Central Nervous System Parenchyma Research Articles

Microglia induce CD4 T lymphocyte final effector function and death.

Microglia, a type of tissue macrophage, are the only cells in the central nervous system (CNS) parenchyma to express some major histocompatibility complex (MHC) class II constitutively or to upregulate expression readily. They are thought to play a role in CD4 T cell activation in autoimmune diseases such as multiple sclerosis, as well as in neurodegenerative conditions, Alzheimer's disease in particular. We show here that highly purified MHC class II+ microglia when tested directly ex vivo do indeed support an effector response by an encephalitogenic myelin basic protein-reactive CD4 T cell line from which production of the proinflammatory cytokines, interferon gamma and tumor necrosis factor, is elicited, but not interleukin (IL)-2 secretion or proliferation. After this interaction, the T cells die by apoptosis. Other nonmicroglial but CNS-associated macrophages isolated in parallel stimulate full T cell activation, including IL-2 production, proliferation, and support T cell survival. Neither CNS-derived population expresses B7.1/B7.2. Resident macrophages that terminate effector T cells in tissues constitute a novel and broadly applicable regulatory measure of particular relevance to processes of self-tolerance against sequestered antigens.

Nature and sequence of simian immunodeficiency virus-induced central nervous system lesions: a kinetic study.

To determine the onsets and specificities of neuropathological features observed after simian immunodeficiency virus (SIV) infection of macaques, brains of 19 clinically unaffected rhesus monkeys (group A) were examined after intervals ranging from 1 to 48 weeks post-infection and compared to 8 animals with AIDS (group B) as well as to 8 uninfected controls. Based on morphological and virological parameters, seven patterns specific for SIV infection of the central nervous system (CNS) were discerned. In both groups of infected but not control animals, we found mononuclear aggregates in meninges, perivascular space, and choroid plexus stroma (designated pattern 1), isolated infected cells within CNS parenchyma (pattern 2), axonal degeneration (pattern 3), spongy change (pattern 4), microglial proliferation (pattern 5), and small vessel proliferation (pattern 6). SIV encephalitis (pattern 7) was only evident in animals with clinically evident disease. Changes characteristic of patterns 3, 5 and 6 appeared to be chronic and non-progressive, whereas lesions of patterns 1, 2 and 4 appeared to have progressed in animals with AIDS. The main component of mononuclear aggregates in animals of group A were lymphocytes, in contrast to animals of group B, in which macrophages dominated the inflammatory infiltrates. Altogether, our results demonstrate that subtle leukoencephalopathy was a specific feature of clinically silent as well as clinically evident phases of SIV infection. This might explain the neurological impairment of HIV-positive non-AIDS individuals.

Characterization of CD4−CD8− T cell receptor αβ+ T cells appearing in the subarachnoid space of rats with autoimmune encephalomyelitis

Inflammation of the central nervous system (CNS) in experimental autoimmune encephalomyelitis (EAE) starts in the subarachnoid space (SAS) and spreads later to the adjacent CNS parenchyma. To characterize the nature of lesion-forming T cells in situ in more detail, T cells were isolated from the SAS and their surface phenotype and the nucleotide sequence of the junctional region of the T cell receptor (TCR) was determined and compared with those of the lymph node (LN) and spinal cord (SC) T cells. Characteristically, more than 70% of SAS TCR alpha beta + T cells isolated at the early stage of EAE lacked both CD4 and CD8 molecules, whereas those from LN and SC were either CD4+ or CD8+. Analysis of nucleotide sequences of the junctional region of TCR revealed that T cells bearing a sequence identical to that for encephalitogenic T cell clones were found in both SAS and SC. Furthermore, purified CD4-CD8- T cells expressed CD4 molecules after culture. At the same time, these T cells acquired reactivity to myelin basic protein and induced passive EAE in naive animals after adoptive transfer. Our results suggest that CD4-CD8- T cells in the SAS are precursors of lesion-forming T cells in the SC and that phenotype switching takes place during the process of T cell infiltration into the CNS parenchyma. The double-negative nature of these T cells may explain an escape of encephalitogenic T cells from negative selection in T cell differentiation.

Chemokines in immune-mediated inflammation of the central nervous system

Inflammatory cell recruitment to the central nervous system (CNS) is a cardinal feature of physiological and pathological processes, including multiple sclerosis (MS). Despite recent progress, the soluble signals that attract inflammatory cells from the vascular compartment into the CNS parenchyma remain obscure. We favor the hypothesis that chemoattractant cytokines termed ‘chemokines’ are uniquely important for mediating leukocyte entry into CNS tissues during immunemediated inflammation. Three lines of evidence supporting this hypothesis will be reviewed. The first regards expression of chemokines in animal models of immune-mediated CNS inflammation and in the human disease, multiple sclerosis. The second line of evidence involves interventional studies of chemokine blockade in such model disorders. The third line of evidence comprises function of chemokines in the CNS, as analysed in transgenic mice. Investigation of CNS chemokine function will enhance our understanding of leukocyte recruitment to the CNS and suggest therapeutic strategies for neurological disorders.

Immune control of the brain.

Immunosurveillance of the brain is the result of elaborate cellular interactions. As the first step in the process of immune surveillance, T lymphocytes of the immune system control the integrity of the central nervous system (CNS) parenchyma. They enter the brain in search of pathogens, and recruit CNS cells as antigen-presenting cells. Upon contact with “their” specific antigens, they initiate local immune responses. Then, in a second step, cells of the local glia and of the immune system communicate bidirectionally with each other and interact to jointly control the immune reactivity within the CNS.

Spontaneous inflammatory demyelinating disease in transgenic mice showing central nervous system-specific expression of tumor necrosis factor alpha.

Cytokines are now recognized to play important roles in the physiology of the central nervous system (CNS) during health and disease. Tumor necrosis factor alpha (TNF-alpha) has been implicated in the pathogenesis of several human CNS disorders including multiple sclerosis, AIDS dementia, and cerebral malaria. We have generated transgenic mice that constitutively express a murine TNF-alpha transgene, under the control of its own promoter, specifically in their CNS and that spontaneously develop a chronic inflammatory demyelinating disease with 100% penetrance from around 3-8 weeks of age. High-level expression of the transgene was seen in neurons distributed throughout the brain. Disease is manifested by ataxia, seizures, and paresis and leads to early death. Histopathological analysis revealed infiltration of the meninges and CNS parenchyma by CD4+ and CD8+ T lymphocytes, widespread reactive astrocytosis and microgliosis, and focal demyelination. The direct action of TNF-alpha in the pathogenesis of this disease was confirmed by peripheral administration of a neutralizing anti-murine TNF-alpha antibody. This treatment completely prevented the development of neurological symptoms, T-cell infiltration into the CNS parenchyma, astrocytosis, and demyelination, and greatly reduced the severity of reactive microgliosis. These results demonstrate that overexpression of TNF-alpha in the CNS can cause abnormalities in nervous system structure and function. The disease induced in TNF-alpha transgenic mice shows clinical and histopathological features characteristic of inflammatory demyelinating CNS disorders in humans, and these mice represent a relevant in vivo model for their further study.

Evolution of neuropathologic abnormalities associated with blood-brain barrier breakdown in transgenic mice expressing interleukin-6 in astrocytes.

As both astrocytes and cytokines modulate the permeability of cerebral endothelial cells, transgenic animal models which overexpress cytokines, such as interleukin-6 (IL-6), may provide insight into the neuropathological consequences of increased BBB permeability. In this study, a GFAP-IL6 transgenic mouse model and horseradish peroxidase (HRP) were used to investigate BBB permeability and associated neuropathologic changes. In the cerebellum of control mice, the BBB developed between postnatal days 7 and 14. In transgenic mice, the BBB never developed and extensive breakdown was evident in both high- and low-expressor animals by 1 month after birth. Vascular proliferation was apparent from birth in association with development and retention of normal cerebellar architecture until 3 and 6 months in high- and low-expressor animals, respectively. At these times, a leptomeningeal inflammatory infiltrate, vacuolated astrocytic foot processes and endothelial abnormalities were apparent in the cerebellum. At 6 months in high-expressor and 12 months in low-expressor animals, parenchymal inflammation, gliosis, spongiform change, axonal degeneration and macrophage accumulation were evident. The findings suggest that increased production of IL-6 can influence the development and physiologic function of the BBB as well as contribute to parenchymal central nervous system injury.

Neuroborreliosis

Lyme disease is a multisystem infectious disease with frequent nervous system involvement. It affects peripheral nerves, the meningeal lining of the central nervous system (CNS), and the CNS parenchyma, but the underlying pathophysiology remains unclear. Considerable data suggest that dividing Lyme neuroborreliosis into early and late disease stages, as has been done with syphilis--the other well-known spirochetosis that affects the nervous system--lacks pathophysiologic validity. Early CNS seeding has been demonstrated, however, and lymphocytic meningitis and facial paralysis tend to occur relatively early in infection, although radiculoneuropathy and cranial neuropathies may also occur later. Less fulminant forms of peripheral nerve or CNS involvement may present later in the disease course. Encephalomyelitis may occur early or late but is rare; encephalopathy is far more common and tends to occur in patients with evidence of systemic (but not necessarily CNS) Lyme disease. Diagnosis of CNS infection has been difficult, and most studies have relied on indirect methods. Demonstration of intrathecal production of anti-Borrelia burgdorferi antibodies provides the strongest evidence, but correction for the amount of peripheral blood immunoreactivity to B. burgdorferi that crosses the blood-brain barrier is essential. Newer technologies have been applied in an effort to improve detection of B. burgdorferi itself--polymerase chain reaction may provide a sensitive tool for organism detection to complement immunologic techniques. The optimal treatment regimen for Lyme disease has not been defined, but a course of ceftriaxone (2 g/day) or cefotaxime (6 g/day) for 3-4 weeks is commonly prescribed. Intravenous penicillin and oral doxycycline (200 mg/day) for 2 weeks have been used successfully to treat Lyme meningitis, but these results require confirmation.

Do chemokines mediate inflammatory cell invasion of the central nervous system parenchyma?

Inflammatory cell recruitment into the central nervous system (CNS) is a critical step in the response to diverse insults, including infection, trauma and infarction, as well as immune-mediated disorders such as multiple sclerosis (MS). Despite considerable advances in understanding immune surveillance and antigen recognition in the CNS, the signals resulting in parenchymal inflammation are incompletely understood. Members of a novel family of chemo-attractant cytokines, the chemokines, are made in the CNS and are emerging as likely mediators of inflammatory cell migration into the CNS.

Boron neutron capture therapy: A guide to the understanding of the pathogenesis of late radiation damage to the rat spinal cord

Purpose : Before the commencement of new boron neutron capture therapy (BNCT) clinical trials in Europe and North America, detailed information on normal tissue tolerance is required. In this study, the pathologic effects of BNCT on the central nervous system (CNS) have been investigated using a rat spinal cord model. Methods and Materials : The neutron capture agent used was 'B enriched sodium mercaptoundecahydro-closododecaborate (BSH), at a dosage of 100 mg/kg body weight. Rats were irradiated on the thermal beam at the Brookhaven Medical Research Reactor. The large spine of vertebra T 2 was used as the lower marker of the irradiation field. Rats were irradiated with thermal neutrons alone to a maximum physical absorbed dose of 11.4 Gy, or with thermal neutrons in combination with BSH, to maximum absorbed physical doses of 5.7 Gy to the CNS parenchyma and 33.7 Gy to the blood in the vasculature of the spinal cord. An additional group of rats was irradiated with 250 kVp X rays to a single dose of 35 Gy. Spinal cord pathology was examined between 5 and 12 months after irradiation. Results : The physical dose of radiation delivered to the CNS parenchyma, using thermal neutron irradiation in the presence of BSH, was a factor of two to three lower than that delivered to the vascular endothelium, and could not account for the level of damage observed in the parenchyma. Conclusion : The histopathological observations of the present study support the hypothesis that the blood vessels, and the endothelial cells in particular, are the critical target population responsible for the lesions seen in the spinal cord after BNCr type irradiation and by inference, after more conventional irradiation modalities such as photons or fast neutrons.

The role of the blood-brain barrier in HIV infection of the central nervous system

The blood-brain barrier (BBB) functions to regulate the entry of macromolecules, microbial pathogens, and circulating leukocytes into the central nervous system (CNS). It consists, in part, of the microvascular endothelium and associated astrocyte foot processes, found in close apposition to the abluminal side of the vascular endothelial cells (EC). During the pathogenesis of certain nervous system diseases with inflammatory components, the BBB may function to facilitate the entry of leukocytes into the CNS parenchyma. A common histologic observation in human immunodeficiency virus type-1 (HIV) encephalitis is the localization of HIV proteins to multinucleated giant cells that co-immunolabel with antibodies specific for cells of the monocyte/macrophage lineage, suggesting that HIV can enter the CNS as cell-associated virus. We previously characterized a tissue culture model of the BBB that consists of the co-culture of autologous EC and astrocytes. In this presentation, we used this model to examine the expression of adhesion molecules by both the EC and astrocyte components of this BBB model, and to characterize the interactions between HIV-infected monocytes and EC. The data presented in this review of our work demonstrates that astrocytes upregulate the expression of intercellular adhesion molecule (ICAM-1) by EC. In a parallel study, western blot analysis demonstrated that ICAM-1 is also expressed in the developing human CNS. When exposed to the proinflammatory cytokine tumor necrosis factor alpha (TNF), both EC cocultured with astrocytes and astrocytes cultured alone expressed the adhesion proteins IG9, ICAM-1, vascular cell adhesion molecule 1 (VCAM) and E-selection.(ABSTRACT TRUNCATED AT 250 WORDS)

Macrophages and inflammation in the central nervous system.

Acute inflammation plays an important role in host tissue defense against injury and infection, and also subsequent tissue repair. In the central nervous system parenchyma, following many types of insults, the acute inflammatory response to rapid neuronal degeneration or challenge with inflammatory substances differs dramatically from that of other tissues. The rapid recruitment of neutrophils is virtually absent and monocytes are only recruited after a delay of several days. It appears that the microenvironment of the central nervous system has evolved mechanisms to protect it from the potentially damaging consequences of some aspects of the acute inflammatory response.

Differential expression of MHC class II antigen in the contused rat spinal cord.

Following contusion injury to the dorsal surface of thoracic rat spinal cord, major histocompatibility complex (MHC) class II (Ia) antigen expression by microglia was evaluated throughout the developing lesion. Past investigations of various central nervous system (CNS) lesions have examined short-term or acute sequelae of post-traumatic Ia expression. This report demonstrates that in animals allowed to recover for 18 (sub-chronic) and 45 (chronic) days post-injury, MHC class II antigen is expressed differently at rostral and caudal extents of the lesion as compared with the lesion's epicenter. Following contusion injury to the thoracic spinal cord, sub-chronically injured animals demonstrated Ia-positive microglial staining throughout the white matter rostral and caudal to the epicenter of the lesion, whereas Ia-positive microglia and/or perivascular cells are localized within the gray matter adjacent to it. MHC class II immunoreactivity is down-regulated on microglia at chronic survival times but clusters of Ia-positive macrophages are prominent in regions of maximal degeneration at the epicenter of the lesion. Our findings support the theory that two distinct populations of macrophages participate in resolving traumatic injury. One population is the parenchymal CNS microglia and the other is presumably exudate macrophages derived from the blood. Furthermore, the immunocompetence of these cells as measured by MHC expression may be differentially regulated. This hypothesis is based on differences in Ia-positive staining observed between microglia and macrophages over time concomitant with differences in the spatial distribution of these cell types.

Intracerebral injection of proinflammatory cytokines or leukocyte chemotaxins induces minimal myelomonocytic cell recruitment to the parenchyma of the central nervous system.

Neither excitotoxic neurodegeneration nor lipopolysaccharide induces an acute myelomonocytic exudate in the murine central nervous system (CNS) parenchyma (Andersson, P.-B., V. H. Perry, and S. Gordon. 1991. Neuroscience, 42:201; Andersson, P.-B., V. H. Perry, and S. Gordon. 1992. Neuroscience 48:169). In this study formyl-methionyl-leucyl-phenylalanine, platelet-activating factor, interleukin 8 (IL-8), IL-1, or tumor necrosis factor alpha were injected into the hippocampus to assess whether these leukocyte chemotaxins and known mediators of recruitment could bypass this block. They induced morphologic activation of microglia and widespread leukocyte margination but little or no cell exudation into the CNS parenchyma. By contrast, there was acute myelomonocytic cell recruitment to the choroid plexus, meninges, and ventricular system, comparable to that in the skin after subcutaneous injection. The normal CNS parenchyma appears to be a tissue unique in its resistance to leukocyte diapedesis, which is shown here to be at a step beyond chemotactic cytokine secretion or induction of leukocyte adhesion to cerebral endothelium.

Experimental cerebrospinal elaphostrongylosis (Elaphostrongylus rangiferi) in goats: II. Pathological findings.

Pathological findings in 17 goat kids inoculated with 100-1,000 infective larvae of Elaphostrongylus rangiferi and autopsied 21-154 days post inoculation (p.i.) are reported. The lungs, heart, diaphragm, liver and kidneys contained small foci of necrosis or fibroblastic scarring and interstitial infiltrates of inflammatory cells. The lungs also contained many parasitic granulomas. Infarcts were observed in the myocardium and kidneys. Accumulations of inflammatory cells and granulomas were seen in the peri- and epineurium of the spinal nerve roots, connective tissue of the spinal ganglia, dura and epidural tissue of the cord, choroid plexus of the brain and leptomeninges of the entire central nervous system (CNS). Within nerve fascicles there were endoneural cell infiltrates, axon and myelin sheath degenerations and granulomas. The CNS parenchyma contained foci of traumatic encephalomyelomalacia, microgliosis, secondary axon degeneration, perivascular cuffs and granulomas. Sections of intact nematodes were found in the subarachnoid spaces, brain ventricles, central canal of the spinal cord and CNS parenchyma. Pathological findings from individual animals are compared to the clinical signs described in a separate paper. The development, migration and pathogenesis of E. rangiferi in goats are discussed.

Determination of the origin and nature of brain macrophages and microglial cells in mouse central nervous system, using non-radioactive in situ hybridization and immunoperoxidase techniques.

The origin and nature of brain macrophages and microglial cells in the mouse central nervous system (CNS) were investigated. First, the expression and localization of determinants recognized by the different monoclonal antibodies (mAbs) MOMA-1, Mac-1-alpha, and F4/80 (raised against cells of the mononuclear phagocyte system) were immunohistochemically studied in the developing and adult mouse brain. In order to clarify the origin of brain macrophages and microglial cells, we used bacteriophage lambda transgenic mice as donors for bone marrow transplantations in recipient mice of different ages. During ontogeny, numerous MOMA-1-, Mac-1-alpha-, and F4/80-positive blood monocyte-derived brain macrophages (amoeboid microglia) infiltrated the CNS parenchyma. These brain macrophages gradually disappeared from the brain parenchyma at postnatal day 7 (P7). From P17 on, Mac-1-alpha- and F4/80-positive cells were detected within the brain parenchyma with the morphology of resting microglial cells. Transitional forms between brain macrophages and "resting" microglia were not observed in the developing brain. Combined non-radioactive in situ hybridization and immunohistochemistry revealed many MOMA-1-positive bone marrow-derived brain macrophages that were located in the leptomeninges, the ventricles, and occasionally the blood vessel walls. These results show that brain macrophages are of bone marrow origin. Many "resting" microglial cells were detected in the brain, mainly in the white matter. It appeared that about 10% of these cells displayed the transgenic signal. This result indicates that the majority of "resting" microglial cells are of local, presumably neuroectodermal, origin.

Preferential regeneration of spinal axons through the scar in hemisected lamprey spinal cord

Axons of lamprey spinal cord can regenerate across a complete spinal transection. Thus, unlike the scar of injured mammalian spinal cords, the scar in the lamprey is not an absolute impediment to regeneration. However, it is still not known whether the scar is a relative impediment or whether it provides a favorable environment for regeneration compared to the spinal cord parenchyma. In order to answer this question, the cords of 12 large larval sea lampreys (4-5 years old) were hemisected at the level of the third gill and the animals allowed to recover for 10 weeks. The large reticulospinal neurons (Müller and Mauthner cells) or their giant axons were injected intracellularly with HRP and their regenerating neurites visualized in central nervous system (CNS) wholemounts. Forty-five of seventy-one regenerating neurites (64%) grew beyond the level of the hemisection. Of these, 36 (82%) regenerated through the scar and remained on the same side of the cord as their parent axons, while only 8 (18%) crossed the midline and grew around the scar. Thus, regenerating neurites of giant reticulospinal axons tended to grow through the hemisection scar rather than around it. Once they passed the level of injury, they continued to elongate in their appropriate paths. It is possible that this tendency for axons to regenerate through the scar reflects the greater amount of empty spaces on the hemisected side. In order to rule this out, 13 animals received contralateral simultaneous hemisections at the level of the 3rd and 7th gills. This procedure created large numbers of degenerating axons and potential empty spaces both rostral and caudal to the scars within both hemicords; 92 of 158 neurites (58%) regenerated beyond the level of their respective hemisections. All of these grew through the scar and none crossed to the contralateral side. Distal to either hemisection, neurites remained on their correct side regardless of whether the contralateral cord contained normal CNS parenchyma or axonal debris and empty spaces produced by Wallerian degeneration. Moreover, in hemisected and double hemisected animals, as well as in completely transected control animals, neurites regenerating in their correct direction grew further than those that were misrouted. Because lamprey spinal axons grow preferentially through a scar rather than around it, the scar may play a positive role in supporting axonal regeneration.

Primary leptomeningeal lymphoma

We describe 9 patients who presented with a neoplastic meningitis of lymphomatous origin. No evidence of parenchymal central nervous system or systemic tumor was identified either at the time of presentation or throughout the course of their disease. We have chosen to call this entity "primary leptomeningeal lymphoma" (PLML). This unusual form of neurologic lymphoma must be differentiated from the more common clinical situations of primary parenchymal lymphoma with meningeal involvement and systemic lymphoma complicated by lymphomatous meningitis.

Detection of HIV in fetal central nervous system tissue

Neurological disease is a common finding in children with AIDS and in others without signs of disease but with evidence of congenital HIV-1 infection. To investigate the possibility that HIV-1 can infect fetal central nervous system (CNS) tissue and therefore possibly serve as the substrate for the abnormal neurodevelopment characteristic of pediatric AIDS, eight abortus CNS samples (one set of twins) from seven HIV-1-seropositive intravenous drug users (IVDUs) and eight control abortus CNS samples from eight HIV-1-seronegative IVDUs were analyzed for HIV-1 infection. HIV-1 nucleic acid was detected only after the use of polymerase chain reaction (PCR) in three of eight CNS samples from HIV-seropositive IVDUs but not in samples from seronegative subjects. In situ hybridization confirmed that HIV-1 DNA sequences were in cells in the CNS parenchyma of two of the three positive samples. This study demonstrates that HIV-1 can infect human fetal CNS tissue in vivo, but that the use of PCR may be necessary for its detection.

A quantitative immunocytochemical study of the infiltrating lymphocytes in the spinal cord of guinea pigs with chronic relapsing experimental allergic encephalomyelitis

The production and characterization of an anti-guinea pig B cell monoclonal antibody is described. Immunocytochemical techniques using this antibody and others recognizing a Pan T cell antigen and T cell subsets were employed to study frozen sections of spinal cord from guinea pigs with chronic relapsing experimental allergic encephalomyelitis. T and B cells were found in both perivascular lesions and the central nervous system parenchyma, with the major T cell infiltration occuring by the end of the acute phase of disease. The distribution of T cell subsets suggests a phenotypic selectivity in favour of the transport of CT6 (putative CD8) +ve cells across the blood-brain barrier.