Microglia articles by MB Graeber

(Feel free to write to me for PDFs, m.graeber@imperial.ac.uk)

  1. Graeber MB, Scheithauer BW, Kreutzberg GW (2002) Microglia in brain tumors. Glia 40:252-259
    Abstract: Microglia have long been ignored by neurooncologists. This has changed with the realization that microglial cells not only occur within and around brain tumors but also contribute significantly to the actual tumor mass, notably in astrocytic gliomas. In addition, it has been speculated that microglia could play a role in the defense against neoplasms of the nervous system. However, the biological success of these tumors, i.e., their highly malignant behavior, indicates that natural microglial defense mechanisms do not function properly in astrocytomas. In fact, there is evidence that microglial behavior is controlled by tumor cells, supporting their growth and infiltration. This unexpected "Achilles heel" of microglial immune defense illustrates the risk of generalizing on the basis of a single aspect of microglial biology. Microglia are highly plastic cells, capable of exerting cytotoxic functions under conditions of CNS infections, but not necessarily during glioma progression. Thus, the suggestion that microglial activation through stimulation by cytokines (e.g., interferon-gamma) will benefit patients with brain tumors could prove fatally wrong. Therapeutic recruitment of microglia to treat such diffusely infiltrative brain tumors as astrocytic gliomas must be considered premature

  2. Flugel A, Hager G, Horvat A, Spitzer C, Singer GM, Graeber MB, Kreutzberg GW, Schwaiger FW (2001) Neuronal MCP-1 expression in response to remote nerve injury. J.Cereb.Blood Flow Metab 21:69-76
    Abstract: Direct injury of the brain is followed by inflammatory responses regulated by cytokines and chemoattractants secreted from resident glia and invading cells of the peripheral immune system. In contrast, after remote lesion of the central nervous system, exemplified here by peripheral transection or crush of the facial and hypoglossal nerve, the locally observed inflammatory activation is most likely triggered by the damaged cells themselves, that is, the injured neurons. The authors investigated the expression of the chemoattractants monocyte chemoattractant protein MCP-1, regulation on activation normal T-cell expressed and secreted (RANTES), and interferon-gamma inducible protein IP10 after peripheral nerve lesion of the facial and hypoglossal nuclei. In situ hybridization and immunohistochemistry revealed an induction of neuronal MCP-1 expression within 6 hours postoperation, reaching a peak at 3 days and remaining up-regulated for up to 6 weeks. MCP-1 expression was almost exclusively confined to neurons but was also present on a few scattered glial cells. The authors found no alterations in the level of expression and cellular distribution of RANTES or IP10, which were both confined to neurons. Protein expression of the MCP-1 receptor CCR2 did not change. MCP-1, expressed by astrocytes and activated microglia, has been shown to be crucial for monocytic, or T-cell chemoattraction, or both. Accordingly, expression of MCP-1 by neurons and its corresponding receptor in microglia suggests that this chemokine is involved in neuron and microglia interaction

  3. Flugel A, Bradl M, Kreutzberg GW, Graeber MB (2001) Transformation of donor-derived bone marrow precursors into host microglia during autoimmune CNS inflammation and during the retrograde response to axotomy. J.Neurosci.Res. 66:74-82
    Abstract: Macrophages in the brain can have a triple source. They may originate from recently blood-derived precursors, from the largely resident perivascular cell population (perivascular macrophages and related cells), and from intrinsic parenchymal as well as perivascular microglia. Although continuous exchange of part of the perivascular cell population with bone marrow-derived precursors is now accepted, the turnover of adult parenchymal microglia has remained enigmatic. Using bone-marrow chimeras carrying an unexpressed marker gene and carbon labeling of peripheral monocyte/macrophages in a combined model of facial nerve axotomy and transfer experimental autoimmune encephalitis, we demonstrate for the first time that there is an easy to induce exchange between parenchymal central nervous system (CNS) microglia and the macrophage precursor cell pool of the bone marrow. Furthermore, very low level infiltration of the CNS parenchyma by recently bone marrow-derived microglia could be observed after simple peripheral nerve axotomy that is followed by neuronal regeneration. Thus, microglial cells can be considered wanderers between the peripheral immune system and the CNS where they may act as a "Trojan horse" in infections. The fact that recently bone marrow-derived parenchymal microglia fully integrate into a regenerating brain nucleus' architecture encourages entirely new approaches for delivering genes into the adult CNS

  4. Flugel A, Labeur MS, Grasbon-Frodl EM, Kreutzberg GW, Graeber MB (1999) Microglia only weakly present glioma antigen to cytotoxic T cells. Int.J.Dev.Neurosci. 17:547-556
    Abstract: Microglia and brain macrophages represent a substantial fraction of the cells present in astrocytic gliomas. Yet, the functional role of microglia in these tumors has remained enigmatic. We have compared rat microglial cells and thymocytes with regard to their ability to present purified CNS proteins, MBP and S100beta, as well as C6 glioma cells to specific T lymphocytes. In addition, a new cytotoxicity assay based on fluorescence activated cell sorting of tumor cells carrying the green fluorescent protein was established. This assay was used to determine the influence of microglial population density and activational state on C6 glioma cell survival in vitro. Microglia were consistently found to present MBP and S100beta less efficiently than thymocytes and appeared to be unable to present C6 glioma cells to cytotoxic T lymphocytes. In addition, high concentrations of microglial cells attenuated the cytotoxic effects of these T cells on C6 glioma cells whereas thymocytes significantly supported their specific killing. It is suggested that defense functions of microglial cells against C6 glioma are severely compromised and that the observed deficiency in antigen presentation may play an important role for astrocytoma growth in vivo

  5. Egensperger R, Kosel S, von Eitzen U, Graeber MB (1998) Microglial activation in Alzheimer disease: Association with APOE genotype. Brain Pathol. 8:439-447
    Abstract: Microglial cells are considered to play an important role in the pathogenesis of Alzheimer disease. Apart from producing the Alzheimer amyloid precursor (APP) as an acute phase protein, microglial cells seem to be involved in the deposition of its amyloidogenic cleavage product, the amyloid-beta peptide (Abeta). Abeta is bound by apolipoprotein E (APOE) in an isoform-specific manner, and it has been demonstrated that inheritance of the AD susceptibility allele, APOE epsilon4, is associated with increased deposition of Abeta in the cerebral cortex. However, the relationship between APOE epsilon4 gene dose and microglial activation is unknown. Using microglial expression of major histocompatibility complex class II molecules as a marker, we have performed a quantitative genotype-phenotype analysis on microglial activation in frontal and temporal cortices of 20 APOE genotyped AD brains. The number of activated microglia and the tissue area occupied by these cells increased significantly with APOE epsilon4 gene dose. When a model of multiple linear regression was used to compare the relative influence of APOE genotype, sex, disease duration, age at death, diffuse and neuritic plaques as well as neurofibrillary tangles on microglial activation, only APOE genotype was found to have a significant effect. Thus, the APOE gene product represents an important determinant of microglial activity in AD. Since microglial activation by APP has been shown to be modulated by apoE in vitro, a direct role of microglia in AD pathogenesis is conceivable

  6. Eitzen U, Egensperger R, Kosel S, Grasbon-Frodl EM, Imai Y, Bise K, Kohsaka S, Mehraein P, Graeber MB (1998) Microglia and the development of spongiform change in Creutzfeldt-Jakob disease. J.Neuropathol.Exp.Neurol. 57:246-256
    Abstract: Recent in vitro experiments suggest that neurotoxicity of the prion protein is dependent on the presence of microglia. We have studied 11 cases of Creutzfeldt-Jakob disease (CJD) using immunocytochemistry in combination with computerized image analysis to clarify the relationship between spongiform change and microglial activation. MHC class II-positive microglia were almost exclusively confined to cortical gray matter where the neuropil area occupied by these cells exceeded that of controls more than 350-fold. In cortical regions with a bimodal distribution of spongiform degeneration, the presence of class II-positive microglia correlated well with the presence of vacuolation in layer V, but significantly less with spongiform change in layers II and III. In areas where spongiform degeneration affected the entire depth of the cortex, activated microglia were predominantly located in the inner one-half of the cortex or were evenly distributed throughout all cortical laminae. Here, microglia exhibited atypical, tortuous cell processes and occasionally intracytoplasmic vacuoles, suggesting that microglia themselves may become a disease target. Taken together, our results provide indirect evidence against an early causative involvement of microglia in the development of spongiform change. At later stages, however, diseased microglia could produce harmful factors which mediate both astrogliosis and neuronal injury

  7. Graeber MB, Lopez-Redondo F, Ikoma E, Ishikawa M, Imai Y, Nakajima K, Kreutzberg GW, Kohsaka S (1998) The microglia/macrophage response in the neonatal rat facial nucleus following axotomy. Brain Res. 813:241-253
    Abstract: Microglia represent a population of brain macrophage precursor cells which are intrinsic to the CNS parenchyma. Transection of the facial nerve in the newborn rat causes death of the affected motor neurons which is accompanied by massive activation of local microglia. Many of these cells develop into macrophages as can be shown by immunocytochemistry for OX-42 and ED1. Using the new polyclonal microglial marker ionized calcium binding adapter molecule 1, iba1, in combination with immunocytochemical double-labeling for the proliferating cell nuclear antigen (PCNA), or [3H]thymidine autoradiography, and confocal microscopy, qualitative as well as quantitative differences can be demonstrated between the newborn and the adult axotomized rat facial nucleus. While microglial cells are the only cell population which responds to axotomy by cell division in the adult facial nucleus, GFAP positive reactive astrocytes can be shown to undergo mitosis following axotomy in the newborn rat. Furthermore, ED1 immunoreactivity, early expression of MHC class II molecules and morphological transformation of microglia into macrophages can only be observed under conditions of neuronal degeneration, i.e., in the neonatal rat facial nucleus. Thus, the combination of cellular markers described here should be useful for studies employing the neonatal rat facial nucleus as an in vivo assay system to test the efficacy of neurotrophic factors

  8. Tran CT, Wolz P, Egensperger R, Kosel S, Imai Y, Bise K, Kohsaka S, Mehraein P, Graeber MB (1998) Differential expression of MHC class II molecules by microglia and neoplastic astroglia: relevance for the escape of astrocytoma cells from immune surveillance. Neuropathol.Appl.Neurobiol. 24:293-301
    Abstract: There is increasing evidence that microglia serve as antigen presenters in the human CNS. Although the occurrence of MHC class II immunoreactive cells has been reported in astrocytic gliomas, the relative contribution of microglia to this cell population has not been studied in detail. Using computer-assisted image analysis, we have investigated the expression of MHC class II molecules and of the microglia/macrophage markers Ki-MIP, RCA-1, KP1 and iba1, in 97 astrocytic gliomas comprising all WHO grades to answer the question whether there is a correlation between tumour grade and the number of MHC class II positive microglia/macrophage profiles. Microglia expressing MHC class II were common in astrocytomas and anaplastic astrocytomas but rare in pilocytic tumours although there was significant variation within each group. MHC class II immunoreactivity was reduced in highly cellular areas of glioblastomas where large numbers of cells expressing macrophage markers were still present. Thus, there was no simple relationship between tumour grade and microglial/macrophage MHC class II expression. In addition, up to 55% of astrocytic gliomas contained MHC class II immunoreactive tumour cells. Microglia but not tumour cells were found to express the BB1/B7 costimulator. We conclude that microglia in astrocytic gliomas are well equipped to function as antigen presenting cells. Yet, neoplastic astroglia appear to acquire the capacity to downregulate microglial MHC class II expression and, at the same time, may induce T-cell clonal anergy through aberrant expression of MHC class II molecules

  9. Jones LL, Banati RB, Graeber MB, Bonfanti L, Raivich G, Kreutzberg GW (1997) Population control of microglia: does apoptosis play a role? J.Neurocytol. 26:755-770
    Abstract: Brain lesions, even of the most subtle type, are accompanied by the activation of microglia, the main immune cells of the brain. Microglial cells dramatically increase in number through proliferation and adhere to the injured neurons, where they displace the synaptic input. After proliferation, microglia gradually migrate into the nearby parenchyma and appear to decrease in number. Here we examined the possible involvement of apoptosis in the regulation of the microglial cell number using Terminal transferase mediated d-UTP Nick End-Labelling (TUNEL). In vitro, cell death is a common phenomenon in microglial cell cultures, and is enhanced by the withdrawal of the mitogen, granulocyte-macrophage colony stimulating factor. In vivo, application of the TUNEL-reaction revealed TUNEL-positive microglia beginning at day 4, with a peak 7 days after transection of the facial nerve. Surprisingly, TUNEL-labelling in vivo was localized on the outer side of the nuclear membrane and in the microglial cytoplasm, with very little staining within the nucleus itself. These TUNEL-labelled cells also lacked other classic morphological signs of apoptosis, like membrane blebbing, chromatin condensation and apoptotic bodies. These data suggest that the regulation of post-mitotic microglia is not mediated by the classic pathway of apoptosis

  10. Kosel S, Egensperger R, von Eitzen U, Mehraein P, Graeber MB (1997) On the question of apoptosis in the parkinsonian substantia nigra. Acta Neuropathol.(Berl) 93:105-108
    Abstract: Apoptosis has been postulated as a mechanism of nerve cell death in Parkinson's disease. In the present study, the substantia nigra of 22 neuropathologically confirmed Parkinson cases and 8 control brains was studied using the in situ end-labeling (TUNEL) method. About 50% of parkinsonian brains showed a small number of TUNEL-positive glial cells in the substantia nigra, whereas no neurons showed convincing TUNEL positivity or any morphological signs of apoptosis. No correlation was observed between the number of TUNEL-positive glial cells and microglial activation. Our results fail to demonstrate apoptosis as a mechanism of cell death in Parkinson's disease

  11. Kosel S, Egensperger R, Bise K, Arbogast S, Mehraein P, Graeber MB (1997) Long-lasting perivascular accumulation of major histocompatibility complex class II-positive lipophages in the spinal cord of stroke patients: possible relevance for the immune privilege of the brain. Acta Neuropathol.(Berl) 94:532-538
    Abstract: Six cases of middle cerebral artery occlusion are presented in which the cellular changes accompanying descending degeneration of the lateral corticospinal tract were studied at different time points (5 days-10 years) following the insult. Microglia and perivascular cells were found to ingest large amounts of myelin degradation products, while expressing high levels of major histocompatibility complex (MHC) class II molecules. Activation of perivascular macrophages, as indicated by increased class II expression, lasted for many years and appeared to follow down-regulation of both phagocytic activity and class II expression on parenchymal microglia. TUNEL labeling was absent from both microglia and perivascular cells at all time points investigated. Indirect evidence is presented that microglia may transfer myelin degradation products to the perivascular space. Perivascular cells which express MHC class II molecules constitutively do not appear to leave the perivascular compartment in large numbers and could release myelin degradation products into the cerebrospinal fluid. The possible immunological consequences of these findings are discussed with respect to their possible relevance for antigen presentation and autoimmune central nervous system disease

  12. Streit WJ, Graeber MB (1996) Microglia: a pictorial. Prog.Histochem.Cytochem. 31:1-89

  13. Banati RB, Graeber MB (1994) Surveillance, intervention and cytotoxicity: is there a protective role of microglia? Dev.Neurosci. 16:114-127
    Abstract: The study of microglial cell biology has become the key to understanding the brain's fundamental tissue reactions as well as the cellular mechanisms underlying CNS disease. This article focuses on glial-neuronal interactions with special reference to human pathology. Three important areas of brain pathology are critically reviewed: multiple sclerosis and CNS inflammation, the brain in AIDS and opportunistic infections, and neurodegenerative disorders. Although microglial cytotoxicity may cause bystander damage, e.g. in ischemia, there is little evidence to support the view that microglial activation per se is pathogenic. Results suggesting that one important normal function of microglia is to protect the integrity of the central nervous system are discussed. The concept is proposed that microglia function as a highly developed guardian to the CNS

  14. Graeber MB, Mehraein P (1994) Microglial rod cells. Neuropathol.Appl.Neurobiol. 20:178-180

  15. Graeber MB (1994) Development of the microglia literature. Neuropathol.Appl.Neurobiol. 20:215-216

  16. Graeber MB, Bise K, Mehraein P (1994) CR3/43, a marker for activated human microglia: application to diagnostic neuropathology. Neuropathol.Appl.Neurobiol. 20:406-408

  17. Graeber MB (1993) Microglia, macrophages and the blood-brain barrier. Clin.Neuropathol. 12:296-297

  18. Graeber MB, Bise K, Mehraein P (1993) Synaptic stripping in the human facial nucleus. Acta Neuropathol.(Berl) 86:179-181
    Abstract: An autopsy case of severe peripheral facial nerve paresis with disconnection of synapses from facial motor neurons is reported. A 77-year-old man presented with left-sided otitis media and subsequent development of facial nerve paresis. Three months later, the patient died of an acute gastrointestinal bleeding from a chronic duodenal ulcer. Gross inspection of the brain revealed non-stenosing arteriosclerotic vascular changes and a single small cystic lesion in the right putamen. Microscopically, marked chromatolytic changes were observed in the left facial nucleus. Immunocytochemistry for synaptophysin revealed a marked loss of afferent synaptic contacts from somatic and stem dendritic surface membranes of all chromatolytic motor neurons. Wrapping of a number of neurons by newly formed glial fibrillary acidic protein-positive astrocytic cell processes could be detected in the regenerating facial motor nucleus. In addition, expression of HLA-DR was increased on a small number of microglia and perivascular cells. These changes were absent from the contralateral, normal-appearing facial nucleus. To our knowledge, this case provides the first evidence for disconnection of synapses following peripheral nerve lesioning in humans. Occurrence of synaptic stripping is likely to explain nuclear hyperexcitability and failure of recovery of complex fine motor movements that are commonly observed following peripheral injury to the facial nerve

  19. Streit WJ, Graeber MB (1993) Heterogeneity of microglial and perivascular cell populations: insights gained from the facial nucleus paradigm. Glia 7:68-74
    Abstract: We reflect here on the development of a neuroimmunological concept which has been formulated over the past 5 years through studying microglial cell responses in the facial nerve system. A simple axotomy of the adult rat facial nerve which causes regeneration of facial motor neurons and little, if any, cell death can activate microglial cells just as easily as a full-blown degeneration of the entire nucleus induced by toxic ricin. In both instances, the prompt microglial reaction is characterized by a series of structural and phenotypic changes which are in many ways similar to an immune response, e.g., there is cell proliferation and upregulation of MHC antigens. However, since white blood cells do not participate in the retrograde response of facial motor neurons, we have adopted a notion which views microglia as a CNS-wide network of immunocompetent cells whose morphological dissimilarities from leukocytes are a result of their unique adaptation to the CNS architecture. We have continued our in vivo investigations of the phagocytic and immunophenotypic properties of microglial and perivascular cells during the retrograde reaction of facial motor neurons by using intra-neural injections of fluorogold (FG) and ricin followed by lectin and immunostaining for microglia. Two new findings can be added to the microglial neuroimmune network: (1) Microglia take up FG only after motor neuron degeneration, whereas perivascular cells may take up FG under nondegenerating conditions. (2) Immunologically important molecules, such as MHC class II, CD4, and leukocyte common antigens, are expressed by different microglial subpopulations. Thus there is functional and phenotypic heterogeneity among immunocompetent cells of the CNS

  20. Graeber MB, Streit WJ, Buringer D, Sparks DL, Kreutzberg GW (1992) Ultrastructural location of major histocompatibility complex (MHC) class II positive perivascular cells in histologically normal human brain. J.Neuropathol.Exp.Neurol. 51:303-311
    Abstract: The expression of major histocompatibility complex (MHC) class I and II antigens was studied in surgical and postmortem brain biopsy tissue using light and electron microscopic immunocytochemistry. In addition, monoclonal antibodies directed against human macrophages (EBM11) and alpha-smooth muscle actin were applied. It is shown that blood vessel-associated MHC class II immunoreactivity in histologically normal human brain can be localized to a distinct class of cells, termed perivascular cells, which share macrophage but not smooth muscle cell antigen. This immunophenotype, the location in the perivascular space as well as the morphology, frequency and tissue distribution distinguish perivascular cells from pericytes and intraparenchymal microglia. It is suggested that MHC class II positive perivascular cells are a normal constituent of the human cerebral microvasculature. The potential role of these cells in immunological reactions occurring at the blood-brain interface is discussed

  21. Schoen SW, Graeber MB, Kreutzberg GW (1992) 5'-Nucleotidase immunoreactivity of perineuronal microglia responding to rat facial nerve axotomy. Glia 6:314-317
    Abstract: The ecto-enzyme 5'-nucleotidase was localized immunocytochemically in the axotomized rat facial nucleus. As revealed by the monoclonal antibody 5N4-2,5'-nucleotidase immunoreactivity markedly increased on perineuronal microglia during the first week following axotomy, and gradually disappeared from these cells by the end of the third post-operative week. Interestingly, parenchymal microglia were not or only weakly stained. These findings indicate that 5'-nucleotidase 5N4-2-immunoreactivity may serve as a marker for perineuronal microglia, a population of satellite glial cells that appear to be actively engaged in lesion-induced synaptic changes during regeneration

  22. Streit WJ, Graeber MB (1991) Perivascular location and phenotypic heterogeneity of microglial cells in the rat brain. J.Neuroimmunol. 33:87

  23. Graeber MB, Streit WJ, Kiefer R, Schoen SW, Kreutzberg GW (1990) New expression of myelomonocytic antigens by microglia and perivascular cells following lethal motor neuron injury. J.Neuroimmunol. 27:121-132
    Abstract: The results of the present study demonstrate that following lethal motor neuron injury microglia and perivascular cells, as well as brain macrophages derived from the latter two cell types, newly express antigens of the myelomonocytic lineage as recognized by the monoclonal antibodies ED1 and ED3. It is suggested that differences in the immunophenotype of resident brain macrophage precursor cells, i.e. microglia and perivascular cells, and macrophages occurring outside the central nervous system (CNS) may be explained by differences in local macrophage antigen expression rather than by a different embryological lineage. The new appearance of antigens common to peripheral macrophages on neural phagocytes in CNS lesions may therefore not necessarily imply that most or all of these cells are of recent blood origin

  24. Graeber MB, Streit WJ, Kreutzberg GW (1990) The third glial cell type, the microglia: cellular markers of activation in situ. Acta Histochem.Suppl 38:157-160

  25. Graeber MB, Streit WJ (1990) Microglia: immune network in the CNS. Brain Pathol. 1:2-5
    Abstract: In recent years much progress has been made toward a better understanding of the nature and function of microglial cells. This review summarizes new developments and attempts to provide a perspective for future avenues to take in microglial research. Microglia are considered to play an active role in a variety of neurological diseases. Their function in forming a network of immune competent cells within the CNS is discussed

  26. Graeber MB, Streit WJ (1990) Perivascular microglia defined. Trends Neurosci. 13:366

  27. Graeber MB, Streit WJ, Kreutzberg GW (1989) Formation of microglia-derived brain macrophages is blocked by adriamycin. Acta Neuropathol.(Berl) 78:348-358
    Abstract: Injection of ricin, the toxic lectin from Ricinus communis, into the rat facial nerve leads to rapid degeneration of motor neurons and concomitant proliferation and transformation of endogenous microglia into brain macrophages. Using [3H]-thymidine autoradiography, immunocytochemistry for microglial markers and electron microscopy, we could show that when ricin was administered together with the cytostatic drug adriamycin, the retrogradely transported adriamycin inhibits the macrophage response induced by toxic ricin. It is concluded that under conditions of neuronal degeneration, e.g., following ricin intoxication, brain macrophages are predominantly, if not exclusively, derived from endogenous microglia

  28. Graeber MB, Streit WJ, Kreutzberg GW (1989) Identity of ED2-positive perivascular cells in rat brain. J.Neurosci.Res. 22:103-106
    Abstract: A controversial, though fundamental, issue in neurobiology concerns the nature, origin, and function of brain macrophages. By immunocytochemical analysis using monoclonal antibodies directed against rat macrophage antigens, i.e., ED1-3, Ox-41, Ox-42, and Ki-M2R, we show that a group of perivascular cells located within the basal membrane of CNS blood vessels are immunoreactive. These cells, which resemble pericytes in terms of their anatomical distribution, are distinct from resting parenchymal microglia immunologically as well as morphologically. Our results demonstrate considerable heterogeneity in the immunophenotype of resident brain macrophages, which may be part of the immune-nervous system interface

  29. Graeber MB, Banati RB, Streit WJ, Kreutzberg GW (1989) Immunophenotypic characterization of rat brain macrophages in culture. Neurosci.Lett. 103:241-246
    Abstract: Five monoclonal antibodies specific for rat monocytes/macrophages were used to characterize macrophages/microglia bulk isolated from neonatal and adult rat brain. The majority of brain macrophages was positive for all antibodies tested with minor differences between cultures derived from developing and mature central nervous tissue. These results contrast in vivo findings indicating that most antigens of peripheral macrophages are absent from resting, activated and phagocytic microglia in situ. We conclude that brain macrophages/microglia newly express antigens of the myelomonocytic lineage when in culture and that cultured brain macrophages may be derived from different types of precursor cells normally present within the CNS

  30. Kreutzberg GW, Graeber MB, Streit WJ (1989) Neuron-glial relationship during regeneration of motorneurons. Metab Brain Dis. 4:81-85
    Abstract: Following axonal interruption, structural, metabolic and physiological parameters change in motorneurons. Also, glial cells are involved in this process. Microglia proliferate and express new proteins such as vimentin or MHC antigens. Astrocytes show hypertrophy, increased GFAP synthesis, and formation of lamellae. Both glial cell types participate in deafferentation and insulation of regenerating neurons, a process with significance for post-lesioning functional impairment

  31. Rieske E, Graeber MB, Tetzlaff W, Czlonkowska A, Streit WJ, Kreutzberg GW (1989) Microglia and microglia-derived brain macrophages in culture: generation from axotomized rat facial nuclei, identification and characterization in vitro. Brain Res. 492:1-14
    Abstract: In order to study microglial cells and microglia-derived brain macrophages in vitro, a method has been developed which allows the transfer of mitotic microglial cells from adult rat brain into tissue culture. The studies were performed on facial motor nuclei which were explanted after axotomy of the facial nerve. Outgrowing cells were identified and characterized by (i) morphological criteria using light and electron microscopy, (ii) in vivo [3H]thymidine labeling combined with subsequent in vitro autoradiography, (iii) immunocytochemistry for vimentin, GFAP, Fc and complement receptors, MHC antigens, laminin, fibronectin, factor VIII related- and 04 antigen as well as lectin histochemistry, and (iv) functional in vitro tests. In addition, a microglial cell line was established from proliferating cells. The results indicate that perineuronal microglia rather than astrocytes, perivascular cells, oligodendrocytes or endothelial cells may become phagocytic after having been activated by axotomy in situ

  32. Streit WJ, Graeber MB, Kreutzberg GW (1989) Peripheral nerve lesion produces increased levels of major histocompatibility complex antigens in the central nervous system. J.Neuroimmunol. 21:117-123
    Abstract: Proliferation of central nervous system (CNS) glia in response to peripheral nerve injury occurs without apparent participation of cells of the immune system. It is shown here that following transection of the rat facial nerve there is strongly elevated expression of class I, and to a lesser extent, class II antigens of the major histocompatibility complex (MHC) in the facial nucleus. It is demonstrated by double-immunofluorescence studies that the cells responsible for increased levels of MHC class I antigens are endogenous brain microglia. These findings emphasize the thought that microglia are immunocompetent cells, but, at the same time, raise the possibility for a non-immunological function of MHC antigens under conditions of neural regeneration

  33. Streit WJ, Graeber MB, Kreutzberg GW (1989) Expression of Ia antigen on perivascular and microglial cells after sublethal and lethal motor neuron injury. Exp.Neurol. 105:115-126
    Abstract: The expression of immune-associated (MHC class II) antigen was studied immunohistochemically over several months in the rat facial nucleus after nerve transection and after intraneural injection of toxic ricin. Cells expressing Ia antigen were of a perivascular type and parenchymal ramified microglia. In the first few weeks after nerve lesions we observed a gradual increase in the number of Ia-immunoreactive cells starting with an initial appearance of Ia-positive perivascular cells which were succeeded by increasing numbers of Ia-positive ramified microglia. In long-term animals Ia expression was almost exclusively found in microglia. We propose (a) the existence of a population of immunocompetent perivascular cells normally present in adult rat brain that can be stimulated to express Ia antigen, and (b) the existence of a subpopulation of ramified microglia that arises through transformation of Ia-positive perivascular cells in the adult under pathological conditions

  34. Graeber MB, Streit WJ, Kreutzberg GW (1988) The microglial cytoskeleton: vimentin is localized within activated cells in situ. J.Neurocytol. 17:573-580
    Abstract: Unlike astrocytes and oligodendrocytes, microglia are extremely plastic making them the chameleon among the glial cells in the CNS. This great mutability of the microglial cell shape suggests the presence of an elaborate cytoskeleton which is demonstrated here by applying a new ultrastructural method. Electron microscopic immunocytochemistry shows the presence of vimentin at intermediate filament sites in reactive microglia stimulated by rat facial nerve axotomy. It is suggested that vimentin-expression may serve as a marker for activated states of microglia, including brain macrophages

  35. Graeber MB, Streit WJ, Kreutzberg GW (1988) Axotomy of the rat facial nerve leads to increased CR3 complement receptor expression by activated microglial cells. J.Neurosci.Res. 21:18-24
    Abstract: Axotomy of the rat facial nerve leads to mitotic divisions of microglial cells without developing into phagocytes. In order to study the functional characteristics of those activated, i.e., proliferating but nonphagocytic, microglia we investigated the expression of monocyte/macrophage antigens by these cells. Our results show that activated microglia lack monocyte/macrophage antigens recognized by the monoclonal antibodies Ox-41, ED1, ED2, and Ki-M2R but express high levels of CR3 complement receptors in situ

  36. Graeber MB, Kreutzberg GW (1988) Delayed astrocyte reaction following facial nerve axotomy. J.Neurocytol. 17:209-220
    Abstract: Transection of the facial nerve causes a rapid increase of glial fibrillary acidic protein in reactive astrocytes and a proliferation of local microglial cells. The latter is associated with a detachment of synaptic terminals from the regenerating motor neurons. About 3 weeks following axotomy the reactive astrocytes begin to form thin, sheet-like lamellar processes which cover virtually all neuronal surfaces. A high 5'-nucleotidase enzymic activity can be demonstrated in the plasma membrane of these thin cell processes. Subsequently, the lamellar processes become arranged in stacks which persist for several months and thus isolate the regenerating motor neurons from their afferent synaptic input. It is speculated that the process may protect the motor neurons during regeneration

  37. Graeber MB, Tetzlaff W, Streit WJ, Kreutzberg GW (1988) Microglial cells but not astrocytes undergo mitosis following rat facial nerve axotomy. Neurosci.Lett. 85:317-321
    Abstract: Transection of the facial nerve leads to a glial response within its central nucleus of origin. Concomitant with a proliferation of satellite microglial cells an astrocytic reaction is also seen. In the present study light and electron microscopic autoradiography were performed in order to clarify whether only microglial cells undergo mitosis following facial nerve axotomy or if astrocytes also divide. Our results provide the first electron microscopical autoradiographic evidence for the labelling of endogenous microglial cells. We suggest that microglial cells are the only proliferating element during this process in the rat facial nucleus

  38. Streit WJ, Graeber MB, Kreutzberg GW (1988) Functional plasticity of microglia: a review. Glia 1:301-307
    Abstract: The present review summarizes recently acquired data in vivo, which support a role of CNS microglia as a source of defense cells in the CNS capable of carrying out certain immune functions autonomously. We have kept the following discussion restricted to microglial cells and have not included work on the immunological functions of astrocytes, which has been recently reviewed elsewhere (Fontana et al.: Immunological Reviews 137:3521-3527, 1987). Resting microglia are scattered uniformly throughout the CNS forming a network of potential immunoeffector cells, which can be activated by stimuli ranging from peripheral nerve injury over viral infections to direct mechanical brain trauma. The term "activated microglia" is used here to describe proliferating cells that demonstrate changes in their immunophenotype but have not undergone transformation into brain macrophages. Such a transformation can be stimulated by neuronal death but not by sublethal neuronal injury. Microglia may function as antigen-presenting cells and may thus represent the effector cell responsible for the recruitment of lymphocytes to the brain resulting in an inflammatory reaction. The recent developments in the understanding of microglial cell function may lead to a redefinition of the often cited "immune privilege" of the brain

  39. Graeber MB, Kreutzberg GW (1986) Astrocytes increase in glial fibrillary acidic protein during retrograde changes of facial motor neurons. J.Neurocytol. 15:363-373
    Abstract: Concomitant with the proliferation of satellite microglial cells occurring in the process of motor neuron regeneration, an astrocytic hypertrophy is also seen. A remarkable increase of glial fibrillary acidic protein (GFAP) immunoreactivity is demonstrated in astrocytes of the facial nucleus within a few days following nerve transection. The increase of GFAP antigenicity is associated with an increased appearance of glial filaments and astrocytic processes. We suggest that resident protoplasmic astrocytes become involved in retrograde changes in facial motor neurons and transform into reactive astrocytes. They are of the fibrous type and highly positive for GFAP