells and sets of cells from patients who have actually suffered the disease, these cultures may provide an important new tool for unravelling the etiology and pathogenesis of human CNS disorders.

Human ramified microglial cells produce nitric oxide upon Escherichia coli lipopolysaccharide and tumor necrosis factor alpha stimulation

This study shows that human ramified microglial cells derived from fetal brain primary cultures, are able to produce nitric oxide (NO). In fact, stimulation with Escherichia coli lipopolysaccharide (LPS) (1 microgram ml-1) or tumor necrosis factor alpha (TNF alpha) (500 U ml-1) enhances nitrite release in cell supernatants, as determined by the Griess reaction. A synergistic effect is achieved following treatment with LPS plus TNF alpha, this effect being inhibited by pretreating cells with NOS inhibitor N omega-nitro-L-arginine methyl ester (L-NAME). Using reverse transcriptase-polymerase chain reaction (RT-PCR) and Southern blot analysis, we also found that LPS/TNF alpha produce an increase of inducible NO synthase (iNOS) mRNA expression.

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.