Transformation of cells of astrocyte lineage into macrophage-like cells in organotypic cultures of mouse spinal cord tissue

Protective Effect of a cAMP Analogue on Behavioral Deficits and Neuropathological Changes in Cuprizone Model of Demyelination

Multiple sclerosis (MS) is an inflammatory demyelinating disease that leads to neuronal cell loss. Cyclic AMP and its analogs are well known to decrease inflammation and apoptosis. In the present study, we examined the effects of bucladesine, a cell-permeable analogue of cyclic adenosine monophosphate (cAMP), on myelin proteins (PLP, PMP-22), inflammation, and apoptotic, as well as anti-apoptotic factors in cuprizone model of demyelination. C57BL/6J mice were fed with chow containing 0.2% copper chelator cuprizone or vehicle by daily oral gavage for 5 weeks to induce reversible demyelination predominantly of the corpus callosum. Bucladesine was administered intraperitoneally at different doses (0.24, 0.48, or 0.7 μg/kg body weight) during the last 7 days of 5-week cuprizone treatment. Bucladesine exhibited a protective effect on myelination. Furthermore, bucladesine significantly decreased the production of interleukin-6 pro-inflammatory mediator as well as nuclear factor-κB activation and reduced the mean number of apoptotic cells compared to cuprizone-treated mice. Bucladesine also decreased production of caspase-3 as well as Bax and increased Bcl-2 levels. Our data revealed that enhancement of intracellular cAMP prevents demyelination and plays anti-inflammatory and anti-apoptotic properties in mice cuprizone model of demyelination. This suggests the modulation of intracellular cAMP as a potential target for treatment of MS.

Interleukin-1 exerts distinct actions on different cell types of the brain in vitro

Interleukin-1 (IL-1) is a critical neuroinflammatory mediator in the central nervous system (CNS). In this study, we investigated the effect of IL-1 on inducing inflammation-related gene expression in three astrocyte, two microglial, and one brain endothelial cell line. Interleukin-1 beta (IL-1β) is found to be produced by the two microglial cell lines constitutively, but these cells do not respond to IL-1β stimulation. The three astrocyte cell lines responded to IL-1β stimulation by expressing MCP-1, CXCL-1, and VCAM-1, but different subtypes of astrocytes exhibited different expression profiles after IL-1β stimulation. The brain endothelial cells showed strongest response to IL-1β by producing MCP-1, CXCL-1, VCAM-1, ICAM-1, IL-6, and COX-2 mRNA. The induction of endothelial COX-2 mRNA is shown to be mediated by p38 MAPK pathway, whereas the induction of other genes is mediated by the NF-κB pathway. These results demonstrate that IL-1 exerts distinct cell type-specific action in CNS cells and suggest that IL-1-mediated neuroinflammation is the result of the summation of multiple responses from different cell types in the CNS to IL-1.

Neural stem cells in the subventricular zone are a source of astrocytes and oligodendrocytes, but not microglia

The developmental origin of microglia remains a controversial subject. While it is generally accepted that primitive fetal macrophages that migrate from the yolk sac to the brain become microglia, it also has been argued that there is a second source of microglia that are of neuroectodermal lineage. To determine whether progenitors in the dorsolateral subventricular zone (SVZDL) are capable of producing microglia as well as macroglia, we infected perinatal rat SVZDL cells with a mixture of two replication-deficient retroviruses, placed these progenitors in vitro and then varied the media formulations to promote microglial differentiation. Mixed macroglial clones were obtained, but no heterogeneous clones containing microglia were observed, regardless of the media components. Among the macroglial clones, we observed every possible combination of type 1 astrocyte and O-2A lineage cells. Some clones were homogeneous and contained cells belonging to a single macroglial lineage. Other clonal clusters were heterogeneous and were comprised of type 1 astrocytes and oligodendrocytes, type 1 and type 2 astrocytes, or type 2 astrocytes and oligodendrocytes. Of 130 clones examined, where we used triple immunofluorescence with antibodies that recognize microglia, 2 clonal clusters contained OX-42+ microglia that were retrovirally labeled, but all of the cells in those clones expressed the microglial marker and none expressed either GFAP or O4. In addition, we isolated neural stem cells from the perinatal SVZDL and assessed their capacity to generate macroglia and microglia. Confirming and extending our previous analyses, neural stem cells generated homogeneous and heterogeneous macroglial clones, but they did not generate microglia. We conclude that brain macroglia and microglia do not share a common precursor, even though the neural stem cells in the SVZDL cells can produce neurons, astrocytes and oligodendrocytes. Therefore, the microglia that reside in the SVZDL are immigrants from nonneural precursors.

The microglial reaction in spinal cords of jimpy mice is related to apoptotic oligodendrocytes

Jimpy is a shortened life-span murine mutant whose genetic disorder results in a severe hypomyelination in the central neruons system associated with a variety of glial abnormalities, including oligodendrocyte death. In this study, we report that oligodendrocyte death in jimpy occurs through an apoptotic mechanism, as demonstrated by in situ labeling of nuclear DNA fragmentation. Compared to those of normal littermates, the spinal cords of jimpy mice showed a significantly higher number of apoptotic cells. Our observations also corroborate that specific glial cell death in jimpy is restricted to oligodendrocytes, as evidenced by double labeling for DNA fragmentation and MBP immunocytochemistry. Cells labeled for DNA fragmentation were always negative for astroglial or microglial markers. Apoptotic oligodendrocytes were not aggregated into clusters and were ubiquitously distributed throughout the jimpy spinal cord, although were more numerous in white matter than in gray matter. We found no physical association between astrocytes and dying cells in jimpy. Microglial cells, however, were found closely attached to and even surrounding apoptotic cells. The possible role of microglial cells in relation to apoptotsis is discussed.

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.

Cytoplasmic inclusions of astrocytic elements of glial tumors: special reference to round granulated body and eosinophilic hyaline droplets

Round granulated body (RGB) and eosinophilic hyaline droplets (EHDs) have been described as cytoplasmic inclusions of certain astrocytic tumors. In the previous literature, however, these inclusions have been described using various terms or regarded as nosologically the same entity. Light microscopically, RGB appeared as a round discrete body filled with fine uniform granules, while EHDs demonstrated a cluster of bright eosinophilic, round objects of various size. They could be clearly distinguished even by conventional histochemical staining such as the Masson trichrome stain and the phosphotungstic acid hematoxylin preparation. Both RGB and EHDs expressed positive immunoreactions for glial fibrillary acidic protein, several lysosomal markers, and some stress-response proteins. The ultrastructural appearances of these inclusions were distinct, however, one common feature was that they consisted of aggregations of numerous membrane-bound electron-dense bodies. Thus, both inclusions appear to be produced by neoplastic astrocytes and are possibly related to the lysosomal system. We examined the presence of RGB and EHDs in 138 astrocytic tumors. Both inclusions occurred most frequently in pleomorphic xanthoastrocytomas, followed by gangliogliomas and pilocytic astrocytomas. Subependymal giant cell astrocytomas exhibited only RGBs. RGBs and EHDs were not seen in any abundance in glioblastomas, gliosarcomas, fibrillary astrocytomas, protoplasmic astrocytomas, or oligo-astrocytomas. Some glioblastomas, however, showed only EHDs in small numbers. Several anaplastic astrocytomas were associated with a large number of RGBs and/or EHDs, and they revealed only rare mitosis despite marked cellular pleomorphism. Although RGB and EHDs have different morphological features, the presence of these inclusions in abundance may represent either a degenerative change, a long-standing lesion, or an indolent growth of the astrocytic tumors.

Quantitation of perivascular monocytes and macrophages around cerebral blood vessels of hypertensive and aged rats

The numbers of monocytes and macrophages in the walls of cerebral blood vessels were counted on perfusion-fixed frozen brain sections (16 microns) of spontaneously hypertensive rats (SHR), stroke-prone SHR (SHR-SP), normotensive Wistar-Kyoto (WKY) rats, and young (16-week-old) and old (2-year-old) normotensive Sprague-Dawley rats (SD-16w and SD-2y, respectively) using monoclonal antibodies against rat macrophages (ED2). The staining was visualized with fluorescein-labeled second antibodies. The ED2-specific staining in brain sections was restricted to macrophages in a perivascular location. The number of perivascular cells per square millimeter of high-power field was significantly greater in SHR-SP (8.6 +/- 2.1; n = 4) and SHR (6.7 +/- 0.9; n = 6) than in normotensive WKY (4.0 +/- 0.5; n = 6; p < 0.01). The number of perivascular macrophages was also greater in SD-2y (7.5 +/- 2.7; n = 9) than in SD-16w (2.9 +/- 1.8; n = 8; p < 0.01). No ED2 staining was found in the resident microglia or in the endothelial cells, which were identified by double staining with rhodamine-labeled anti-factor VIII-related antigen antibodies. The results suggest that the stroke risk factors hypertension and advanced age are associated with increased subendothelial accumulation of monocytes and macrophages. This accumulation could increase the tendency for the endothelium to convert from an anticoagulant to a procoagulant surface in response to mediators released from these subendothelial cells.

Increased release of tumor necrosis factor-alpha into the cerebrospinal fluid and peripheral circulation of aged rats

BACKGROUND AND PURPOSE

We earlier reported that risk factors for stroke prepare brain stem tissue for a modified Shwartzman reaction, including the development of ischemia and hemorrhage and the production of tumor necrosis factor-alpha, after a provocative dose of lipopolysaccharide. In the present study, we sought to determine whether blood and central nervous system cells of rats with the stroke risk factor of advanced age produce more proinflammatory and prothrombotic mediators than do those of young rats of the same strain.

METHODS

Levels of tumor necrosis factor-alpha and platelet activating factor in the cerebrospinal fluid and tumor necrosis factor-alpha in the serum of 2-year-old and 16-week-old Sprague-Dawley rats were monitored before and after challenge with lipopolysaccharide.

RESULTS

No consistent tumor necrosis factor-alpha activity was found in the cerebrospinal fluid or blood of control animals. Intravenous administration of lipopolysaccharide (1.8 mg/kg) increased serum tumor necrosis factor-alpha levels but had no effect on tumor necrosis factor-alpha in the cerebrospinal fluid. Serum tumor necrosis factor-alpha increased much more in aged rats than in young rats. When lipopolysaccharide was injected intracerebroventricularly, tumor necrosis factor-alpha activity in cerebrospinal fluid increased significantly more in old rats than in young rats. Baseline levels of platelet activating factor in cerebrospinal fluid were significantly higher in old rats than in young rats, and the levels increased to a greater degree in aged rats on stimulation.

CONCLUSIONS

Rats with the stroke risk factor of advanced age respond to lipopolysaccharide with a more exuberant production of tumor necrosis factor-alpha and platelet activating factor than young rats of the same strain. These findings are consistent with our working hypothesis that perivascular cells are capable of exaggerated signaling of endothelium through cytokines such as tumor necrosis factor-alpha in animals with stroke risk factors. The effect of such signaling might be to prepare the endothelium of the local vascular segment for thrombosis or hemorrhage in accord with the local Shwartzman reaction paradigm.

Phagocytosis of myelin by astrocytes in explants of adult rabbit cerebral white matter maintained on Gelfoam matrix

The role of astrocytes in the process of demyelination has been controversial. A culture system in which explants of adult cerebral rabbit white matter were maintained on a Gelfoam matrix was used for evaluating the phagocytosis of myelin by astrocytes without an influx of phagocytic cells derived from actively circulating blood-borne cells. Adult neurons were not viable for more than a few days in these explant cultures, thus resulting in empty myelin sheaths following loss of their axons. After 7 days in vitro, astrocytes, recognized by positivity for glial fibrillary acidic protein by electron microscopic immunocytochemistry, contained numerous membrane-bound vesicles filled with myelin in various stages of degradation. Although the majority of macrophage-like cells were negative for glial fibrillary acidic protein, a minority were positive, in spite of the lack of bundles of intermediate filaments, and were interpreted as astrocytic. Astrocytes were also often positive for glutamine synthetase. This study presents evidence suggesting that astrocytes may actively participate in the phagocytosis and degradation of myelin, a function generally attributed to reactive macrophages.

Microglia progenitor cells: a subpopulation in cultures of mouse neopallial astroglia

We have shown that astroglia cultures initiated from newborn mouse neopallium contain microglia progenitor cells. Astroglia secrete growth factor(s) that transform the progenitor cells into microglia. One of the trophic factors is bone marrow macrophage growth factor CSF-1. Mouse embryonic fibroblast cells STO also secrete trophic factor(s) that acts synergistically or additively with CSF-1 on microglia progenitor cells. Using limiting dilution analysis we estimated that in the presence of CSF-1 and STO cells, 1 in every 8 cells in astroglia cultures is a potential microglia progenitor cell.

Release of proinflammatory and prothrombotic mediators in the brain and peripheral circulation in spontaneously hypertensive and normotensive Wistar-Kyoto rats

BACKGROUND AND PURPOSE

We reported previously that stroke risk factors prepared the brain stem for the development of ischemia and hemorrhage and induced the production of tumor necrosis factor following an intrathecal injection of lipopolysaccharide, a prototypic monocyte-activating stimulus. This study evaluates whether blood or brain cells of hypertensive rats produce more proinflammatory and prothrombotic mediators than do blood or brain cells of normotensive rats.

METHODS

Levels of tumor necrosis factor, platelet-activating factor, 6-ketoprostaglandin F1 alpha, and thromboxane B2 in the cerebrospinal fluid and blood of spontaneously hypertensive and normotensive Wistar-Kyoto rats were monitored before and after a challenge with lipopolysaccharide.

RESULTS

Little or no activity from these mediators was found in the cerebrospinal fluid or blood of saline-injected control animals. Intravenous administration of lipopolysaccharide (0.001, 0.1, and 1.8 mg/kg) produced dose-dependent increases in blood levels of all mediators in hypertensive rats. In normotensive rats the levels were less than in hypertensive rats and were not clearly dose-related. When lipopolysaccharide was injected intracerebroventricularly, more tumor necrosis factor was measured in the cerebrospinal fluid than in the blood, suggesting local synthesis of this cytokine. Levels of tumor necrosis factor and platelet-activating factor in the cerebrospinal fluid were higher in hypertensive than in normotensive rats. The thromboxane A2/prostacyclin ratio was not altered significantly between the two rat strains.

CONCLUSIONS

It is suggested that the higher incidence of brain stem ischemia and hemorrhage after the intrathecal injection of lipopolysaccharide in hypertensive rats than in normotensive rats might be related to the higher levels of the two cytotoxic factors tumor necrosis factor and platelet-activating factor produced in response to such challenge.

Ki-M1P as a marker for microglia and brain macrophages in routinely processed human tissues

The monoclonal antibody Ki-M1P recognizes a formalin/paraffin-resistant differentiation epitope of monocytes and their macrophage derivatives [Radzun et al., Lab Invest 65:306, 1991]. To evaluate its usefulness for neuropathology, we examined a variety of routinely processed tissues using immunohistochemistry. In normal brains, positivity was restricted to ramified microglial cells. Intense labeling of macrophages, ramified and ameboid microglial cells, and rod cells was seen in brains with various degenerative and inflammatory disorders. Astrocytes were negative as determined by double-immunofluorescence labeling using Ki-M1P and anti-glial fibrillary acidic protein (GFAP). Histiocytic lesions (histiocytosis X, xanthogranulomas, granulomatous inflammation) were immunopositive. Among 107 tumors, reactivity of Ki-M1P was observed with some schwannoma and meningioma tumor cells. In addition to macrophages, most gliomas contained small, elongated Ki-M1P-positive cells, which were negative for GFAP. Positivity was also found in two glioblastoma cell lines. Immunoblotting performed on spleen, meningioma and glioblastoma specimens revealed one to three bands in the range of 110 to 130 kDa. We conclude that Ki-M1P can serve as a reliable marker for brain macrophages and microglial cells in routinely processed normal and non-neoplastic tissues, whereas due to the unexpected immunoreactivities results obtained with neoplastic tissues should be carefully interpreted.

Polymorphonuclear leukocytes and monocytes/macrophages in the pathogenesis of cerebral ischemia and stroke

BACKGROUND

The extent to which polymorphonuclear leukocytes and monocytes/macrophages contribute to the pathobiology of cerebral ischemia and stroke is an issue of long-standing contradiction and controversy. Recent developments in the ability to selectively modify leukocyte adhesion with antiadhesion antibodies and the potential clinical application of this therapeutic approach have spurred a resurgence of experimental studies examining the role of leukocytes in cerebral ischemia and stroke.

SUMMARY OF REVIEW

We review studies examining leukocyte accumulation, initiation of thrombosis, and exacerbation of ischemic brain injury in stroke, and we examine other proposed contributions of leukocytes to cerebrovascular pathophysiology.

CONCLUSIONS

The importance of specific characteristics of a given ischemia model and of underlying stroke risk factors in determining the degree of leukocyte involvement and effectiveness of therapies directed against these cells is discussed.

Immunocompetent cell markers in human fetal astrocytes and neurons in culture

During the past few years, evidence has accumulated that interaction with peripheral immune cells as well as immunoregulatory functions in the central nervous system (CNS) can be played by several types of brain resident cells. Since very little information is available in man, however, we investigated the presence of markers so far considered typical of immunocompetent cells in in vitro cultures of human fetal brain. Immunocytochemistry at the light, scanning, and transmission electron microscopic levels revealed positivity for a very restricted range of macrophage antigens in astrocytes, which, however, were incapable of phagocytosis. In particular, expression of the major histocompatibility complex-class II antigen HLA-DR was observed in the cytoplasm and on the cell surface of GFA-P+ astrocytes and increased with time in culture and cell passages. Among the T-lymphocyte markers tested, Thy.1 and CD4 were positive. Both neurons and astrocytes carried Thy.1 from early cell passages. Noteworthy was the presence of CD4, which serves as the receptor for AIDS virus, in neurons from the first 2 weeks, whereas astrocytes became positive after only 4-6 weeks. Even if most staining was in the cytoplasm, some was exposed on cell surface. Astrocytes were found positive for the B-lymphocyte marker CD21, the cellular receptor for Epstein-Barr virus, whereas CD24 was detected in both neurons and astrocytes. Both antigens are related to B-cell proliferation. Results are in favour of the hypothesis of human brain cells being actively involved in CNS immunological events.

The role of swollen astrocytes in human brain lesions after edema--an immunohistochemical study using formalin-fixed paraffin-embedded sections

Swollen astrocytes (SAs) in the white matter after brain edema were immunohistochemically studied in cases with cerebral vascular events, brain tumor and protracted non-missile head injury. SAs showed a decrease in reactivity to glial fibrillary acidic protein (GFAP) and, on the other hand, were positive for laminin, an extracellular matrix glycoprotein known to be secreted by astrocytes. SAs in protracted lesions were strongly positive for both vimentin and plasma proteins including IgG, IgM, C3d and C4d. Remarkable vimentin expression in SAs, instead of GFAP, strongly suggests that SAs are not going to degenerate but are bearing up to regenerate in such circumstances. A number of vimentin-positive buttons also appeared in such protracted lesions, demonstrating disintegration of the processes of SAs. Immunohistochemical detection of plasma proteins in SAs are believed to indicate a facilitated activation in SAs to transform to macrophage-like cells and to act as phagocytes. In addition, demonstration of laminin may suggest hyperactivity of laminin production in SAs after both axonal injury and concomitant edema in order to stimulate neuritic regeneration.

Lipopolysaccharide-induced production of tumor necrosis factor activity in rats with and without risk factors for stroke

Rats produced more TNF activity in cerebrospinal fluid (CSF) than in blood after intracerebroventricular (i.c.v.) injection of lipopolysaccharide (LPS). After intravenous (i.v.) LPS, blood TNF levels exceeded CSF levels. Thus, brain cells appear to produce TNF in response to LPS. Rats with the stroke-risk factors hypertension or combined hypertension and genetic stroke-proneness produce more TNF in response to a provocative dose of LPS i.v. than control animals free of these risk factors. The possible relevance to stroke vulnerability is discussed.

Axonal growth and glial migration from co-cultured hippocampal and septal slices into fibrin-fibronectin-containing matrix of peripheral regeneration chambers: a light and electron microscope study

In order to investigate whether a fibrin-fibronectin-containing matrix of a peripheral regeneration chamber could promote the growth of central nervous system neurons, hippocampal and septal slices were co-cultured in the presence of this acellular substrate. In introducing the peripheral matrix into a 2-mm-long tube between hippocampal and septal slices, a spatio-temporal sequence of cell migration and axonal growth was described by light and electron microscopy. Axons were able to elongate directly into the flocculent material constituting the matrix and a possible neurite-promoting activity was implicated in this process as axonal growth was not detected in direct contact with rat plasma coagulated with calcium, or chicken plasma coagulated with thrombin, used as control matrices. However, in the 3 different substrates tested, astrocytes were able to migrate and dilated astroglial processes containing intermediate filaments were detected. Axonal processes were observed growing on the glial cell surface. GFAP-positive phagocytic cells, that could be of the same origin as astrocytes, were involved in matrix removing. Neuronal growth and glial migration arose from hippocampal and septum slices and acetylcholinesterase-containing fibers were seen in the bridging structure suggesting that cholinergic axons were able to progress to the hippocampal slice. This technique appeared to provide a model in which axonal growth and cell migration can be studied 'in vitro' in a 3-dimensional environment.

Monoclonal antibodies identify three IgG Fc receptors in normal human central nervous system

Functional Fc receptors have been described in the central nervous system (CNS) in the subependymal periventricular regions, leptomeninges, including brain perivascular tissues, and choroid plexus. The distribution of this receptor activity suggests a role in protection of adjacent nervous tissue from IgG-opsonized antigens, including microorganisms. In this report, we have utilized monoclonal antibodies to human Fc gamma RI, II, and III; 32, IV.3, and 3G8, respectively, to immunohistochemically examine the distribution of these receptors in the CNS. Fc gamma RI was only occasionally present in the CNS where it was identified most often in the choroid plexus. Fc gamma RII was the predominant receptor in brain. It as consistently present in leptomeninges, including brain perivascular regions, arachnoid granulations, and choroid plexus stroma. Some samples of subependymal periventricular tissue also displayed Fc gamma RII. Fc gamma RIII was only identified in subependymal periventricular tissue but not in choroid plexus and arachnoid. These results demonstrate that regions of normal adult brain which produce cerebral spinal fluid (CSF) and border on CSF and vascular compartments display Fc gamma R heterogeneity consistent with that of blood monocytes and systemic macrophages.

Lineage relationship between oligodendrocytes and brain macrophages?

Cells which adhere rapidly in vitro were purified from embryonic rat brain and characterized as macrophages. These characterizations rely on (1) phagocytic behaviour, (2) non-specific esterase activity, (3) immunocytochemical criteria such as the detection of CD4, Mac 1 and class II products of the major histocompatibility complex (MHC II). Morphological transformations observed in the cultures and labeling with anti-galactocerebroside (GalC) antibodies suggest a possible transition between brain-macrophagic and oligodendrocytic phenotypes.

Histopathological features of recurrent pleomorphic xanthoastrocytomas: further corroboration of the glial nature of this neoplasm. A study of 3 cases

Pleomorphic xanthoastrocytoma (PXA), a tumor most often presenting superficially over the cerebral hemisphere of young subjects, has certain morphological similarities to fibrous histiocytoma (or fibrous xanthoma) of the meninges and brain, namely the occurrence of lipid-laden neoplastic cells and, frequently, a dense reticulin fiber network. The detection of glial fibrillary acidic (GFA) protein in the tumor cells helped to establish its astrocytic derivation, but it has been advanced that, in spite of this agreed observation, the tumor should still be regarded as a fibrous xanthoma of meningeal origin. Although many patients have a long symptom-free postoperative survival, local recurrences at varying intervals after surgery have been noted in some instances. Weldon-Linne et al. first reported that such a recurrence had the morphology of a small-cell glioblastoma. We are reporting three further examples of locally recurrent neoplasms in patients whose original meningocerebral tumors had the typical features of PXA; the recurrences (developing 7 months, 7 years and 15 years, respectively, after surgery) were small-cell glioblastomas. The rich reticulin network present in the initial tumor was mostly lost in the recurrences. This anaplastic evolution further confirms the astrocytic nature of the PXA.

Multiple sclerosis: effects of activated T-lymphocyte-derived products on organ cultures of nervous tissue

Supernatants from multiple sclerosis (MS) T-lymphocytes cause damage to both myelin and glial cells in cerebellar cultures assessed visually and by radiolabel release. Control T-lymphocytes, even after phytohaemagglutinin (PHA) stimulation, yielded supernatants which induced only slight damage, and at later times patients with other neurological diseases (OND) gave variable results. These differences suggest that MS T-lymphocytes are pre-activated in vivo to produce demyelinating factors while control T-lymphocytes are not pre-activated to the same extent. The visual evidence of activation of cerebellar macrophage-like cells was a common finding after MS T-lymphocyte supernatant treatment but there was no correlation with the severity of demyelination. There was a positive correlation between the percentage IL-2 receptor-bearing lymphocytes and the degree of supernatant-induced in vitro demyelination.

Does the pleomorphic xanthoastrocytoma exist? Problems in the application of immunological techniques to the classification of brain tumors

A case of a fibrous xanthomatous tumor of the meninges is reported. This is a rare tumor of childhood in which the characteristic pleomorphic histology contrasts with the good clinical prognosis. These tumors were reclassified as pleomorphic xanthoastrocytomas (PXA) due to their glial fibrillary acidic protein (GFAP) positivity. In the present tumor, GFAP was absent from nearly all cell bodies in most of the leptomeningeal regions of the tumor but could be detected with greater frequency at the cortical-leptomeningeal border zones and in the areas in which the tumor had infiltrated the cortex. All the tumor cells expressed vimentin and in, addition, most expressed alpha-1-antitrypsin, alpha-1-antichymotrypsin, tartrate-resistant acid phosphatase, common leukocyte antigen, and OKM1. This spectrum of marker staining corresponded not only to the pattern observed in two cutaneous fibrous histiocytomas and one malignant fibrous histiocytoma, but also to the results previously published in the literature with regard to fibrohistiocytic tumors. By contrast, this spectrum of monocytic-histiocytic marker staining was not seen in gliomas. We, therefore, regard the PXA as a mesenchymal tumor of the meninges, identical to benign fibrous histiocytomas elsewhere in the body. The possible reasons why this mesenchymal tumor can show GFAP positivity in the leptomeningeal border zone are discussed.

Demyelination in canine distemper encephalomyelitis: an ultrastructural analysis

A morphological study of selected white matter lesions was carried out in three dogs with canine distemper encephalomyelitis. Two dogs had experimental infections while the third was a spontaneous case. Two stages were identified in the process of demyelination. The earliest evidence of myelin injury was a ballooning change in myelin sheaths involving single or multiple axons. This was followed by a progressive stripping of compact sheaths by the cytoplasmic fingers of phagocytic cells which infiltrated and removed myelin lamellae. Some axonal necrosis also accompanied these changes. Where demyelination occurred, canine distemper viral nucleocapsids were found in astrocytes, macrophages, ependymal cells and infiltrating lymphocytes. In contrast, oligodendrocytes were conspicuous by their apparent lack of infection. Thus it seems that myelin loss cannot be ascribed to oligodendrocyte infection. Perturbed astrocyte function following canine distemper viral infection may cause oedema of myelin sheaths, leading to ballooning and primary demyelination. Cells which phagocytosed myelin were mainly identified as microglial cells with lesser involvement by astrocytes. Rarely, oligodendrocytes also acted as macrophages. Myelin debris was engulfed in bulk or as small droplets into coated pits. Remyelination was present in established plaques although not in great abundance, perhaps due to the diminished oligodendrocyte numbers and a relative increase in immature forms of these cells. These observations are compared to similar changes observed in other demyelinating diseases of animals and man.

Antigen presentation and tumor cytotoxicity by interferon-gamma-treated microglial cells

In this study microglial cells isolated from brain cell cultures of newborn mice were characterized and investigated for morphology, their responses to growth factors and their functional properties. The microglial cells were phagocytic, contained nonspecific esterase activity and expressed Fc (IgG1/2b) and type-3 complement receptors. Scanning electron microscopy revealed that in analogy to brain tissue two types of microglial cells are present in the cultures: the ameboid and the ramified type which both display similar appearance by transmission electron microscopy. Interleukin 3 and the granulocyte-macrophage colony-stimulating factor were potent growth factors for the cultured microglial cells. The cells were negative for class II antigens (Ia) of the major histocompatibility antigen complex. However, upon treatment with interferon-gamma (IFN-gamma) microglial cells became Ia+ and functioned as antigen-presenting cells when tested on ovalbumin-specific Ia-restricted helper T cells. Furthermore, microglial cells exposed to IFN-gamma and endotoxin developed tumor cell cytotoxicity and produced tumor necrosis factor alpha. Taken together, microglial cells share the characteristics of cells of the macrophage lineage.

Astrocytomas: old and newly recognized variants, their spectrum of morphology and antigen expression

The relationship between the morphology of astrocytomas and their prognosis is complex, with the localization of the tumour, the predominant cell type and the degree of anaplasia all playing an important part in determining the patient's future. Since many astrocytomas have a diversity of patterns, small needle biopsies taken from just one or a few areas may fail to elucidate the principal features of a given tumour. In addition to the astrocytoma subtypes listed in the WHO's International Histological Classification of brain tumours, new entities have been observed in the last few years. These include lipidized forms, such as the relatively benign pleomorphic xanthoastrocytoma and the highly malignant lipidized glioblastoma. Neoplastic astrocytes are capable of forming basal laminae and of phagocytosis, and often contain alpha-1-antitrypsin, features that may lead to confusing them with histiocytes. They may be arranged in a whorled pattern imitating meningiomas, their myxoid intercellular stroma may assume the morphology of cartilage and closely packed tumour cells in "epithelioid" astrocytomas come close to imitate metastatic carcinoma. Some astrocytomas contain cells indistinguishable from those of granular cell tumours of other tissues. The presence of reactive lymphocytes in astrocytomas and reactive astrocytes in malignant lymphomas can be the source of confusion between those two kinds of neoplasms.

Leptomeningeal and adventitial gliosis as a consequence of chronic inflammation

Astroglial cell bodies and processes identified ultrastructurally and immunocytochemically are described within the subarachnoid and Virchow-Robin spaces of white matter throughout the CNS of Strain 13 guinea-pigs with chronic relapsing experimental allergic encephalomyelitis. These heterotopic astroglial elements, invariably in close proximity to subpial chronically-demyelinated lesions, were derived from subpial astrocytes and extended for great distances perpendicular and circumferential to the underlying white matter. Subpial astrocytes overlying adjacent grey matter regions appeared unaffected. This phenomenon is probably a subpial astrocyte response to inflammation and demyelination and may be related to the protection of damaged white matter against subsequent inflammatory events.